which type of filter is fast and nice to make analog output

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I have a PLL circuit, which owns a PLL IC CD4046. CD4046 outputs PWM, and after a lowpass filter ,it outputs an analog output(DC). This is known by us. But i want to read the DC output as fast as possible, and of course acurrately. As far as I try, I only know the higher order the filter is ,the best result I can get.
But I can't apply too many of them ,considering cost. So I just want to ask , which type of filter is best for such situation?
nowadays, I just tried butterworth and normal RC filter. And i am not quite familiar with the other types.
thank you

Our Martians are beginning to learn AVR

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Chebyshev should give you less ripple at the same corner frequency.

I don't know how you are getting PWM out of a CD4046. It is a phase locked loop. The oscillator output is a square-wave with a duty cycle close to 50%. There is no practical way that I know about to get a PWM from this!

Jim

 

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Quote:
i want to read the DC output as fast as possible

I'm guessing you are using a processor to read this? Why not a software filter? Simple averaging over, say, 20 or 30 points would make a nice filter.

If you're really motivated, implement Jim's idea of a Chebyshev filter in software (probably more work than you need, but a fun exercise).

Regards,
Paul

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'As fast as possible' with 'a man in the loop' is about 30hz. If you have an RC filter at 150hz, it will have settled 5 time constants every 30hz.

Imagecraft compiler user

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Are you perhaps talking about one of the phasedetector outputs? And you want to measure phase difference between two signals?

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Absolutely right! I do really want to detect the phase of two signal. Although CD4046 datasheet does not say that , but I create this useful function.

Our Martians are beginning to learn AVR

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About software filter, I am afraid I can't use it . Because my frequency is between 20kHz and 200kHz, take 200kHz for an instance, its period time is 5us, my AVR is not able to place so many points in one cycle

Our Martians are beginning to learn AVR

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The PLL feedback signal in a 4046 is pretty high source impedance. You cannot load it down with a passive filter. That means active is the only way to go.

If the frequency range is between 20KHz and 200KHz, then the pole (or poles) have to be BELOW 20KHz. No matter how many poles you have, they have to be below 20KHz. You will get lots of filtering when it is at 200KHz, not so much when it is at 20KHz.

You will have a basic trade off. The faster the response, the greater the ripple. No way around it. All filter types.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!