How to measure phase noise of HCMOS oscillators?

[Anders Time]

A while a go i bought some low phase noise Crystek CVHD-950 and now I want
to meas the phase noise of the oscillators.
Is it best to try to impedance match the output signal and filter and
amplify the hcmos before i feed it in to the phase detector? or Just hope
that the signal is high enough to drive the mixer? What about all the
harmonics? Does it alter the phase noise result?
/Anders

[John Miles]

Your main concern will be injection locking, followed by the additive noise
of the buffer amps that you use to prevent it. The CMOS output buffers in
the oscillators themselves may provide enough isolation, but don't count on
it. Injection locking is easy to spot with a scope. You can adjust the
tuning voltage of one oscillator to match the frequency of the other, and
see if their phases snap into coincidence.

If necessary, LMH6702 opamps can be used at the frequencies covered by the
CVHD-950 parts. They will provide plenty of isolation with little or no
effect on noise measurements in the -165 dBc/Hz vicinity, given strong
signals to work with (+10 dBm or more).

If I were driving a mixer with 3.3V HCMOS, I'd try a series 50-ohm
termination first. Basically, pretend that you have a perfect voltage
source whose output impedance will be that of whatever resistor you place in
series with it. It won't be, of course, but the effect will be close
enough. The connections between the oscillators and mixers will not be long
enough to make exact impedance matching necessary.

There should be no need to filter the signal; mixers are switches, and they
like square waves. If you want, you can use an L-network to handle both
lowpass filtering and matching, of course. The only filter necessary is the
LPF that follows the mixer.

-- john, KE5FX
Miles Design LLC

-----Original Message-----
Sent: Monday, March 10, 2014 8:33 AM
Subject: [time-nuts] How to measure phase noise of HCMOS oscillators?
A while a go i bought some low phase noise Crystek CVHD-950 and now I want
to meas the phase noise of the oscillators.
Is it best to try to impedance match the output signal and filter and
amplify the hcmos before i feed it in to the phase detector? or Just hope
that the signal is high enough to drive the mixer? What about all the
harmonics? Does it alter the phase noise result?
/Anders
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To unsubscribe, go to https://www.febo.com/cgi-
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[Magnus Danielson]

Post by Anders Time
A while a go i bought some low phase noise Crystek CVHD-950 and now I want
to meas the phase noise of the oscillators.
Is it best to try to impedance match the output signal and filter and
amplify the hcmos before i feed it in to the phase detector? or Just hope
that the signal is high enough to drive the mixer? What about all the
harmonics? Does it alter the phase noise result?

What phase detector do you have? It depends.

For a DBM you don't want to overdrive it, I expect that to give you
excess flicker noise. I expect overtones to mix with white noise.

What frequency and by the way, what is the rest of the setup?

Cheers,
Magnus

[d0ct0r]

Hello,

I am experimenting to build frequency counter using external OCXO and
ST32 MCU. The OCXO is external DATUM 2750013-1 device which produce
10Mhz sine wave. I connected its output to OC_IN on MCU. I have few
challenges now.

First, looks like I need to create some delay to turn on MCU _after_
OCXO. If I try to start both devices simultaneously, I got following
result for 10 kHz TTL measurement:


System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
16000000 16000000 16000000

# Starting SuperLoop...
FREQ: 105197
FREQ: 105263
FREQ: 105263
FREQ: 105263


As soon as I push reset button on MCU, I got correct results for its
clocks and correct value for the counter:


System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
168000000 42000000 84000000

# Starting SuperLoop...
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10018
FREQ: 10019


Another challenge is the fact, that if I increase the input signal
frequency, then performance of the MCU decreased. In the other word, I
need to wait much more time to have a result. Probably MCU is super busy
to handle the interrupt. Say for 10 kHz range its pretty fast. Then for
1 mHz its much slower.

Here is main loop:

while (1) {
if(j++ < 0xF00000) {
accum += deltaREF; // Moving Average
accum = (accum >> 1);
} else {
uwTIM1Freq = (uint32_t) SystemCoreClock / accum;
printf("FREQ: %ul\n\r", uwTIM1Freq);
accum = j = 0;
}
}

The counter is based on timer in "input capture" mode and driven by
interrupt:
[ See STM32F4xx_StdPeriph_Examples\TIM\TIM_InputCapture ]

Also this counter shows incorrect results for low frequency. For
example, for 100 Hz:

FREQ: 4968
FREQ: 5030
FREQ: 5056
FREQ: 4916

I would be interesting to hear any advise how to improve it.

And another question is: what will be "pros" and "cons" to transform
10Mhz sine to square to feed MCU ? I tried it, but didn't catch any
difference.

Here is schema
Loading Image...

[Chris Albertson]

Are you putting the "unknown signal" to be measured on an interrupt pin?
that will work for low enough frequencies but most uPs have a built-in
counter. It is a hardware register on the uP chip that will increment for
each pulse on a pin. then you read that number and divide by the gate
time. At some point the frequency will be to high for the counter pin so
then you switch in a hardware frequency diver as a pre-scaler.

Post by d0ct0r
Hello,
I am experimenting to build frequency counter using external OCXO and ST32
MCU. The OCXO is external DATUM 2750013-1 device which produce 10Mhz sine
wave. I connected its output to OC_IN on MCU. I have few challenges now.
First, looks like I need to create some delay to turn on MCU _after_ OCXO.
If I try to start both devices simultaneously, I got following result for
System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
16000000 16000000 16000000
# Starting SuperLoop...
FREQ: 105197
FREQ: 105263
FREQ: 105263
FREQ: 105263
As soon as I push reset button on MCU, I got correct results for its
System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
168000000 42000000 84000000
# Starting SuperLoop...
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10018
FREQ: 10019
Another challenge is the fact, that if I increase the input signal
frequency, then performance of the MCU decreased. In the other word, I need
to wait much more time to have a result. Probably MCU is super busy to
handle the interrupt. Say for 10 kHz range its pretty fast. Then for 1 mHz
its much slower.
while (1) {
if(j++ < 0xF00000) {
accum += deltaREF; // Moving Average
accum = (accum >> 1);
} else {
uwTIM1Freq = (uint32_t) SystemCoreClock / accum;
printf("FREQ: %ul\n\r", uwTIM1Freq);
accum = j = 0;
}
}
The counter is based on timer in "input capture" mode and driven by
[ See STM32F4xx_StdPeriph_Examples\TIM\TIM_InputCapture ]
Also this counter shows incorrect results for low frequency. For example,
FREQ: 4968
FREQ: 5030
FREQ: 5056
FREQ: 4916
I would be interesting to hear any advise how to improve it.
And another question is: what will be "pros" and "cons" to transform 10Mhz
sine to square to feed MCU ? I tried it, but didn't catch any difference.
Here is schema
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_
Ideas/Sine-to-Square_Wave_BJT_Converter_Wenzel.gif
--
WBW,
V.P.
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/time-nuts
and follow the instructions there.

[Chris Albertson]

Sorry forgot to add this.

As for delayed turn on. That can work but why not simply have the software
go into a 5 or 10 second wait before it does anything else. Display
"warming up" or "please wait" on the LCD.


On Wed, Mar 12, 2014 at 7:18 AM, Chris Albertson

Post by Chris Albertson
Are you putting the "unknown signal" to be measured on an interrupt pin?
that will work for low enough frequencies but most uPs have a built-in
counter. It is a hardware register on the uP chip that will increment for
each pulse on a pin. then you read that number and divide by the gate
time. At some point the frequency will be to high for the counter pin so
then you switch in a hardware frequency diver as a pre-scaler.

Post by d0ct0r
Hello,
I am experimenting to build frequency counter using external OCXO and
ST32 MCU. The OCXO is external DATUM 2750013-1 device which produce 10Mhz
sine wave. I connected its output to OC_IN on MCU. I have few challenges
now.
First, looks like I need to create some delay to turn on MCU _after_
OCXO. If I try to start both devices simultaneously, I got following result
System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
16000000 16000000 16000000
# Starting SuperLoop...
FREQ: 105197
FREQ: 105263
FREQ: 105263
FREQ: 105263
As soon as I push reset button on MCU, I got correct results for its
System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
168000000 42000000 84000000
# Starting SuperLoop...
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10018
FREQ: 10019
Another challenge is the fact, that if I increase the input signal
frequency, then performance of the MCU decreased. In the other word, I need
to wait much more time to have a result. Probably MCU is super busy to
handle the interrupt. Say for 10 kHz range its pretty fast. Then for 1 mHz
its much slower.
while (1) {
if(j++ < 0xF00000) {
accum += deltaREF; // Moving Average
accum = (accum >> 1);
} else {
uwTIM1Freq = (uint32_t) SystemCoreClock / accum;
printf("FREQ: %ul\n\r", uwTIM1Freq);
accum = j = 0;
}
}
The counter is based on timer in "input capture" mode and driven by
[ See STM32F4xx_StdPeriph_Examples\TIM\TIM_InputCapture ]
Also this counter shows incorrect results for low frequency. For example,
FREQ: 4968
FREQ: 5030
FREQ: 5056
FREQ: 4916
I would be interesting to hear any advise how to improve it.
And another question is: what will be "pros" and "cons" to transform
10Mhz sine to square to feed MCU ? I tried it, but didn't catch any
difference.
Here is schema
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_
Ideas/Sine-to-Square_Wave_BJT_Converter_Wenzel.gif
--
WBW,
V.P.
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/time-nuts
and follow the instructions there.

--
Chris Albertson
Redondo Beach, California

[d0ct0r]

LCD connected to the same MCU. And it has relation to the core clock
too. So, nothing on LCD before I reset entire MCU. I think initial
incorrect core clock reading cause a lot of issues. Probably my only
option will be to implement some external relay and timer to turn on MCU
few seconds after OCXO. Or may be to put 10Mhz oscillator to PCB and
connect OCXO output in parallel to it (not sure if its good idea or it
will works).

Regards,
V.P.

 Sorry forgot to add this.
As for delayed turn on.  That can work but why not simply have the
software go into a 5 or 10 second wait before it does anything else.
 Display "warming up" or "please wait" on the LCD.
On Wed, Mar 12, 2014 at 7:18 AM, Chris Albertson

Post by Chris Albertson
Are you putting the "unknown signal" to be measured on an interrupt
pin?  that will work for low enough frequencies but most uPs have a
built-in counter.   It is a hardware register on the uP chip that
will increment for each pulse on a pin.  then you read that number
and divide by the gate time.   At some point the frequency will be
to high for the counter pin so then you switch in a hardware
frequency diver as a pre-scaler.

Post by d0ct0r
Hello,
I am experimenting to build frequency counter using external OCXO
and ST32 MCU. The OCXO is external DATUM 2750013-1 device which
produce 10Mhz sine wave. I connected its output to OC_IN on MCU. I
have few challenges now.
First, looks like I need to create some delay to turn on MCU
_after_ OCXO. If I try to start both devices simultaneously, I got
System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
16000000         16000000        16000000
# Starting SuperLoop...
FREQ: 105197
FREQ: 105263
FREQ: 105263
FREQ: 105263
As soon as I push reset button on MCU, I got correct results for
System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
168000000        42000000        84000000
# Starting SuperLoop...
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10018
FREQ: 10019
Another challenge is the fact, that if I increase the input
signal frequency, then performance of the MCU decreased. In the
other word, I need to wait much more time to have a result.
Probably MCU is super busy to handle the interrupt. Say for 10 kHz
range its pretty fast. Then for 1 mHz its much slower.
while (1) {
        if(j++ < 0xF00000) {
            accum += deltaREF; // Moving Average
            accum = (accum >> 1);
        } else {
            uwTIM1Freq = (uint32_t) SystemCoreClock /
accum;
            printf("FREQ: %ulnr", uwTIM1Freq);
            accum = j = 0;
        }
    }
The counter is based on timer in "input capture" mode and driven
[ See STM32F4xx_StdPeriph_ExamplesTIMTIM_InputCapture ]
Also this counter shows incorrect results for low frequency. For
FREQ: 4968
FREQ: 5030
FREQ: 5056
FREQ: 4916
I would be interesting to hear any advise how to improve it.
And another question is: what will be "pros" and "cons" to
transform 10Mhz sine to square to feed MCU ? I tried it, but
didn't catch any difference.
Here is schema

http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Sine-to-Square_Wave_BJT_Converter_Wenzel.gif

Post by Chris Albertson

Post by d0ct0r
[1]
--
WBW,
V.P.
_______________________________________________
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts [2]
and follow the instructions there.

--
Chris Albertson
Redondo Beach, California

--
Chris Albertson
Redondo Beach, California
------
[1]
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Sine-to-Square_Wave_BJT_Converter_Wenzel.gif
[2] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

[cfo]

Post by d0ct0r
LCD connected to the same MCU. And it has relation to the core clock
too. So, nothing on LCD before I reset entire MCU. I think initial
incorrect core clock reading cause a lot of issues. Probably my only
option will be to implement some external relay and timer to turn on MCU
few seconds after OCXO. Or may be to put 10Mhz oscillator to PCB and
connect OCXO output in parallel to it (not sure if its good idea or it
will works).

You could start the MCU up on the internal clock , write to the lcd ,
wait 5 sec. And then switch to the external clock.


Btw:
Is the Ext clock input on the STM fed directly from the OCXO ?
Can the STM handle the OCXO voltage swing ?

If you have a conditioning circuit betewwn the OCXO and the STM , i'd
like to see it. As i have the need for one , trying to interface a 5v OCXO
to a NXP 1114 Arm , that wants max 1.8v in the clockinput.

CFO

[Chris Albertson]

Post by cfo
If you have a conditioning circuit betewwn the OCXO and the STM , i'd
like to see it. As i have the need for one , trying to interface a 5v OCXO
to a NXP 1114 Arm , that wants max 1.8v in the clockinput.

There are logic level converter chip made for this purpose or you can use a
comparator and compare the 5V clock to ground. Or just a diode to clip the
sine wave. If you connect a code. Sometimes you can set buy with a pair
of resisters wired as a voltage divider. I like the comparator best
because it will not load the clock. Diodes will load it for other users.

[cfo]

Post by Chris Albertson
There are logic level converter chip made for this purpose or you can
use a comparator and compare the 5V clock to ground. Or just a diode to
clip the sine wave. If you connect a code. Sometimes you can set buy
with a pair of resisters wired as a voltage divider. I like the
comparator best because it will not load the clock. Diodes will load it
for other users.

Could you come up with some part numbers please.

Ie. witch comparator would handle 10Mhz

CFO

[Bruce Griffiths]

Try:

http://www.linear.com/product/LTC6957

Bruce

Post by cfo

Post by Chris Albertson
There are logic level converter chip made for this purpose or you can
use a comparator and compare the 5V clock to ground. Or just a diode to
clip the sine wave. If you connect a code. Sometimes you can set buy
with a pair of resisters wired as a voltage divider. I like the
comparator best because it will not load the clock. Diodes will load it
for other users.

Could you come up with some part numbers please.
Ie. witch comparator would handle 10Mhz
CFO
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[Alex Pummer]

Analog Devices, Linear Technology and Maxim have fast comparators
73
Alex

Post by cfo

Post by Chris Albertson
There are logic level converter chip made for this purpose or you can
use a comparator and compare the 5V clock to ground. Or just a diode to
clip the sine wave. If you connect a code. Sometimes you can set buy
with a pair of resisters wired as a voltage divider. I like the
comparator best because it will not load the clock. Diodes will load it
for other users.

Could you come up with some part numbers please.
Ie. witch comparator would handle 10Mhz
CFO
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[Brian Lloyd]

LCD connected to the same MCU. And it has relation to the core clock too.
So, nothing on LCD before I reset entire MCU. I think initial incorrect
core clock reading cause a lot of issues. Probably my only option will be
to implement some external relay and timer to turn on MCU few seconds after
OCXO. Or may be to put 10Mhz oscillator to PCB and connect OCXO output in
parallel to it (not sure if its good idea or it will works).

Why not debounce reset from power-up using an RC network and a Schmitt
trigger? Set the time constant so that it will hold the mpu in reset until
power has been asserted long enough to ensure that the OCXO is producing
output.

[Tom Harris]

Post by Chris Albertson
Sorry forgot to add this.
As for delayed turn on. That can work but why not simply have the software
go into a 5 or 10 second wait before it does anything else. Display
"warming up" or "please wait" on the LCD.

Never present the customer with this sort of message. Something like
"optimising settings" or "contacting boot sever... OK". Makes them think
that they have got value for money.

[d0ct0r]

I am using old Wavetek 180 signal generator for the tests. I just hooked
its TTL output directly to the pin of MCU. The STM32F4xx has core clock
168 mHz and its inputs capable to handle pretty wide range of frequency.
I don't think 1-2 mHz connected to the pin should be a problem. At least
in my setup it shows me adequate result for that frequency. But its
slows done the "main loop" a lot because its interrupting million time
per second. For 2 mHz input, I'll need to wait several seconds to see
the result. Of course I could remove averaging or decrease number of
samples to improve that time.
I am still thinking why I have incorrect results for low frequency. May
be counter overflows could impact the result.
The counter for my timer is 16 bit. That means it will generate overflow
after 65535 counts. The timer frequency is 168 mHz. Then it will
overflows around every 400 uS (or 2563.5 Hz). Probably any frequency
which is lower than 2.5 kHz will shows me incorrect results. Probably
I'll need to think how to handle that.

Regards,

V.P.

Post by Chris Albertson
Are you putting the "unknown signal" to be measured on an interrupt
pin?  that will work for low enough frequencies but most uPs have a
built-in counter.   It is a hardware register on the uP chip that
will increment for each pulse on a pin.  then you read that number
and divide by the gate time.   At some point the frequency will be to
high for the counter pin so then you switch in a hardware frequency
diver as a pre-scaler.

Post by d0ct0r
Hello,
I am experimenting to build frequency counter using external OCXO
and ST32 MCU. The OCXO is external DATUM 2750013-1 device which
produce 10Mhz sine wave. I connected its output to OC_IN on MCU. I
have few challenges now.
First, looks like I need to create some delay to turn on MCU
_after_ OCXO. If I try to start both devices simultaneously, I got
System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
16000000         16000000        16000000
# Starting SuperLoop...
FREQ: 105197
FREQ: 105263
FREQ: 105263
FREQ: 105263
As soon as I push reset button on MCU, I got correct results for
System Core Clock: 168000000 Hz
SYSCLK_Frequency PCLK1_Frequency PCLK2_Frequency
168000000        42000000        84000000
# Starting SuperLoop...
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10019
FREQ: 10018
FREQ: 10019
Another challenge is the fact, that if I increase the input signal
frequency, then performance of the MCU decreased. In the other word,
I need to wait much more time to have a result. Probably MCU is
super busy to handle the interrupt. Say for 10 kHz range its pretty
fast. Then for 1 mHz its much slower.
while (1) {
        if(j++ < 0xF00000) {
            accum += deltaREF; // Moving Average
            accum = (accum >> 1);
        } else {
            uwTIM1Freq = (uint32_t) SystemCoreClock / accum;
            printf("FREQ: %ulnr", uwTIM1Freq);
            accum = j = 0;
        }
    }
The counter is based on timer in "input capture" mode and driven by
[ See STM32F4xx_StdPeriph_ExamplesTIMTIM_InputCapture ]
Also this counter shows incorrect results for low frequency. For
FREQ: 4968
FREQ: 5030
FREQ: 5056
FREQ: 4916
I would be interesting to hear any advise how to improve it.
And another question is: what will be "pros" and "cons" to
transform 10Mhz sine to square to feed MCU ? I tried it, but didn't
catch any difference.
Here is schema

http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Sine-to-Square_Wave_BJT_Converter_Wenzel.gif

Post by d0ct0r
[1]
--
WBW,
V.P.
_______________________________________________
To unsubscribe, go to
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and follow the instructions there.

--
Chris Albertson
Redondo Beach, California
------
[1]
http://www.qsl.net/va3iul/Homebrew_RF_Circuit_Design_Ideas/Sine-to-Square_Wave_BJT_Converter_Wenzel.gif
[2] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts

[Anders Time]

Thanks a lot for the input!
I will try to use the LMH6702 as buffer.
The correct way to measure the HCMOS oscillator would probably be to use a
high impedance buffer with very low noise, to simulate driving a 10pF load
or so. But I guess that is not easy to do. The LMH6702 voltage noise is
probably low enough, but I do not know if it is possible to bias the HCMOS
signal so it matches the LMH6702 input voltage range without increasing the
noise level.

I´m using a double balanced mixer form mini circuits as phase detector that
can take 14dBm signals and a SRS FFT analyzer to measure the noise. The
oscillator that I´m measuring is a 100MHz Crystek.
/Anders

[Bruce Griffiths]

Why not AC couple the HCMOS output to the LMH6702 input?

Bruce

Post by Anders Time
Thanks a lot for the input!
I will try to use the LMH6702 as buffer.
The correct way to measure the HCMOS oscillator would probably be to use a
high impedance buffer with very low noise, to simulate driving a 10pF load
or so. But I guess that is not easy to do. The LMH6702 voltage noise is
probably low enough, but I do not know if it is possible to bias the HCMOS
signal so it matches the LMH6702 input voltage range without increasing the
noise level.
I´m using a double balanced mixer form mini circuits as phase detector that
can take 14dBm signals and a SRS FFT analyzer to measure the noise. The
oscillator that I´m measuring is a 100MHz Crystek.
/Anders
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[Magnus Danielson]

Post by Anders Time
Thanks a lot for the input!
I will try to use the LMH6702 as buffer.
The correct way to measure the HCMOS oscillator would probably be to use a
high impedance buffer with very low noise, to simulate driving a 10pF load
or so. But I guess that is not easy to do. The LMH6702 voltage noise is
probably low enough, but I do not know if it is possible to bias the HCMOS
signal so it matches the LMH6702 input voltage range without increasing the
noise level.
I´m using a double balanced mixer form mini circuits as phase detector that
can take 14dBm signals and a SRS FFT analyzer to measure the noise. The
oscillator that I´m measuring is a 100MHz Crystek.

OK. What is the other signal to the mixer? What is the ref?
A known quiet 100 MHz? Another Crystek? Delayed version of itself?
Oscillator locked to the input?

Cheers,
Magnus

[Didier Juges]

The LMH6702 is a wicked fast op amp which will react accordingly it there are parasitics in the feedback path. I have only used them with well laid out PWBs and extremely short traces to surface mount resistors. Under those conditions, they work beautifully as advertised. Not sure anyone other than John can actually breadboard with them :)

Didier KO4BB

Post by Anders Time
Thanks a lot for the input!
I will try to use the LMH6702 as buffer.
The correct way to measure the HCMOS oscillator would probably be to use a
high impedance buffer with very low noise, to simulate driving a 10pF load
or so. But I guess that is not easy to do. The LMH6702 voltage noise is
probably low enough, but I do not know if it is possible to bias the HCMOS
signal so it matches the LMH6702 input voltage range without increasing the
noise level.
I´m using a double balanced mixer form mini circuits as phase detector that
can take 14dBm signals and a SRS FFT analyzer to measure the noise. The
oscillator that I´m measuring is a 100MHz Crystek.
/Anders
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[Hal Murray]

If you have a conditioning circuit betewwn the OCXO and the STM , i'd like
to see it. As i have the need for one , trying to interface a 5v OCXO to a
NXP 1114 Arm , that wants max 1.8v in the clockinput.

What's wrong with a simple resistive divider?

[Hal Murray]

The ref output is the minimal delay through the chip covering the input and
output pad buffers. It will vary slightly with temperature and voltage.

There are no negative delays in that sort of chip. It's just a bunch of
gates/buffers with a carefully calibrated delay. (For a negative delay, you
would need something like a PLL.)

If the delay from the M12+T might be negative, set the antenna cable delay to
be a bit short and add on a constant in software.

[Tom Van Baak (lab)]

Hal,

Yes, there are negative delays. The goal is that the physical 1PPS output is, on average, exactly on-time. If designed right, that means as many negative offset pulses occur as positive offset pulses. The spread gives you the RMS value.

This is exactly what you want for a GPS timing receiver.

/tvb (i5s)

Post by Hal Murray
The ref output is the minimal delay through the chip covering the input and
output pad buffers. It will vary slightly with temperature and voltage.
There are no negative delays in that sort of chip. It's just a bunch of
gates/buffers with a carefully calibrated delay. (For a negative delay, you
would need something like a PLL.)
If the delay from the M12+T might be negative, set the antenna cable delay to
be a bit short and add on a constant in software.