OVERVIEW

Throughout most of this book, we have studied the components that make up RF circuits. Now we put all these pieces together to form one of the most critical subsystems in any communication system namely, the RF front end. We ll start by showing where the RF front end fits in today s modern applications, and then decompose or tear down this subsystem into its basic components and functions, many of which have already been covered in earlier chapters. This approach will also provide a logical way to introduce key receiver types and associated performance specifications, such as signal-to-noise ratio (SNR), receiver sensitivity, and selectivity.

The RF front end is part of an overall radio receiver-transmitter or transceiver system. It is generally defined as everything between the antenna and the digital baseband system. For a receiver, this between area includes all the filters, low-noise amplifiers (LNAs), and down-conversion mixer(s) needed to process the modulated signals received at the antenna into signals suitable for input into the baseband analog-to-digital converter (ADC). For this reason, the RF front end is often called the analog-to-digital or RF-to-baseband portion of a receiver.

Radios work by receiving RF waves containing previously modulated information sent by a RF transmitter. The receiver is basically a low noise amplifier that down converts the incoming signal. Hence, sensitivity and selectivity are the primary concerns in receiver design.

Conversely, a transmitter is an up converts an outgoing signal prior to passage through a high power amplifier. In this case,...