FREQUENCY RESPONSE OF OPAMP



FREQUENCY RESPONSE OF OPAMP

Goal:

Construct a two stage opamp and find its,

a) Frequency response,

b) Open-loop Bandwidth,

c) 3-dB point and

d) Unity gain frequency.

Set up:

TWO STAGE OPAMP

Bias Details:

1) First ground (+) and (–) terminals. Now adjust the R1 so that the voltage at A is centered.

2) Similarly, adjust R2 and R3 to center the output.

Procedure:

1) Now input a sine wave [1Vpp - 5 Hz – zero DC offset] between (+) and (-).

2) Observe the output using an oscilloscope.

3) Now sweep the frequency from 5 Hz to 5 MHz.

4) Draw the frequency response and phase margin graphs in logarithmic sheets.

Analysis:

a) Find the 3-db point and the unity gain frequency.

b) What is the phase lag at the point of unity gain?

Now lets analyze Miller Effect for this opamp.

So add a Capacitor of 8 pF across the gate and the drain of T1.

Repeat the same procedure 1 through 4.

Draw the frequency response and phase response graphs.

a) Find the 3-db point and the unity gain frequency.

b) What is the phase lag at the point of unity gain?

RESULTS:

Without miller effect,

1) The 3-dB frequency is ___

2) The Unity gain frequency is ___

3) The phase lag at unity gain point is___

With miller effect,

1) The 3-dB frequency is ___

2) The Unity gain frequency is ___

3) The phase lag at unity gain point is___

-----------------------

+10 V

-10 V

10k

o/p

R2

R3

+

-

10k

R1

A

10k

0.01(F

Gain in dB

Hz

Frequency response plot

Phase response plot

Phase in -(

Hz

T1

T2

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