TM840 Service Manual
Then the system starts to initiate and set the electrical level of Soft_ctr to high to keep DCDC working on enabled status to
finish power on action. When powering off, when the system detects the power button is off , and system will implement the
power off procedure, then set the electrical level of Soft_ctr to low, and cut the DCDC, the radio is poweref off then.
3.2.3 Audio processing
Figure 3.8 Audio Processing Diagrams
Audio module is made for audio output and input. This system employs U17 as the audio codec, which is to proceed the
analog and digital signal converting. Power amplifier U18 is used to amplify the analog signal and drive power.
DSP processes the digital audio signal(audio encoding/decoding etc), while the IF processor U4000 will convert and process
the RF IF frequency signal, and send the I/Q signal to DSP for further processing, then DAC U103 will processes the
digital-analog converting.
(1) Audio singal Flow
The microphone converts the audio signal to electrical signal, which will be amplified by PGA of codec, then sent to ADC of
codec for sampling. The signal will be sent to DSP processing after digital audio processing, then will be sent to DAC(U105)
to convert to modulation signal. The modulation signal will be modulated again and amplified in the RF module before finally
sent out by antenna. This radio has two MIC signal, which are internal MIC and external MIC. The internal MIC signal comes
from handheld speaker, while the external MIC signal is from 26PIN of second development interface. Also the internal MIC
signal is divided into two parts, and one will be sent to codec U17 for analog-digital converting,and the other one will be
sent to 26PIN second development interface for second development after processed by auxiliary audio circuit.
The RF signal received from RF module will be sent to DSP after converting by IF processor U4000. Then it will be
demodulated and processed by DSP, then sent to codec digital audio processing module for digital audio processing. And
then the signal is sent to DAC of codec to convert to analog audio signal. Codec U17 has five analog audio signal output
ends. Two of them will be sent to audio amplifier(U18) for amplification as the drive signal for internal and external speaker.
Then the other two will be sent to 26PIN second development interface. The other one is for the MIC input signal for optional
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