[time-nuts] DMTD - analog multiplier vs. diode mixer ?

[Magnus Danielson]

Hi Poul-Henning,

On 01/06/2016 12:28 AM, Poul-Henning Kamp wrote:
> --------
> In message <568C46B9.4020303 at rubidium.dyndns.org>, Magnus Danielson writes:
>
>> The white noise will be particularly annoying as it then converts to
>> jitter through the slew-rate limitation as you go into the
>> trigger-circuit.
>
> Digitize the LPF output and do a curve-fit to find the zero-crossings ?
>

That would work. You could least-square fit it with very cheap 
processing. The LPF would mainly need to reject the sum frequencies to 
act as anti-aliasing filter, and the noise would be filtered out by the 
least-square processing.

Estimating the phase and slew-rate, and then use those to calculate the 
actual through-zero phase would not be too hard. As a consequence you 
get a slew-rate monitor, which act as an observation of signal level.

Cheers,
Magnus