op amp
three basic op-amp configurations
inverting, noninverting, and voltage-follower.
Zin(cm) common mode input impedance
is the resistance between each input and ground
Z(out) output impedance
is the resistance viewed from the output of the circuit
Negative feedback
lowers the gain and increases the bandwidth
Negative feedback
occurs when a portion of the output voltage is connected back to the inverting input such that it subtracts from the input voltage, thus reducing the voltage gain but increasing the stability and bandwidth.
Input offset voltage
produces an output error voltage (with no input voltage)
most op-amps
require both a positive and a negative dc supply voltage
The basic op-amp
has three terminals not including power and ground: inverting (−) input, noninverting (+) input, and output.
A practical op-amp
has very high input impedance, very low output impedance, and very high open-loop voltage gain.
All practical op-amps
have small input bias currents and input offset voltages that produce small output error voltages.
Voltage-follower
A closed-loop, noninverting op-amp with a voltage gain of 1.
Common mode
A condition characterized by the presence of the same signal on both op-amp inputs.
Gain-bandwidth product
A constant parameter which is always equal to the frequency at which the op-amp's open-loop gain is unity (1).
Differential mode
A mode of op-amp operation in which two opposite-polarity signal voltages are applied to the two inputs (double-ended) or in which a signal is applied to one input and ground to the other input (single-ended).
Operational amplifier (op-amp)
A type of amplifier that has very high voltage gain, very high input impedance, very low output impedance, and good rejection of common-mode signals.
Differential amplifier
A type of amplifier with two inputs and two outputs that is used as the input stage of an op-amp.
Inverting amplifier
An op-amp closed-loop configuration in which the input signal is applied to the inverting input.
Noninverting amplifier
An op-amp closed-loop configuration in which the input signal is applied to the noninverting input.
CMRR
Common-mode rejection ratio; the ratio of open-loop gain to common-mode gain; a measure of an op-amp's ability to reject common-mode signals.
Negative feedback
The process of returning a portion of the output signal to the input of an amplifier such that it is out of phase with the input signal.
Slew rate
The rate of change of the output voltage of an op-amp in response to a step input.
Phase shift
The relative angular displacement of a time-varying function relative to a reference.
Closed-loop voltage gain (ACT)
The voltage gain of an op-amp with external feedback.
Open-loop voltage gain (Aol)
The voltage gain of an op-amp without external feedback.
common-mode rejection ratio (CMRR)
a measure of an op-amp's ability to reject common-mode inputs.
noise
degrades the performance of an amplifier by the introduction of an unwanted signal.
Two types of op-amp input operation
differential mode and the common mode
The gain-bandwidth product
equals the frequency at which unity voltage gain occurs.
differential amplifier
forms the input stage of an op-amp
A noninverting amplifier configuration
has a higher input impedance and a lower output impedance than the op-amp itself (without feedback).
An inverting amplifier configuration
has an input impedance approximately equal to the input resistor Ri and an output impedance approximately equal to the output impedance of the op-amp itself.
The ideal op-amp
has infinite input impedance, zero output impedance, infinite open-loop voltage gain, and infinite bandwidth.
The voltage-follower
has the highest input impedance and the lowest output impedance of the three amplifier configurations.
Closed-loop voltage gain
the gain of an op-amp with external feedback.
Open-loop voltage gain
the gain of an op-amp with no external feedback connections
Zin(d) differential input impedance
the total resistance between the inputs
