3.4 Baseband Circuits
3.4.1 Power Supply Circuit
The H603 master module is powered by a 3.7V lithium battery through rotating the volume knob. The inner
circuit of baseband and RF is powered independently. The power supply of the baseband is composed of
a two-stage conversion circuit. In the first stage the battery voltage is reduced to 2.8V through the DC-DC,
and in the second stage the voltage is converted from 3.7V to 1.8V through the power management
module.
Power On/Off: The radio is powered on/off through the control over the NPN triode by the volume knob.
To power on the radio, turn on the volume knob, the triode Q402 is on, the PWON is at logic high level, the
Q400 is off, and the PWRKEY is at logic high level.
To power off the radio, turn off the volume knob, a logic low level is detected, the poweroff process is
executed, the PWON is set to low, and the triode is off.
3.4.2 Audio Frequency Circuit
Diagram of Audio Frequency Amplifier
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