[time-nuts] ? phase comparison or other device

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Jun 30 18:27:34 EDT 2007

Pete wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+bruce.griffiths=xtra.co.nz+bruce.griffiths=xtra.co.nz at febo.com
> Magnus,
> This discussion is why I have allowed the ADA4899-1 to saturate in the ZCD
> posted earlier. The transition times up & down in the second stage are 350 
> to
> 400 ns; thus I believe the <50ns overload recovery doesn't degrade the
> measured jitter. With 500MHz 'scope bandwidth, the 1KHz squarewave
> output has <1% over/under shoot & appears noise free at the zero crossing.
> The output transitions are fast enough for my HP 5370A to  show < 1ns
> jitter over 1K or 10K samples.
> Regards,
> Pete Rawson 

What about the power supply noise that appears at the amplifier output 
during saturation?
Power supply noise is almost always much larger than the opamp input noise.
A simple resistor + diode clamp in addition to the feedback clamp will 
easily attenuate the output noise of an opamp with diode clamps across 
its feedback resistor.

An npn plus a pnp resistor ccan also be used to clamp the output of an 
opamp whilst still suppressing the noise gain to a very low value and 
prevent opamp saturation.


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