I have been studying the Tuner Front End Designs. According to suggestions from previous discussions, I studied the application notes and circuit diagrams of front end modules. The following things are those that I am getting confused with:
- According to my understanding, there are several allocated channels for television according to CCIR, France, USA, or China Tables. Let's say a tuner front end is connected to the antenna, the first thing it needed to be done is to select a typical channel among the channels available. I understand that 'tank circuit' is used with variable capacitance to tune to the desired channel.
So I imagine that a tuning unit with varicap diode will do the selection of channel. The capacitance is set by the voltage applied (up to 33V range). And this voltage might be supplied by a typical DAC and register where the values are set by I2C control.
But practically, when I studied the tuner application note, I found no clue for setting the capacitance for tuner tank circuit. What I found is something 'Charge Pump', Prescaler, Divider, 15 Bit Counter, Phase Detector, Op-amp unit, detecting Local Oscillators, (sorry if I presume wrongly) and the output VTU controls the tuning part. (according to a tuner front end design using the IC: SN761678B TV TUNER IC. There I am confused!
Can anybody show me some links or explain to me about it so that I could start learning?
Regards