Question

Suppose that you design an amplifier circuit but measuring the output on the oscilloscope shows that it is just oscillating wildly. List the first three things to check to understand what is causing the oscillation.

Answer 1

Types Amplifiers:

1) Negative Feedback :

Negative feed back is used to stabilize the amplifier

but it reduces the voltage gain ( G' = ) and increases the bandwith {}

sensitivity effectivelay reduced with this type of feed back .

2) Positive Feedback:

But in given problem the output of the amplifier is oscillating , the oscillation in an amplifier occur only

because of positive feed back.

in positive feedback amplifiers overall gain is enoromusly increases

, and sensitivity as High as 1.

with small disturbance also the amplifier enter into oscillation mode.

the above explanation is about +ve and -ve feedback ampifiers.

Answer:

1) In feed back amplifiers only positive feedback amplifiers only produce oscillations

2) to produce oscillations, closed loop gain of feed back amplifiers must be unity (that is ).

3) with small disturbace such as out side noise itself is the input to generatie oscillations. other than noise no other input is required.