AW8155B
Jul. 2022 V1.3
www.awinic.com
17
COPYRIGHT ©2022 SHANGHAI AWINIC TECHNOLOGY CO. LTD.
nals to the base station, the signals sent from the base stations to the plurality of mobile terminals are ar-
ranged in a predetermined time slot in the transmission. In this case, each TDMA frame contains 8 time slots,
the entire frame is about 4.615ms long, and each slot time is 0.577ms.
With GSM handset, the RF power amplifier will transmit once every 4.615ms (217Hz), and the signal will
produce intermittent Burst current and strong electromagnetic radiation. Intermittent Burst current will form a
power fluctuation of 217 Hz; High frequency (900MHz and 1800MHz) RF signals form a 217Hz RF envelope
signal. 217Hz power fluctuations will be conducted through the conduction to the audio signal path, 217Hz RF
envelope signal will be coupled through the radiation into the audio signal path, if the protection is not good, it
will produce an audible TDD Noise, which includes the 217Hz noise And a harmonic noise signal of 217 Hz.
VBAT
Voltage
RF
Signal
4.615ms
Figure 14.
Schematic Diagram of Power Supply Voltage and RF Signal during GSM RF Operation
RNS
fully inhibit the conduction and radiation interference by the AWINIC unique circuit architecture. Effec-
tively improve the ability to suppress TDD Noise.
Conduction noise suppression
When the RF power amplifier is operating, it will draw the current from the battery by 217Hz frequency, Power
supply will be introduced to 217Hz power ripple since the battery has a certain internal resistance, it will be
coupled to the speaker through the audio power amplifier. The ability to suppress power fluctuations depends
on the PSRR of the audio power amplifier.
ac
ac
vdd
PSRR
20 log(
)
vout
=
Due to the input and output of the fully differential amplifier is perfectly symmetrical, theoretically, the effect of
the power supply fluctuation on the two outputs is exactly the same, and the differential output is completely
unaffected by the power supply fluctuation. In practice, due to process bias and other factors, the amplifier will
have a certain mismatch, PSRR is generally better than 60dB, it shows the output relative to the power fluc-
tuations can be reduced by 1000 times, such as 500mVp power fluctuations, the differential output of 0.5 mV,
which basically can meet the application requirements.
But in practical applications, the power amplifier may encounter conduction of TDD Noise problem even if its
PSRR is 60dB or 80dB, why is this? Because we also need to consider the impact of peripheral power mis-
matches of audio power amplifiers
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