Datasheet

Analyzer
20Hz-20kHz
(a)BasicClass-AB
APA
Signal
Generator
PowerSupply
Analyzer
20Hz-20kHz
R
L
(b)Filter-FreeandTraditionalClass-D
Class-D APA
Signal
Generator
PowerSupply
R
L
Low-PassRC
Filter
Low-PassRC
Filter
(Seenote A)
TPA3100D2
www.ti.com SLOS469F –OCTOBER 2005–REVISED AUGUST 2010
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 35(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 35(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.
A. For efficiency measurements with filter-free Class-D, R
L
should be an inductive load like a speaker.
Figure 35. Audio Measurement Systems
The TPA3100D2 uses a modulation scheme that does not require an output filter for operation, but they do
sometimes require an RC low-pass filter when making measurements. This is because some analyzer inputs
cannot accurately process the rapidly changing square-wave output and therefore record an extremely high level
of distortion. The RC low-pass measurement filter is used to remove the modulated waveforms so the analyzer
can measure the output sine wave.
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