TABLE OF CONTENTS In wireless receivers, the LNA is typically followed by a number of mixers that perform frequency translation, as depicted in Fig. 18 [3]. The main purpose of this operation is to shift the RF signal to a lower frequency where processing is easier and more efficient. Mixers have two sets of inputs, an RF signal that is to be processed and an LO signal that establishes the output IF frequency as shown in Fig. 19. The important performance specifications of mixers are: conversion gain, linearity, noise figure, RF, LO and IF frequency ranges, and isolation.
In the following section, different types of mixers and their applications are discussed and several innovative topologies that have emerged recently to target specific shortcomings of conventional mixers are described. In particular, two CMOS implementations are discussed in detail: A CMOS even-harmonic mixer targeting direct-conversion receivers, and an image-rejection down-converter for low-IF receivers.
Mixers are broadly classified into two types: passive and active [30]. Passive mixers, as the name suggests, do not dissipate dc power on their own, which is a very attractive characteristic. However, as a result, they have a negative conversion gain, and are therefore not very popular due to noise considerations. They are usually realized as a series of switches that are commutated such that the RF and LO signals are mixed...
