HCF4046 frequency multiplier synchrnized with mains (50Hz)

crutschow

Joined Mar 14, 2008
34,283
If you were triggering from the clock itself then the first pulse should be more stable than the last, but in your video all the pulses seem to be jittering together, not necessarily changing frequency.

Are you using an expanded or delayed sweep on the 'scope?
 

crutschow

Joined Mar 14, 2008
34,283
Some scopes have filter settings on the trigger to minimize jitter from noise.
If you scope has that, you might give that a try.
 

Thread Starter

Alberto Carboni

Joined Apr 21, 2016
12
I think the problem is somewhere else:

1. here is the signal coming from the phase comparator 2(blue) and the signal entering in the VCO (yellow)
TEK0004.JPG
zooming
TEK0003.JPG

PC2.PNG

so that jitter is caused by those pulses, in fact:

TEK0000.JPG
 

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Alec_t

Joined Sep 17, 2013
14,280
What are you now using as a LPF? The VCOin signal, coming from the LPF, should be a steady DC level at lock and a smoothly varying signal when not at lock. Your yellow trace has sharp pulses on it.
 

Thread Starter

Alberto Carboni

Joined Apr 21, 2016
12
What are you now using as a LPF? The VCOin signal, coming from the LPF, should be a steady DC level at lock and a smoothly varying signal when not at lock. Your yellow trace has sharp pulses on it.
here is the filter

RRC.PNG

Now I am studying the equations for the LPF, maybe I can fix this issue
 

Alec_t

Joined Sep 17, 2013
14,280
The rounded leading edge on the yellow trace could be explained by the VCOin input having a ~60pF capacitance. That is consistent with the input pin being connected to a FET gate.
What are your R1 and C1 values?
For the real 4046 (not the sim) what is the voltage between pins 9 (VCOin) and 11 (R1 connection)?
 
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