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Design >> Analog Design >> Open Loop Opamp Hysteresis
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Message started by DanielLam on Oct 31^st, 2017, 7:01pm

Title: Open Loop Opamp Hysteresis
Post by DanielLam on Oct 31^st, 2017, 7:01pm

Hi everybody,

I'm sweeping the open-loop characteristic of a 2-stage opamp (measured, not simulated), and I'm noticing about a 0.2 mV hysteresis. That is, the offset changes by about 0.2 mV depending if I start with a positive voltage or if I start with a negative voltage.

Has anyone experienced this? I also noticed the open-loop curve doesn't look exactly like the textbook symmetric inverse tan function. If I start with a positive voltage, the output will slowly go down (like the inverse tan), but then step down to the negative rail. Similar characteristic if I start from a negative voltage.

Regards,
Daniel Lam

Title: Re: Open Loop Opamp Hysteresis
Post by Horror Vacui on Nov 1^st, 2017, 11:37am

Do you run a DC or a transient sweep? How big is your step? Have you checked all the simulatied points (i.e. do not just simply look at the lines in the waveform, but all the points simulated). Maybe it is just one step error. (Can't explain why would it be the case, but I would forgive one step, i.e. 1LSB to the simulator)