Constant amplitude output circuit design?

[dr pepper]

I was thinking generic logic, cd40106, woudnt be as good as a pll.

 

[pavjayt]

I'm puzzled as to why you have all those caps in parallel/series? Isn't that likely to make the circuit less stable?

Well that second schematic is not actually mine, I inherited it from previous guy. It happens to work with sine wave input, so I didn't modify it.

 

[pavjayt]

I may give that AD790 a try when it arrives, but I am not hoping for it to solve my issue as the source sine wave itself might be having a jitter in itself. I am guessing probably I may well have to go back to PLL route. But this time I would like to make it more stable while using the source sine wave or using both sine/TTL combo in some way.

I will start on working on this too if you guys have better ideas on implementing a stable PLL. I did play with ADSimPll program, but it seems way too complicated for me to work with it. Has anyone had experience with it?

thanks

 

[MrAl]

If it is offset the AD790 will be better, but you may see multiple pulses at the zero crossing from noise. But certainly worth a try. Is it better with the high amplitude signal?

Hi,

If there are multiply zero detections then a little hysteresis is in order. This might have to be in the form of some AC hysteresis rather than the usual resistors only solution.

 

[pavjayt]

I just got 790 comparators today, will try them tomorrow, meanwhile could someone help me in finetuning the PLL design that I have to get a more stable output from my sine way?

thanks

 

[ronv]

I'm no pll guy, but it seems like you just need to really roll it off at a low frequency. Seems like it should be easy since you don't have to worry about lock range.

 

[pavjayt]

Does anyone have a sample schematic using AD790? I hooked it up with a ±15VDC and 5VDC logic supply and used a 1K on the input bipolar sine wave going through a diode to IN+. I grounded the IN-, connected latch to +5V. I dont see any TTL on the output, its just a DC value.

thanks

 

[alec_t]

Sounds like the diode is blocking the path for the In+ bias current.

 

[MrAl]

Yeah, try without diode.

 

[pavjayt]

It works now with out the diode, I added the diode based on their datasheet's sample circuit for bipolar input. Anyways, the output has about the same jitter as the TTL provided by the driver, except that the zero triggering is a bit off. This makes me think that the source since wave itself has some jitter to it. The jitter lowers as the amplitude of the sine wave increases.

Is there any other ideal solution for this problem or maybe I should just live with it.

 

[MrAl]

Hi,

Well what kind of problem is the jitter causing in the first place?

More gain in the AC amplifier perhaps.

Perhaps a bandpass filter ahead of the comparator, unless the frequency has to change.