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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,

My DC issue was mainly happening in the mixing. I have attached the matlab plot of my baseband results.

The input is 28.05 MHz which is 124 dBm above 28MHz where as the nco 28 MHz cosine/sin is 115 dBm above 28.05MHz. These show that the input and nco sin/cos does not cause major DC.

However, in the 16 bit baseband result (i+j*Q), the DC is 1 dBM and the 50KHz peak is 82 dBm. This is a strong DC. Interestingly, in the 32 bit baseband plot, the DC has been reduced to -71dBm. This shows that increase in the baseband bit width reduces the DC significantly. Do you have any idea why?

Many Thanks,

Lee