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How to design an AGC system for a RF device?

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brmadhukar

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AGC control

Hi,
How do I design an AGC system for a RF device. I have the MAXIM RF Chip which gives analog output. I have quantized tha sampled signal and now want provide a feed back. If I use just two bit quantization, how do I provide AGC.
 

MonkeyBusiness

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As an example, I can think of the following:
With two quantization levels, I assume that the signal DC level is 0, and that the binary quantized numbers are
00 = signal positive, level OK
01 = signal positive, level too high
11 = signal negative, level OK
10 = signal negative, level too high

So AGC would be:
a. Appearance if either 01 or 10 means reduce the gain
b. If there is no toggling between 00 and 11, increase the gain

Now you can design a digital machine that detects these conditions, and feeds a DAC (two bits should suffice). Feed the DAC through a narrow enough LPF, and your loop should be fine.
 

brmadhukar

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Hi,
Thanks for the info.

If I have to maintain the mag bit high for 33% of the time might be I have to fees the AGC through a proper LPF or should the digital logic be somehow tweaked for this.
 

flatulent

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time constants

The feedback system should have time constants so that it does not oscilllate. One method is to use a fast time constant in reducing the gain and a slow one in raising it. This works for most cases. It all depends upon the environment. If you are in a highly mulltipath situation where the signal level canges rapidly, the time constants should be made short.
 

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