A2323
AUDIO AMPLIFIER
AiT Semiconductor Inc.
www.ait-ic.com
2.65W CLASS-D AUDIO POWER AMPLIFIER
Conducting Noise Suppression
The RF power amplifier operating, abstracting battery current form 217Hz frequency, due to the internal
battery impedance, which will caused 217Hz power wavering, power wavering will passed the audio power
amplifier through coupling to speaker. The capability of power wavering suppression depends on the audio
power amplifier PSRR.
V
V
OUT
AC
PSRR = 20log(
)
DD
AC
Figure 3 Diagram of power voltage and RF signal when GSM operating in Radio Frequency
As full differential amplifier input, output complete complement, theoretical the effect of power wavering
related to the two output signal is the same, the differential output was not affect by the power wavering
completely. In real situation, affect by the manufacturing defect cause, the power amplifier will mismatch in
great deal, the PSRR are greater than -60dB, the -60dB represent 1000 decade of the output signal related to
power wavering, for example of 500mVp power wavering, differential output signal will be 0.5mV, basically
satisfied the need of application. But in the real world application, the PSRR -60dB even -80dB power
amplifier could encounter conducting TDD noise problem, this is why? We still need to consider the
mismatched impedance effect of the audio power amplifier component in this point. For the traditional audio
power amplifier, as input resistance Rin, input capacitor Cin mismatching, affected greatly to audio power
amplifier PSRR index. Consider resistance deviate between ±1%, capacitance deviate between ±10%, even
the power amplifier performance is complete idea in this moment, the hole audio system PSRR theoretical
level remain -30dB no more, affected deeply degrade conducting TDD suppression capability. While power
wavering enhance, easily caused auditable TDD noise. For increasing the audio power amplifier PRSS at the
input resistance, the input capacitance under mismatched condition, A2323 designed with special conducting
noise reduction circuit, which can maintain highly PSRR level when the input resistance, the input
capacitance deviated 10% even more that condition, greatly suppressed conducting noise source.
REV3.0
- MAY 2013 RELEASED, APR 2016 UPDATED -
- 12 -
AITSEMI [ AiT Semiconductor ]
