Chapter 1 Introduction - Audio Precision AUX-0025 User Manual

Figure 1. The Audio Precision AUX-0025 Switching Amplifier Measurement Filter.
Audio analyzers are generally designed to have broad measurement
bandwidths, broader than a typical audio circuit or system and much
wider than the audio passband. Such designs enable accurate analysis of
fast, high-performance audio circuits and also allow measurement of any
low-level high-frequency spurious signals that may accompany the audio
signal.
This design philosophy is based on the assumption that the audio signal
and its overtones are the dominant signal components applied to the ana-
lyzer; this is the case for the output of conventional audio power amplifiers
of Class A or Class AB design. In such a case the analyzer can range its cir-
cuits to the amplitude of the audio signal for optimum measurement
conditions.
Recent practice, however, has often turned to other amplifier designs for
improvements in efficiency and weight as compared to Class A and Class
AB amplifiers. Although these amplifier designs vary, as do the names ap-
plied to them, they have in common an output signal that is a high-fre-
quency switching carrier modulated by the audio signal. Many of these
"switching amplifiers" or "digital amplifiers" present a difficulty to conven-
tional measurement and analysis techniques due to the out-of-band switch-
ing carrier components that are in the output signal. When the amplitude
of the switching carrier components remains high in comparison to the
AUX-0025 User's Manual
Chapter 1
Introduction
1