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adding reset function to D Flip FLOP

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yefj

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adding reset function to D Flip FLOP for phase detector

Hello, I have designed a rising edge D-flipflop as shown bellow using CML method.
I could have just connect the output to NMOS switch and discharge it to ground.
However in our reset signal comes at Q, so basickly if we have Q=1 then this Q=1 is used to turn Q into Q=0.
so we have oscilation.

How do i add "reset" to my D-flip flop So i could use it in phase detector as shown bellow?
Thanks.
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Last edited:

I don't recognize an edge sensitive DFF, it's a level sensitive latch. You need to connect two of it in a master-slave structure and feed the reset to both stages.
 

Hello, i have painted on the clock signal the rising edges and we see that output Q changes as clock rises.
could you please show on the signal photo why its not edge triggered?

Thanks
 

Supplement the diagram with an D input changing during CLK high, e.g. shift the falling edge from 2.0 ns to 1.5 ns and you'll see that it's not edge triggered.
 

Yes, i saw that its level Triggerd not edge triggered,i will fix that.
Regarding my reset issue:
Our reset signal comes from the FLIP FLOP it self,so there is a problem where in certain case as Q gets high we get in the phase detector AND gate of both Q
and the FLIP FLOP recieves RESET=1 and at once it has to turn Q=0,
there is a problem in hear because the Q=1 signal basickly has to create RESET=1 which immidiatly turns Q=0
so there is an oscliation problem.If our reset signal was external then it was no proble , but here its self generating.
How do i implement RESET for this CML flip flop configuration for phase detector use?
Thanks.
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There's no general "oscillation" problem with a proper DFF, but it may be a problem related to reset input hold time. If the required hold time is larger than the R to Q propagation delay, than the output waveform is unpredictable and may be even oscillating.

You know, that this phase detector topology is often discussed in literature, e.g. by Razavi. I'd assume that it's least working with the DFF designs used therein.

Did you re-check with the the master-slave structure, resetting both master and slave output signal?
 

I managed to create a D-FLIP FLOP as shown bellow.
The question remains is how to insert in the following diagram the reset functionality?
connecting the Q output to ground VIA NMOS (where reset connected to gate)is not the best idea.
What reset is used for phase detector?
Thanks.

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Im sure CML FF with reset is discussed in literature. I had an idea how to implement it, but I'm not regularly working with CML and don't want to suggest my reinvented square wheel.
 

Hello, I am trying to implement the following phase detector shown bellow with my CML flip flop, it samples 4 times the data and somehow shows if CLK lags behind the data.
I cant see the last part,The difference between the upper sampling and lower is theat the lower samples at first with falling edge.
Another thing is Why for UP it uses 1,3 DATA but for down it uses 2,3 DATA
What is the logic in that?
Thanks.

https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4149052
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yefj said:
Hello, I am trying to implement the following phase detector shown bellow with my CML flip flop, it samples 4 times the data and somehow shows if CLK lags behind the data.
I cant see the last part,The difference between the upper sampling and lower is theat the lower samples at first with falling edge.
Another thing is Why for UP it uses 1,3 DATA but for down it uses 2,3 DATA
What is the logic in that?
Click to expand...

The clock input is inverted on the lower left DFF (DFF3).
Three samples are used, taken with a half clock cycle interval between the samples.
With your numbering, no 2 is the oldest sample, no 3 is the middle and no 1 is the newest.
It is logical to compare with the middle sample, so no 3 is used for both UP and DOWN.
 

(1) is one clock cycle delay (2) is two clocks delay so (3) i assume is 1.5 cycles delay.
Why a data sampled falling edge with respect to data of high edge sampling is half cycle delay?
Thanks?

yefj said:
Hello, I am trying to implement the following phase detector shown bellow with my CML flip flop, it samples 4 times the data and somehow shows if CLK lags behind the data.
I cant see the last part,The difference between the upper sampling and lower is theat the lower samples at first with falling edge.
Another thing is Why for UP it uses 1,3 DATA but for down it uses 2,3 DATA
What is the logic in that?
Thanks.

https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=4149052
View attachment 158301
View attachment 158300
Click to expand...
 

Hello, have tried to implement half clock dlay by inverting the clock on my CML.
but there is no shift of signal i get unuque signal from each output.
Where did i go wrong?
Thanks.

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