Kenwood NX-720 Service Manual page 25

6-5. DSP
The DSP circuit consists of a DSP (IC502) and process-
es the baseband signal. The DSP operates on an external
clock of 18.432MHz (the same as the IC507), the I/O section
operates at 3.3V and the core section operates at 1.5V. The
DSP carries out the following processes:
• 4 level FSK processing
• Analog FM pre-emphasis/de-emphasis
• Vocoder processing between the audio codec and mod-
ulation/demodulation
• CAI processing, such as error correction encoding
• QT/DQT encoding/decoding
• DTMF encoding/decoding
• MSK encoding/decoding
• 2-tone encoding/decoding
• Compressor/expander processing
• Voice scrambler processing
• Transmit/receive audio fi ltering processing
• Microphone amplifi er AGC processing
• Audio mute processing
• Modulation level processing
7. Power Supply Circuit
+B is connected to the Final amplifier and the DC/DC
converter IC (IC405). IC405 regulates the +B voltage to 5.0V
(50M). 50M operates whenever +B is supplied. IC401 (33M)
and IC408 (15M) are enabled while the 50M is operating.
33M and 15M provide the power to the ASIC (IC507),
DSP (IC502), and Flash memory. At this time the ASIC
starts working. The voltage detector IC (IC402) watches the
+B voltage. If the +B voltage is higher than 8.6V, IC402 (/
BINT) outputs High. If the /BINT signal is high, Q403 (SB
SW) is turned on by the SBC signal from the ASIC. (High :
SBC=ON, Low : SBC=OFF). When the SB is turned on, IC1
(80C), IC404 (50C), Q402 (80ANT), Q404 (80T), Q415, 416
(150C), Q417 (50R) and Q408 (50CS) start working. IC409,
Q409 and Q410 are controlled by the SBC signal. If the
SBC signal becomes High, IC409 (33C) operates, and Q409
(33A_2) and Q410 (50MC SW) turn on.
The ASIC sets the TXC signal to High during transmis-
sion to the supply power (80T) for the transmission circuit.
The ASIC sets the signals (RXC) to High during reception to
the supply power (50R) for the reception circuit.
When the ASIC detects the PSW (Power switch) signal,
IGN (Ignition sense) signal or /BINT signal, it sets the SBC
signal to Low, and turns the transceiver power (SB) off.
When D401 and Q401 detect an over-voltage condition, they
turn Q403 (SB SW) off, but the ASIC continues to function.
CIRCUIT DESCRIPTION / 电路说明
6-5. DSP
DSP 电路由 DSP (I C502) 组成，用以处理基带信号。D S P
在 18.432MHz 的外部时钟上运行 ( 与 IC507 相同 )，I/O 部分
以 3.3V 运行，核心部分以 1.5V 运行。DSP 进行以下处理 ：
· 4 级 FSK 处理
· 模拟 FM 预加重 / 去加重
· 音频编解码器和调制 / 解调之间的声码器处理
· CAI 处理，例如纠错编码
· QT/DQT 编码 / 解码
· DTMF 编码 / 解码
· MSK 编码 / 解码
· 2 音编码 / 解码
· 压缩器 / 扩展器处理
· 语音扰频器处理
· 发射 / 接收音频滤波处理
· 麦克风放大器 AGC 处理
· 音频静音处理
· 调制电平处理
7. 电源电路
+B 连接至末级放大器和 DC/DC 转换器 IC (IC405)。IC405
将 + B 电压调整至 5.0V (50M)。提供 +B 时，50M 运行。50M
运行时，IC401 (33M) 和 IC408 (15M) 启用。
33M 和 15M 对 ASIC (IC507)、DSP (IC502) 和闪存供电。
此时 ASIC 开始工作。电压检测 IC (IC402) 观测 +B 电压。如
果 +B 电压高于 8.6V，则 IC402 (/BINT) 输出高。如果 /BINT
信号高，则 Q403 (SB SW) 由 ASIC 的 SBC 信号开启。( 高 :
SBC=ON， 低 : SBC=OFF)。SB 开启时， IC1 (80C)、 IC404 (50C)、
Q402 (80ANT)、Q404 (80T)、Q415、416 (150C)、Q417 (50R)
和 Q408 (50CS) 开始工作。IC409、Q409 和 Q410 由 SBC 信号
控制。如果 SB C 信号变高，I C409 (33C) 运行，并开启 Q409
(33A_2) 和 Q410 (50MC SW)。
发射期间，ASIC 将 TXC 信号控制为高，为发射电路供电
(80T)。接收期间，ASIC 将信号 (RXC) 控制为高，为接收电
路供电 (50R)。
当 A SIC 检测 P SW ( 电源开关 ) 信号、IGN ( 点火感应 )
信号或 /B INT 信号时，它将 S BC 信号控制为低，关闭车载对
讲机电源 (SB)。当 D401 和 Q401 检测到过电压情况时，它们
将关闭 Q403 (SB SW)。但 ASIC 仍然工作。
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