Audio Block - Panasonic BB-HCM547A Service Manual

BB-HCM547A
4.4.

Audio Block

The audio circuit is mounted on the IO board, and included the internal MIC terminal (MIC901) and the external MIC terminal
(CN504) as the audio input and included the SP terminal (CN505) as the audio output, and supports one channel respectively
for audio input of the microphone and audio output from the camera. The internal MIC (MIC901) audio signal is mounted on the
LED board, and is connected with the PCM codec (IC531) via CN901→CN505.
When the audio is output from the camera, the audio output become possible that external speaker is connected with the SP
terminal.
ALC Amplifier (IC532/533)
Power Supply: 3.3 V
Amplifier for Auto Level Control
PCM Codec (IC531)
Power Supply Voltage: 3.3 V
Clock Frequency: Contains a built-in PLL function and generates a clock from the BCLK (256 KHz).
That contains an amplifier, LPF, gain adjustment, AD/DA converter, host I/F, PCM serial I/F and speaker output function.
Flow of audio Signal
[Microphone audio]
1. Ordinarily microphone audio is selected internal MIC audio, the audio signal, after being amplified by the amplifier in the PCM
codec (IC531) and by the ALC (IC532), is applied to the PCM codec (IC531) again. When the input audio signal level exceeds
a certain level, the ALC (IC532) changes the gain to keep the output signal level constant and to constrain the distortion in the
voice.
On the other hand, when the external microphone connect with CN504, the audio signal, after being amplified by the amplifier
in the PCM codec (IC531) and by the ALC (IC533), is applied to the PCM codec (IC531) again. And the MIC changeover
detection signal send the CPU, is switched the audio signal from the internal MIC to the external MIC in CPU codec (IC531).
2. In the PCM Codec (IC531), by a register setting from the host, amplification, AD conversion and gain adjustment are per-
formed.
The sampling frequency of the A/D conversion is 8kHz and it is converted to the PCM in the format of 8bit and µ law. Then,
64kbps data are output to the IC101 on the Main board through the Serial I/F.
The data transfer of the Serial I/F is BCLK (256 kHz).
3. The data compression of 32 kbps is performed in the ADPCM Block inside of the IC101 and the data transferred as audio
data.
[Speaker audio]
1. The ADPCM audio data are sent from the PC and, after data decompression in the ADPCM block of the CPU (IC101), the
data are transferred as the audio data of 64 kbps to the PCM Codec (IC601) through the Serial I/F.
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