analog_fever
Junior Member level 3
I am currently designing a CIC decimation filter in verilog. I followed Hogeaneur's paper and other threads in this forum. I am not sure if I am getting the proper response from the filter, and hence need help on it. I am very new to FFT, filters, and Matlab.
Given below are filter requirements. The only requirement on the output is that it should have 13 bit resolution:
Filter input bits from SD modulator - 3 (2's complement, no fractional bits)
Output resolution needed - 13 bits (no fractional bits)
Higher sampling frequency - 1.4MHz
Decimation factor - 100
Filter stages used - 3
From Hogenauer's paper, I got Bmax -24bits (size of each integrator, and comb section)
Questions:
1. I coded the 3 stage filter in Verilog. Supplied a 1024 point unit impulse input. Attached is the image of the output response. While plotting FFT, I used my sampling frequency to be 1.4MHz. I am not seeing proper output response here, can somebody tell me what is the problem? Am I doing the FFT correct?
2. I used the FDA tool in matlab for the same specifications, it is using S36.15 (36 integer, and 15 fractional bits) for the integrators, and comb sections. This is different from the calculation in Hogenauer's paper. Why is it so? The response looks good, and similar to what I wanted here.
Any response is appreciated.
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Given below are filter requirements. The only requirement on the output is that it should have 13 bit resolution:
Filter input bits from SD modulator - 3 (2's complement, no fractional bits)
Output resolution needed - 13 bits (no fractional bits)
Higher sampling frequency - 1.4MHz
Decimation factor - 100
Filter stages used - 3
From Hogenauer's paper, I got Bmax -24bits (size of each integrator, and comb section)
Questions:
1. I coded the 3 stage filter in Verilog. Supplied a 1024 point unit impulse input. Attached is the image of the output response. While plotting FFT, I used my sampling frequency to be 1.4MHz. I am not seeing proper output response here, can somebody tell me what is the problem? Am I doing the FFT correct?
2. I used the FDA tool in matlab for the same specifications, it is using S36.15 (36 integer, and 15 fractional bits) for the integrators, and comb sections. This is different from the calculation in Hogenauer's paper. Why is it so? The response looks good, and similar to what I wanted here.
Any response is appreciated.
[/b]