Re: [time-nuts] Stepping up the output of an OCXO

[Bill Hawkins]

Have you investigated the concept of an attenuator, to use
before the RF gain block?

Bill Hawkins 

-Original Message-
Stephan Sandenbergh wrote,

"The easiest, of course, would be if there exists some integrated
solution. I browsed through the list of RF gain blocks on the
Mini-Circuits site - these little guys seem perfect for the job.
However, the typical situation is that it amplifies by at least
10dBs while the maximum output of it sits at around 13dBm. 5dBm
will thus more than saturate the poor thing."


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Re: [time-nuts] Stepping up the output of an OCXO

[Stephan Sandenbergh]

Hi Bill,

Judging by your question - that is probably something that I should do?

Considering that you'll attenuate the 5dBm signal to about 0dBm and then
amplifying it back up to about 10dBm. My gut tells me that by attenuating
the signal before amplifying it will raise the noise floor. (I wouldn't want
to ruin my -165dB noise floor)  However, I must confess that I'm new to RF
components and sinusoidal signals, so I might be argumenting completely
wrong.

I guess I should do the math on that one.

Regards,

Stephan.


On 2/1/07, Bill Hawkins <[EMAIL PROTECTED]> wrote:
>
> Have you investigated the concept of an attenuator, to use
> before the RF gain block?
>
> Bill Hawkins
>
> -Original Message-
> Stephan Sandenbergh wrote,
>
> "The easiest, of course, would be if there exists some integrated
> solution. I browsed through the list of RF gain blocks on the
> Mini-Circuits site - these little guys seem perfect for the job.
> However, the typical situation is that it amplifies by at least
> 10dBs while the maximum output of it sits at around 13dBm. 5dBm
> will thus more than saturate the poor thing."
>
>
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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Stephan Sandenbergh wrote:
> Hi All,
>
>  
>
> Say for instance you have a 5dBm clean 10MHz sinusoid (such as that provided
> by an OCXO). Now you want to run this signal to a device that will take a
> minimum of 10dBm and maximum of 15dBm as input. How does one amplify the
> 5dBm?
>
>  
>
> The first thing that sprang to mind is a step-up RF transformer. However, it
> is impossible to step-up because the following device has an input impedance
> of 50ohm. To step it up you'll need a higher input impedance. A step-up
> transformer will also mess with the matching.
>
>  
>
> After Googling a bit I found that another option might be LC-resonance. This
> seems like a good idea since resonance is per definition a filter-like
> effect. 
>
>  
>
> The easiest, of course, would be if there exists some integrated solution. I
> browsed through the list of RF gain blocks on the Mini-Circuits site - these
> little guys seem perfect for the job. However, the typical situation is that
> it amplifies by at least 10dBs while the maximum output of it sits at around
> 13dBm. 5dBm will thus more than saturate the poor thing.
>
>  
>
> My final idea is a high speed opamp. I suspect this would add nasty 1/f
> noise. Probably the same with a simple RF transistor amplifier. 
>
>  
>
> Do you guys have any better ideas?  Your thoughts on this are much
> appreciated.
>
>  
>
> Kind regards,
>
>  
>
> Stephan Sandenbergh
>
>  
>
>  
>
>   
>
>  
>
>  
>
>  
>
> ___
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>
>   
Stephen

The optimum method depends on the load characteristics.
If you want to drive a CMOS logic gate then using a series tuned LC tank 
to step up the voltage will be satisfactory see:
http://www.wenzel.com/documents/waveform.html
Or for a version that allows the effect of tuning the tank to be 
monitored without significantly loading the stepped up output see

Silicon Chip February 2007 p71.

If you need to drive a 50 ohm load, consider using a common base 
amplifier with an input and output stepdown transformers.
Suitable transformers are readily availble from minicircuits or you can 
wind your own.

Use a 2:1 turns ratio (4:1 impedance ratio) input step down transformer 
and a 4:1 turns ratio (16:1 impedance ratio) stepdown output transformer 
with a shunt 800 ohm impedance matching  resistor connected across the 
primary windings. Use a resistor (~8.2 ohm) in series with the emitter 
to set the RF input impedance at 50 ohms as seen from the primary of the 
input transformer. A common base amplifier has the advantage of having 
high reverse isolation independent of source and load impedances.
If you want circuit schematics just ask, but when you do so I need to 
know the OCXO frequency.

A bandpass filter can always be used to cleanup the amplifier output if 
required.

If you must use one of the minicircuits amplifiers just place an 
attenauator between the OCXO output and the amplifier input.

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Stephan Sandenbergh wrote:
>> Hi All,
>>
>>  
>>
>> Say for instance you have a 5dBm clean 10MHz sinusoid (such as that provided
>> by an OCXO). Now you want to run this signal to a device that will take a
>> minimum of 10dBm and maximum of 15dBm as input. How does one amplify the
>> 5dBm?
>>
>>  
>>
>> The first thing that sprang to mind is a step-up RF transformer. However, it
>> is impossible to step-up because the following device has an input impedance
>> of 50ohm. To step it up you'll need a higher input impedance. A step-up
>> transformer will also mess with the matching.
>>
>>  
>>
>> After Googling a bit I found that another option might be LC-resonance. This
>> seems like a good idea since resonance is per definition a filter-like
>> effect. 
>>
>>  
>>
>> The easiest, of course, would be if there exists some integrated solution. I
>> browsed through the list of RF gain blocks on the Mini-Circuits site - these
>> little guys seem perfect for the job. However, the typical situation is that
>> it amplifies by at least 10dBs while the maximum output of it sits at around
>> 13dBm. 5dBm will thus more than saturate the poor thing.
>>
>>  
>>
>> My final idea is a high speed opamp. I suspect this would add nasty 1/f
>> noise. Probably the same with a simple RF transistor amplifier. 
>>
>>  
>>
>> Do you guys have any better ideas?  Your thoughts on this are much
>> appreciated.
>>
>>  
>>
>> Kind regards,
>>
>>  
>>
>> Stephan Sandenbergh
>>   
>> 
Stephan

A differentially driven common base pair with transformer coupled input 
and output is another option with lower distortion than a single ended 
input common base amplifier.

Another option is a common base noiseless feedback amplifier using 
transformer feedback.
However these have a similar input output isolation to a transformer, 
they are in effect a"transformer" with power gain.
If the lack of input output isolation is is acceptable then these have 
the lowest noise of any RF feedback amplifier.
You will need to wind your own feedback transformer.

A cascode amplifier with transformer output could also be used.

A high speed opamp could be used however it will be noisier than a 
common base or cascode amplifier.
1/f noise isnt important as long as there is no upconversion to 
frequencies close to the carrier.
Feedback minimises this effect.
AC coupling the output with a suitable time constant will virtually 
eliminate any 1/f noise on the output.
Using a bandpass filter will filter out harmonics and even more of the 
output noise.

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Stephan Sandenbergh wrote:
> Hi Bill,
>
> Judging by your question - that is probably something that I should do?
>
> Considering that you'll attenuate the 5dBm signal to about 0dBm and then
> amplifying it back up to about 10dBm. My gut tells me that by attenuating
> the signal before amplifying it will raise the noise floor. (I wouldn't want
> to ruin my -165dB noise floor)  However, I must confess that I'm new to RF
> components and sinusoidal signals, so I might be argumenting completely
> wrong.
>
> I guess I should do the math on that one.
>
> Regards,
>
> Stephan.
>
>
> On 2/1/07, Bill Hawkins <[EMAIL PROTECTED]> wrote:
>   
>> Have you investigated the concept of an attenuator, to use
>> before the RF gain block?
>>
>> Bill Hawkins
>>
>> 
Stephan

I presume your OCXO phase noise floor is actually -165dBc/Hz.
Which corresponds to -160dBm/Hz in the 5dBm output.
An amplifier with a 0dB noise figure has an input phase noise floor of 
around -174dBm/Hz
So you can degrade the noise floor by 10dB or more by using an 
attenuator and an amplifier with a more realistic noise figure of a few 
dB without appreciably degrading the OCXO phase noise floor.
For hints and phase noise figures for some microcircuit amplifiers see:
http://www.wenzel.com/documents/hints.htm


For example a Minicircuits MAV11SM has a 1dB compression output of 
+17.5dBm and a gain of 10.5dB with a noise figure of 3.5dB so you would 
need much input attenuation to achieve the required output level. This 
amplifier wont appreciably degrade the OCXO phase noise floor. low pass 
filtering the output will reduce its harmonic content.
Its input phase noise floor with no input attenuator and a 5dBm input 
will be about -175.5dBc/Hz or about 10dBc/Hz better than your OCXO.

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Stephan

Attached GIF file is the schematic for a common base amplifier with 
about 12dB of gain into a 50 ohm load.

The amplifier will not saturate even if the load is open circuited.
Q102 temperature compensates Q103 which regulates the dc collector 
current of the common base transistor.

Other transistor types with equivalent performance may be susbstituted.
The RF transformers are coupled to the amplifier with series capacitors 
to avoid saturating the cores with dc current.


Bruce


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Re: [time-nuts] Stepping up the output of an OCXO

[Stephan Sandenbergh]

Hi Bruce,

A great many thanks for all the hints and tips you gave me.

Yes, I have actually started working my way through Wenzel's hints & tips
pages after I posted the first message. I remembered that you pointed me
there in a previous conversation we had.

I find the schematic you attached in your last post very interesting - I
happen to have a soft spot for discrete analog solutions that can still beat
their integrated counterparts. 

However, I still tend to lean towards the "mini-circuits" type
attenuator/Gain block idea. The reasons are all the reasons why everyone is
leaning toward integrated solutions. (e.g. the integrated solutions might
cost a bit more, but it uses a lot less board space; if a unit fails you
simply replace it with another one, less components, etc, etc.) 

Nevertheless, I noted you use the word 'must' as in: if you must use the
mini-circuits So I suspect there might be a down-side to using this kind
of approach. Or is it just that the discrete solution works somewhat better?
Do you mind elaborating a bit on this?

Regards,

Stephan Sandenbergh

> -Original Message-
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
> Behalf Of Dr Bruce Griffiths
> Sent: 02 February 2007 05:46 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Stepping up the output of an OCXO
> 
> Stephan
> 
> Attached GIF file is the schematic for a common base amplifier with
> about 12dB of gain into a 50 ohm load.
> The amplifier will not saturate even if the load is open circuited.
> Q102 temperature compensates Q103 which regulates the dc collector
> current of the common base transistor.
> Other transistor types with equivalent performance may be susbstituted.
> The RF transformers are coupled to the amplifier with series capacitors
> to avoid saturating the cores with dc current.
> 
> Bruce



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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Stephan Sandenbergh wrote:
> Hi Bruce,
>
> A great many thanks for all the hints and tips you gave me.
>
> Yes, I have actually started working my way through Wenzel's hints & tips
> pages after I posted the first message. I remembered that you pointed me
> there in a previous conversation we had.
>
> I find the schematic you attached in your last post very interesting - I
> happen to have a soft spot for discrete analog solutions that can still beat
> their integrated counterparts. 
>
> However, I still tend to lean towards the "mini-circuits" type
> attenuator/Gain block idea. The reasons are all the reasons why everyone is
> leaning toward integrated solutions. (e.g. the integrated solutions might
> cost a bit more, but it uses a lot less board space; if a unit fails you
> simply replace it with another one, less components, etc, etc.) 
>
> Nevertheless, I noted you use the word 'must' as in: if you must use the
> mini-circuits So I suspect there might be a down-side to using this kind
> of approach. Or is it just that the discrete solution works somewhat better?
> Do you mind elaborating a bit on this?
>
> Regards,
>
> Stephan Sandenbergh
>
>   

Stephan

The RF amp IC's generally have inferior noise figures and reverse 
isolation (20dB for RFIC, > 40dB for common base stage) than a well 
designed discrete common base amplifier. In fact by stacking common base 
amplifiers the reverse isolation  can be made very high, at least at low 
frequencies like 5MHz or 10MHz, without a severe impact on the noise 
figure. HP used a dc coupled common base + common gate + common base 
cascade in their 8554 RF signal generator.
NBS used cascaded common base stages in their high (120dB) reverse 
isolation amplifiers.
If an OCXO buffer amplifier has poor reverse isolation then a variable 
load impedance will have a measurable effect on the OCXO frequency.

It is easy to tailor the gain of a discrete amplifier to suit the 
application without degrading the noise figure by using an input 
attenuator as is required by an RFIC.
RF IC amplifiers also tend to misbehave (saturate) when the load is high 
impedance such as when one attempts to drive a logic gate input whereas 
it is easy to design a discrete amplifier to work into either an open 
circuit or short circuit load without distorting the waveform whether it 
is the voltage waveform for an open circuit load or current waveform for 
a short circuit load. Such ICs are not used in OCXOs because of their 
inferior performance and the fact that their dc power supply currents 
tend to be somewhat larger than that of a well designed discrete amplifier.

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Didier Juges]

 Dr Bruce Griffiths <[EMAIL PROTECTED]> wrote: 
> The RF amp IC's generally have inferior noise figures and reverse 
> isolation (20dB for RFIC, > 40dB for common base stage) than a well 
> designed discrete common base amplifier. In fact by stacking common base 
> amplifiers the reverse isolation  can be made very high, at least at low 
> frequencies like 5MHz or 10MHz, without a severe impact on the noise 
> figure. HP used a dc coupled common base + common gate + common base 
> cascade in their 8554 RF signal generator.
> NBS used cascaded common base stages in their high (120dB) reverse 
> isolation amplifiers.
> If an OCXO buffer amplifier has poor reverse isolation then a variable 
> load impedance will have a measurable effect on the OCXO frequency.
> 
> Bruce

Bruce,

In cases where the output signal does not need to be a sinewave, how would a 
common base amplifier compare to a fast comparator and if necessary a digital 
buffer as necessary to deliver the necessary power level? If this is designed 
to drive a mixer, a square wave may actually be better than a sine wave (lower 
conversion loss), and I would venture that the isolation (at least load 
independence) in most comparators is much better than that of a monolithic 
amplifier. 

Didier



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Re: [time-nuts] Stepping up the output of an OCXO

[Ulrich Bangert]

Bruce and Didier,

> > The RF amp IC's generally have inferior noise figures and reverse
> > isolation (20dB for RFIC, > 40dB for common base stage) than a well 
> > designed discrete common base amplifier. In fact by 
> stacking common base 
> > amplifiers the reverse isolation  can be made very high, at 
> least at low 
> > frequencies like 5MHz or 10MHz, without a severe impact on 
> the noise 
> > figure. HP used a dc coupled common base + common gate + 
> common base 
> > cascade in their 8554 RF signal generator.
> > NBS used cascaded common base stages in their high (120dB) reverse 
> > isolation amplifiers.
> > If an OCXO buffer amplifier has poor reverse isolation then 
> a variable 
> > load impedance will have a measurable effect on the OCXO frequency.

i had the opportunity to measure the output to output as well as the
output to input isolation of a diy MAX477 based distribution amplifier
very similar to the TADD-1 (but not identical). The output to output
isolation was in the order of 75 dB while the output to input isolation
was in the order of 90 dB. This is not too bad for this simple design
and perhaps more than adequate for most of us time nuts. I have not been
able to measure the increase in terms of noise figure but this statement
must be read as: The increase in noise figure was less than the noise
floor of my equipment. Nevertheless my statement of beliefs is the same
as Bruce's one: A single transistor stage may be more easily optimized
than a multi-transistor-design.

Best regards
Ulrich Bangert   

> -Ursprüngliche Nachricht-
> Von: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] Im Auftrag von Didier Juges
> Gesendet: Freitag, 2. Februar 2007 20:45
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Stepping up the output of an OCXO
> 
> 
>  Dr Bruce Griffiths <[EMAIL PROTECTED]> wrote: 
> > The RF amp IC's generally have inferior noise figures and reverse
> > isolation (20dB for RFIC, > 40dB for common base stage) than a well 
> > designed discrete common base amplifier. In fact by 
> stacking common base 
> > amplifiers the reverse isolation  can be made very high, at 
> least at low 
> > frequencies like 5MHz or 10MHz, without a severe impact on 
> the noise 
> > figure. HP used a dc coupled common base + common gate + 
> common base 
> > cascade in their 8554 RF signal generator.
> > NBS used cascaded common base stages in their high (120dB) reverse 
> > isolation amplifiers.
> > If an OCXO buffer amplifier has poor reverse isolation then 
> a variable 
> > load impedance will have a measurable effect on the OCXO frequency.
> > 
> > Bruce
> 
> Bruce,
> 
> In cases where the output signal does not need to be a 
> sinewave, how would a common base amplifier compare to a fast 
> comparator and if necessary a digital buffer as necessary to 
> deliver the necessary power level? If this is designed to 
> drive a mixer, a square wave may actually be better than a 
> sine wave (lower conversion loss), and I would venture that 
> the isolation (at least load independence) in most 
> comparators is much better than that of a monolithic amplifier. 
> 
> Didier
> 
> 
> 
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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Didier Juges wrote:
>  Dr Bruce Griffiths <[EMAIL PROTECTED]> wrote: 
>   
>> The RF amp IC's generally have inferior noise figures and reverse 
>> isolation (20dB for RFIC, > 40dB for common base stage) than a well 
>> designed discrete common base amplifier. In fact by stacking common base 
>> amplifiers the reverse isolation  can be made very high, at least at low 
>> frequencies like 5MHz or 10MHz, without a severe impact on the noise 
>> figure. HP used a dc coupled common base + common gate + common base 
>> cascade in their 8554 RF signal generator.
>> NBS used cascaded common base stages in their high (120dB) reverse 
>> isolation amplifiers.
>> If an OCXO buffer amplifier has poor reverse isolation then a variable 
>> load impedance will have a measurable effect on the OCXO frequency.
>>
>> Bruce
>> 
>
> Bruce,
>
> In cases where the output signal does not need to be a sinewave, how would a 
> common base amplifier compare to a fast comparator and if necessary a digital 
> buffer as necessary to deliver the necessary power level? If this is designed 
> to drive a mixer, a square wave may actually be better than a sine wave 
> (lower conversion loss), and I would venture that the isolation (at least 
> load independence) in most comparators is much better than that of a 
> monolithic amplifier. 
>
> Didier
>
>
>
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>   
Didier

In general comparators tend to have excessive phase noise floors and 
will degrade the phase noise of the mixer system.
However if the RF signal phase noise floor is already high this may not 
matter.
There is little data on the phase noise of modern comparators, it would 
be useful if someone actually made some measurements of this both for 
comparators and for simpler devices used to square up sinewaves such as 
long tailed pairs and logic gates.
However I would expect a comparator to be somewhere around 20dB or more 
worse than a common base stage, or for that matter any amplifier 
employing  RF negative feedback.

Its not the choice of a monolithic implementation rather than a discrete 
component implementation that limits the reverse isolation but rather 
the circuit topology.
A series shunt feedback amplifier as used in most RFIC amplifiers has 
inherently poor reverse isolation. Other factors such as the inductance 
of bond wires and mutual coupling between them can also be a factor 
especially at high frequencies.

If one cascades enough stages with relatively low reverse isolation one 
can, at the expense of increased phase noise, increase the effective 
isolation between the input and output of the entire circuit. This is 
what can give multistage devices like comparators reasonably high 
reverse isolation. However one must be mindful of the effects of the PCB 
layout. For example a hybrid LM733 (100x 100MHz diff amp) cascaded with 
a AMD685 ECL comparator had problems with coupling between the amplifier 
input and comparator output until a closely spaced grounded shield plate 
was mounted above the pins. The effect was subtle in that it distorted 
the expected Gaussian shape of the plot of output pulse rate versus 
comparator threshold with zero input. The circuit was triggering on the 
amplifiers output noise.

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Dr Bruce Griffiths wrote:
> Didier Juges wrote:
>   
>> Bruce,
>>
>> In cases where the output signal does not need to be a sinewave, how would a 
>> common base amplifier compare to a fast comparator and if necessary a 
>> digital buffer as necessary to deliver the necessary power level? If this is 
>> designed to drive a mixer, a square wave may actually be better than a sine 
>> wave (lower conversion loss), and I would venture that the isolation (at 
>> least load independence) in most comparators is much better than that of a 
>> monolithic amplifier. 
>>
>> Didier
>> 
Didier

Perhaps the major reason that comparators and logic gates have inferior 
phase noise than linear amplifiers is that comparators do not use 
negative feedback (except for some Plessey comparators that used series 
shunt feedback in the signal path). A comparator that employed negative 
feedback in a limiting preamp would be expected to have a lower phase 
noise than that of the comparator without the preamp. The critical 
region is around the input signal zero crossing, if RF feedback is 
effective noise around this transition then the effective noise of the 
following comparator should be suppressed.

Unfortunately AFAIK there is no data on the phase noise properties of 
the Plessey comparators, nor has anyone tried using a limiting preamp 
with RF feedback.

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Ulrich Bangert wrote:
> Bruce and Didier,
>
> i had the opportunity to measure the output to output as well as the
> output to input isolation of a diy MAX477 based distribution amplifier
> very similar to the TADD-1 (but not identical). The output to output
> isolation was in the order of 75 dB while the output to input isolation
> was in the order of 90 dB. This is not too bad for this simple design
> and perhaps more than adequate for most of us time nuts. I have not been
> able to measure the increase in terms of noise figure but this statement
> must be read as: The increase in noise figure was less than the noise
> floor of my equipment. Nevertheless my statement of beliefs is the same
> as Bruce's one: A single transistor stage may be more easily optimized
> than a multi-transistor-design.
>
> Best regards
> Ulrich Bangert   
>
>   

Ulrich

Since the MAX477 has an input noise of around 5nV/rtHz at 10MHz compared 
to around 1nV/rtHz for a low noise bipolar transistor, the MAX477 may be 
expected to be have a phase noise floor of up to 14dB higher than that 
of an optimised discrete transistor amplifier. This however may not be a 
concern unless one has an OCXO with a phase noise floor approaching the 
state of the art (-180dBc/Hz).

There are wideband opamps with lower noise than the MAX477 available.
One could always use 4 MAX 477s inparallel to lower the phase noise 
floor by about 6dB.

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Don Collie]

Why not use an optocoupler as an isolation amplifier? - to the best of my 
knowledge it would provide infinite isolation.
Cheers,...Don Collie


- Original Message - 
From: "Dr Bruce Griffiths" <[EMAIL PROTECTED]>
To: "Discussion of precise time and frequency measurement" 

Sent: Saturday, February 03, 2007 12:29 PM
Subject: Re: [time-nuts] Stepping up the output of an OCXO


> Ulrich Bangert wrote:
>> Bruce and Didier,
>>
>> i had the opportunity to measure the output to output as well as the
>> output to input isolation of a diy MAX477 based distribution amplifier
>> very similar to the TADD-1 (but not identical). The output to output
>> isolation was in the order of 75 dB while the output to input isolation
>> was in the order of 90 dB. This is not too bad for this simple design
>> and perhaps more than adequate for most of us time nuts. I have not been
>> able to measure the increase in terms of noise figure but this statement
>> must be read as: The increase in noise figure was less than the noise
>> floor of my equipment. Nevertheless my statement of beliefs is the same
>> as Bruce's one: A single transistor stage may be more easily optimized
>> than a multi-transistor-design.
>>
>> Best regards
>> Ulrich Bangert
>>
>>
>
> Ulrich
>
> Since the MAX477 has an input noise of around 5nV/rtHz at 10MHz compared
> to around 1nV/rtHz for a low noise bipolar transistor, the MAX477 may be
> expected to be have a phase noise floor of up to 14dB higher than that
> of an optimised discrete transistor amplifier. This however may not be a
> concern unless one has an OCXO with a phase noise floor approaching the
> state of the art (-180dBc/Hz).
>
> There are wideband opamps with lower noise than the MAX477 available.
> One could always use 4 MAX 477s inparallel to lower the phase noise
> floor by about 6dB.
>
> Bruce
>
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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Don
Don Collie wrote:
> Why not use an optocoupler as an isolation amplifier? - to the best of my 
> knowledge it would provide infinite isolation.
> Cheers,...Don Collie
>
>
>   
And lots of noise.
You will need a cleanup PLL on the output side.
Also optocoupler isolation isn't infinite, there is a finite capacitance 
between the closely spaced emitter and detector.
Not all optoisolators are fast enough.
The most effective way of using optical isolation is in fact to modulate 
a stabilised laser and then couple the output into a fibre.
This technique is employed to distribute stable frequencies to Radio 
telescope antennas especially when a large number are employed in an array.
A phase locked loo is used at the other end to cleanup the signal after 
the photodetector.
Fibre has the advantage in this and other applications where long runs 
are involved that its propagation delay tempco is significantly lower 
than that of coax.
It is also possible to use fibre stretchers and other techniques to 
actively compensate variations in the fibre propagation delay.

Isolation becomes particularly important when one mixes a pair of 
signals a few Hz apart and then analyses the zero crossing times of the 
mixer output beat signal.
It is easier to achieve a high isolation between RF frequencies than at 
frequencies of a few Hz, JPL found fibre optic isolation can be 
invaluable in this case.

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Dave Brown]

Not sure if the NVE Isoloop range of GMR based high speed data 
couplers would have any advantages in this regard-their data is a bit 
sketchy but they would likely have similar issues- aside from 
certainly being fast enough.
DaveB

- Original Message - 
From: "Dr Bruce Griffiths" <[EMAIL PROTECTED]>
To: "Don Collie" <[EMAIL PROTECTED]>; "Discussion of precise time and 
frequency measurement" 
Sent: Saturday, February 03, 2007 6:43 PM
Subject: Re: [time-nuts] Stepping up the output of an OCXO


> Don
> Don Collie wrote:
>> Why not use an optocoupler as an isolation amplifier? - to the best 
>> of my
>> knowledge it would provide infinite isolation.
>> Cheers,...Don Collie
>>
>>
>>
> And lots of noise.
> You will need a cleanup PLL on the output side.
> Also optocoupler isolation isn't infinite, there is a finite 
> capacitance
> between the closely spaced emitter and detector.
> Not all optoisolators are fast enough.
> The most effective way of using optical isolation is in fact to 
> modulate
> a stabilised laser and then couple the output into a fibre.
> This technique is employed to distribute stable frequencies to Radio
> telescope antennas especially when a large number are employed in an 
> array.
> A phase locked loo is used at the other end to cleanup the signal 
> after
> the photodetector.
> Fibre has the advantage in this and other applications where long 
> runs
> are involved that its propagation delay tempco is significantly 
> lower
> than that of coax.
> It is also possible to use fibre stretchers and other techniques to
> actively compensate variations in the fibre propagation delay.
>
> Isolation becomes particularly important when one mixes a pair of
> signals a few Hz apart and then analyses the zero crossing times of 
> the
> mixer output beat signal.
> It is easier to achieve a high isolation between RF frequencies than 
> at
> frequencies of a few Hz, JPL found fibre optic isolation can be
> invaluable in this case.
>
> Bruce
>
> ___
> time-nuts mailing list
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>
>
> -- 
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> Checked by AVG Free Edition.
> Version: 7.5.432 / Virus Database: 268.17.19/663 - Release Date: 
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>
> 

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Re: [time-nuts] Stepping up the output of an OCXO

[Don Collie]

I am depantsd, Dr Bruce  ;-)Don.

PS : How much reverse transconductance would a typical high speed opto have 
[ball park figure]?
What sort of SNR is necessary to prevent an uncertaincy of 1part in 
10^13?


- Original Message - 
From: "Dr Bruce Griffiths" <[EMAIL PROTECTED]>
To: "Don Collie" <[EMAIL PROTECTED]>; "Discussion of precise time and 
frequency measurement" 
Sent: Saturday, February 03, 2007 6:43 PM
Subject: Re: [time-nuts] Stepping up the output of an OCXO


> Don
> Don Collie wrote:
>> Why not use an optocoupler as an isolation amplifier? - to the best of my 
>> knowledge it would provide infinite isolation.
>> Cheers,...Don Collie
>>
>>
>>
> And lots of noise.
> You will need a cleanup PLL on the output side.
> Also optocoupler isolation isn't infinite, there is a finite capacitance 
> between the closely spaced emitter and detector.
> Not all optoisolators are fast enough.
> The most effective way of using optical isolation is in fact to modulate a 
> stabilised laser and then couple the output into a fibre.
> This technique is employed to distribute stable frequencies to Radio 
> telescope antennas especially when a large number are employed in an 
> array.
> A phase locked loo is used at the other end to cleanup the signal after 
> the photodetector.
> Fibre has the advantage in this and other applications where long runs are 
> involved that its propagation delay tempco is significantly lower than 
> that of coax.
> It is also possible to use fibre stretchers and other techniques to 
> actively compensate variations in the fibre propagation delay.
>
> Isolation becomes particularly important when one mixes a pair of signals 
> a few Hz apart and then analyses the zero crossing times of the mixer 
> output beat signal.
> It is easier to achieve a high isolation between RF frequencies than at 
> frequencies of a few Hz, JPL found fibre optic isolation can be invaluable 
> in this case.
>
> Bruce
>
>
> -- 
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.432 / Virus Database: 268.17.20/664 - Release Date: 2/2/2007 
> 3:42 PM
>
> 


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Re: [time-nuts] Stepping up the output of an OCXO

[Ulrich Bangert]

Don,

> What sort of SNR is necessary to prevent an uncertaincy 
> of 1part in 10^13?

I see, you are a non believer! But Bruce was talking about comparing
zero crossings of signals at a few (!) Hz, which needs indeed tremendous
amounts of SNR to get to an uncertainity of 1 part in 10^13! The reason
is that for precice timing not the signal-to-noise-ratio is the figure
of merit but the slope-to-noise-ratio. 

With a 10 MHz signal and a 1 Hz signal having the same SNR the 1 Hz
signal will be inferior 10E7 in terms of slope-to-noise-ratio which
gives raise to the necessity of an 140 dB improved SNR on 1 Hz against
the 10 MHz signal if you want to measure the zero crossings with the
SAME incertainity as on the 10 MHz signal.

If you are still critical about it: A zero crossing detector for a 1 Hz
signal giving a uncertainity of better than 1E-6 (some universes  apart
from your 10E-13) has been celebrated as an first grade scientifical
breakthrough some years ago.   

Best regards
Ulrich Bangert

P.S.

Of course the above applies only to sinusoidal signal forms where the
slope of the zero crossings depends on the signal's frequency. So one
might pretend he is going to measure the zero crossings of DIGITAL
signals of a few Hz which may be indeed easy to measure due to their
high slew rates. The people that argument this way must ask themselves
how to make a digital signal from a sine signal which is pretty much the
same problem as measuring the zero crossing with high precision.  

> -Ursprüngliche Nachricht-
> Von: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] Im Auftrag von Don Collie
> Gesendet: Samstag, 3. Februar 2007 07:57
> An: Dr Bruce Griffiths; Discussion of precise time and 
> frequency measurement
> Betreff: Re: [time-nuts] Stepping up the output of an OCXO
> 
> 
> I am depantsd, Dr Bruce  ;-)Don.
> 
> PS : How much reverse transconductance would a typical high 
> speed opto have 
> [ball park figure]?
> What sort of SNR is necessary to prevent an uncertaincy 
> of 1part in 
> 10^13?
> 
> 
> - Original Message - 
> From: "Dr Bruce Griffiths" <[EMAIL PROTECTED]>
> To: "Don Collie" <[EMAIL PROTECTED]>; "Discussion of precise 
> time and 
> frequency measurement" 
> Sent: Saturday, February 03, 2007 6:43 PM
> Subject: Re: [time-nuts] Stepping up the output of an OCXO
> 
> 
> > Don
> > Don Collie wrote:
> >> Why not use an optocoupler as an isolation amplifier? - to 
> the best 
> >> of my
> >> knowledge it would provide infinite isolation.
> >> Cheers,...Don Collie
> >>
> >>
> >>
> > And lots of noise.
> > You will need a cleanup PLL on the output side.
> > Also optocoupler isolation isn't infinite, there is a finite 
> > capacitance
> > between the closely spaced emitter and detector.
> > Not all optoisolators are fast enough.
> > The most effective way of using optical isolation is in 
> fact to modulate a 
> > stabilised laser and then couple the output into a fibre.
> > This technique is employed to distribute stable frequencies 
> to Radio 
> > telescope antennas especially when a large number are 
> employed in an 
> > array.
> > A phase locked loo is used at the other end to cleanup the 
> signal after 
> > the photodetector.
> > Fibre has the advantage in this and other applications 
> where long runs are 
> > involved that its propagation delay tempco is significantly 
> lower than 
> > that of coax.
> > It is also possible to use fibre stretchers and other techniques to 
> > actively compensate variations in the fibre propagation delay.
> >
> > Isolation becomes particularly important when one mixes a pair of 
> > signals
> > a few Hz apart and then analyses the zero crossing times of 
> the mixer 
> > output beat signal.
> > It is easier to achieve a high isolation between RF 
> frequencies than at 
> > frequencies of a few Hz, JPL found fibre optic isolation 
> can be invaluable 
> > in this case.
> >
> > Bruce
> >
> >
> > --
> > No virus found in this incoming message.
> > Checked by AVG Free Edition.
> > Version: 7.5.432 / Virus Database: 268.17.20/664 - Release 
> Date: 2/2/2007 
> > 3:42 PM
> >
> > 
> 
> 
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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Ulrich, Don
Ulrich Bangert wrote:
> Don,
>
>   
>> What sort of SNR is necessary to prevent an uncertaincy 
>> of 1part in 10^13?
>> 
>
>   
110dB or more for Tau = 1sec.
> I see, you are a non believer! But Bruce was talking about comparing
> zero crossings of signals at a few (!) Hz, which needs indeed tremendous
> amounts of SNR to get to an uncertainity of 1 part in 10^13! The reason
> is that for precice timing not the signal-to-noise-ratio is the figure
> of merit but the slope-to-noise-ratio. 
>
> With a 10 MHz signal and a 1 Hz signal having the same SNR the 1 Hz
> signal will be inferior 10E7 in terms of slope-to-noise-ratio which
> gives raise to the necessity of an 140 dB improved SNR on 1 Hz against
> the 10 MHz signal if you want to measure the zero crossings with the
> SAME incertainity as on the 10 MHz signal.
>
> If you are still critical about it: A zero crossing detector for a 1 Hz
> signal giving a uncertainity of better than 1E-6 (some universes  apart
> from your 10E-13) has been celebrated as an first grade scientifical
> breakthrough some years ago.   
>
> Best regards
> Ulrich Bangert
>
> P.S.
>
> Of course the above applies only to sinusoidal signal forms where the
> slope of the zero crossings depends on the signal's frequency. So one
> might pretend he is going to measure the zero crossings of DIGITAL
> signals of a few Hz which may be indeed easy to measure due to their
> high slew rates. The people that argument this way must ask themselves
> how to make a digital signal from a sine signal which is pretty much the
> same problem as measuring the zero crossing with high precision.  
>
>
>   
Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[John Ackermann N8UR]

Dr Bruce Griffiths said the following on 02/02/2007 06:29 PM:

> Since the MAX477 has an input noise of around 5nV/rtHz at 10MHz compared 
> to around 1nV/rtHz for a low noise bipolar transistor, the MAX477 may be 
> expected to be have a phase noise floor of up to 14dB higher than that 
> of an optimised discrete transistor amplifier. This however may not be a 
> concern unless one has an OCXO with a phase noise floor approaching the 
> state of the art (-180dBc/Hz).

I had a chance to measure a TADD-1 using an HP-3048 phase noise system
last year.  I've attached a screen shot of the results; in short it was
below -140dBc/Hz from 100 Hz on out (by the way, I'm not sure I would
trust the noise floor shown in this test; I am not certain we had the
best test set-up).  That's within a few dB of what HP said their 5087A
amplifier would do.

I'll soon have access to a new phase noise measurement system and will
relook at the TADD-1 performance with it.

John


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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

John Ackermann N8UR wrote:
> I had a chance to measure a TADD-1 using an HP-3048 phase noise system
> last year.  I've attached a screen shot of the results; in short it was
> below -140dBc/Hz from 100 Hz on out (by the way, I'm not sure I would
> trust the noise floor shown in this test; I am not certain we had the
> best test set-up).  That's within a few dB of what HP said their 5087A
> amplifier would do.
>
> I'll soon have access to a new phase noise measurement system and will
> relook at the TADD-1 performance with it.
>
> John
>
>   
John

My calculations using the component values in the circuit indicate that 
the TADD-1 noise figure should be about 19dB and its corresponding phase 
noise floor should be lower than -160dBc/Hz. when the input signal is 
+7dBm or greater. So unless you had an unusually noisy set of opamps 
and/or resistors the measurement setup phase noise floor probably 
exceeds that of the TADD-1 by around 20dB.

With a 10V supply instead of 9V and a +13dBm input the phase noise floor 
should be about -168dBc/Hz which is respectable but a few (~10) dB shy 
of the state of the art.

The only way to achieve the state of the art performance with opamps 
using a 9 or 10V supply is to use lower noise (2nV/rtHz appears 
feasible) opamps pairs driven in push pull by an input step up (1:2 
turns ratio) transformer with an output stepdown transformer driven in 
pushpull by the 2 opamp outputs. The noisy 1K input protection resistor 
would also have to be reduced in value as would the opamp feedback 
network resistors.

NIST's 1995 distribution amplifier claims a phase tempco of 0.3ps/K and 
120dB isolation between channels.
http://www.physics.nist.gov/News/Update/950626.html

Bruce

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Re: [time-nuts] Stepping up the output of an OCXO

[Ulrich Bangert]

Bruce,

I have seen this specs before but do you know how to find the
schematics?

Best regards
Ulric Bangert

> -Ursprüngliche Nachricht-
> Von: [EMAIL PROTECTED] 
> [mailto:[EMAIL PROTECTED] Im Auftrag von Dr Bruce Griffiths
> Gesendet: Sonntag, 4. Februar 2007 08:32
> An: Discussion of precise time and frequency measurement
> Betreff: Re: [time-nuts] Stepping up the output of an OCXO
> 
> 
> John Ackermann N8UR wrote:
> > I had a chance to measure a TADD-1 using an HP-3048 phase 
> noise system 
> > last year.  I've attached a screen shot of the results; in short it 
> > was below -140dBc/Hz from 100 Hz on out (by the way, I'm not sure I 
> > would trust the noise floor shown in this test; I am not certain we 
> > had the best test set-up).  That's within a few dB of what HP said 
> > their 5087A amplifier would do.
> >
> > I'll soon have access to a new phase noise measurement 
> system and will 
> > relook at the TADD-1 performance with it.
> >
> > John
> >
> >   
> John
> 
> My calculations using the component values in the circuit 
> indicate that 
> the TADD-1 noise figure should be about 19dB and its 
> corresponding phase 
> noise floor should be lower than -160dBc/Hz. when the input signal is 
> +7dBm or greater. So unless you had an unusually noisy set of opamps
> and/or resistors the measurement setup phase noise floor probably 
> exceeds that of the TADD-1 by around 20dB.
> 
> With a 10V supply instead of 9V and a +13dBm input the phase 
> noise floor 
> should be about -168dBc/Hz which is respectable but a few 
> (~10) dB shy 
> of the state of the art.
> 
> The only way to achieve the state of the art performance with opamps 
> using a 9 or 10V supply is to use lower noise (2nV/rtHz appears 
> feasible) opamps pairs driven in push pull by an input step up (1:2 
> turns ratio) transformer with an output stepdown transformer 
> driven in 
> pushpull by the 2 opamp outputs. The noisy 1K input 
> protection resistor 
> would also have to be reduced in value as would the opamp feedback 
> network resistors.
> 
> NIST's 1995 distribution amplifier claims a phase tempco of 
> 0.3ps/K and 
> 120dB isolation between channels. 
> http://www.physics.nist.gov/News/Update/950626> .html
> 
> Bruce
> 
> 
> 
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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Ulrich Bangert wrote:
> Bruce,
>
> I have seen this specs before but do you know how to find the
> schematics?
>
> Best regards
> Ulric Bangert
>
>   
Ulrich

NO, I'm still looking, I presume you mean the NIST amplifier schematics 
and not the TADD-1 schematics at:
http://www.tapr.org/~n8ur/ 

JPL claim a phase tempco of about 1ps/K for their 1981 distribution 
amplifiers.

It should be possible to achieve a phase noise floor or around 
-180dBc/Hz with a transformer coupled common base amplifier, but it can 
probably only achieve about 90dB isolation between outputs, by taking 
advantage of the 30 dB isolation between splitter outputs, without 
cascading common base stages which inevitably degrades the phase noise 
floor.

It would be interesting to see if coupling via the common power supply 
limits the isolation of the TADD-1.
The power supply noise may also limit the performance.
Its easy to reduce the the power supply noise by 20-30dB with a low 
noise active filter or a low noise regulator.

Bruce


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Re: [time-nuts] Stepping up the output of an OCXO

[Dr Bruce Griffiths]

Ulrich Bangert wrote:

Bruce,

I have seen this specs before but do you know how to find the
schematics?

Best regards
Ulric Bangert

  

Ulrich

Since the earlier NBS isolation/distribution amplifiers consisted of dc 
coupled cascaded common base stages (according to Magnus who had looked 
at some), the newer generation developed in conjunction with the 
technical university of Torino may merely use the same topology with 
faster transistors (SiGe??) perhaps in IC or hybrid form.


I suspect that the 0.3ps/K may have been a typo and they use amplifiers 
similar to the Spectradynamics Distribution amplifiers rated at 3ps/K. 
These distribution amplifiers  are recommended by the BIPM.

For the 1-20MHz amplifier see:
http://www.spectradynamics.com/HPDA-15.html
See attached files for phase noise plot and mechanical shielding used.

I guess there's a passive splitter in there somewhere and a bandpass 
filter (which probably contributes most of the phase tempco) in there as 
well.


Everyone of note in the professional timing community, including the 
Italians, seems to be buying them.


Bruce

<>
<>
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Re: [time-nuts] Stepping up the output of an OCXO

[John Ackermann N8UR]

Dr Bruce Griffiths said the following on 02/04/2007 02:32 AM:

> My calculations using the component values in the circuit indicate that 
> the TADD-1 noise figure should be about 19dB and its corresponding phase 
> noise floor should be lower than -160dBc/Hz. when the input signal is 
> +7dBm or greater. So unless you had an unusually noisy set of opamps 
> and/or resistors the measurement setup phase noise floor probably 
> exceeds that of the TADD-1 by around 20dB.

Thanks for running that calculation, Bruce!  I am somewhat suspect of
our test setup as the fellow who owned the 3048 had never done this type
of measurement before.  I also don't recall just what the input level
was for our test.

In the next month or so, I'm hoping to rerun the measurements with an
easier-to-use, if not actually better, phase noise system and will
report those results.

> With a 10V supply instead of 9V and a +13dBm input the phase noise floor 
> should be about -168dBc/Hz which is respectable but a few (~10) dB shy 
> of the state of the art.
> 
> The only way to achieve the state of the art performance with opamps 
> using a 9 or 10V supply is to use lower noise (2nV/rtHz appears 
> feasible) opamps pairs driven in push pull by an input step up (1:2 
> turns ratio) transformer with an output stepdown transformer driven in 
> pushpull by the 2 opamp outputs. The noisy 1K input protection resistor 
> would also have to be reduced in value as would the opamp feedback 
> network resistors.
> 
> NIST's 1995 distribution amplifier claims a phase tempco of 0.3ps/K and 
> 120dB isolation between channels.
> http://www.physics.nist.gov/News/Update/950626.html
> 
> Bruce
> 
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Re: [time-nuts] Stepping up the output of an OCXO

[Magnus Danielson]

From: Dr Bruce Griffiths <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] Stepping up the output of an OCXO
Date: Mon, 05 Feb 2007 01:22:54 +1300
Message-ID: <[EMAIL PROTECTED]>

> Ulrich Bangert wrote:
> > Bruce,
> >
> > I have seen this specs before but do you know how to find the
> > schematics?
> >
> > Best regards
> > Ulric Bangert
> >
> >   
> Ulrich
> 
> Since the earlier NBS isolation/distribution amplifiers consisted of dc 
> coupled cascaded common base stages (according to Magnus who had looked 
> at some),

One of the NBS/NIST articles is "Design Considerations in State-of-the-Art 
Signal Processing and Phase Noise Measurement Systems" by F.L. Walls, S.R. 
Stein, J.E. Gray, and D.J. Glaze:
http://tf.nist.gov/timefreq/general/pdf/90.pdf

See Fig 1 for the amp that I was talking about. Look - no coils!
I actually wander if they have not made a point of building it off 3 2N3904
rather than some more suitable transistor. I've seen similar stuff from these
culprits before.

> the newer generation developed in conjunction with the 
> technical university of Torino may merely use the same topology with 
> faster transistors (SiGe??) perhaps in IC or hybrid form.

Why not? ;O)

> I suspect that the 0.3ps/K may have been a typo and they use amplifiers 
> similar to the Spectradynamics Distribution amplifiers rated at 3ps/K. 
> These distribution amplifiers  are recommended by the BIPM.
> For the 1-20MHz amplifier see:
> http://www.spectradynamics.com/HPDA-15.html
> See attached files for phase noise plot and mechanical shielding used.
> 
> I guess there's a passive splitter in there somewhere and a bandpass 
> filter (which probably contributes most of the phase tempco) in there as 
> well.

Indeed. Probably an initial boost, passive splitter and iso-amps.

Cheers,
Magnus

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