kevin_microelecrronic
Newbie level 4
I have designed too many op amps and none of them have any issue with a wide range variations of supply voltage , temperature , corners of process , worst case pvt circumstances , etc . but the problem is the monte carlo analysis by which my op amps are all totally devastated .I know the monte carlo analysis has quite a different scenario from the abovementioned ones and it contains the random mismatches but I tried so many bias circuits with different levels of bias voltages and different schems for sizing the transistors in both 0.35um and 0.18um and mostly for folded-cascode and telescopic topologies and I mostly use the bias circuit presented in gray (p. 847) for folded-cascode , as I already mentioned I used othe circuits as well , but mostly that one in the gray . but the results of just monte carlo are terrible(I really do mean it) in either technologies and any bias strategies or any topologies ( either traditional op amps or proposed ones) and any overdrive levels and any sizing regimes (specially large sizes to reduce the random mismatch effects but neither small nor large size did work )and it is really exhausting and I do not know what the solution to this problem is . I already googled over and over to find a solution to cope with it there was some literature which said to set the overdrive voltages of diff pairs low and the current mirrors high to lower the mismatches and I did so but it did make no difference whatsoever . Here is the way by which I perform monte carlo analysis for threshold voltage mismatches(a traditional way which is used mostly in monte carlo analysis) I put a voltage source in series with the gate of all paired transistors but with opposite polarity in each and for example I write the following commands in hspice for an NMOS transistor with w=100um , l=0.18um , m=1.
m1 3 vin+ 1 0 nch l=.18u w=100u m=1
vmcin+ vin+ vinp dvthin+
.param dvthin+ =agauss(0,0.001,1) ( according to the formula (5e-9(v)/sqrt (w*l*m))
is that right? because I have seen way more larger values for that ( for example 0.01 with which my op amps are all completely bled white.)please somebody tells me if the problem stems from the biasing technique or sizing strategy or the way by which I do the simulation or any other cases .
m1 3 vin+ 1 0 nch l=.18u w=100u m=1
vmcin+ vin+ vinp dvthin+
.param dvthin+ =agauss(0,0.001,1) ( according to the formula (5e-9(v)/sqrt (w*l*m))
is that right? because I have seen way more larger values for that ( for example 0.01 with which my op amps are all completely bled white.)please somebody tells me if the problem stems from the biasing technique or sizing strategy or the way by which I do the simulation or any other cases .