gsensor
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Ok, thanks Loose-Electron. Is there a way to lower the differential pair input mismatch from the beginning of the design (schematic), or only layout techniques can have an effect ?
I have follow RobG and Vladislav D advices in order to reduce the noise and the offset of my folded cascode opamp, essentially:
- High length, low gm and saturation operation for current mirrors. - High gm, high length and sub-threshold for input differential pair.
I have a high gain (87 dB) but also a very high offset: 272 mV (Measured by connecting the non-inverting input to GND and the inverting input in feedback configuration to Vout, Vout = Voffset).
I have noticed that keeping the cascode transistors in subthreshold contributed to the high offset considerably, so I kept them in saturation, giving offset = 272 mV, instead of 364 mV. Lowering the wide of input differential pair had also a positive effect on lowering the offset.
I tried to lower gm of mirror NMOS and PMOS as much as possible to keep a high gain (at least 80 dB) and maintain them in saturation. I have no clue how to lower this offset more. Is there something I'm doing wrong that I can't see ??
(schematic, gain/phase, and output simulations are attached)
Thanks, your help is very appreciated.
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