open-source-silicon.dev

<@U016EM8L91B>,Execuse me, which resistor is more precise, poly resistor on pwell or without pwell? thanks in a advance

Being on pwell / nwell / substrate does not affect the resistor precision.  It affects the resistor noise.  The resistor will couple to whatever substrate is below it.  The bare substrate is noisiest;  nwell is good (one reverse-biased diode separation from the noisy substrate);  and pwell in a deep nwell structure is the best (two reverse-biased diodes separation from the noisy substrate).

That assumes, of course, that for an nwell or pwell-in-deep-nwell, the resistor is the _only_ thing in that well;  otherwise, the resistor will pick up noise from whatever else is sharing the well.  Likewise, you would want to bias the nwell or pwell from a quiet supply line not directly connected to any digital circuitry or other noisy source.