OP AMP MODELS

Ideal op amp

• V_o = A(V₊ - V_-) where A is infinite.
• No current flows into either input (R_in = infinity).

Almost ideal op amp

• V_o = A(V₊ - V_-) where the gain, A is very large ~ 10⁵
• V_o saturates at the power supply voltages.
• Often good model for commercial op amps.

Additions for higher frequencies

• The gain, A decreases at 20 dB per decade starting at a low frequency (about 10-100 Hz) and reaching 1 at f_t (about 1-10 MHz).
• the output can not change faster than the slew rate.