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Design >> Analog Design >> How does this circuit start up? D flip flops for phase frequency detection
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Message started by Rosh on Sep 15^th, 2015, 8:48pm

Title: How does this circuit start up? D flip flops for phase frequency detection
Post by Rosh on Sep 15^th, 2015, 8:48pm

This is a CMOS D Flip flop courtesy Razavi.

The circuit is made up of NOR gates.

But if you try to work out by pen and paper when Reset is 0 and CK is 1 you will find you can't really find out what Q is. Does this circuit need some additional star-up circuitry?

Update : If I combine two of these circuits in the form of a phase frequency detector as shown below, the circuit works correctly. How is this happening?

Title: Re: How does this circuit start up? D flip flops for phase frequency detection
Post by AnilReddy on Sep 15^th, 2015, 10:29pm

Hi,

somehow, i couldn't able to see those images. can you please check.

Bye

Title: Re: How does this circuit start up? D flip flops for phase frequency detection
Post by Rosh on Sep 15^th, 2015, 10:37pm

@AnilReddy

How about now?