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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
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10 years ago

Hi Kaz,

NCO's sin and cos frequency is 28MHz. So the baseband signal has a strong peak at 50KHz (28.05 - 28 MHz = 50 KHz).

28.05 MHz Input bit width: 16 bits

28 MHz NCO bit width: 16 bits

The 32 bit baseband signal (I+j*Q) shows the relatively small DC. But 16 bit baseband (casting the lower 16 bits) shows very strong DC, as shown in the plot above . Why is that?

Many Thanks,

Lee