Hi There! I am designing a digital AM/FM receiver in a Vertex-4 FPGA. I have designed the system blocks but have one question regarding digital filtering.
convert IF 45MHz down to baseband. After this we are using a 40MSPS A/ D to sample and output parallel 12-bit I, Q data to the FPGA. The FPGA front end has to have a LPF with a cut-off frequency of 5kHz. After the LPF, AM and FM need to be demodulated. I intend to do demodulation as follows FM -> (Q(n)I(n-1) - I(n)Q(n-1))/(I-Sq + Q-Sq) AM -> (I-Sq + Q-Sq) My question is: I need to do some decimation (to make my life easier when it comes to5kHz LPF design)...what is the best way of doing this? I have read some material and it seems to point towards cascaded CIC filters. Please comment and also let me know if you notice any flaw in my design methodology. Moreover, due to my inexperience in this field, I wanted to know if decimation upstream would affect (adversely) my AM/ FM demodulation process.