Simulation for Offset Voltage of a high speed comparator.

Hi everyone,

I am currently designing a high speed comparator which consist of differential pairs input and a latch output stage with clock frequency of 20MHz. I am aware that to simulate for offset voltage of conventional opamp, I just input a fixed DC voltage at one of the input terminal and the other terminal I sweep say from 0V-3.3V. The syntax I used is : .DC Vin 0 3.3 1mV

The problem is when I want to implement this method to simulate for offset voltage of a high speed comparator, It won't work. I roughly guess that the solution is to use monte carlo analysis but I don't know how! (I have no experience in running monte carlo analysis). Can someone help me on this and is there any good reference on this topic?

Im kinda desperate to get it done correctly so I really appreciate your helps!

cheers

Re: Simulation for Offset Voltage of a high speed comparator

Well Monte Carlo analysis is not for switching waveforms. One very good technique is to do a parametric sweep of one of the inputs at the mean level and then run a transient solution. Another good technique is to use the .NODESET/.FORCE option and run a DC analysis. By using the NODESET option, you can always maintain whatever voltage you want to maintain at the latching phase..........

I hope that it works for you......

Re: Simulation for Offset Voltage of a high speed comparator

Thanks Vamsi,

I will try your suggestion. CHEERS

Re: Simulation for Offset Voltage of a high speed comparator

In a latched comparator, the offset is only important at the beginning of the comparison period. Due to the structure of a latched compartor (positive FeedBack), a small difference in its input should give an almost rail-to-rail output.

So, my point is that you are able to simulate the offset in a DC analysis. You just have to force your clocks at the beginning of the comparison phase, and put an input ramp from say common mode minus 20mV to plus 20mV by step of 1mV (or higher depending on your comparator).

That way, you should see your offset easily.