digital PLL

[mit_mohit]

Is it posible to design a 'DIGITAL' circuit which functions like a PLL. (i mean no analog components are there.)
If yes then how?
ALso can we design the above said digital circuit without using locally generated clock?

 

[Nigel Goodwin]

Is it posible to design a 'DIGITAL' circuit which functions like a PLL. (i mean no analog components are there.)
If yes then how?
ALso can we design the above said digital circuit without using locally generated clock?

Please don't keep starting multiple threads on the same question!.

By definition a PLL has a clock, it's method of operation is to lock that (the 'phase lock' part of PLL) to another signal.

If you want a digital PLL, then look at the CD4046 which is a standard CMOS logic version!.

 

[mit_mohit]

Sorry ,but my aim is not to start multiple threads . Just to keep this question seprate from the previous question i posted it as new topic
Thanks for your information!!!
I have seen the datasheet but it does not give all the circuit details .
Can i get circuit level details from anywhere?

 

[Russlk]

The CD4046 is not strictly digital because it has an analog filter. You could make an all digital PLL with a microprocessor (PIC) using digital integration or Z transforms. (Don't ask me how to do that!)

 

[Roff]

The CD4046 is not strictly digital because it has an analog filter. You could make an all digital PLL with a microprocessor (PIC) using digital integration or Z transforms. (Don't ask me how to do that!)

I agree. Lots of people refer to the 4046 as a digital PLL. It also has an analog VCO, so it doesn't match mit_mohit's definition.
A synthesizer with a numerically controlled oscillator is another "digital PLL", but I'm pretty sure the VCO output is from a D/A converter, which is analog.
As Russ said, an all-digital PLL is possible, but I have never seen one.

 

[Nigel Goodwin]

The CD4046 is not strictly digital because it has an analog filter. You could make an all digital PLL with a microprocessor (PIC) using digital integration or Z transforms. (Don't ask me how to do that!)

I agree. Lots of people refer to the 4046 as a digital PLL. It also has an analog VCO, so it doesn't match mit_mohit's definition.
A synthesizer with a numerically controlled oscillator is another "digital PLL", but I'm pretty sure the VCO output is from a D/A converter, which is analog.
As Russ said, an all-digital PLL is possible, but I have never seen one.

But the 4046 is from a digital 'logic' family, and the same applies to other 'logic' chips as well (such as monostables) - but as this is most probably a school question?, then I would imagine it meets the requirements?.

 

[tavib]

:?: the question is:
Is it posible to design a 'DIGITAL' circuit which is not an analog circuit in fact?
even a simple inverter or gate is an analog circuit at base

 

[mit_mohit]

OK if a stictly digitalPLL is not available but can we think of some digital circuit which does the job of a PLL

 

[Mike - K8LH]

OK if a stictly digitalPLL is not available but can we think of some digital circuit which does the job of a PLL

There's an interesting pdf document here FLL VFO for a PIC microprocessor controller Frequency Locked Loop but it uses an RC integrator output to provide an analog control voltage to a Varactor Diode for tuning purposes and so is still partly analog...

Regards, Mike

 

[Roff]

OK if a stictly digitalPLL is not available but can we think of some digital circuit which does the job of a PLL

The VCO and the loop filter are the two analog circuits that are the most difficult to eliminate. Imagine a high-frequency crystal oscillator (analog, but you can't avoid it). Now, for your VCO, imagine a variable-modulus counter and/or a pulse-dropping circuit, depending on your requirements. This is your new "VCO". The loop filter can now be done digitally.
Don't even think about asking me to desing something like this. It's beyond my capabilities.
If the crystal oscillator is a problem because it's analog, just have it come in from a pin and call it the system clock. :lol:

 

[mit_mohit]

thanks for u'r suggestion