DETERMINATION OF OPERATIONAL AMPLIFIER

CHARACTERISTICS

1.Measurement of open loop gain (AOL) and closed loop gain (ACL) :

Circuit diagram with output :

Plot to determine the open loop gain :

From probe document it is found that : V0rms = 6.65 V & V3rms = 60.41uV

A3 = V0rms / V3rms = 110081.1124

The open loop gain , AOL = 20*log(A3) = 100.834(db)

From table , it is found to be 106 .

2. Measurement of open loop break frequency , f0:

Circuit diagram :

Plot of V0 :

The frequency at which the output is 1/√2 is 652.672 kHz.

f1 = 2*652.672 kHz =1.305344 MHz

Open loop break frequency , f0 = f1 / AOL = 1.305344M/100.834 = 12.945kHz

3. Input offset voltage , Vio:

Circuit diagram :

The input offset voltage , Vio =

V 0

1+R fR1

= 1.94mV

1+(5k50

) = 1.92 x 10-5 V

4. Bias currents (IB- , IB+) and input offset current ( Ios ):

Circuit diagram for negative bias current -

In the above configuration , the effect of input offset voltage has been considered .

The negative bias current IB- = ( V1 –Vio )/Rf = (79.8*10-3 -1.92*10-5)/106

= 7.97808x 10-8 A

Circuit diagram for positive bias current –

The positive bias current , IB+ = (Vio - V1) / Rf

= (1.92*10-5 + 79.65*10-3 )/106

= 7.96692 x 10-8 A

Hence, Input offset current , Ios = | IB+ | - | IB- |

= - 1.9662 x 10-10 A

5. Slew Rate :

Circuit diagram :

Derived plot after simulation :

Here , V0 = 10 V , TSR = .0382ms

Therefore , the slew rate is = V 0T SR

= 10

.0382 X10−3 = 261.780 kV / s