Hi dear fellows.
I have not much experience designing comparators, so I need your help.
From the research I did, there are basically two types of comparators, those which use clock (latch type) and those who not, for example the basic 3-stage comparator (pre-amp, positive feedback, ouput drive) or the comparator with internal feedback (cross coupled bistable) and yet another variant known as Clamped CMOS voltage comparator (Allen's book).
Because I am not interested on using a clock, those last three are of my interest.
From what I read, I concluded that maybe the best one is the comparator with internal feedback (cross coupled bistable) whose circuit is this one:
![](http://s29.postimg.org/r7a0x7hrn/2222.jpg)
Is fast, has less delay, relatively good gain;
Regarding this, I would like to hear from you, in your opinion which one is best.
The next question is: What consideration I must have in mind when designing the comparator? Should I use the lowest L in all transistors? The differential pair must have a large W? What current should I point? (I don't have restrictions) All the transistors must be in deep saturation or close to subthreshold? (100mV to 200mV(?)) The tech that I am using is UMC 130nm.
To finish, I tried to design that comparator with internal feedback (cross coupled bistable) based on some examples and the results were:
The circuit with dc operating points (both inputs with 1.65V):
![](http://s27.postimg.org/fjg0qdklb/1_3_dc_op.jpg)
The circuit operating as a comparator:
![](http://s29.postimg.org/eqhlyn7oz/1_2.jpg)
And the DC characteristic (don't know if it is a relevant detail):
![](http://s27.postimg.org/vbfmr5v27/1_4.jpg)
The waveforms:
![](http://s28.postimg.org/qfdu4y3ix/1_1.jpg)
Last, the AC response, using the AC analysis on the Vin- pin, with a DC source around 1.65V:
![](http://s10.postimg.org/6eoc2ejmd/1_5.jpg)
The differential pair dimensions are 40um/0.3um.
The overdrive voltages I think are very high! ::)
I would like to hear from you and I appreciate any tip.
Thank you very much in advance.
Best regards.