9.1.1 What Are Sampled Channels?

Sampled channels are similar to analog channels in many ways. Both channel types consist of a signal transmission path from one or more inputs to one or more outputs. Unlike analog channels, though, sampled channels operate on discrete waveforms rather than continuous ones. Discrete waveforms consist of a sequence of instantaneous voltage samples that are either represented as digital values or as sampled-and-held analog voltages.

Examples of sampled channels include digital-to-analog converters (DACs), analog-to-digital converters (ADCs), switched capacitor filters (SCFs), sample-and-hold (S/H) amplifiers, and cascaded combinations of these and other circuits. The test requirements for sampled channels are very similar to those described in Chapter 8, "Analog Channel Testing." However, the sampled nature of the signals transmitted by sampled channels forces some additional considerations in their test requirements. Because sampled circuits may be subject to quantization errors, aliased interference tones, and reconstruction image tones, they require additional test considerations that are not applicable to continuous analog channels.

Sampled channels are often tested for gain error, distortion, signal-to-noise ratio, PSRR, CMRR, and all the other tests common to analog channels. The similarities and differences between analog channel testing and sampled channel testing will be discussed later in this chapter. First, let us look at examples of sampled channels and how they are applied in system-level applications like cellular telephones and disk drive read channels.

9.1.2 Examples of Sampled Channels

Sampled channels form the interface between the physical world around us and the mathematical world...