Electrical Engineering ⇒ Topic : Differentiator

Differentiator

In this circuit, the passive elements of integrator, i.e., R and C are interchanged. Figure (1) shows the schematic diagram of a differentiator. In this case, the output voltage is proportional to the derivative of input voltage.

                       Figure (a) Differentiating circuit using OP Amp.

Using KCL at node 1, it can be written as:

                                                                    I_C = I_R

If V_i is the voltage at node 1, it can be given as:

                                                                                                             ............ (1)

Therefore, the output voltage V, is equal to the product of time constant RC and the negative rate of change of input voltage with time.

A differentiator circuit performs the reverse of the integrator circuit, i.e., if the input of differentiation is rectangular wave, the output will be square wave.

   It is generally used in wave-shaping circuits to detect high frequency components in an input signal. It is also used as a rate of change of detector in frequency modulator. It has the following drawbacks:

• Its gain is given by R/X_c = ωRC So ωRC increases with increase in frequency making the circuit unstable.
• The input impedance Xc decreases with increase in frequency as X_c = 1/ωC. This makes the circuit very susceptible to high frequency noise. When amplification is done, this noise will dominate the differential input signal