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vcvs has a wrong gain in montecarlo simulation

zuiying

Hello！I build a differential OTA and use vcvs to get a CMFB, as follows:

The gain of E0 and E1 is 0.5. The gain of E4 is 1.

In ADE XL, I run 100 points of montecarlo simulation.

Then, I find the gain of E4 is 0 at some points! For example:

In summary, 13 points has wrong gain(The gain of E4 is 0) while 87 points has right gain(The gain of E4 is 1). The gain of E0 and E1 is all right at 100 points.

The settings of E4 is as follows:

My virtuoso version is 6.1.7-64b. My spectre version is 15.1.0.284.isr1 64bit -- 12 Nov 2015.

Is there anyway to solve this problem? Thank you!

  • Your input voltage is -96.252mV (the NC+ pin is lower than the NC- pin) which means that the output should be the same - however, you have set the minimum output voltage to 0, so it can't produce negative voltages and hence clips it to 0V. The simulator is doing what it was told from what I can see! Perhaps set the minimum output voltage to -1.8V? Or not set the min/max voltages?

    Andrew

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