The task of my student research project is to implement a digital VSB modulator for analog TV in an FPGA. The design has three inputs: CVBS (Color Video Baseband Signal) and audio1 (mono/left) as well as audio2 (right) - digital sampled as YCbCr and I2S, respectively. The output shall be "sampled" analog TV baseband (real-values) as input for direct digital synthesis to TV RF.
Can anyone help me with an idea how to solve this task?
Thanks in advance!
The Vestigal SideBand modulation gives a spectrum where the baseband DC level modulated up to the carrier frequency is half amplitude with the signal falling to zero on the one side and up to full scale on the other side of the carrier ( the side where almost all the information is maintained).
Since you can't mix a signal with real-only samples (no I-Q modulation) up to that carrier frequency with lobes that are different on both sides of the carrier, you need to either preform your filtering in complex space and translate it to real or translate your signal to something that can be filtered to produce real, filtered results.
I'd recommend you think about how you might accomplish either approach and get back to us on how you'd like to proceed.
- John_H
I just remembered that the 1/2 amplitude at the carrier I spoke of is in the demodulation side. Vestigal Side Band modulation has flat response to the carrier on the useful lob side but lops off most of the unimportant lobe, keeping only close-in information flat.
The suggestion still applies: produce complex filter results and convert (indirectly) to real or convert your baseband signal to something you can filter to produce real outputs.
If the output is baseband, then you don't have any vestigial sideband. That doesn't happen until the RF modulator.
-- glen
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