adesign
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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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