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

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Service Manual

Audio Section

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

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.

EXT_Mic Bias

EXT_Mic Enable

HANDSET_AUDIO

Baseband Section

PUB_ADDRESS1

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