Chapter 13 - Wireless Communication: Signal Conditioning for IF Sampling

Abstract

This chapter focuses on the requirements for the op amp and a number of techniques used in wireless communication systems to interface high-speed op amps to analog to digital converters (ADCs) and digital-to-analog converters (DACs). It provides several examples of different op amp usage. In communication applications, the dc nonlinearity specifications that describe the converter's static performance are less important than the dynamic performance of the ADC. The receiver (overall system) specifications depend very much on the ADC dynamic performance parameters: effective number of bits (ENOB), spurious free dynamic range (SFDR), total harmonic distortion (THD), and SNR (signal-to-noise ratio). Good dynamic performance and fast sampling rate are required for accurate conversion of the baseband analog signal at RF or IF frequencies. The SFDR specification describes the converter's in-band harmonic characterization and represents the converter's dynamic range. SFDR is slew rate and converter input frequency dependent. Modern communication DACs are, effectively, an array of matched current sources optimized for frequency domain performance. The most important dynamic specifications are SFDR, SNR, THD, IMD, ACPR, and settling time. The dc parameters, INL and DNL, are considered important because of their influence on the SFDR parameter. Typical SFDR figures for 12-bit to 14-bit DACs, with a 5-MHz single-tone input at 50 MSPS, ranges from 75 dB to 80 dB. In order to prevent adjacent communication channels from interfering with each other, the DAC must exhibit a good SFDR specification.