Audio Section; Rx Audio Circuit; Figure 4-9 Diagram Of Audio Section - Hytera MD78X Service Manual

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4.5

Audio Section

Vol _Ctl
U302
SSI
Vol _Ctl
MCBSP1
ADC
4.5.1

RX Audio Circuit

U302 sends digital audio to the audio processor codec via the SSI bus of MCBSP1. This bus is
composed of CLKX, FSX, DX and DR. It sends the demodulated PCM audio signal to the codec, and
adjusts the signal to appropriate amplitude according to the volume (RMS should be 80mv when
frequency is 1 KHz and deviation is 3 KHz). Then the codec converts PCM data into analog audio data
via DAC.
U231 provides two outputs: SPK1 and SPK2. SPK1 is amplified by U238 and then is fed to the PA
U201, to derive two outputs of received audio, which will be applied to the front panel speaker and
further development interface respectively. SPK2 is amplified and divided into the four paths of signal
HANDSET_AUDIO, RX_AUDIO, PUB_ADDESS1 and PUB_ADDESS2. The first two paths are
amplified by U235, and the last two paths are amplified by U236. Output of HANDSET_AUDIO,
PUB_ADDESS1 and PUB_ADDESS2 are controlled by Q231, Q235 and Q233 respectively.
U231
DAC
Right
DAC
Left
EXT_Mic Bias
EXT_Mic Enable

Figure 4-9 Diagram of Audio Section

U201
PA_Enable
Mic Bias
U235B
HANDSET_AUDIO
MMP
15
Baseband Section
INT_SPK
U236B
U236C
PUB_ADDRESS1
Enable
EXT_MIC
MAP

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