# gain

Discussion in 'General Electronics Chat' started by gani, Jun 7, 2005.

1. ### gani Thread Starter Active Member

May 15, 2005
46
0
i understand that damping happens in ckts with rlc but i also read that damping happens in ckts which has gain.

can someone explain the meaning of this?gain cud be current gain or voltage gain,correct?so wat does it mean by

ckts which has gain???

thanx for any and all help!

2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
The term "Gain" is used to refer to a circuits effect on the input signal. It is expressed in terms of (voltage out)/(voltage in) or (current out)/current in).

Generally speaking, a circuit is said to have gain when the ratio of the "voltage out" divided by the "voltage in" is greater than one.

When the "voltage in" equals the "voltage out" the circuit is said to have unity gain.

The term "attenuation" is often used to refer to circuits whose "voltage out" divided by the "voltage in" is less than one.

The above explanation works for current gain as well as voltage gain circuits.

At least this is the way I interpret "gain".

hgmjr

3. ### gani Thread Starter Active Member

May 15, 2005
46
0

Thankyou so much hgmjr,
That was a very precise and clear information. Do you know why
damping occurs in circuits with gain?
I really appreciate your sincere help.
gani

4. ### hgmjr Moderator

Jan 28, 2005
9,030
214
I believe by damping you are referring to the tendency of an oscillatory condition to be triggered by a step change in the input signal (sometimes referred to as "ringing"). If I am correct in my understanding of your question then the explanation lies in the existence of a unstable feedback path that is unable to sustain the conditions that must exist for an oscillation to be maintained.

In general, for oscillation to be maintained requires the signal circulating in the feedback path to simultaneously undergo a 360 degree phase shift and a gain greater than one. One method of verifying that these two conditions exists requires that the feedback path be temporarily opened up and a signal from a function generator be injected at the input while the output at the end of the open feedback loop is monitored using an oscilloscope.

A more rigorous method used to predict the existence of the conditions for oscillation involve the use of a Bode Plot that shows the frequency response of the feedback path and the phase shift as a function of frequency. If the phase shift plot reaches a net 360 phase shift before the frequency response drops below unity gain. then the conditions are set for an oscillation to occur. Using the Bode Plot, It is even possible to predict the frequency at which the oscillations will occur.

I fear I have provided too much information.

hgmjr

5. ### gani Thread Starter Active Member

May 15, 2005
46
0
I owe u a lot of thanx really.
I have understood what i wanted to know.
Once again,THANKYOU SO MUCH!!!

gani