8.1.1 Types of Analog Channels

Analog channels include any nonsampled circuit with analog inputs and analog outputs. Examples of analog channels include continuous-time filters, amplifiers, analog buffers, programmable gain amplifiers (PGAs), single-ended to differential converters, differential to single-ended converters, and cascaded combinations of these circuits. Channels including ADCs, DACs, switched capacitor filters, and other sampling circuits will be discussed in Chapter 9, "Sampled Channel Testing." However, we will see in Chapter 14, "Design for Test (DfT)," that a sampled channel may be broken into subsections using DfT test modes, as illustrated in Figure 8.1.

DfT allows the filter and PGA in Figure 8.1 to be isolated from the rest of the sampled channel for more thorough testing. Since DfT allows portions of sampled channels to be reduced to analog channel subsections, analog channel testing is extremely common in mixed-signal device testing.

Figure 8.1: Analog bus DfT for a DAC mixed-signal channel.

It is critically important for the mixed-signal test engineer to gain a solid understanding of analog channel testing. The analog tests described in this chapter will represent at least half of many mixed-signal test programs. Although many analog channel tests can be measured without DSP-based techniques, this chapter will concentrate only on DSP-based methods of channel testing.

As previously explained in Chapter 7, DSP-based testing is the primary technique used in high-volume production testing of mixed-signal devices. A principal advantage of DSP-based testing is that many of the parameters described in this chapter can be measured simultaneously.