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PRINTED-CIRCUIT BOARD (PCB) LAYOUT GENERAL GUIDELINES
BASIC MEASUREMENT SYSTEM
SLOS516B – OCTOBER 2007 – REVISED MARCH 2007
Because the TPA3106D1 is a class-D amplifier that switches at a high frequency, the layout of the printed-circuit
board (PCB) should be optimized according to the following guidelines for the best possible performance.
Decoupling capacitors—The high-frequency 1-F decoupling capacitors should be placed as close to the
PVCC and AVCC terminals as possible. The VBYP capacitor, VREG capacitor, and VCLAMP capacitor
should be placed near the TPA3106D1 on the PVCCL, PVCCR, and AVCC.
Grounding—The AVCC decoupling capacitor, VREG capacitor, VBYP capacitor, and ROSC resistor should
each be grounded to analog ground. Analog ground and power ground should be connected at the thermal
pad, which should be used as a central ground connection or star ground for the TPA3106D1.
Output filter—The ferrite EMI filter (if used) should be placed as close to the output terminals as possible for
the best EMI performance. The LC filter should be placed close to the outputs.
For an example layout, see the TPA3106D1 Evaluation Module User Manual, (
SLOU191). Both the EVM user
manual and the thermal pad application note are available on the TI Web site at
http://www.ti.com.
This application note focuses on methods that use the basic equipment listed below:
Audio analyzer or spectrum analyzer
Digital multimeter (DMM)
Oscilloscope
Twisted-pair wires
Signal generator
Power resistor(s)
Linear regulated power supply
Filter components
EVM or other complete audio circuit
Figure 34 shows the block diagrams of basic measurement systems for class-AB and class-D amplifiers. A sine
wave is normally used as the input signal because it consists of the fundamental frequency only (no other
harmonics are present). An analyzer is then connected to the APA output to measure the voltage output. The
analyzer must be capable of measuring the entire audio bandwidth. A regulated dc power supply is used to
reduce the noise and distortion injected into the APA through the power pins. A System Two audio measurement
system (AP-II) (Reference 1) by Audio Precision includes the signal generator and analyzer in one package.
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 PAs is not high. Conversely, the
analyzer-input impedance should be high. The output resistance, ROUT, of the PA is normally in the hundreds of
milliohms and can be ignored for all but the power-related calculations.
Figure 34(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 34(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.
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Copyright 2007, Texas Instruments Incorporated