Advanced
Finite open-loop gain
When loop gain AOLβ is very large, the feedback network dominates closed-loop behavior. As loop gain falls, gain error and distortion increase.
Dominant-pole compensation
Many voltage-feedback op-amps are internally compensated so one low-frequency pole dominates open-loop response over a wide range.
Gain-bandwidth
CMRR and PSRR
CMRR measures rejection of voltage common to both inputs. PSRR measures rejection of supply changes. Both are frequency dependent.
Noise model
Useful calculations include input voltage-noise density, input current-noise density, source-resistor Johnson noise, and 1/f noise at low frequency.
Input-stage crossover
Some rail-to-rail-input amplifiers use two input pairs. As common-mode voltage moves, control transfers between them, and offset or noise may change slightly.
Fully differential amplifiers
These produce two complementary outputs and often provide a separate output-common-mode control input, making them useful as ADC drivers.
Current-feedback amplifiers
Current-feedback devices use a different internal architecture. Their bandwidth and stability do not follow the ordinary voltage-feedback gain-bandwidth rule in the same way, and feedback-resistor value is often critical.