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nwell is a real, lightly doped, i.e. relatively high-ohmic semiconductor material, as such has a much higher voltage dependency and a distinctively higher temperature dependency than, e.g., polysilicon, which is a highly-doped, relatively low-ohmic, thus already degenerated semiconductor, whose conductivity mechanism is caused by less semiconductor-like but more metal-like conductivity, thus exhibits much lower voltage and temperature dependencies. Metal resistors, of course, show still much lower VT dependencies.khotkar said:"Why there is more variation in nwell resistor?"
erikl said:nwell is a real, lightly doped, i.e. relatively high-ohmic semiconductor material, as such has a much higher voltage dependency and a distinctively higher temperature dependency than, e.g., polysilicon, which is a highly-doped, relatively low-ohmic, thus already degenerated semiconductor, whose conductivity mechanism is caused by less semiconductor-like but more metal-like conductivity, thus exhibits much lower voltage and temperature dependencies. Metal resistors, of course, show still much lower VT dependencies.khotkar said:"Why there is more variation in nwell resistor?"
kenliao18 said:nwell is built on the substrate,noises from the substrate will easily affect the nwell resistor.
and just as erikl have said, it is VT dependent.
Am sorry 4 u ;-)sandeep_torgal said:Am still unclear about what u said...
Sure; but this P-dependency results in the same variation contribution to all types of resistors and other devices on the chip. It doesn't explain the large differences of their VT dependencies between e.g. active-p, active-n, nwell, high-poly, low-n-poly & low-p-poly resistors.sandeep_torgal said:The variation is due to the process shifts is what i thought.
No, not at all: noise doesn't influence the resistor value (only the other way round). I guess, kenliao18 just meant that nwell resistors (like active-p & active-n resistors) are very prone to pick up noise from nwell (or substrate, for active-n resistors).sandeep_torgal said:kenliao18 said:nwell is built on the substrate,noises from the substrate will easily affect the nwell resistor.
and just as erikl have said, it is VT dependent.
... to find out the resistance of a nwell resistor we need to calculate the substrate noise and the resistance varies because of that..