Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
So you think Skipp Isaham's oscillator has feedback pulses at the peak of the sinewave? Interesting. Jerry On Mon, Jul 27, 2015 at 8:58 PM, Bill Byrom wrote: > Bob, I think you meant to write: "Hook a 100 pf cap from emitter > to ground." > > Also remember that the feedback loop can use multiple active devices. > You can design a crystal oscillator which has only linear loading on the > crystal but which has nonlinear characteristics somewhere in the > feedback loop. Some oscillators use a filter to insure that only a > linear signal is fed back from a very nonlinear amplifier in the loop. > The output can be taken from various places in the feedback loop, and > the harmonic content varies depending on that location. > > One idea is to only add energy to the crystal at the peak of the > sinewave voltage, when the derivative of the voltage is zero. If a short > pulse is added at the peak the amplitude is increased without > significantly affecting the phase. But if the pulse is added at the > middle "zero crossing" of the sinewave (with resepect to the peak-to- > peak swing) where the derivative is large, the phase can be affected by > the feedback. Ideally you want to add just enough energy each cycle to > overcome the energy lost in the crystal due to limited Q. > > If the feedback loop is linear, then the noise generated by the active > and passive devices is continuously fed back to the crystal, generating > amplitude noise. Due to the angle of the feedback (described above) and > AM to PM conversion due to device characteristics (junction capacitance > changes with voltage), some of the amplitude noise gets converted to > phase noise. The total resulting noise sidebands (made up of both > ampitude and phase noise) is what everyone wants to minimize. > > You could also use a feedback loop which was very nonlinear by using an > active switch with a low ON resistance (so hopefully a low noise figure > when closed) to send spikes back to the crystal resonator at the peak of > the voltage waveform. If you could arrange the circuit so that the duty > cycle of this switch was low, the residual noise would only be amplified > and fed back to the crystal resonator over a small portion of each > cycle, reducing the average noise figure of the oscillator. If the > feedback circuit is highly nonlinear the amplitude noise might be > clipped and reduced. Of course, the jitter in the feedback circuit is > important. > > The active devices need to be well bypassed at audio frequencies so that > low frequency shot noise isn't amplified with high efficiency. Since the > junction capacitance (and other AM to PM conversion sources) in > downstream amplifiers can be affected by audio frequency noise, I think > that it's very important that such noise isn't allowed to phase modulate > the desired RF signal. > > -- > Bill Byrom N5BB > > > > On Mon, Jul 27, 2015, at 05:39 PM, Bob Camp wrote: > > Hi > > > > > >> On Jul 27, 2015, at 11:52 AM, jerry shirᴀr > wrote: > >> > >> Here's the rub Bob. I have been trying to find a way or have you explain > >> how a high harmonic oscillator stage > > > > You are confusing the current through the crystal with the current in the > > oscillator transistor. > > So: > > > > Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC > > couple that resistor to your spectrum analyzer. > > Connect the base of the transistor with a 10K to +12 and a 10K to ground > > Connect a 1K ohm resistor from the emitter of the transistor to ground > > Hook a 100 pf cap from base to emitter > > Hook a 100 pf cap from emitter to base > > Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms to > > the base of the transistor. > > Hook a 32 pf cap from the other side of the crystal to ground > > > > I **hope** that’s specific enough for you. > > > > That circuit **will** oscillate. > > > > Look at the current on the 50 ohm resistor. It’s got plenty of harmonics. > > > > With me so far or is this still to theoretical? > > > > Now, this **does** get a bit exciting, but it’s the way this circuit has > > been analyzed since the 1930’s (when it used a tube): > > > > You shift the ground to the emitter for the purposes of seeing what’s > > going on. You now have an “input side” and an “output side” to > > the active stage. This lets you break the loop for analysis. > > > > In this format, the current in the collector is more clearly flowing > > through the 1K resistor and one of the 100 pf caps. > > The current that passes through the crystal flows through the other 100 > > pf cap (and the base) to ground. > > > > The current in the oscillator stage is every bit as nonlinear as you saw > > before. > > > > Since this is an oscillator, the current flows in a loop. There is no > > independent current in any one leg. They all are related. > > If you want to see this, hook up an oscilloscope to the collector > > resistor and apply power to the oscillator. The output does not > > go instant
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi Yup, the second cap goes to ground not in parallel with the first cap. > On Jul 27, 2015, at 10:42 PM, jerry shirᴀr wrote: > > Thanks Bob, > > I had no intention of being offensive. It is just my manner. Forgive me. I get a bit feisty from time to time - sorry about that. > > First of all, I think you had intended to say "100pF from emitter to > ground" rather than "100pF from emitter to base." I think that's a typo. > > Next, how much crystal drive level is there? I guess it depends on the > crystal resistance, but I think there will be a lot of crystal current. Which is not unintentional ….that circuit will have pretty good phase noise for a simple to wire circuit. > > Then I don't know why you would purposely want to clip the signal of the > oscillator, but it is the designer's prerogative. Ok, how would you propose to build an oscillator that does not have limiting, since 99.999% of all precision (and otherwise) crystal oscillators have that feature? Without a limiter in the feedback loop, there is no way to meet Barkenhausen’s criteria on a fast enough basis. > For low noise > applications, I have always used an AGC so the oscillator will have a lot > of drive at startup and then backs off greatly for steady state operation. Which speeds up startup. > You can also more easily control the drive level to a small enough amount > so that the drive won't mess up the frequency accuracy. Except all the AGC does is to eliminate the massive extra gain at startup. It’s far to slow to take care of the loop it’s self. > Also the buffer > from the oscillator stage buffers the actual crystal current so the base to > emitter noise does not get amplified to the collector and propagated down > the line. I could beat a -145dBc/Hz spec at 100Hz and -168dBc/Hz at > 10kHz. Both of which are pretty noisy compared to the stuff I do these days. A lot depends on the frequency ... > > I don't have anything here to breadboard these things up. I don't > understand why when there is already a clean crystal current in the > circuit, Possibly for one of three reasons: 1) They don’t want to degrade the Q (or more correctly phase slope) of the crystal by putting the resistance of the buffer in series with it. 2) They want better isolation in a single oscillator stage than they get with a series arrangement. 3) They want to double (or triple) the output frequency *and* do any / all of these things without degrading (and actually in case 1 improving) the phase noise. > someone wouldn't want to take advantage of that signal and use > that rather than add filters and poor biasing to the mix to claim that > something can be done when we are talking about ideal situations where the > lowest phase noise is desired. Your claim is that harmonics in the oscillator will keep you from having low phase noise. That simply is not correct. > > Someday you might end up needing to design a low noise oscillator and you > will need to consider these design obstacles. Well oddly enough, I have designed a few (thousand) low noise oscillators over the last 4 or 5 decades. I’ve also torn down more oscillators than I can count and looked at how they are done. The “no limiting” crystal oscillator has never popped up in any of that. It’s also never shown up in any of the papers, going back into the 1920’s. Put simply: You (even with an AGC) will have a few db of excess gain. That gain causes part of the loop current to be converted to harmonic energy. That energy does not circulate with the same efficiency as the main mode. (crystals have “harmonics”, or more commonly acoustic overtones). To say that there is one part of the oscillator that is the crystal and another part that is the sustaining stage is fine. To say that the oscillator is only one or the other half of that complete circuit is not correct. > > Take care, Bob. Have fun Bob > > Jerry > > On Mon, Jul 27, 2015 at 5:39 PM, Bob Camp wrote: > >> Hi >> >> >>> On Jul 27, 2015, at 11:52 AM, jerry shirᴀr wrote: >>> >>> Here's the rub Bob. I have been trying to find a way or have you explain >>> how a high harmonic oscillator stage >> >> You are confusing the current through the crystal with the current in the >> oscillator transistor. >> So: >> >> Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC >> couple that resistor to your spectrum analyzer. >> Connect the base of the transistor with a 10K to +12 and a 10K to ground >> Connect a 1K ohm resistor from the emitter of the transistor to ground >> Hook a 100 pf cap from base to emitter >> Hook a 100 pf cap from emitter to base >> Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms to the >> base of the transistor. >> Hook a 32 pf cap from the other side of the crystal to ground >> >> I *hope* that’s specific enough for you. >> >> That circuit *will* oscillate. >> >> Look at the current on the 50 ohm resistor. It’s got plenty of ha
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Am 28.07.2015 um 03:58 schrieb Bill Byrom N5BB: [ nice and understandable summary of the Lee / Hajimiri ideas ] OTOH with this Dirac-style resonator feeding one collects the noise sidebands from order 1 to MAXINT and one needs to align all these harmonics nicely. It also does not help against low frequency effects that require stability over many cycles, such as the 1/f region. And it is only half the work. We not only need to feed the resonator, we also want RF from it. Thus, to stay in this principle, the sustaining amplifier would have to fetch its input also in Dirac style. Now we are pretty close to an ultra wideband nonlinear loop gain. Any low pass filtering would have to be done in front of the feeding pulse former, or the harmonics will not align. And apart from BW limiting we need something to set the net loop phase to 0. The pulse output of the sustaining amplifier is also not nice to use unless we want to feed a sampler or 1:2-FlipFlop. Output filtering via the resonator, say, in the elegant Burgeon(?) style would also be forbidden. As I see it, L/H creates a lot of problems, and worse, it does not provide a design algorithm, even if we accept the complications. regards, Gerhard, DK4XP (Arghh, I'm writing this on a 4*2 thread machine at 3.8 GHz, and Thunderbird produces typing delays... Turbo-C on Z80 with a Wyse-50 terminal felt better.) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Thanks Bob, I had no intention of being offensive. It is just my manner. Forgive me. First of all, I think you had intended to say "100pF from emitter to ground" rather than "100pF from emitter to base." I think that's a typo. Next, how much crystal drive level is there? I guess it depends on the crystal resistance, but I think there will be a lot of crystal current. Then I don't know why you would purposely want to clip the signal of the oscillator, but it is the designer's prerogative. For low noise applications, I have always used an AGC so the oscillator will have a lot of drive at startup and then backs off greatly for steady state operation. You can also more easily control the drive level to a small enough amount so that the drive won't mess up the frequency accuracy. Also the buffer from the oscillator stage buffers the actual crystal current so the base to emitter noise does not get amplified to the collector and propagated down the line. I could beat a -145dBc/Hz spec at 100Hz and -168dBc/Hz at 10kHz. I don't have anything here to breadboard these things up. I don't understand why when there is already a clean crystal current in the circuit, someone wouldn't want to take advantage of that signal and use that rather than add filters and poor biasing to the mix to claim that something can be done when we are talking about ideal situations where the lowest phase noise is desired. Someday you might end up needing to design a low noise oscillator and you will need to consider these design obstacles. Take care, Bob. Jerry On Mon, Jul 27, 2015 at 5:39 PM, Bob Camp wrote: > Hi > > > > On Jul 27, 2015, at 11:52 AM, jerry shirᴀr wrote: > > > > Here's the rub Bob. I have been trying to find a way or have you explain > > how a high harmonic oscillator stage > > You are confusing the current through the crystal with the current in the > oscillator transistor. > So: > > Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC > couple that resistor to your spectrum analyzer. > Connect the base of the transistor with a 10K to +12 and a 10K to ground > Connect a 1K ohm resistor from the emitter of the transistor to ground > Hook a 100 pf cap from base to emitter > Hook a 100 pf cap from emitter to base > Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms to the > base of the transistor. > Hook a 32 pf cap from the other side of the crystal to ground > > I *hope* that’s specific enough for you. > > That circuit *will* oscillate. > > Look at the current on the 50 ohm resistor. It’s got plenty of harmonics. > > With me so far or is this still to theoretical? > > Now, this *does* get a bit exciting, but it’s the way this circuit has > been analyzed since the 1930’s (when it used a tube): > > You shift the ground to the emitter for the purposes of seeing what’s > going on. You now have an “input side” and an “output side” to > the active stage. This lets you break the loop for analysis. > > In this format, the current in the collector is more clearly flowing > through the 1K resistor and one of the 100 pf caps. > The current that passes through the crystal flows through the other 100 pf > cap (and the base) to ground. > > The current in the oscillator stage is every bit as nonlinear as you saw > before. > > Since this is an oscillator, the current flows in a loop. There is no > independent current in any one leg. They all are related. > If you want to see this, hook up an oscilloscope to the collector resistor > and apply power to the oscillator. The output does not > go instantly to a full output. It slowly builds up to the full value. The > current circulates around the loop *many* times as the > stage oscillates. > > Now: > > Break the circuit (AC) at any of the connection points. It stops > oscillating. (A DC break also does the same thing, but that’s cheating). > Without everything hooked in a loop, you do not have oscillation. > > Next: > > Charles posted a long list of interesting transistors a few messages back. > Try them one at a time and look at phase noise at 20 KHz offset. > You will find that some are better than others. Take a look at the > harmonics in the collector. They don’t correlate with the phase noise… > > So, unless you are looking at the crystal as being the oscillator (which > it is not), there’s not much way to say that there are no harmonics > running around in this circuit. > > Is that simple enough? > > > is even possible and zip. You don't > > know and I certainly don't know. So there's that. > > *IF* your desire is for an explanation, offensive comments probably are > not a good idea…. > > Bob > > > > > Jerry > > On Jul 27, 2015 9:33 AM, "Bob Camp" wrote: > > > >> Hi > >> > >> Here’s the basic point: > >> > >> What is *required* for low phase noise? > >> > >> If you can build *one* oscillator that violates a “law” then that “law” > is > >> not > >> valid. In tis case the question is “do you *need* low harmonics in the > >> oscillato
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Bob, I think you meant to write: "Hook a 100 pf cap from emitter to ground." Also remember that the feedback loop can use multiple active devices. You can design a crystal oscillator which has only linear loading on the crystal but which has nonlinear characteristics somewhere in the feedback loop. Some oscillators use a filter to insure that only a linear signal is fed back from a very nonlinear amplifier in the loop. The output can be taken from various places in the feedback loop, and the harmonic content varies depending on that location. One idea is to only add energy to the crystal at the peak of the sinewave voltage, when the derivative of the voltage is zero. If a short pulse is added at the peak the amplitude is increased without significantly affecting the phase. But if the pulse is added at the middle "zero crossing" of the sinewave (with resepect to the peak-to- peak swing) where the derivative is large, the phase can be affected by the feedback. Ideally you want to add just enough energy each cycle to overcome the energy lost in the crystal due to limited Q. If the feedback loop is linear, then the noise generated by the active and passive devices is continuously fed back to the crystal, generating amplitude noise. Due to the angle of the feedback (described above) and AM to PM conversion due to device characteristics (junction capacitance changes with voltage), some of the amplitude noise gets converted to phase noise. The total resulting noise sidebands (made up of both ampitude and phase noise) is what everyone wants to minimize. You could also use a feedback loop which was very nonlinear by using an active switch with a low ON resistance (so hopefully a low noise figure when closed) to send spikes back to the crystal resonator at the peak of the voltage waveform. If you could arrange the circuit so that the duty cycle of this switch was low, the residual noise would only be amplified and fed back to the crystal resonator over a small portion of each cycle, reducing the average noise figure of the oscillator. If the feedback circuit is highly nonlinear the amplitude noise might be clipped and reduced. Of course, the jitter in the feedback circuit is important. The active devices need to be well bypassed at audio frequencies so that low frequency shot noise isn't amplified with high efficiency. Since the junction capacitance (and other AM to PM conversion sources) in downstream amplifiers can be affected by audio frequency noise, I think that it's very important that such noise isn't allowed to phase modulate the desired RF signal. -- Bill Byrom N5BB On Mon, Jul 27, 2015, at 05:39 PM, Bob Camp wrote: > Hi > > >> On Jul 27, 2015, at 11:52 AM, jerry shirᴀr wrote: >> >> Here's the rub Bob. I have been trying to find a way or have you explain >> how a high harmonic oscillator stage > > You are confusing the current through the crystal with the current in the > oscillator transistor. > So: > > Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC > couple that resistor to your spectrum analyzer. > Connect the base of the transistor with a 10K to +12 and a 10K to ground > Connect a 1K ohm resistor from the emitter of the transistor to ground > Hook a 100 pf cap from base to emitter > Hook a 100 pf cap from emitter to base > Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms to > the base of the transistor. > Hook a 32 pf cap from the other side of the crystal to ground > > I **hope** that’s specific enough for you. > > That circuit **will** oscillate. > > Look at the current on the 50 ohm resistor. It’s got plenty of harmonics. > > With me so far or is this still to theoretical? > > Now, this **does** get a bit exciting, but it’s the way this circuit has > been analyzed since the 1930’s (when it used a tube): > > You shift the ground to the emitter for the purposes of seeing what’s > going on. You now have an “input side” and an “output side” to > the active stage. This lets you break the loop for analysis. > > In this format, the current in the collector is more clearly flowing > through the 1K resistor and one of the 100 pf caps. > The current that passes through the crystal flows through the other 100 > pf cap (and the base) to ground. > > The current in the oscillator stage is every bit as nonlinear as you saw > before. > > Since this is an oscillator, the current flows in a loop. There is no > independent current in any one leg. They all are related. > If you want to see this, hook up an oscilloscope to the collector > resistor and apply power to the oscillator. The output does not > go instantly to a full output. It slowly builds up to the full value. The > current circulates around the loop **many** times as the > stage oscillates. > > Now: > > Break the circuit (AC) at any of the connection points. It stops > oscillating. (A DC break also does the same thing, but that’s cheating). > Without everything hooked i
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi > On Jul 27, 2015, at 11:52 AM, jerry shirᴀr wrote: > > Here's the rub Bob. I have been trying to find a way or have you explain > how a high harmonic oscillator stage You are confusing the current through the crystal with the current in the oscillator transistor. So: Connect a 2N918 with the collector to +12V through a 50 ohm resistor. AC couple that resistor to your spectrum analyzer. Connect the base of the transistor with a 10K to +12 and a 10K to ground Connect a 1K ohm resistor from the emitter of the transistor to ground Hook a 100 pf cap from base to emitter Hook a 100 pf cap from emitter to base Hook a 10.0 MHz fundamental crystal with a resistance of < 10 ohms to the base of the transistor. Hook a 32 pf cap from the other side of the crystal to ground I *hope* that’s specific enough for you. That circuit *will* oscillate. Look at the current on the 50 ohm resistor. It’s got plenty of harmonics. With me so far or is this still to theoretical? Now, this *does* get a bit exciting, but it’s the way this circuit has been analyzed since the 1930’s (when it used a tube): You shift the ground to the emitter for the purposes of seeing what’s going on. You now have an “input side” and an “output side” to the active stage. This lets you break the loop for analysis. In this format, the current in the collector is more clearly flowing through the 1K resistor and one of the 100 pf caps. The current that passes through the crystal flows through the other 100 pf cap (and the base) to ground. The current in the oscillator stage is every bit as nonlinear as you saw before. Since this is an oscillator, the current flows in a loop. There is no independent current in any one leg. They all are related. If you want to see this, hook up an oscilloscope to the collector resistor and apply power to the oscillator. The output does not go instantly to a full output. It slowly builds up to the full value. The current circulates around the loop *many* times as the stage oscillates. Now: Break the circuit (AC) at any of the connection points. It stops oscillating. (A DC break also does the same thing, but that’s cheating). Without everything hooked in a loop, you do not have oscillation. Next: Charles posted a long list of interesting transistors a few messages back. Try them one at a time and look at phase noise at 20 KHz offset. You will find that some are better than others. Take a look at the harmonics in the collector. They don’t correlate with the phase noise… So, unless you are looking at the crystal as being the oscillator (which it is not), there’s not much way to say that there are no harmonics running around in this circuit. Is that simple enough? > is even possible and zip. You don't > know and I certainly don't know. So there's that. *IF* your desire is for an explanation, offensive comments probably are not a good idea…. Bob > > Jerry > On Jul 27, 2015 9:33 AM, "Bob Camp" wrote: > >> Hi >> >> Here’s the basic point: >> >> What is *required* for low phase noise? >> >> If you can build *one* oscillator that violates a “law” then that “law” is >> not >> valid. In tis case the question is “do you *need* low harmonics in the >> oscillator >> stage to get low phase noise?” >> >> Here on the list, we get obsessed about all sorts of stuff. That’s fine. >> It’s fun. >> We learn things taking stuff past “the limit”. The gotcha is that can make >> it >> hard to keep track of “what is necessary ”. >> >>> On Jul 27, 2015, at 12:47 AM, jerry shirᴀr wrote: >>> >>> Thanks Tim. I love reading these papers. However my copy states "In >> fact, >>> were it not for this slight non-linearity, it would be virtually >>> impossible to build a simple lamp-stabilized RC oscillator with good >>> envelope stability over a wide frequency range." rather than "In fact, >> were >>> it not for [amplifier] nonlinearity, it would be impossible to build a >>> simple oscillator with good envelope stability." The meaning changes a >>> little bit. >>> >>> Thanks Bob, >>> >>> Even looking at Tim's article, they are talking about a low degree of >>> distortion with an RC oscillator. I am assuming that the Q of the RC >> would >>> be quite low with respect to the overtone crystals you speak, and yet the >>> RC oscillator described here has low distortion from the oscillator >> stage. >> >> The objective of an RC lab oscillator design *is* low harmonic distortion. >> They >> have awful phase noise. >> >>> >>> Putting a filter in the feedback path with the high Q crystal seems like >>> you would be de-Q-ing the crystal and losing the high Q characteristics >> of >>> the crystal. >> >> The oscillator must be a closed loop to operate. There will *always* be >> things >> “in series” with the crystal. >> >>> Any changes of filter components over time seems like it >>> would necessarily add drift to the oscillator. >> >> Since you *must* tune the oscillator on frequency and you *mu
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Here's the rub Bob. I have been trying to find a way or have you explain how a high harmonic oscillator stage is even possible and zip. You don't know and I certainly don't know. So there's that. Jerry On Jul 27, 2015 9:33 AM, "Bob Camp" wrote: > Hi > > Here’s the basic point: > > What is *required* for low phase noise? > > If you can build *one* oscillator that violates a “law” then that “law” is > not > valid. In tis case the question is “do you *need* low harmonics in the > oscillator > stage to get low phase noise?” > > Here on the list, we get obsessed about all sorts of stuff. That’s fine. > It’s fun. > We learn things taking stuff past “the limit”. The gotcha is that can make > it > hard to keep track of “what is necessary ”. > > > On Jul 27, 2015, at 12:47 AM, jerry shirᴀr wrote: > > > > Thanks Tim. I love reading these papers. However my copy states "In > fact, > > were it not for this slight non-linearity, it would be virtually > > impossible to build a simple lamp-stabilized RC oscillator with good > > envelope stability over a wide frequency range." rather than "In fact, > were > > it not for [amplifier] nonlinearity, it would be impossible to build a > > simple oscillator with good envelope stability." The meaning changes a > > little bit. > > > > Thanks Bob, > > > > Even looking at Tim's article, they are talking about a low degree of > > distortion with an RC oscillator. I am assuming that the Q of the RC > would > > be quite low with respect to the overtone crystals you speak, and yet the > > RC oscillator described here has low distortion from the oscillator > stage. > > The objective of an RC lab oscillator design *is* low harmonic distortion. > They > have awful phase noise. > > > > > Putting a filter in the feedback path with the high Q crystal seems like > > you would be de-Q-ing the crystal and losing the high Q characteristics > of > > the crystal. > > The oscillator must be a closed loop to operate. There will *always* be > things > “in series” with the crystal. > > > Any changes of filter components over time seems like it > > would necessarily add drift to the oscillator. > > Since you *must* tune the oscillator on frequency and you *must* select > the overtone, you will have caps and inductors in the loop. > > > What do you think? Of > > course I am not saying that you can't put filters in the crystal circuit > > but rather that is something I would never recommend doing that in a > > precision oscillator design. > > Except you have to do it. Since you have to do it, every example out there > of a low phase noise oscillator has at least some caps in series with the > crystal. The vast majority have both coils and caps. > > > > > I realize what the impedance plot looks like of AT-cut and SC-cut > crystals > > but my question was specifically about harmonics. That is the topic of > > this thread. Are you thinking that crystals are rich in harmonics? I am > > not really seeing an idea of where you are saying the harmonic components > > come from in these high precision oscillators in the oscillator circuit. > > The limiting action in the oscillator device creates harmonics. > > > > > What are the "impedance properties" of the crystal? > > There are literally thousands of papers on this. The simple answer is that > they have *many* resonant modes. > > > Why use a crystal > > rather than slapping a cap and a coil in there to get your desired > > frequency? > > 1) Because it’s Q is higher > 2) Because it’s more stable > > > > > When you "pick off" the collector current, wouldn't that include the > > amplified base to emitter junction noise inherent in simple transistor > > oscillator circuits? > > Again, it’s a loop. The current goes around in circles. There is no magic > “clean here” current. If you are looking at an OCXO that doubles the > crystal > before the output is created, it’s a really good bet they pulled the signal > off the collector of the oscillator. The net result is still a low phase > noise > oscillator. > > > Would that be the same as the crystal current? > > You can’t have an oscillator with just a crystal. You also need other > “stuff”…. > > Bob > > > > > Thanks. > > > > Jerry > > ___ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi Here’s the basic point: What is *required* for low phase noise? If you can build *one* oscillator that violates a “law” then that “law” is not valid. In tis case the question is “do you *need* low harmonics in the oscillator stage to get low phase noise?” Here on the list, we get obsessed about all sorts of stuff. That’s fine. It’s fun. We learn things taking stuff past “the limit”. The gotcha is that can make it hard to keep track of “what is necessary ”. > On Jul 27, 2015, at 12:47 AM, jerry shirᴀr wrote: > > Thanks Tim. I love reading these papers. However my copy states "In fact, > were it not for this slight non-linearity, it would be virtually > impossible to build a simple lamp-stabilized RC oscillator with good > envelope stability over a wide frequency range." rather than "In fact, were > it not for [amplifier] nonlinearity, it would be impossible to build a > simple oscillator with good envelope stability." The meaning changes a > little bit. > > Thanks Bob, > > Even looking at Tim's article, they are talking about a low degree of > distortion with an RC oscillator. I am assuming that the Q of the RC would > be quite low with respect to the overtone crystals you speak, and yet the > RC oscillator described here has low distortion from the oscillator stage. The objective of an RC lab oscillator design *is* low harmonic distortion. They have awful phase noise. > > Putting a filter in the feedback path with the high Q crystal seems like > you would be de-Q-ing the crystal and losing the high Q characteristics of > the crystal. The oscillator must be a closed loop to operate. There will *always* be things “in series” with the crystal. > Any changes of filter components over time seems like it > would necessarily add drift to the oscillator. Since you *must* tune the oscillator on frequency and you *must* select the overtone, you will have caps and inductors in the loop. > What do you think? Of > course I am not saying that you can't put filters in the crystal circuit > but rather that is something I would never recommend doing that in a > precision oscillator design. Except you have to do it. Since you have to do it, every example out there of a low phase noise oscillator has at least some caps in series with the crystal. The vast majority have both coils and caps. > > I realize what the impedance plot looks like of AT-cut and SC-cut crystals > but my question was specifically about harmonics. That is the topic of > this thread. Are you thinking that crystals are rich in harmonics? I am > not really seeing an idea of where you are saying the harmonic components > come from in these high precision oscillators in the oscillator circuit. The limiting action in the oscillator device creates harmonics. > > What are the "impedance properties" of the crystal? There are literally thousands of papers on this. The simple answer is that they have *many* resonant modes. > Why use a crystal > rather than slapping a cap and a coil in there to get your desired > frequency? 1) Because it’s Q is higher 2) Because it’s more stable > > When you "pick off" the collector current, wouldn't that include the > amplified base to emitter junction noise inherent in simple transistor > oscillator circuits? Again, it’s a loop. The current goes around in circles. There is no magic “clean here” current. If you are looking at an OCXO that doubles the crystal before the output is created, it’s a really good bet they pulled the signal off the collector of the oscillator. The net result is still a low phase noise oscillator. > Would that be the same as the crystal current? You can’t have an oscillator with just a crystal. You also need other “stuff”…. Bob > > Thanks. > > Jerry > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Thanks Tim. I love reading these papers. However my copy states "In fact, were it not for this slight non-linearity, it would be virtually impossible to build a simple lamp-stabilized RC oscillator with good envelope stability over a wide frequency range." rather than "In fact, were it not for [amplifier] nonlinearity, it would be impossible to build a simple oscillator with good envelope stability." The meaning changes a little bit. Thanks Bob, Even looking at Tim's article, they are talking about a low degree of distortion with an RC oscillator. I am assuming that the Q of the RC would be quite low with respect to the overtone crystals you speak, and yet the RC oscillator described here has low distortion from the oscillator stage. Putting a filter in the feedback path with the high Q crystal seems like you would be de-Q-ing the crystal and losing the high Q characteristics of the crystal. Any changes of filter components over time seems like it would necessarily add drift to the oscillator. What do you think? Of course I am not saying that you can't put filters in the crystal circuit but rather that is something I would never recommend doing that in a precision oscillator design. I realize what the impedance plot looks like of AT-cut and SC-cut crystals but my question was specifically about harmonics. That is the topic of this thread. Are you thinking that crystals are rich in harmonics? I am not really seeing an idea of where you are saying the harmonic components come from in these high precision oscillators in the oscillator circuit. What are the "impedance properties" of the crystal? Why use a crystal rather than slapping a cap and a coil in there to get your desired frequency? When you "pick off" the collector current, wouldn't that include the amplified base to emitter junction noise inherent in simple transistor oscillator circuits? Would that be the same as the crystal current? Thanks. Jerry ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
We seem to have wandered into one of my favorite subjects, oscillators that make very low distortion sine waves. I found this 1960 HP journal article to be most useful: http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1960-04.pdf Best quote:"In fact, were it not for [amplifier] nonlinearity, it would be impossible to build a simple oscillator with good envelope stability [...] This is borne out by the fact that occasionally oscillators show up in production which, because of a fortuitous combination of tube characteristics, exhibit extremely low distortion. Invariably these units give trouble with with envelope bounce [...] N1EKV also had a nice article in a 2010 QEX about the battle between amplitude stability and low distortion sine wave output (not sure this is available online). Tim N3QE On Sun, Jul 26, 2015 at 2:48 PM, jerry shirᴀr wrote: > Hi Bob, > > Help me to understand your remarks. > > A. The oscillator stage has a limiter. (Agreed.) > B. You can *easily* get <-160 dbc/Hz with an oscillator that has > harmonics in the > -10 to -20 range? > C. But we are not talking about the signal from the oscillator stage > itself? > D. Tuned buffers can have these higher harmonics and all is well? > E. Okay. We are now talking about downstream harmonics and not the actual > oscillator stage harmonics? > > Ideally the oscillator stage should have no tuned circuits so that the > feedback of this oscillator stage utilizes only the tuned circuit of the > high Q resonator. Okay. What frequency components should the hi Q > resonator exhibit? Should it be rich in harmonics or should it be pretty > limited to one frequency represented by a sinewave? Are we talking about > the harmonics at the output of the actual oscillator stage or after a few > buffer stages? > > Help me out here. > > Thanks, > > Jerry N9XR > > > On Sun, Jul 26, 2015 at 8:44 AM, Bob Camp wrote: > > > Hi > > > > Ummm …. errr…. > > > > The oscillator loop has a limiter in it or it’s not going to work very > > well. > > > > You can *easily* get <-160 dbc/Hz with an oscillator that has harmonics > in > > the > > -10 to -20 range. With some tweaking you can get into the 170’s. > > > > It’s not the limiting by it’s self, it’s *how* the limiting is achieved. > > > > In most cases the “oscillator output” you are looking at is not the > signal > > from > > the oscillator stage it’s self. You are looking at a signal that has been > > through > > several (like tuned) buffers before you see it. The same narrow band > tuned > > stages > > can be used to “clean up” harmonics on any signal. The old style rack > mount > > OCXO’s did a *lot* of this. > > > > Bob > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi > On Jul 26, 2015, at 2:48 PM, jerry shirᴀr wrote: > > Hi Bob, > > Help me to understand your remarks. > > A. The oscillator stage has a limiter. (Agreed.) > B. You can *easily* get <-160 dbc/Hz with an oscillator that has > harmonics in the > -10 to -20 range? yes > C. But we are not talking about the signal from the oscillator stage > itself? yes > D. Tuned buffers can have these higher harmonics and all is well? not if they are properly tuned. The tuning is bandpass in nature. > E. Okay. We are now talking about downstream harmonics and not the actual > oscillator stage harmonics? nope. > > Ideally the oscillator stage should have no tuned circuits so that the > feedback of this oscillator stage utilizes only the tuned circuit of the > high Q resonator. Fine unless you have an overtone crystal. Roughly 99.99% of all low noise stuff runs on an overtone. That forces you to some sort of “zonal filter” in the feedback path. > Okay. What frequency components should the hi Q > resonator exhibit? The resonator has impedance properties. > Should it be rich in harmonics or should it be pretty > limited to one frequency represented by a sine wave? All *real* resonators have “rich” impedance plots. An SC very much so. > Are we talking about > the harmonics at the output of the actual oscillator stage or after a few > buffer stages? No, we’re talking about the signals present in a typical oscillator stage it’s self *before* you decide to clean them up and *after* you make this or that choice about where to get a signal from. > > Help me out here. Your oscillator *must* meat Barkenhausen’s criteria. It’s got to have a gain of *exactly* one and a phase shift of *exactly* zero degrees (modulo 360 degrees). Anything else and it will not sustain oscillation. If the oscillator has a gain of one all the time, it’s unlikely it will ever start oscillating. The only practical way to make an oscillator work is to provide “excess gain” at starting. If that gain is in the 3 to 6 db range, the norm is to take care of it by limiting. If you look at a very conventional circuit that runs a single transistor as the oscillator stage, that stage is both a limiter and the sustaining stage for the oscillation. If you take a look at the collector current, it’s far from continuous. Pick off from there without any bandpass tuning and shove the result into a phase noise analyzer. Phase noise is as good as any other point on the oscillator. Harmonics *may* be down 6 db (more likely 10) …. Bob > > Thanks, > > Jerry N9XR > > > On Sun, Jul 26, 2015 at 8:44 AM, Bob Camp wrote: > >> Hi >> >> Ummm …. errr…. >> >> The oscillator loop has a limiter in it or it’s not going to work very >> well. >> >> You can *easily* get <-160 dbc/Hz with an oscillator that has harmonics in >> the >> -10 to -20 range. With some tweaking you can get into the 170’s. >> >> It’s not the limiting by it’s self, it’s *how* the limiting is achieved. >> >> In most cases the “oscillator output” you are looking at is not the signal >> from >> the oscillator stage it’s self. You are looking at a signal that has been >> through >> several (like tuned) buffers before you see it. The same narrow band tuned >> stages >> can be used to “clean up” harmonics on any signal. The old style rack mount >> OCXO’s did a *lot* of this. >> >> Bob >> > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi Bob, Help me to understand your remarks. A. The oscillator stage has a limiter. (Agreed.) B. You can *easily* get <-160 dbc/Hz with an oscillator that has harmonics in the -10 to -20 range? C. But we are not talking about the signal from the oscillator stage itself? D. Tuned buffers can have these higher harmonics and all is well? E. Okay. We are now talking about downstream harmonics and not the actual oscillator stage harmonics? Ideally the oscillator stage should have no tuned circuits so that the feedback of this oscillator stage utilizes only the tuned circuit of the high Q resonator. Okay. What frequency components should the hi Q resonator exhibit? Should it be rich in harmonics or should it be pretty limited to one frequency represented by a sinewave? Are we talking about the harmonics at the output of the actual oscillator stage or after a few buffer stages? Help me out here. Thanks, Jerry N9XR On Sun, Jul 26, 2015 at 8:44 AM, Bob Camp wrote: > Hi > > Ummm …. errr…. > > The oscillator loop has a limiter in it or it’s not going to work very > well. > > You can *easily* get <-160 dbc/Hz with an oscillator that has harmonics in > the > -10 to -20 range. With some tweaking you can get into the 170’s. > > It’s not the limiting by it’s self, it’s *how* the limiting is achieved. > > In most cases the “oscillator output” you are looking at is not the signal > from > the oscillator stage it’s self. You are looking at a signal that has been > through > several (like tuned) buffers before you see it. The same narrow band tuned > stages > can be used to “clean up” harmonics on any signal. The old style rack mount > OCXO’s did a *lot* of this. > > Bob > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi Ummm …. errr…. The oscillator loop has a limiter in it or it’s not going to work very well. You can *easily* get <-160 dbc/Hz with an oscillator that has harmonics in the -10 to -20 range. With some tweaking you can get into the 170’s. It’s not the limiting by it’s self, it’s *how* the limiting is achieved. In most cases the “oscillator output” you are looking at is not the signal from the oscillator stage it’s self. You are looking at a signal that has been through several (like tuned) buffers before you see it. The same narrow band tuned stages can be used to “clean up” harmonics on any signal. The old style rack mount OCXO’s did a *lot* of this. Bob > On Jul 25, 2015, at 11:47 PM, jerry shirᴀr wrote: > > "Not necessarily. Many oscillator circuits do not deliver a good sine wave > to begin with" > > This is very true. However if it is worse than -30dB harmonic sinewave back > stream then the oscillator is probably extremely high in phase noise > anyway. Since the threshold is off center, the phase noise of the 20% duty > cycle squarewave will have additional amounts from the AM noise on the > signal adding in from that threshold offset. The reason we want 50% is to > get the cleanest signal possible with what we have to work with. :) > > Jerry N9XR. > On Jul 25, 2015 3:17 PM, "Alexander Pummer" wrote: > >> it is relative easy to make a perfect 50% square wave from almost any >> input wave form >> >> U1 could be any-- fast enough for the desired frequency--comparator or a >> transistor pair similar to Charles Wenzel's circuit, R1 C1 is a long time >> integrator,[ RxC >> 1/f of the incoming frequency] the voltage at "A" is >> proportional with the duty cycle, U 2 is some high gain low noise, low >> input offset voltage high input impedance amplifier, the duty-cycle is set >> by R4/R5, fine tuning with R6, C2v removes the noise Vr is well stabilized >> reference voltage, >> To set up the circuit the output should be connected -- with DC decoupling >> -- to a spectrum analyzer's input for watching the second harmonic [a >> perfect 50% duty cycle square wave lacks of even harmonics ..] of the input >> frequency, which has to be adjusted to minimum with R6, using the same >> stile resistors for ±0,1%, R4 and R5, with value 100 times of R6 a very >> good temperature stability could be achieved. for better short time >> stability R2 's top could bealso connected to Vr, >> If the drive capability of U1 is not enough for the load non-inverting >> buffers could be inserted to U1's output, of course that circuit wil >> contribute some phase noise/ jitter too. >> 73 >> KJ6UHN >> Alex >> >> >> On 7/25/2015 1:34 AM, tim...@timeok.it wrote: >> >>> >>> bypassing the inverter you will improve phase noise. Yuo will probably need a sine buffer at 10MHz to drive 50 ohms. >>> This separator con be the solution: >>> http://www.timeok.it/files/hp5065AoptH10v200.pdf >>> high input impedance, output 50Ohm, high power handling and low additive >>> phase noise. >>> >>> But before measure using an oscilloscope the output of the GPS OCXO >>> directly on the output pin to verify if there is a sine-wave or square >>> >>> Luciano >>> timeok >>> Message sent via Atmail Open - http://atmail.org/ >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
"Not necessarily. Many oscillator circuits do not deliver a good sine wave to begin with" This is very true. However if it is worse than -30dB harmonic sinewave back stream then the oscillator is probably extremely high in phase noise anyway. Since the threshold is off center, the phase noise of the 20% duty cycle squarewave will have additional amounts from the AM noise on the signal adding in from that threshold offset. The reason we want 50% is to get the cleanest signal possible with what we have to work with. :) Jerry N9XR. On Jul 25, 2015 3:17 PM, "Alexander Pummer" wrote: > it is relative easy to make a perfect 50% square wave from almost any > input wave form > > U1 could be any-- fast enough for the desired frequency--comparator or a > transistor pair similar to Charles Wenzel's circuit, R1 C1 is a long time > integrator,[ RxC >> 1/f of the incoming frequency] the voltage at "A" is > proportional with the duty cycle, U 2 is some high gain low noise, low > input offset voltage high input impedance amplifier, the duty-cycle is set > by R4/R5, fine tuning with R6, C2v removes the noise Vr is well stabilized > reference voltage, > To set up the circuit the output should be connected -- with DC decoupling > -- to a spectrum analyzer's input for watching the second harmonic [a > perfect 50% duty cycle square wave lacks of even harmonics ..] of the input > frequency, which has to be adjusted to minimum with R6, using the same > stile resistors for ±0,1%, R4 and R5, with value 100 times of R6 a very > good temperature stability could be achieved. for better short time > stability R2 's top could bealso connected to Vr, > If the drive capability of U1 is not enough for the load non-inverting > buffers could be inserted to U1's output, of course that circuit wil > contribute some phase noise/ jitter too. > 73 > KJ6UHN > Alex > > > On 7/25/2015 1:34 AM, tim...@timeok.it wrote: > >> >> bypassing the inverter you will improve phase noise. Yuo will probably >>> need a sine buffer at 10MHz to drive 50 ohms. >>> >> This separator con be the solution: >> http://www.timeok.it/files/hp5065AoptH10v200.pdf >> high input impedance, output 50Ohm, high power handling and low additive >> phase noise. >> >> But before measure using an oscilloscope the output of the GPS OCXO >> directly on the output pin to verify if there is a sine-wave or square >> >> Luciano >> timeok >> Message sent via Atmail Open - http://atmail.org/ >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
it is relative easy to make a perfect 50% square wave from almost any input wave form U1 could be any-- fast enough for the desired frequency--comparator or a transistor pair similar to Charles Wenzel's circuit, R1 C1 is a long time integrator,[ RxC >> 1/f of the incoming frequency] the voltage at "A" is proportional with the duty cycle, U 2 is some high gain low noise, low input offset voltage high input impedance amplifier, the duty-cycle is set by R4/R5, fine tuning with R6, C2v removes the noise Vr is well stabilized reference voltage, To set up the circuit the output should be connected -- with DC decoupling -- to a spectrum analyzer's input for watching the second harmonic [a perfect 50% duty cycle square wave lacks of even harmonics ..] of the input frequency, which has to be adjusted to minimum with R6, using the same stile resistors for ±0,1%, R4 and R5, with value 100 times of R6 a very good temperature stability could be achieved. for better short time stability R2 's top could bealso connected to Vr, If the drive capability of U1 is not enough for the load non-inverting buffers could be inserted to U1's output, of course that circuit wil contribute some phase noise/ jitter too. 73 KJ6UHN Alex On 7/25/2015 1:34 AM, tim...@timeok.it wrote: bypassing the inverter you will improve phase noise. Yuo will probably need a sine buffer at 10MHz to drive 50 ohms. This separator con be the solution: http://www.timeok.it/files/hp5065AoptH10v200.pdf high input impedance, output 50Ohm, high power handling and low additive phase noise. But before measure using an oscilloscope the output of the GPS OCXO directly on the output pin to verify if there is a sine-wave or square Luciano timeok Message sent via Atmail Open - http://atmail.org/ ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
all of these oscillators, which do not deliver sinusoid output, have some threshold, which changes the form of the original sinusoid wave shape -- since the best phase-noise performance could be generated with a resonator and resonators inherently generate sinusoid wave form -- and that said threshold is always modulated by noises [at least by thermal voltage noise] which causes jitter-> phase noise 73 KJ6UHN Alex On 7/25/2015 3:47 AM, Charles Steinmetz wrote: Jerry wrote: But back there somewhere is a sinewave. Not necessarily. Many oscillator circuits do not deliver a good sine wave to begin with (in which case you may need as much filtering to get a clean sine wave as if you started with an asymmetrical square wave), and many packaged oscillators have CMOS logic outputs (in which case you would have to break into the sealed package to get at any sine or sine-ish signal there may be). Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi > On Jul 25, 2015, at 6:23 AM, Magnus Danielson > wrote: > > Hi, > > On 07/25/2015 03:35 AM, Charles Steinmetz wrote: >> skipp wrote: >> >>> [the 10MHz output is] not even close to being symmetrical. The waveform >>> on-portion (duty cycle) appears (surprising to me) to be much less >>> than 20% >>> >>> Now I'm under the assumption that proper rounding or conversion of the >>> non >>> symmetrical 10 MHz square to a sine wave will be a bit more involved. >> >> That means there are significant even harmonics present, including the >> second harmonic, which is a lot closer to the fundamental and, >> therefore, harder to remove by filtering (a perfect square wave contains >> only the fundamental and its odd harmonics). > > If the symmetry error is minor, the second harmonic at 20 MHz will still be > relatively small. However, it if turns out to be important, an LCR-serial > link tuned to 20 MHz and with some resistance for sufficiently low Q can eat > some of that energy up as it is placed between signal and ground. > The problem with any “shunt to ground” approach on the output of a CMOS gate is that they (essentially) are voltage output devices. Virtually all of their life is spent with the output shorted to either the supply line or to ground. If you hook them up to an open circuit ( = a typical CMOS load) this does not create any idle current flow. If you hook them up to something that looks like a load to ground or B+, there is current flow and they are hotter / less happy / more likely to burn out. With a gate driven filter, the idea is to have as few shunt elements as possible. You also want to isolate them from the output with a “reciprocal” series element between them and the gate. This may sound like a minor thing. Give it a try and see. You can easily get a 10:1 change in supply current on a gate simply by flipping filter elements around. Yes, low Q can reduce that ratio a bit. Often you can only hit your harmonic numbers with a high(er) Q. Bob > Cheers, > Magnus > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Jerry wrote: But back there somewhere is a sinewave. Not necessarily. Many oscillator circuits do not deliver a good sine wave to begin with (in which case you may need as much filtering to get a clean sine wave as if you started with an asymmetrical square wave), and many packaged oscillators have CMOS logic outputs (in which case you would have to break into the sealed package to get at any sine or sine-ish signal there may be). Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi, On 07/25/2015 03:35 AM, Charles Steinmetz wrote: skipp wrote: [the 10MHz output is] not even close to being symmetrical. The waveform on-portion (duty cycle) appears (surprising to me) to be much less than 20% Now I'm under the assumption that proper rounding or conversion of the non symmetrical 10 MHz square to a sine wave will be a bit more involved. That means there are significant even harmonics present, including the second harmonic, which is a lot closer to the fundamental and, therefore, harder to remove by filtering (a perfect square wave contains only the fundamental and its odd harmonics). If the symmetry error is minor, the second harmonic at 20 MHz will still be relatively small. However, it if turns out to be important, an LCR-serial link tuned to 20 MHz and with some resistance for sufficiently low Q can eat some of that energy up as it is placed between signal and ground. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
> bypassing the inverter you will improve phase noise. Yuo will probably > need a sine buffer at 10MHz to drive 50 ohms. This separator con be the solution: http://www.timeok.it/files/hp5065AoptH10v200.pdf high input impedance, output 50Ohm, high power handling and low additive phase noise. But before measure using an oscilloscope the output of the GPS OCXO directly on the output pin to verify if there is a sine-wave or square Luciano timeok Message sent via Atmail Open - http://atmail.org/ ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
If you are tearing into the oscillator for correcting the 20% duty cycle, you may as well bypass the digital inverter at the output driving the output pin. The signal going into the inverter will be a sinewave. The reason it is at 20% duty cycle is that the DC bias running into the inverter stage is too low for the digital device. If the reason for the 20% is farther backstream then the sinewave could be distorted. The phase noise could then be poor. But back there somewhere is a sinewave. By bypassing the inverter you will improve phase noise. Yuo will probably need a sine buffer at 10MHz to drive 50 ohms. Jerry On Fri, Jul 24, 2015 at 8:35 PM, Charles Steinmetz wrote: > skipp wrote: > > [the 10MHz output is] not even close to being symmetrical. The waveform >> on-portion (duty cycle) appears (surprising to me) to be much less than >> 20% >> >> Now I'm under the assumption that proper rounding or conversion of the non >> symmetrical 10 MHz square to a sine wave will be a bit more involved. >> > > That means there are significant even harmonics present, including the > second harmonic, which is a lot closer to the fundamental and, therefore, > harder to remove by filtering (a perfect square wave contains only the > fundamental and its odd harmonics). > > Before I launch toward part two of this latest saga, I'd really be >> interested in reading >> suggestions and comments regarding methods to improve/fix the 10 MHz >> waveform >> symmetry. >> > > You could do a lot better than 20/80 by simply using the 10MHz pulses to > trigger a 50nS one-shot (astable multivibrator). However, that is a > quick-and-dirty solution, not a precision solution -- the duty cycle would > wander around with temperature, power supply voltage, noise, and other > factors. > > Alternatively, you could use very aggressive filtering, but that could > degrade the phase noise of the output sine wave due to the temperature > coefficient of the filter cutoff frequency. > > One sure way to get a symmetrical output would be to use a Dflop frequency > divider to generate a symmetrical 5MHz square wave, followed by a frequency > doubler to get back to 10MHz. There would be a phase noise penalty, but it > could be less than the phase noise penalty of a sufficiently aggressive > filter. > > Finally, you could use the 10MHz pulse train as the reference for a 1:1 > PLL. I suspect this would be the best way to go about it. > > Best regards, > > Charles > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
skipp wrote: [the 10MHz output is] not even close to being symmetrical. The waveform on-portion (duty cycle) appears (surprising to me) to be much less than 20% Now I'm under the assumption that proper rounding or conversion of the non symmetrical 10 MHz square to a sine wave will be a bit more involved. That means there are significant even harmonics present, including the second harmonic, which is a lot closer to the fundamental and, therefore, harder to remove by filtering (a perfect square wave contains only the fundamental and its odd harmonics). Before I launch toward part two of this latest saga, I'd really be interested in reading suggestions and comments regarding methods to improve/fix the 10 MHz waveform symmetry. You could do a lot better than 20/80 by simply using the 10MHz pulses to trigger a 50nS one-shot (astable multivibrator). However, that is a quick-and-dirty solution, not a precision solution -- the duty cycle would wander around with temperature, power supply voltage, noise, and other factors. Alternatively, you could use very aggressive filtering, but that could degrade the phase noise of the output sine wave due to the temperature coefficient of the filter cutoff frequency. One sure way to get a symmetrical output would be to use a Dflop frequency divider to generate a symmetrical 5MHz square wave, followed by a frequency doubler to get back to 10MHz. There would be a phase noise penalty, but it could be less than the phase noise penalty of a sufficiently aggressive filter. Finally, you could use the 10MHz pulse train as the reference for a 1:1 PLL. I suspect this would be the best way to go about it. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Symmetry is based on the biasing of the sinewave feeding the gate that you are trying to create a sinewave from. Jerry N9XR. On Jul 24, 2015 7:19 PM, "skipp Isaham via time-nuts" wrote: > Hello again, > > First off, I want to thank everyone who replied direct and through the > group > regarding my recent 10 MHz square to sine wave conversion info request. > > I obtained a mini-circuits 10.7 MHz low pass filter from Ebay cheap > enough and I also plan on "rolling my own" based on some of the information > and links provided in your generous replies. > > Part 2: > > With things in place, I actually looked at the actual square wave output > port with > a decent scope to see it's not even close to being symmetrical. The > waveform > on-portion (duty cycle) appears (surprising to me) to be much less than 20% > > Now I'm under the assumption that proper rounding or conversion of the non > symmetrical 10 MHz square to a sine wave will be a bit more involved. > > Before I launch toward part two of this latest saga, I'd really be > interested in reading > suggestions and comments regarding methods to improve/fix the 10 MHz > waveform > symmetry. > > Again, thank you in advance for your replies... > > Regards, > > skipp > skipp...@yahoo.com > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Square to sine wave symmetrical conversion (part 2)
Hi If your 10 MHz is the result of a “divide by 2 then divide by 5” approach, the output will not be a 50/50 duty cycle square wave. The best way to fix that is to move up the chain and play with the dividers. You need to re-aragne them so the final divider is a divide by 2. When you do so, consider that the final divider may be running a hundred ma of supply current rather than 10 or 20 ma. The shunt capacitor on that filter *does* make a difference. Bob > On Jul 24, 2015, at 4:30 PM, skipp Isaham via time-nuts > wrote: > > Hello again, > > First off, I want to thank everyone who replied direct and through the group > regarding my recent 10 MHz square to sine wave conversion info request. > > I obtained a mini-circuits 10.7 MHz low pass filter from Ebay cheap > enough and I also plan on "rolling my own" based on some of the information > and links provided in your generous replies. > > Part 2: > > With things in place, I actually looked at the actual square wave output port > with > a decent scope to see it's not even close to being symmetrical. The waveform > on-portion (duty cycle) appears (surprising to me) to be much less than 20% > > Now I'm under the assumption that proper rounding or conversion of the non > symmetrical 10 MHz square to a sine wave will be a bit more involved. > > Before I launch toward part two of this latest saga, I'd really be interested > in reading > suggestions and comments regarding methods to improve/fix the 10 MHz waveform > symmetry. > > Again, thank you in advance for your replies... > > Regards, > > skipp > skipp...@yahoo.com > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Square to sine wave symmetrical conversion (part 2)
Hello again, First off, I want to thank everyone who replied direct and through the group regarding my recent 10 MHz square to sine wave conversion info request. I obtained a mini-circuits 10.7 MHz low pass filter from Ebay cheap enough and I also plan on "rolling my own" based on some of the information and links provided in your generous replies. Part 2: With things in place, I actually looked at the actual square wave output port with a decent scope to see it's not even close to being symmetrical. The waveform on-portion (duty cycle) appears (surprising to me) to be much less than 20% Now I'm under the assumption that proper rounding or conversion of the non symmetrical 10 MHz square to a sine wave will be a bit more involved. Before I launch toward part two of this latest saga, I'd really be interested in reading suggestions and comments regarding methods to improve/fix the 10 MHz waveform symmetry. Again, thank you in advance for your replies... Regards, skipp skipp...@yahoo.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
