Re: Complex baseband



morpheus wrote:

Howdy,
For FM/AM demod, you require a complex baseband.

Not necessarily. Complex baseband is just one of the possible ways.

I am downconverting
the IF from 1MHz to baseband by multiplying the input stream (12 bits)
from the ADC with Sin and Cosine outputs of a DDS and therefore,
generating I, Q
I am using standard 18x18 signed multipliers in Xilinx to do the
mixing. Is this right or should I use a complex multiplier?

????
Generating I and Q by mutiplying by sin and cos *is* a complex multiplier.

The reason why I am asking this question is because, I had implemented
the whole datapath (Downconversion, Rate decimation, Compensating FIR)
and verified it on the bench and then implemented CORDIC for getting
FM, which never worked.
So instead I tried to do AM demod by not using CORDIC but (Sq(I) +
Sq(Q)) using standard 18x18 signed multipliers and still no AM demod
which is supposed to be simple.
Then I took the CIC and CFIR filters out and tried to do demod
straight after the mixing, still nothing.
So I'm kinda stuck here, any help will be appreciated

Look for bugs.

p.s. I don't have access to Matlab and System generator, but I'm
buying them next week. I figured, doing digital radio design without
modeling tools is like digging your own grave!!!

Matlab is a glitter toy for students with many useless bells and whistles. A model of the system can be easily built in any programming language that you are using.


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com


.

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