EECE 311 Electronic Circuits Part 4 OPERATIONAL AMPLIFIER

EECE 311: Electronic Circuits Part 4

OPERATIONAL AMPLIFIER 2

n Ideal Op-Amp n n Open loop gain Infinite input impedance Zero output impedance Infinite open-loop gain Infinite bandwidth … n …

n Inverting Amplifier Configuration n n Input and output signals out of phase Trade-off between a large input resistance and a large gain

¨ Effect of Finite Open-Loop Gain

n Summing Amplifier

n Non-Inverting Amplifier Configuration n n Infinite input resistance Input and output signals in-phase

n Voltage Follower n n n Infinite input resistance Zero output resistance Input and output signals are equal

n Difference Amplifier: Amplify the difference of two signals Two input signals: let Difference signal Common-mode

n Difference Amplifier: Amplify the difference of two signals Two input signals:

Common-Mode Rejection Ratio In a differential amplifier, Acm is ideally zero and CMRR is ideally infinite 11

Op-Amp Difference Amplifier Circuit 12

By superposition:

For the difference amplifier, the output should be a function of v. ID only. For the difference amplifier, Acm should be zero:

n Effect of Finite Bandwidth n fb = f 3 d. B is made very low to stabilize the op-amp

¨ Frequency Response of the Inverting Op-Amp

¨ Frequency Response of the Inverting Op-Amp n Example: R 2/R 1 = 10

n Large-Signal Operation of Op-Amps ¨ Output Voltage Saturation The op-amp output voltage saturates within 1 V of the power supplies voltages (rail-to-rail op-amps reach to within a few m. V) ¨ Output Current Limits Output current limited to a few m. A (or few tens of m. A, usually 20 m. A) in either direction (source or sink)

¨ Slew Rate There is a maximum rate of change possible at the output of the op-amp.

¨ Slew Rate For a voltage follower: For a step input V: Slew-rate distortion if dvo/dt > SR

¨ Full-Power Bandwidth The output of the op-amp can be slew rate limited or frequency limited. It is slew rate limited when (for a sinusoidal input): Frequency at which op amp stops behaving linearly n Example:

n Op-Amp Integrator and Differentiator Integrator: Differentiator:

¨ Op-Amp Integrator

¨ Op-Amp Differentiator

Simple CMOS Op-Amp