TAS5704PAPR datasheet(28/39 Pages) TI1

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Analyzer

20Hz-20kHz

(a)BasicClass-AB

APA

Signal

Generator

PowerSupply

Analyzer

20Hz-20kHz

(b)TraditionalClass-D

Class-D APA

Signal

Generator

PowerSupply

filt

TAS5704

SLOS563A – MARCH 2008 – REVISED AUGUST 2010

www.ti.com

The generator output and amplifier input must be ac-coupled. However, the EVMs already have the ac-coupling

capacitors, (CIN), 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, ROUT, of the APA is normally in the hundreds of

milliohms and can be ignored for all but the power-related calculations.

Figure 31(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 31(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 31. Audio Measurement Systems

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TAS5704PAPR Datasheet(PDF) 28 Page - Texas Instruments