SNR at the output of Dechopper

[sumit_techkgp]

Here I am playing with a dechopper which has a 16 bit input and is being used with a chopper in connection. Now when I am taking FFT of the output signal I am finding a 40dB signal close to my 92 dB fundamental (6 db gone for quantization) which essentially limits my SNR to 52 dB, i.e., 8 and 1/2 bits!. i need to have it 16 bits. I understand that this 40dB signal comes out of low pass nature of dechopper (when used with chopper only, otherwise bandpass) as the high frequencies at the sharp transitions offered by chopper is getting suppressed by dechopper. Some amount should be from aliasing! also. Here is another observation. If I increase the input bit resolution to 31 bits(nearly) I get the SNR of the output 98 dB(seems fine). But I wont be having that much SNR at the dechopper input. How to resolve that? Anybody has any Idea.
Best Regards,
Sumit