After finishing the Aleph I started experiments with it (my recommendation - Aleph is easy to understand, lot of fun). I replaced the MOSFETs in input differential pait to BJT. But now I am not able to reach zero ( or almost zero) DC offset when using current mirror. Offset ( about 0.6 to 2V) moves with bias current. Why? Has it something to do with lower input resistance of BJTs? Or different "opening" voltage of BJTs? Why is not the pair with current mirror able to set 0V offset? Any literature to learn about?
Nelson Pass said:It is my experience that current mirrors offer more gain,
not necessarily more linearity.
What about a current "sink" at the source (emitter) pins of a common-emitter or diff-pair? Does that help linearity (akin somehow to emitter degeneration with a resistor, but with a much higher dynamic impedance)?
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