Hi all
How exactly the tuned circuit of the the RF stage in a digitally controlled radio reciver is controlled .
I understand that the local oscilator is based on a PLL , which is controlled by some micro controller .
My question is how the front end tuned circuit is tuned to the relevant frequency which is local oscillator freq +/- IF freq ?
Thanks Elico
by some micro controller .
Thanks Elico
The LO can be based on a PLL, on a direct-digital synthesis system (DDS), or some combination.
Like Jan said, often it isn't. In theory you could use varicaps in the front end that are matched to the ones in the PLL, and tune them with the VCO voltage. If that's done at all it's probably just in cheap AM radios.
The better radios would have switched bandpass filters, with the microprocessor being responsible for deciding when to switch in what filter.
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