[time-nuts] Updated Divider Jitter Results - 74HC390
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Sun Apr 5 01:09:35 UTC 2009
For start stop measurements with the same slew rate signal at each input
channel
Total jitter = SQRT [16E-24 + 5.06E-7/(S*S)]
where the effective (combined) input noise is 711 uV rms.
and the intrinsic jitter is 4ps rms.
Bruce
Bruce Griffiths wrote:
> John
>
> The parameters for a simple model for the Wavecrest input jitter can be
> derived from your measurements as
>
> For each channel:
> Jitter = SQRT[8E-24 + 2.53E-7/(S*S)]
> Where S is the input signal slew rate at the trigger threshold
>
> Input noise ~ 503 uV rms. (2.53E-7 = square of input rms noise)
> 8E-24 = square of Wavecrest input channel intrinsic jitter (2.8ps rms).
>
> Bruce
>
> John Ackermann N8UR wrote:
>
>> Bruce Griffiths said the following on 04/04/2009 07:30 PM:
>>
>>
>>> John
>>>
>>> I can't find a spec for the Wavecrest 2075 input amplifier/trigger
>>> circuit noise but it could be as high as 1mV rms given its 800MHz+ input
>>> bandwidth.
>>>
>>> If the noise is 1mV rms:
>>> Then an input signal slew rate of 1V/ns is required to keep the jitter
>>> contribution of the amplifier input noise below 1ps rms.
>>> A 3 stage limiter cascade with an overall slope gain of about 12x can be
>>> used to increase the slew rate of a 10MHz 2V pp input signal to 1V/ns.
>>> With an appropriate distribution of limiter stage gain and bandwidth,
>>> the jitter contribution due to limiter noise and Wavecrest input noise
>>> can be held below1.2ps rms.
>>> The jitter contribution due to amplifier input noise with such an input
>>> signal connected directly to the Wavecrest input would be about 16ps rms.
>>>
>>>
>> Bruce --
>>
>> A simple experiment just verified your hunch that input amp noise is a
>> limiting factor. Using the Wavecrest in time interval ("total
>> propagation delay") mode with signal going into channel 1, then through
>> a 4 foot cable into channel 2 to generate about 6 ns of delay (with a
>> tee at channel 2 providing a 50 ohm load):
>>
>> A 10 MHz sine wave at 1.0V P-P shows a 100K sample jitter of 23 ps.
>>
>> A 10 MHz pulse train at 1.0V P-P from a 5359A Time Synthesizer (with < 5
>> ns transition time) shows a 100K sample jitter of 4 ps.
>>
>> I think I missed the point of your suggestion a couple of messages ago,
>> but I get it now -- to measure the input circuit performance, I probably
>> need to use two input circuits, one fed to start and the other to stop,
>> so the Wavecrest can get a better slew rate to deal with, then divide by
>> sqrt(2). That'll be part of tomorrow's experiments...
>>
>> John
>>
>>
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>
>
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