A frontend refers to the actual portion of a receiver device that acquires a radio frequency (RF) signal and then extracts/recovers the underlying information that was modulated on that RF carrier wave.
The term is often used interchangeably with demodulator, but generally speaking, the concept of a frontend should be thought of as that which includes both the tuning and demodulation functions.
In traditional designs, this typically means (at least) two different chips and related circuitry are employed; a tuner IC and a separate demodulator IC.
- The tuner's function is to acquire a RF signal transmitted from some source (e.g. terrestrial broadcast towers; cable headend; satellite transponder), usually perform AGC (automatic gain control) on the signal, then convert it into an IF (intermediate frequency) and provide this as output.
- A demodulator IC (specific to the type of digital television transmission being acquired) will input the IF and decode/demodulate the underlying information that was being conveyed on the original RF signal. What is recovered, and output by the demodulator, is a bitstream -- specifically a MPEG2 Transport Stream.
Modern frontend architectures that consolidate the tuning and demodulation functions into a single silicon IC are beginning to appear. Some, like the Fujitsui MB86A15 for example, are "Direct Conversion" receivers, whereby the traditional intermediate stage of RF to IF conversion has been dispensed with, and hence a pure RF-to-bits process is carried out.
Nonetheless, the concept of a frontend remains the same: tuning + demodulation.