Characterstic parameters of opamp

slew rate of opamp

It is the maximum rate at which output can change in an opamp. It is one of the major limitations in an opamp. It is expressed in volt/second. The output gets distorted if the rate at which output changes exceeds slew rate.

Consider a opamp with slew rate specified in manufacturers datasheet as 10 v/microsecond if we apply a sine wave with frequency w and amplitude A maximum product A*W*gain can be at most 10v/microsecond before opamp input output characteristics steps into nonlinear regime.

 CMRR of opamp

CMMR is acronym for Common Mode Rejection Ration which is used to quantify how good a differential amplifier is. Let V1=V1d+Vn and V2=V2d+Vn where differential input signal is Vd = V1d-V2d and Vn is the common input signal. The output of differential amplifier will be of the form Vo = Ad*(Vd) +Ac*Vn, then the Common Mode Rejection Ratio of an differential amplifier is defined as the

                   

Where Ad is differential mode signal gain and Ac is common mode signal gain.

input bias current of opamp

Input bias current is defined as average of currents entering the input terminals of an Opamp. Typically these currents are of the order of nano amperes. Let I1 and I2 be the currents entering the input terminals of an Opamp the input bias current is given by

                                                         Ib = (I1+I2)/2

Inputs offset currents of opamp

Offset current is defined as difference of bias currents entering the input terminals of an Opamp. Typically these currents are of the order of nano amperes. Let I1 and I2 be the currents entering the input terminals of an Opamp the input bias current is given by

                                                          If = (I1-I2)

input offset voltage of opamp

Input offset voltage is the voltage applied at the input terminals of an Opamp to make output zero, typically of the order of milli volts.

output offset voltage of opamp

Output offset voltage is defined as Opamp output voltage when both the input terminal voltages of the Opamp are grounded. Universal balancing techniques with potentiometers are often used to balance offset voltages.

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