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Nonideal Operational Amplifiers and Feedback Amplifier Stability - Coggle…
Nonideal Operational Amplifiers and Feedback Amplifier Stability
DC Error Sources and Output Range Limitations
Result from need to bias internal circuits
Result from mismatches of solid-state devices
Input-offset voltage, V_OS
Inputs are both 0
Output not truly 0
Rests at some nonzero dc voltage
Sign unknown
Only magnitude of worst-case offset voltage typically specified
Reconnect amplifier as voltage follower (due to high gain)
Output voltage = offset voltage
Except small gain error
Effect:
Offset-voltage adjustment
Most can be manually adjusted via potentiometer
Input-bias and offset currents
Small but nonzero dc bias current at each input terminal
Offset current I_OS = difference
Sign unknown
Input-bias currents
Produce undesired voltage at output
Reduce by placing bias current compensation resistor R_B
In series with noninverting input
Output voltage and current limits
Limited range of capability at output
Protection from short circuits
Common-mode rejection and input resistance
Common-mode input voltage v_ic
Amplified by common-mode gain A_cm
Overall output voltage:
Differential-mode gain A or A_dm
Ideal amplifier
Amplifies differential-mode input voltage v_id
Totally reject common-mode input signal (A_cm = 0)
Actual amplifier
CMRR (common-mode rejection ration)
