What should be the minimum feedback factors to realize an oscillator using an amplifier of gain 20 ?
Answers
Explanation:
The gain of an amplifier with negative feedback is given by ´ 1
A A
A = +β
Taking logs of both sides, we have loge A´ = loge A – loge
(1 + βA)
Differentiating both sides, we get
´ . 1 1 ( /)
´1 11 1
dA dA dA dA dA A dA
A A A A A AA A
β β =− = − = = +β +β +β +β
If βA » 1, then the above expression becomes
´ 1 . ´
dA dA
A AA =
β
Example 62.6. An amplifier has an open-loop gain of 400 and a feedback of 0.1. If open-loop
gain changes by 20% due to temperature, find the percentage change in closed-loop gain.
(Electronics-III, Bombay 1991)
Solution. Here, A = 400, β = 0.1, dA/A = 20% = 0.2
Now,
´1 1 . 20%
´ 0.1 400
dA dA
A AA
= = ×=
β × 0.5%
It is seen that while the amplifier gain chan
The gain of an amplifier with negative feedback is given by 1
A A
A = +B
Taking logs of both sides, we have loge A´ = loge A – loge
(1 +BA)
Differentiating both sides, we get
. 1 1 ( /)
1 11 1
β β =− = − = = +β +β +β +β
If βA » 1, then the above expression becomes
1 .
A AA =
β
Example 62.6. An amplifier has an open-loop gain of 400 and a feedback of 0.1. If open-loop
gain changes by 20% due to temperature, find the percentage change in closed-loop gain.
(Electronics-III, Bombay 1991)
Solution. Here, A = 400, β = 0.1, dA/A = 20% = 0.2
Now,
´1 1 . 20%
´ 0.1 400
dA dA
A AA
= = ×=
β × 0.5%
It is seen that while the amplifier gain chan