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Design >> Mixed-Signal Design >> Phase/Frequency Detector
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Message started by Fei on Apr 25^th, 2005, 6:08am

Title: Phase/Frequency Detector
Post by Fei on Apr 25^th, 2005, 6:08am

I implemented a PFD using TSMC 0.18 um lib model. The design is proposed in Razavi's book "RF micronelectronics", which is composed of four Nor gates in each D flip flop. The interesting thing about the PFD is that it is sensitive to the initial states of the circuit. For example, the output can be different for the same delay between reference clock and VCO clock if the set of initial states of the two DFF is changed.

I check the DC solutions of the circuit. It has a metastable state, which means that the output is neither 0 nor Vdd. Does it cause the problem?

Any comments on it are welcome.

Thanks

Fei

Title: Re: Phase/Frequency Detector
Post by jfyan on Apr 25^th, 2005, 7:51am

hi fei:

i met the similar thing as you stated, but the outputs
(v(up) and v(dn) ) are sensive the some gates's sizes.
please check the signal reset and v(ref) and v(vco), whether a missing clock eage is happened.
for more information about nonideal linear PFD characteristic, please refer to Mozhgan Mansuri's phd thesis. (she is a phd of UCLA), you also can find her jssc paper in ieee.
ps:

who can tell me how can i simulate the dead zone of PFD, and how much dead zone can i ignore, and has no serious effect in jitter characterictic .

thanks advance.

Title: Re: Phase/Frequency Detector
Post by vijay on Oct 25^th, 2005, 4:15am

The dead zone of the PFD along with the charge pump is what you are looking for??

Title: Re: Phase/Frequency Detector
Post by Ken Kundert on Oct 25^th, 2005, 10:42am

In general the metastable state is not a problem. All flip-flops and latches have them. In general they are unstable equilibrium points, so they are never reached in practice.

-Ken