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Converting a RF signal into baseband using VHDL

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mertberkea

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Hello friends,

I am a junior d&v engineer at a relatively small company. I assigned for a task that I need to convert an high frequency RF signal into baseband signal.
From my telecommunication lectures I know that I need a carrier wave to obtain low and high frequency components of my original signal. Then if I apply a lowpass filter, only baseband component of my original signal will remain. Please correct me if I am wrong.

All apart from that I need to implement this phenomenon with VHDL. Thank you in advance for all kinds of help for this problem.

I am not asking for a ready-to use code. You can write your experiences or recommend me some books about it too.

Regards
 

Multiply the RF signal with the carrier, you will get the baseband signal after lowpass filering. Is your RF signal digital or analogue? If it is digital signal, just multiply with exp (-j*2PI*f*n) to shift the signal to baseband.
 

Look for "digital IQ demodulator".
In short the understanding of the following is needed:
* complex signal
* complex sinusoid
* spectrum shifting
* equivalence between convolution in time domain and multiplication in the frequency domain (and vice-versa)
* how ADC sampling changes the signal spectrum
* ...

At start I recommend to read this.
 

It sounds like you have a problem that can be solved using the graychip style DDC. This is the DDS (sine/cosine generator), then a CIC filter, a half-band filter, and compensating filter. This gives efficient frequency translation and sample rate reduction. It doesn't demodulate the signal though -- it just performs the RF to baseband aspect.
 

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