Re: [time-nuts] 50 ohm driver
The MOSFET drivers are limited in the max frequency they can operate at without burning. At 1 Hz it is of course not a problem but at 10MHz it most definitely would be. Since Martin did not originally say at what frequency he wanted to operate, it was most relevant. MOSFET drivers can deliver a few nS edges while driving significant capacitance at several hundred kHz. They can be very useful for "low" frequency clock drivers. Didier KO4BB On March 7, 2015 10:10:45 AM CST, Graham / KE9H wrote: >The question is not the frequency, but the edge rate. For a 1 PPS >signal, >how fast a rise time do you need? Do you want to know the time of the >edge to 1/100 second? one microsecond? one nano-second? A few >pico-seconds? > >If you want to know the time of the edge to one nano-second, then you >need a driver that can push sine-waves at over a few GHz. Not 10 MHz. > >--- Graham / KE9H > >== > >On Sat, Mar 7, 2015 at 7:58 AM, Didier Juges >wrote: > >> Martyn, if you only need 1Hz, I recommend you use a MOSFET driver >like the >> MIC4420 series or the UCC27531, powered from 10V with a 50 ohm output >> resistance. These parts have several A current capability, 18V or >more max >> VCC and are designed to drive capacitive loads (large MOSFET gate >> capacitance). It would not work at 10MHz (because of propagation >delay and >> self heating), but at lower frequencies, they work very well. >> The UCC27531 has lower propagation time and comes in an SOT-23 >package, the >> others are available in DIP-8 and SO-8. >> >> Didier KO4BB >> >> On Thu, Mar 5, 2015 at 3:59 PM, Martyn Smith >wrote: >> >> > Hello, >> > Thanks for all the feedback. >> > I should explain. I have an existing product that uses the 74AC14. >> > I have a customer who needs 5V into 50 ohm and can’t wait for the >> > competitive product that does this, or for me to re-design my unit. >> > So I have been looking for a quick fix. >> > I got excited when I found the SN74AS1004AD which has the exact >same >> > function and pin out but delivers 48 mA per channel. >> > While one output did give me 0-3.0 V into 50 ohm, combining them, >as we >> do >> > for the 74AC, actually produced worse results. >> > Maybe the output driver is different. >> > Anyway I’ve managed to get 0-4.8V by jacking up the supply voltage >to 5.7 >> > V for the 74AC14 and making the three 47 ohm resistors 0 ohm. >> > Risetime < 4 ns. >> > Basically to ideas that TimeNuts gave me. >> > I’m just worried the IC may die after a few months. But since the >> > customer will only use it at 1 Hz and hopefully 50:50 duty, or >less, I >> hope >> > to get away with it. >> > Of course if he removes the input and the outputs are on high, then >that >> > may be a problem. >> > BTW, the reason he wants this high voltage is because he is driving >a >> very >> > long cable from the distribution amp to the actual receiver. >> > Anyway I have an IC on test for a week to make sure it lasts. >> > Regards >> > Martyn >> > >> > >> > Today's Topics: >> > >> >1. Re: 50 ohm Driver (Bob Albert) >> >2. Re: 50 ohm Driver (Graham / KE9H) >> >3. Re: 50 ohm Driver (Tom Van Baak) >> >4. Re: 50 ohm Driver (Hal Murray) >> >5. Re: 50 ohm Driver (Dan Kemppainen) >> > 6. Re: Trimble Thunderbolt NMEA ? (Didier Juges) >> >7. Re: 50 ohm Driver (Bob Camp) >> >8. Re: 50 ohm Driver (Charles Steinmetz) >> >9. Re: new tdc from Texas (Angus) >> > 10. Re: new tdc from Texas (Attila Kinali) >> > >> > >> > >-- >> > >> > Message: 1 >> > Date: Wed, 4 Mar 2015 16:49:11 + (UTC) >> > From: Bob Albert >> > To: Discussion of precise time and frequency measurement >> > >> > Subject: Re: [time-nuts] 50 ohm Driver >> > Message-ID: >> > <1276775018.2671439.1425487751520.javamail.ya...@mail.yahoo.com> >> > Content-Type: text/plain; charset=UTF-8 >> > >> > 5V into 50 Ohms means 100 mA. Perhaps you need a medium power >transistor >> > amplifier or opamp. >> > Bob >> > >> > >> > On Wednesday, March 4, 2015 6:09 AM, Martyn Smith < >> mar...@ptsyst.com> >> > wrote: >> > >> > >> > Hello, >> > >> > A quick question. >> > >&g
Re: [time-nuts] 50 ohm driver
Martyn wrote: Charles asked for a link to the IC I mentioned. Thanks, but I have databooks for the various logic types, including AS. What I asked for is a link to the datasheet for your product -- the product the customer is using -- so we have some context for what you (and they) are trying to accomplish, which will give us a better idea of what sort of solutions might help you. 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] 50 ohm driver
The question is not the frequency, but the edge rate. For a 1 PPS signal, how fast a rise time do you need? Do you want to know the time of the edge to 1/100 second? one microsecond? one nano-second? A few pico-seconds? If you want to know the time of the edge to one nano-second, then you need a driver that can push sine-waves at over a few GHz. Not 10 MHz. --- Graham / KE9H == On Sat, Mar 7, 2015 at 7:58 AM, Didier Juges wrote: > Martyn, if you only need 1Hz, I recommend you use a MOSFET driver like the > MIC4420 series or the UCC27531, powered from 10V with a 50 ohm output > resistance. These parts have several A current capability, 18V or more max > VCC and are designed to drive capacitive loads (large MOSFET gate > capacitance). It would not work at 10MHz (because of propagation delay and > self heating), but at lower frequencies, they work very well. > The UCC27531 has lower propagation time and comes in an SOT-23 package, the > others are available in DIP-8 and SO-8. > > Didier KO4BB > > On Thu, Mar 5, 2015 at 3:59 PM, Martyn Smith wrote: > > > Hello, > > Thanks for all the feedback. > > I should explain. I have an existing product that uses the 74AC14. > > I have a customer who needs 5V into 50 ohm and can’t wait for the > > competitive product that does this, or for me to re-design my unit. > > So I have been looking for a quick fix. > > I got excited when I found the SN74AS1004AD which has the exact same > > function and pin out but delivers 48 mA per channel. > > While one output did give me 0-3.0 V into 50 ohm, combining them, as we > do > > for the 74AC, actually produced worse results. > > Maybe the output driver is different. > > Anyway I’ve managed to get 0-4.8V by jacking up the supply voltage to 5.7 > > V for the 74AC14 and making the three 47 ohm resistors 0 ohm. > > Risetime < 4 ns. > > Basically to ideas that TimeNuts gave me. > > I’m just worried the IC may die after a few months. But since the > > customer will only use it at 1 Hz and hopefully 50:50 duty, or less, I > hope > > to get away with it. > > Of course if he removes the input and the outputs are on high, then that > > may be a problem. > > BTW, the reason he wants this high voltage is because he is driving a > very > > long cable from the distribution amp to the actual receiver. > > Anyway I have an IC on test for a week to make sure it lasts. > > Regards > > Martyn > > > > > > Today's Topics: > > > >1. Re: 50 ohm Driver (Bob Albert) > >2. Re: 50 ohm Driver (Graham / KE9H) > >3. Re: 50 ohm Driver (Tom Van Baak) > >4. Re: 50 ohm Driver (Hal Murray) > >5. Re: 50 ohm Driver (Dan Kemppainen) > >6. Re: Trimble Thunderbolt NMEA ? (Didier Juges) > >7. Re: 50 ohm Driver (Bob Camp) > >8. Re: 50 ohm Driver (Charles Steinmetz) > >9. Re: new tdc from Texas (Angus) > > 10. Re: new tdc from Texas (Attila Kinali) > > > > > > -- > > > > Message: 1 > > Date: Wed, 4 Mar 2015 16:49:11 + (UTC) > > From: Bob Albert > > To: Discussion of precise time and frequency measurement > > > > Subject: Re: [time-nuts] 50 ohm Driver > > Message-ID: > > <1276775018.2671439.1425487751520.javamail.ya...@mail.yahoo.com> > > Content-Type: text/plain; charset=UTF-8 > > > > 5V into 50 Ohms means 100 mA. Perhaps you need a medium power transistor > > amplifier or opamp. > > Bob > > > > > > On Wednesday, March 4, 2015 6:09 AM, Martyn Smith < > mar...@ptsyst.com> > > wrote: > > > > > > Hello, > > > > A quick question. > > > > My output driver for a simple amplifier. > > > > I use three gates (in parallel with resistors) from a 74AC14 to give me > > about 0-3.2V into 50 ohm. > > > > I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing > > into 50 ohms. > > > > Can anyone recommend an IC that can delivery this. > > > > But it needs to have similar jitter performance to the 74AC14. > > > > I use it up to 10 MHz. > > > > Best Regards > > > > Martyn > > > > ___ > > 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. > > > > > > > > > > -- > > > > Message: 2 > > Date: Wed, 4 Mar 2015 12:16:02
Re: [time-nuts] 50 ohm driver
Martyn, if you only need 1Hz, I recommend you use a MOSFET driver like the MIC4420 series or the UCC27531, powered from 10V with a 50 ohm output resistance. These parts have several A current capability, 18V or more max VCC and are designed to drive capacitive loads (large MOSFET gate capacitance). It would not work at 10MHz (because of propagation delay and self heating), but at lower frequencies, they work very well. The UCC27531 has lower propagation time and comes in an SOT-23 package, the others are available in DIP-8 and SO-8. Didier KO4BB On Thu, Mar 5, 2015 at 3:59 PM, Martyn Smith wrote: > Hello, > Thanks for all the feedback. > I should explain. I have an existing product that uses the 74AC14. > I have a customer who needs 5V into 50 ohm and can’t wait for the > competitive product that does this, or for me to re-design my unit. > So I have been looking for a quick fix. > I got excited when I found the SN74AS1004AD which has the exact same > function and pin out but delivers 48 mA per channel. > While one output did give me 0-3.0 V into 50 ohm, combining them, as we do > for the 74AC, actually produced worse results. > Maybe the output driver is different. > Anyway I’ve managed to get 0-4.8V by jacking up the supply voltage to 5.7 > V for the 74AC14 and making the three 47 ohm resistors 0 ohm. > Risetime < 4 ns. > Basically to ideas that TimeNuts gave me. > I’m just worried the IC may die after a few months. But since the > customer will only use it at 1 Hz and hopefully 50:50 duty, or less, I hope > to get away with it. > Of course if he removes the input and the outputs are on high, then that > may be a problem. > BTW, the reason he wants this high voltage is because he is driving a very > long cable from the distribution amp to the actual receiver. > Anyway I have an IC on test for a week to make sure it lasts. > Regards > Martyn > > > Today's Topics: > >1. Re: 50 ohm Driver (Bob Albert) >2. Re: 50 ohm Driver (Graham / KE9H) >3. Re: 50 ohm Driver (Tom Van Baak) >4. Re: 50 ohm Driver (Hal Murray) >5. Re: 50 ohm Driver (Dan Kemppainen) >6. Re: Trimble Thunderbolt NMEA ? (Didier Juges) >7. Re: 50 ohm Driver (Bob Camp) >8. Re: 50 ohm Driver (Charles Steinmetz) >9. Re: new tdc from Texas (Angus) > 10. Re: new tdc from Texas (Attila Kinali) > > > -- > > Message: 1 > Date: Wed, 4 Mar 2015 16:49:11 + (UTC) > From: Bob Albert > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] 50 ohm Driver > Message-ID: > <1276775018.2671439.1425487751520.javamail.ya...@mail.yahoo.com> > Content-Type: text/plain; charset=UTF-8 > > 5V into 50 Ohms means 100 mA. Perhaps you need a medium power transistor > amplifier or opamp. > Bob > > > On Wednesday, March 4, 2015 6:09 AM, Martyn Smith > wrote: > > > Hello, > > A quick question. > > My output driver for a simple amplifier. > > I use three gates (in parallel with resistors) from a 74AC14 to give me > about 0-3.2V into 50 ohm. > > I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing > into 50 ohms. > > Can anyone recommend an IC that can delivery this. > > But it needs to have similar jitter performance to the 74AC14. > > I use it up to 10 MHz. > > Best Regards > > Martyn > > ___ > 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. > > > > > -- > > Message: 2 > Date: Wed, 4 Mar 2015 12:16:02 -0600 > From: "Graham / KE9H" > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] 50 ohm Driver > Message-ID: > > Content-Type: text/plain; charset=UTF-8 > > Building on top of John's comments, if you are using a logic gate, look at > the > maximum output (pull up) current per pin, set the series resistor so that > this > current is not exceeded into a short, then also see if there is a maximum > total > current draw for all gates combined, or some power input pin, and do not > exceed > that. > > You can also look at switching the termination resistor from a simple 50 > Ohm > resistor to ground, to a "Thevenin" load, which is 100 Ohms from +V to the > load point, > and another 100 Ohm resistor from the load point to ground. This way you > still have a 50 Ohm termination, but only draw one half the DC current. > In the event of no input, the receiver voltage will go to half scale. Make
[time-nuts] 50 ohm driver
Hello, Charles asked for a link to the IC I mentioned. http://www.mouser.com/ds/2/405/sdas074b-192680.pdf It has a 48 mA output drive capability but doesn’t like the outputs in parallel even with resistors. The reason my customer wants 0-5V is that he is feeding the distribution amp output over 100 m of cable to the end receiver (don’t know his actual set-up so can’t comment why the devices are so far away). So Charles's comment on overshoots blowing my device is probably what’s going to happen. Best Regards Martyn ___ 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] 50 ohm driver
I got excited when I found the SN74AS1004AD which has the exact same function and pin out but delivers 48 mA per channel. While one output did give me 0-3.0 V into 50 ohm, combining them, as we do for the 74AC, actually produced worse results. Can you post a link to the datasheet for your product, so we have some idea of what you're attempting? The AS devices are bipolar logic (fancy modern schottky TTL) -- they don't even pretend to pull closer than 1.5v to VCC (so, 3.5v with Vcc = 5v), and the spec is only >2v. The datasheet clearly indicates this (if one didn't already know that they were bipolar parts from the AS series designation). When you are depending on the analog performance of logic gates, it is up to you to pay attention to everything on the datasheet, not just one spec. Any ringing on the line (from mistermination) will very likely destroy the AC14s if you run them with no series resistors. At least build a discrete CMOS inverter stage with medium power, low-threshold MOSFETS. 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] 50 ohm driver
Martyn, How long is the cable you are driving? If you have large ground differentials you may destroy the chips very easily. Especially if between industrial buildings. Some of the things discussed here are fine for a hobby environment but somewhat questionable in a commercial business. Regards Paul WB8TSL On Thu, Mar 5, 2015 at 4:59 PM, Martyn Smith wrote: > Hello, > Thanks for all the feedback. > I should explain. I have an existing product that uses the 74AC14. > I have a customer who needs 5V into 50 ohm and can’t wait for the > competitive product that does this, or for me to re-design my unit. > So I have been looking for a quick fix. > I got excited when I found the SN74AS1004AD which has the exact same > function and pin out but delivers 48 mA per channel. > While one output did give me 0-3.0 V into 50 ohm, combining them, as we do > for the 74AC, actually produced worse results. > Maybe the output driver is different. > Anyway I’ve managed to get 0-4.8V by jacking up the supply voltage to 5.7 > V for the 74AC14 and making the three 47 ohm resistors 0 ohm. > Risetime < 4 ns. > Basically to ideas that TimeNuts gave me. > I’m just worried the IC may die after a few months. But since the > customer will only use it at 1 Hz and hopefully 50:50 duty, or less, I hope > to get away with it. > Of course if he removes the input and the outputs are on high, then that > may be a problem. > BTW, the reason he wants this high voltage is because he is driving a very > long cable from the distribution amp to the actual receiver. > Anyway I have an IC on test for a week to make sure it lasts. > Regards > Martyn > > > Today's Topics: > >1. Re: 50 ohm Driver (Bob Albert) >2. Re: 50 ohm Driver (Graham / KE9H) >3. Re: 50 ohm Driver (Tom Van Baak) >4. Re: 50 ohm Driver (Hal Murray) >5. Re: 50 ohm Driver (Dan Kemppainen) >6. Re: Trimble Thunderbolt NMEA ? (Didier Juges) >7. Re: 50 ohm Driver (Bob Camp) >8. Re: 50 ohm Driver (Charles Steinmetz) >9. Re: new tdc from Texas (Angus) > 10. Re: new tdc from Texas (Attila Kinali) > > > -- > > Message: 1 > Date: Wed, 4 Mar 2015 16:49:11 + (UTC) > From: Bob Albert > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] 50 ohm Driver > Message-ID: > <1276775018.2671439.1425487751520.javamail.ya...@mail.yahoo.com> > Content-Type: text/plain; charset=UTF-8 > > 5V into 50 Ohms means 100 mA. Perhaps you need a medium power transistor > amplifier or opamp. > Bob > > > On Wednesday, March 4, 2015 6:09 AM, Martyn Smith > wrote: > > > Hello, > > A quick question. > > My output driver for a simple amplifier. > > I use three gates (in parallel with resistors) from a 74AC14 to give me > about 0-3.2V into 50 ohm. > > I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing > into 50 ohms. > > Can anyone recommend an IC that can delivery this. > > But it needs to have similar jitter performance to the 74AC14. > > I use it up to 10 MHz. > > Best Regards > > Martyn > > ___ > 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. > > > > > -- > > Message: 2 > Date: Wed, 4 Mar 2015 12:16:02 -0600 > From: "Graham / KE9H" > To: Discussion of precise time and frequency measurement > > Subject: Re: [time-nuts] 50 ohm Driver > Message-ID: > > Content-Type: text/plain; charset=UTF-8 > > Building on top of John's comments, if you are using a logic gate, look at > the > maximum output (pull up) current per pin, set the series resistor so that > this > current is not exceeded into a short, then also see if there is a maximum > total > current draw for all gates combined, or some power input pin, and do not > exceed > that. > > You can also look at switching the termination resistor from a simple 50 > Ohm > resistor to ground, to a "Thevenin" load, which is 100 Ohms from +V to the > load point, > and another 100 Ohm resistor from the load point to ground. This way you > still have a 50 Ohm termination, but only draw one half the DC current. > In the event of no input, the receiver voltage will go to half scale. Make > sure your system will not misbehave when this happens. > > Alternate driver is to use a video line driver with sufficient bandwidth. > > --- Graham / KE9H > > == > > On Wed, Mar 4, 2015 at 7:54 AM, John Ackermann N8
Re: [time-nuts] 50 ohm driver
mar...@ptsyst.com said: > BTW, the reason he wants this high voltage is because he is driving a very > long cable from the distribution amp to the actual receiver. If you have a long cable, the rise time at the driver isn't critical. It will get filtered out by the cable. Of course, how long is long? Here are some scope pictures for 100 ft of coax. The driver is a TBolt. I forget what chip they use. http://www.megapathdsl.net/~hmurray/time-nuts/coax/Coax-20ns.png If you are going to redesign the board and prefer chips to transistors, check out the bus driver chips. They typically come 8 drivers to a package. There used to be some with 16. There were also some chips that included a 25 ohm resister. They were intended for driving memory busses. -- These are my opinions. I hate spam. ___ 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] 50 ohm driver
Hello, Thanks for all the feedback. I should explain. I have an existing product that uses the 74AC14. I have a customer who needs 5V into 50 ohm and can’t wait for the competitive product that does this, or for me to re-design my unit. So I have been looking for a quick fix. I got excited when I found the SN74AS1004AD which has the exact same function and pin out but delivers 48 mA per channel. While one output did give me 0-3.0 V into 50 ohm, combining them, as we do for the 74AC, actually produced worse results. Maybe the output driver is different. Anyway I’ve managed to get 0-4.8V by jacking up the supply voltage to 5.7 V for the 74AC14 and making the three 47 ohm resistors 0 ohm. Risetime < 4 ns. Basically to ideas that TimeNuts gave me. I’m just worried the IC may die after a few months. But since the customer will only use it at 1 Hz and hopefully 50:50 duty, or less, I hope to get away with it. Of course if he removes the input and the outputs are on high, then that may be a problem. BTW, the reason he wants this high voltage is because he is driving a very long cable from the distribution amp to the actual receiver. Anyway I have an IC on test for a week to make sure it lasts. Regards Martyn Today's Topics: 1. Re: 50 ohm Driver (Bob Albert) 2. Re: 50 ohm Driver (Graham / KE9H) 3. Re: 50 ohm Driver (Tom Van Baak) 4. Re: 50 ohm Driver (Hal Murray) 5. Re: 50 ohm Driver (Dan Kemppainen) 6. Re: Trimble Thunderbolt NMEA ? (Didier Juges) 7. Re: 50 ohm Driver (Bob Camp) 8. Re: 50 ohm Driver (Charles Steinmetz) 9. Re: new tdc from Texas (Angus) 10. Re: new tdc from Texas (Attila Kinali) -- Message: 1 Date: Wed, 4 Mar 2015 16:49:11 + (UTC) From: Bob Albert To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 50 ohm Driver Message-ID: <1276775018.2671439.1425487751520.javamail.ya...@mail.yahoo.com> Content-Type: text/plain; charset=UTF-8 5V into 50 Ohms means 100 mA. Perhaps you need a medium power transistor amplifier or opamp. Bob On Wednesday, March 4, 2015 6:09 AM, Martyn Smith wrote: Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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. -- Message: 2 Date: Wed, 4 Mar 2015 12:16:02 -0600 From: "Graham / KE9H" To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] 50 ohm Driver Message-ID: Content-Type: text/plain; charset=UTF-8 Building on top of John's comments, if you are using a logic gate, look at the maximum output (pull up) current per pin, set the series resistor so that this current is not exceeded into a short, then also see if there is a maximum total current draw for all gates combined, or some power input pin, and do not exceed that. You can also look at switching the termination resistor from a simple 50 Ohm resistor to ground, to a "Thevenin" load, which is 100 Ohms from +V to the load point, and another 100 Ohm resistor from the load point to ground. This way you still have a 50 Ohm termination, but only draw one half the DC current. In the event of no input, the receiver voltage will go to half scale. Make sure your system will not misbehave when this happens. Alternate driver is to use a video line driver with sufficient bandwidth. --- Graham / KE9H == On Wed, Mar 4, 2015 at 7:54 AM, John Ackermann N8UR wrote: > One comment on the parallel AC gate approach. It may not be directly > applicable to Martyn's issue, but there is a common confusion about the > value of the summing resistors. > > Per Tom Clark, who came up with the idea, they are *not* intended to > provide a near-end line termination to 50 ohms, but are simply there to > protect the paralleled devices if the gates have slightly different delays > (in which case one gate could end up sinking the other two). > > So, the commonly used 47 ohm value isn't magic. You can use a lower > value, and thus get more voltage at the far end. I haven't experimented to > see how far you can take that idea before destroying gates. > > John > > > On 3/4/2015 5:26 AM, Martyn Smith wrote: > >> Hello, >> >> A quick question. >> >> My output driver for a simple amplifier. >> >> I use thre
Re: [time-nuts] 50 ohm Driver
Is [one gate sourcing or sinking current into paralleled gates that don't switch at exactly the same time] a real problem? How far off can the prop delay be for 2 gates on the same chip? I seem to remember reading something saying it was OK to just wire them up in parallel. It could have been an app note, or it could have been a rumor on usenet. Most manufacturers sanction direct paralleling of gates on the same chip (and forbid any paralleling, ballasted or otherwise, of outputs from different chips). However, there are other considerations (short-circuit protection, maximum output current rating per gate, maximum supply and/or ground current rating per package, maximum power dissipation, etc.). Good design practice is to put series resistors on each gate output that will prevent any of these ratings from being exceeded into a short circuit to ground or to Vcc. For HC, AC, NC7NZ, and NC7SZ, the per-gate output current rating is +/- 24 (or 25) mA, which suggests that each gate should have a 200 ohm series resistor -- but you need to check all of the other ratings mentioned above for the chip you use, to make sure they won't be violated. Unfortunately, if the load is 50 ohms to ground, pulling it to even 4.5v from a 5v logic supply requires a source resistance of only 5.6 ohms, or 36 parallel gates each with 200 ohms in series (this assumes that the gates can pull all the way to 5v while delivering rated current, which they can't -- so the reality is even worse). You can make things a little better by terminating the output into 50 ohms to 1/2 Vcc (i.e, the center of a voltage divider with 100 ohms to Vcc and 100 ohms to ground), but (i) it only gets a little better, and (ii) now it won't pull all the way to ground. All that said, why do you want to generate a high-current square wave, anyway? If you're distributing a frequency standard, it is much better to distribute a sine wave (you don't have to worry about the harmonics being skewed, and there is exponentially less of a problem with it radiating and getting into every radio and other sensitive electronic device in your house and the other houses on the block). 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] 50 ohm Driver
Hi If you want to drive out of a 50 ohm source into your 50 ohm load *and* get 5V into the load … that’s a fancy amp. 10V power and some careful work to get it going. If you just want to get roughly 5V into a 50 ohm load, then it’s a matter of how many gates you decide to parallel. If you go with “32 ma” drivers, you should be able to get it done with 8 of them in parallel. Drive them all off of a single dedicated fast gate that’s on the same supply. Probably best to stuff a 20 or 30 ohm resistor in series with each of the outputs. If it’s *got* to be a full 5V, don’t use the resistors. Bob > On Mar 4, 2015, at 5:26 AM, Martyn Smith wrote: > > Hello, > > A quick question. > > My output driver for a simple amplifier. > > I use three gates (in parallel with resistors) from a 74AC14 to give me about > 0-3.2V into 50 ohm. > > I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing > into 50 ohms. > > Can anyone recommend an IC that can delivery this. > > But it needs to have similar jitter performance to the 74AC14. > > I use it up to 10 MHz. > > Best Regards > > Martyn > > ___ > 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] 50 ohm Driver
Hi, Correct me if I'm wrong but being that AC series gates are MOS devices, isn't there inherent current limiting in the MOS junction itself? I would think that for the few nanoseconds of skew across gates the tens of ohms of junction resistance would make 'shoot through' negligible in terms of heating and gate damage. Of course, a TTL device would be a completely different story and I would fully expect summing or balancing resistor would be needed there. Does anyone have further input regarding paralleling MOS logic devices? Dan One comment on the parallel AC gate approach. It may not be directly applicable to Martyn's issue, but there is a common confusion about the value of the summing resistors. Per Tom Clark, who came up with the idea, they are*not* intended to provide a near-end line termination to 50 ohms, but are simply there to protect the paralleled devices if the gates have slightly different delays (in which case one gate could end up sinking the other two). So, the commonly used 47 ohm value isn't magic. You can use a lower value, and thus get more voltage at the far end. I haven't experimented to see how far you can take that idea before destroying gates. John ___ 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] 50 ohm Driver
j...@febo.com said: > Per Tom Clark, who came up with the idea, they are *not* intended to > provide a near-end line termination to 50 ohms, but are simply there to > protect the paralleled devices if the gates have slightly different delays > (in which case one gate could end up sinking the other two). Is that a real problem? How far off can the prop delay be for 2 gates on the same chip? I seem to remember reading something saying it was OK to just wire them up in parallel. It could have been an app note, or it could have been a rumor on usenet. -- These are my opinions. I hate spam. ___ 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] 50 ohm Driver
Martyn -- the 74AC spec allows Vcc to go up to 6.0 VDC (absolute max is 7.0 VDC) so that might help you meet your 4.5 VDC goal, especially if this is for play and not a product. Pick the resistors and use more than 3 gates if necessary. Note the peak current spec is 50 mA per gate. Not sure what the combined gate current limit is; there is a package thermal limit. You also have to decide if you want some level of short-circuit protection or if you can always assume 50R termination. John -- have you tried long duration output shorts on the TADD-2? I figured that was also a reason for each gate having its own resistor. /tvb ___ 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] 50 ohm Driver
Building on top of John's comments, if you are using a logic gate, look at the maximum output (pull up) current per pin, set the series resistor so that this current is not exceeded into a short, then also see if there is a maximum total current draw for all gates combined, or some power input pin, and do not exceed that. You can also look at switching the termination resistor from a simple 50 Ohm resistor to ground, to a "Thevenin" load, which is 100 Ohms from +V to the load point, and another 100 Ohm resistor from the load point to ground. This way you still have a 50 Ohm termination, but only draw one half the DC current. In the event of no input, the receiver voltage will go to half scale. Make sure your system will not misbehave when this happens. Alternate driver is to use a video line driver with sufficient bandwidth. --- Graham / KE9H == On Wed, Mar 4, 2015 at 7:54 AM, John Ackermann N8UR wrote: > One comment on the parallel AC gate approach. It may not be directly > applicable to Martyn's issue, but there is a common confusion about the > value of the summing resistors. > > Per Tom Clark, who came up with the idea, they are *not* intended to > provide a near-end line termination to 50 ohms, but are simply there to > protect the paralleled devices if the gates have slightly different delays > (in which case one gate could end up sinking the other two). > > So, the commonly used 47 ohm value isn't magic. You can use a lower > value, and thus get more voltage at the far end. I haven't experimented to > see how far you can take that idea before destroying gates. > > John > > > On 3/4/2015 5:26 AM, Martyn Smith wrote: > >> Hello, >> >> A quick question. >> >> My output driver for a simple amplifier. >> >> I use three gates (in parallel with resistors) from a 74AC14 to give me >> about 0-3.2V into 50 ohm. >> >> I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing >> into 50 ohms. >> >> Can anyone recommend an IC that can delivery this. >> >> But it needs to have similar jitter performance to the 74AC14. >> >> I use it up to 10 MHz. >> >> Best Regards >> >> Martyn >> >> ___ >> 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] 50 ohm Driver
5V into 50 Ohms means 100 mA. Perhaps you need a medium power transistor amplifier or opamp. Bob On Wednesday, March 4, 2015 6:09 AM, Martyn Smith wrote: Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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] 50 ohm Driver
One comment on the parallel AC gate approach. It may not be directly applicable to Martyn's issue, but there is a common confusion about the value of the summing resistors. Per Tom Clark, who came up with the idea, they are *not* intended to provide a near-end line termination to 50 ohms, but are simply there to protect the paralleled devices if the gates have slightly different delays (in which case one gate could end up sinking the other two). So, the commonly used 47 ohm value isn't magic. You can use a lower value, and thus get more voltage at the far end. I haven't experimented to see how far you can take that idea before destroying gates. John On 3/4/2015 5:26 AM, Martyn Smith wrote: Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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] 50 ohm Driver
Hello, A quick question. My output driver for a simple amplifier. I use three gates (in parallel with resistors) from a 74AC14 to give me about 0-3.2V into 50 ohm. I want to have a driver that gives me a full 0-5V (at least 0-4.5V) swing into 50 ohms. Can anyone recommend an IC that can delivery this. But it needs to have similar jitter performance to the 74AC14. I use it up to 10 MHz. Best Regards Martyn ___ 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.
