Opamp Differentiator

Opamp Differentiator

Opamp Differentiator

Download Opamp Differentiator.epb

  Aim

   To design and simulate a Differentiator circuit using opamp.

   Components

 

Name

EDWin Components Used

Description

Number of components required

RES RC05 Resistor 4
CAP CASE-A600 Capacitor 2
OPAMP 741A Comparator 1
VGEN VGEN AC Voltage source 1
VDC VDC DC Voltage source 2
GND SPL0 Ground 5

            

 Theory

   A circuit in which output waveform is the derivative of the input waveform is known as the differentiator or the differentiation amplifier. Such a circuit is obtained by using operational amplifier in the inverting configuration connecting a capacitor, C1 at the input. Applying KCL the expression for output voltage is obtained as follows.

Since

    But because A is very large. Therefore

   Thus the output vo is equal to RFC1 times the negative instantaneous rate of change of the input voltage vin with time. The gain of the circuit increases with increase in frequency at a rate of 20 dB/decade. This makes the circuit unstable. Also the input impedance XC1 decreases with increase in frequency which makes the circuit susceptible to high frequency noise. When amplified the noise can completely override the differentiated output signal. The frequency at which gain is zero dB is given by

   The stability and high frequency noise problems can be corrected by the addition of two components:- R1 and CF. The gain limiting frequency fb isgiven by

  R1CF and RFCF make the circuit more stable by preventing the increase in gain with frequency. The value of fb and in turn R1C1 and RFCF
values should be selected such that fa<fb<fc where

   and fc is the unity gain bandwidth of the opamp. Thus the input signal will be differentiated properly if the time period of the input signal is larger than or equal to RFC1

   i.e. .

 

   Procedure

   EDWinXP -> Schematic Editor: The circuit diagram is drawn by loading components from the library. Wiring and proper net assignment has been made. The values are assigned for relevant components.

   EDWinXP> Mixed Mode Simulator: The circuit is preprocessed. Waveform markers are placed at the input and output of the circuit. GND net is set as reference net. The Transient Analysis parameters have been set. The Transient Analysis is executed and output waveform is observed in the Waveform Viewer.

   Result

   The output waveform may be observed in the waveform viewer.