Datasheet

Analyzer
20Hz-20kHz
(a)BasicClass-AB
APA
Signal
Generator
PowerSupply
Analyzer
20Hz-20kHz
R
L
(b)TraditionalClass-D
Class-D APA
Signal
Generator
PowerSupply
L
filt
C
filt
R
L
TAS5602
SLAS593B – JUNE 2008 – REVISED NOVEMBER 2008 ................................................................................................................................................... www.ti.com
The generator output and amplifier input must be ac-coupled. However, the EVMs already have the ac-coupling
capacitors, (C
IN
), so no additional coupling is required. The generator output impedance should be low to avoid
attenuating the test signal, and is important because the input resistance of APAs is not high. Conversely, the
analyzer input impedance should be high. The output resistance, R
OUT
, of the APA is normally in the hundreds of
milliohms and can be ignored for all but the power-related calculations.
Figure 23 (a) shows a class-AB amplifier system. It takes an analog signal input and produces an analog signal
output. This amplifier circuit can be directly connected to the AP-II or other analyzer input.
This is not true of the class-D amplifier system shown in Figure 23 (b), which requires low-pass filters in most
cases in order to measure the audio output waveforms. This is because it takes an analog input signal and
converts it into a pulse-width modulated (PWM) output signal that is not accurately processed by some
analyzers.
Figure 23. Audio Measurement Systems
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