RF front end
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In a radio receiver circuit, the RF front end is a generic term for all the circuitry between the antenna and the first intermediate frequency (IF) stage. It consists of all the components in the receiver that process the signal at the original incoming radio frequency (RF), before it is converted to a lower intermediate frequency (IF). In microwave and satellite receivers it is often called the low-noise block (LNB) or low-noise downconverter (LND) and is often located at the antenna, so that the signal from the antenna can be transferred to the rest of the receiver at the more easily handled intermediate frequency.
For most super-heterodyne architectures, the RF front end consists of:
- An impedance matching circuit to match the input impedance of the receiver with the antenna, so the maximum power is transferred from the antenna;
- A 'gentle' band-pass filter (BPF) to reduce strong out-of-band signals and image frequency response;
- An RF amplifier, often called the low-noise amplifier (LNA). Its primary responsibility is to increase the sensitivity of the receiver by amplifying weak signals without contaminating them with noise, so they are above the noise level in succeeding stages. It must have a very low noise figure (NF). The RF amplifier can be omitted (or switched off) on frequencies below 30 MHz, where the signal-to-noise ratio is defined by atmospheric and man-made noise.
- The mixer, which mixes the incoming signal with the signal from a local oscillator (LO) to convert the signal to the intermediate frequency (IF).
Digital circuits can often require an analog front-end.
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