This document defines and describes several key parameters of operational amplifiers (op-amps): input offset voltage, output offset voltage, input offset current, input bias current, common mode rejection ratio (CMRR), and slew rate. It provides detailed explanations of each parameter, including their ideal and practical definitions, units of measurement, and symbols used. The document aims to comprehensively cover the technical specifications and characteristics of op-amps.

1. - A.Usha Rani
M.Sc. Physics

2. The following are the parameters
of Op-Amp
Input offset voltage
Output offset voltage
Input offset current
Input bias current
CMRR(Common Mode Rejection Ratio)
Slew Rate

3. Input offset voltage
It is the amount of voltage that must be applied at
the input terminals to make the output voltage zero
and is denoted by Vio.
For an ideal Op-Amp, the output voltage must be
zero if the voltage at both the input terminals is zero.
But in practice a small amount of voltage appears(due
to imbalance in the differential amplifier in the Op-
Amp) at the output even if the voltage at both input
terminals is zero.
To make this output voltage zero, an equal amount
of voltage is applied at input terminals which is called
input offset voltage.

4. Output offset voltage
It is the amount of voltage that appears at the
output terminal (due to imbalance in the differential
amplifier in the OP-Amp), even if the voltage at both
the input terminals is zero.
To make this output voltage zero, an equal amount
of voltage is applied at input terminal.
It is denoted by Voo

5. Input bias current
Ideally no current flows into the input
terminals of Op-Amp.
But in practice a small amount of current flows
into the input terminals when power supply is
given to an Op-Amp. These currents are called
bias currents.
It is the average of both the bias currents
flowing into the input terminals of Op-Amp.
It is denoted by IB

6. Input offset current
It is the difference between the two input bias
currents flowing into the input terminals of Op-
Amp.
It is denoted by Iio

7. CMRR(Common Mode Rejection Ratio)
CMRR gives the ability of the Op-Amp to reject
common mode signals.
It is defined as the ratio of differential mode
gain to common mode gain.
CMRR = Ad/Ac
Where Ad is gain of the Op-Amp in differential
mode and Ac is the gain of the Op-Amp in
common mode.

8. When two signals of same magnitude are applied
at the two inputs of Op-Amp, the gain of the Op-
Amp is called common mode gain(Ac).
When two signals of different magnitude are
applied the two inputs of Op-Amp the gain of the
Op-Amp is called differential mode gain(Ad).
Since Op-Amp is a differential amplifier, ideally
common mode gain should be zero. Hence the
ideal value of CMRR for an Op-Amp is ∞.

9. Practically for an Op-Amp CMRR is very large.
Hence to express the large value of CMRR,
logarithm is used and CMRR is given by
20log(Ad/Ac)dB.

10. Slew Rate
Slew rate is defined as the rate of change of
output voltage of an Op-Amp with respect to the
change in input voltage.
It is defined at unity gain of Op-Amp and is
expressed as Volts/micro second.
 Let a voltage VoSinωt be applied to Op-Amp.
Then rate of change of output voltage with
respect to time is
dVo/dt = VoωCosωt
Slew rate is given by maximum rate of change of
output voltage i.e.,
S = (dVo/dt)max = Voω = 2πfVo