The limiting amplifier before the quadrature detector

[hr.praveenraj]

limiting if amplifier

in reciever ckt,after mixer limiting amplifier haveing 92db of gain,no. of stages of amplifier in limiting amplifier is 6 stages.i/p to amplifier is 50mpp
then from this data we will get o/p arround 1.5kv.
from this data we have to get o/p arround 800mpp.
onething we have to note o/p is feed back to i/p, he is mentioning that for
dc cancellation & for dc biasing.get me the answer.

 

[hr.praveenraj]

in reciever ckt,after mixer limiting amplifier haveing 92db of gain,no. of stages of amplifier in limiting amplifier is 6 stages.i/p to amplifier is 50mpp
then from this data we will get o/p arround 1.5kv.
from this data we have to get o/p arround 800mpp.
onething we have to note o/p is feed back to i/p, he is mentioning that for
dc cancellation & for dc biasing.get me the answer.

 

[brmadhukar]

Re: limiting if amplifier

Hi,
Do be clear in your "requests". It is very difficult to follow what you need.
BRM

 

[FANT]

Re: limiting if amplifier

If I have understood well, you are speaking about the limiting amplifier before the quadrature detector.
The limiting effect is necessary to give to the quadrature detector a signal with constant amplitude at any input signal level, i.e. close the transmitting antenna or far away.
If you don't give a constant amplitude to the detector, you will detect also the AM components, that usually are unwanted.
The limiting effect don't affect the signal because it is FM modulated, so changes only the frequency and not the level.
The DC balancing is necessary to allow all the 6 stages to work in the linear region, otherwise the last stages will be saturated on one side or the other by the existing offset of the differential amplifiers ( single stage)
Let's suppose the first stage has 10 mV offset, and all the stages amplify 4 ( say 12 dB ).
At the input of the second stage yopu will have 40 mV offset, at the third stage 160 mV and so on.
You will see that after the 4-5 stage the amplifiers will be saturated.

Hope to have solved your problems.

Mandi

 

[mike_bihan]

do not forget the self-biasing effect of the DC feedback path. Also refer to DC offset-compensation with negative DC feedback.

The feedback path was often implement by R-C-R filter.