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https://designers-guide.org/forum/YaBB.pl Design >> Analog Design >> Programmable gain variation in Sigma Delta modulator https://designers-guide.org/forum/YaBB.pl?num=1253873388 Message started by adesign on Sep 25th, 2009, 3:09am |
Title: Programmable gain variation in Sigma Delta modulator Post by adesign on Sep 25th, 2009, 3:09am Hi, I'm designing a Sigma Delta modulator with programmable input gain. The circuit for the first stage is attached herewith. The default cap ratios are: C3/C1 = 4/1 C3/C2 = 4/1 With default cap ratios and full scale input(say Vf), the SNR at the output is coming OK. When I change the cap ratios as under: C3/C1 = 4/0.8 C3/C2 = 4/1 and increase the input to 1.25 x Vf, the SNR degrades drastically by almost 40dB. Could anyone explain me this behavior? Thanks in advance for your time and comments. Best Regards, ADesign |
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