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Application Report
SLOA068 – October 2001
Guidelines for Measuring Audio Power Amplifier
Performance
Audio Power Amplifiers
ABSTRACT
This application note provides guidelines for measuring the data sheet parameters of
Texas Instruments audio power amplifiers (APAs) using prefabricated evaluation modules
(EVMs). The primary equipment used for the measurements consists of the System
Two™ audio measurement system by Audio Precision™, a digital multimeter (DMM), and
a dc power supply.
Contents
1 Introduction .....................................................................................................................................2
2 Basic Measurement System...........................................................................................................3
3 Interfacing to the APA.....................................................................................................................5
3.1 Differential Input and BTL Output (TPA731 and TPA2000D1)..................................................5
3.2 SE Input and SE Output (TPA0211 and TPA711).....................................................................6
3.3 Other Configurations .................................................................................................................7
3.4 Class-D RC Low-Pass Filter......................................................................................................7
4 Total Harmonic Distortion Plus Noise (THD+N) ...........................................................................9
4.1 THD+N vs Output Power.........................................................................................................10
4.2 THD+N vs Frequency..............................................................................................................11
4.3 Maximum Output Power Bandwidth ........................................................................................11
4.4 Maximum Input Voltage...........................................................................................................11
5 Noise ..............................................................................................................................................12
5.1 Integrated Noise vs Frequency ...............................................................................................12
5.2 Signal-to-Noise Ratio ..............................................................................................................13
6 Gain and Phase .............................................................................................................................13
7 Crosstalk........................................................................................................................................15
8 Supply Rejection ...........................................................................................................................17
9 Power Measurements and Related Calculations........................................................................21
9.1 Efficiency Measurements ........................................................................................................21
9.2 Power Dissipated vs Power to the Load..................................................................................24
9.3 Crest Factor and Output Power...............................................................................................25
10 Measurement Pitfalls ....................................................................................................................26
10.1 Effects of Improper Interfacing and Grounding .......................................................................26
10.2 THD+N Measurements............................................................................................................27
10.3 Noise Measurements ..............................................................................................................27
10.4 Gain and Phase Measurements..............................................................................................28
10.5 Crosstalk Measurements.........................................................................................................28
10.6 Supply Rejection Measurements.............................................................................................28
10.7 Efficiency Measurements ........................................................................................................28
11 References.....................................................................................................................................28
Audio Precision and System Two are trademarks of Audio Precision, Inc.
Other trademarks are the property of their respective owners.
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