Chapter 4 - The Receiver Front End: An Overview

Abstract

The front end of the receiver is the key to its dynamic performance. Specifications, such as, the dynamic range, intermodulation distortion, -1 dB compression point, and the third-order intercept point demonstrate how well the front end of the receiver performs. Various architectures are used in receiver front-end circuits. It consists of a mixer stage and local oscillator preceded by a bandpass filter. The input signal to the bandpass filter will come from the antenna. The bandpass filter can be narrow or broad depending on design. The performance of the first mixer is the key to the performance of a receiver. It is a nonlinear device. Furthermore, it usually sees the highest-level radio frequency signals in the system (the LO, largely). Therefore, it needs to have a very high intercept point. Single-device active mixers are cheap, but they have the poorest performance of all the mixers. The single-sideband phase noise performance of the local oscillator is important to the receiver's adjacent channel selectivity. All radio reception is a matter of manipulating the signal-to-noise ratio (SNR) of the system. Because of this problem, the noise generated by the mixer, local oscillator, bandpass filters, and RF amplifier should be minimized. The RF amplifier can have a deleterious effect on the performance of the mixer stage; hence, the entire receiver. A number of methods can be used to reduce the effect.