Speaker Phone - Sony IT-M708 Operation Manual

6-4. SPEAKER PHONE

MC33219 (IC701) is used as SPEAKER PHONE IC. By this IC, voice switch is performed and
SPEAKER PHONE operation is performed without howling.
Operation mode to this IC is divided into IDLE, TX, and RX. By comparing transmitting signal
and receiving signal, it shifts to each mode, and ATT(attenuation) is inserted into TX/RX circuit.
MODE
IDLE
TX
RX
16 STEPS SPEAKER VOLUME can be adjusted by CPU. Speaker impedance is 8 ohm and
power IC NJM386 provide 300mW.
Operation timing of MC33219
EVENT
ATT is not inserted into both TX/RX.
TX>RX ATT is inserted into RX.
TX<RX ATT is inserted into TX.
STATE
I IDLE
R RX
T TX
FUNCTION
FUNCTION
ATT is not inserted into both RX/TX
ATT is inserted into RX
ATT is inserted into TX
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