Chapter: Linear Integrated Ciruits - Characteristics of op-amp

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Slew Rate

Another important frequency related parameter of an op-amp is the slew rate. (Slew rate is the maximum rate of change of output voltage with respect to time. Specified in V/μs).

Slew Rate:

 

Another important frequency related parameter of an op-amp is the slew rate. (Slew rate is the maximum rate of change of output voltage with respect to time. Specified in V/μs).

 

Reason for Slew rate:

 

There is usually a capacitor within 0, outside an op-amp oscillation. It is this capacitor which prevents the o/p voltage from fast changing input. The rate at which the volt across the capacitor increases is given by

dVc/dt = I/C --------(1)

I -> Maximum amount furnished by the op-amp to capacitor C. Op-amp should have the either a higher current or small compensating capacitors.

 

For 741 IC, the maximum internal capacitor charging current is limited to about 15μA. So the slew rate of 741 IC is

 

SR = dVc/dt |max = Imax/C .

 

 For a sine wave input, the effect of slew rate can be calculated as consider volt follower -> The input is large amp, high frequency sine wave .

 

If Vs = VmSinwt then output V0 = Vmsinwt . The rate of change of output is given

dV0/dt = Vm w coswt.





The max rate of change of output across when coswt =1

 

(i.e) SR = dV0/dt |max = wVm.

SR = 2∏fVm

V/s = 2∏fVm v/ms.

 

Thus the maximum frequency fmax at which we can obtain an undistorted output volt of peak value Vm is given by

 

fmax (Hz) = Slew rate/6.28 * Vm .

 

called the full power response. It is maximum frequency of a large amplitude sine wave with which op-amp can have without distortion.

 

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