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Altera_Forum's avatar
Altera_Forum
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11 years ago

DC in the CIC-FIR filter result

Hi All, I have attached a figure showing my filter issue. Please subtract 28 MHz from the x axis values (it was a typo). It is apparent that there is a strong DC peak in the plot. My question i...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
10 years ago

Hi Kaz,

I got two major peaks in the 16 bit baseband signal. The main peak is 82 dB at 50 KHz and the second peak is 1 dB of DC whereas the noise level is around -100 dB. This 1dB DC is not acceptable. Once I extended the baseband signal to 32 bits, the DC reduced to -71 dB where as the 50KHz still still the same 82 dB. This reduced DC is what I want. I just have no idea why extending the baseband bit width reducing the DC level. I copied this technique from a project without knowing what is the theory behind it.

Lee