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Design >> Analog Design >> Loop gain in Sigma Delta modulator
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Message started by adesign on Oct 7^th, 2007, 10:17pm

Title: Loop gain in Sigma Delta modulator
Post by adesign on Oct 7^th, 2007, 10:17pm

Hi,

I've found in one of the book that 1-bit quantizer act as an AGC over most of the input range and maintains a loop gain at unity.

Why and what forces the quantizer to maintain this unity loop gain?

Please comment on this.

Regards,

Title: Re: Loop gain in Sigma Delta modulator
Post by Berti on Oct 7^th, 2007, 10:34pm

Since the output sequence of a 1b-quantizer only contains 1s or -1s, it's output power is constant. As the input power can change, the gain
of the quantizer changes correspondingly.

The loop gain of one is not forced. But it is rather a condition for stability. Assuming the input power of the quantizer increases, the 1b-quantizer
gain drops and the modulator will become unstable.

Regards