Need Help AGC Circuit - AM_DemodTuned

[Rezcixa]

Need Help AGC Circuit

I want to learn about AGC circuit.

I have example of the circuit from ADS software, but i still confused about one part.

What is the role / function of "AM_DemodTuned" in the circuit ?

Anyone can explain about that ?

see the attachment....

**broken link removed**

 

[LvW]

Re: Need Help AGC Circuit

I want to learn about AGC circuit.

I have example of the circuit from ADS software, but i still confused about one part.
What is the role / function of "AM_DemodTuned" in the circuit ?
Anyone can explain about that ?
see the attachment....

You should read the text at the left of the figure.
If you compare the output with a reference voltage (which is DC !!) the output also must be something like DC (or a slowly changing DC) . Therefore the demodulation process.

 

[Rezcixa]

Re: Need Help AGC Circuit

i'm sorry, but i still don't understand.

is the function of AM_DemodTuned as a detector to change AC to DC for sampling the output signal ?

 

[LvW]

Re: Need Help AGC Circuit

i'm sorry, but i still don't understand.
is the function of AM_DemodTuned as a detector to change AC to DC for sampling the output signal ?

No, there is no "sampling".
The output of your main amplifier is a carrier - probably AM modulated with a signal.
You have to compare the mean value of this carrier (rms or peak) with the reference. Thus, the carrier frequency has to be removed by a detection/demodulation process.
By the way: If there is an AM on the carrier which shall NOT be regulated (because it is a signal), there must be a corresponding low pass within the loop to prevent regulation for theses frequencies.

 

[Rezcixa]

Re: Need Help AGC Circuit

thanks to your quick response to my question. it is very helpful for me.

according to your explanation, the function of demodulator is to separate information signal from carrier.

carrier frequency = 1 GHz ?
information frequency = 0 Hz ?

is it right ?

what about if i change the "AM_DemodTuned" with "True RMS detector" ? is it the same ?

 

[LvW]

Re: Need Help AGC Circuit

thanks to your quick response to my question. it is very helpful for me.

according to your explanation, the function of demodulator is to separate information signal from carrier.

carrier frequency = 1 GHz ?
information frequency = 0 Hz ?
is it right ?

what about if i change the "AM_DemodTuned" with "True RMS detector" ? is it the same ?

How can I know what´s on the carrier ?
If there is no intended modulation but only unwanted fluctuations - yes, in this case you are right.
Second question: Yes, if you adapt the ref voltage correspondingly to rms.

 

[Rezcixa]

Re: Need Help AGC Circuit

I still learning the circuit, and there is switch (part of integrator). what is the function of switch ?

can i change the switch with resistor ?

thanks..

 

[LvW]

Re: Need Help AGC Circuit

I still learning the circuit, and there is switch (part of integrator). what is the function of switch ?
can i change the switch with resistor ?
thanks..

Read the information besides the switch: Closed at t=0, and then open !
That means, at the beginning of the working period the cap is decharged by the closed switch and, then, the opamp circuit can integrate from the initial state.
If you replace the switch by a resistor, the integrator changes into a low pass.
This may work as well - but the value of the resistor determines its properties - together with the other resistor and the cap value.