6.1.1 Traditional versus DSP-Based Testing of AC Parameters

AC measurements such as gain and frequency response can be measured with relatively simple analog instrumentation, as mentioned in Section 5.4.1. To measure gain, an AC continuous sine wave generator can be programmed to source a single tone at a desired voltage level, V _in, and at a desired frequency. A true RMS voltmeter can then measure the output response from the DUT, V _out. Then gain can be calculated using a simple formula: gain = V _out/ V _in.

The pure analog approach to AC testing suffers from a few problems, though. First, it is relatively slow when AC parameters must be tested at multiple frequencies. For example, each frequency in a frequency response test must be measured separately, leading to a lengthy testing process. Second, traditional analog instrumentation is unable to measure distortion in the presence of the fundamental tone. Thus the fundamental tone must be removed with a notch filter, adding to test hardware complexity. Third, analog testing measures RMS noise along with RMS signal, making results unrepeatable unless we apply averaging or band-pass filtering.

In the early 1980s, a new approach to production testing of AC parameters was widely adopted in the ATE industry. The new approach became known as DSP-based testing. ^[1] Digital signal processing (DSP) is a powerful methodology that allows faster, more accurate, more repeatable measurements than traditional AC measurements using an RMS...