4.1 - 18 MTM700 Mobile Radio / Detailed Service Manual THEORY OF OPERATION (400 MHz)
5V_TX Linear Regulator U0304
Regulator U0304 gets its input voltage from the 9.3 volt regulator U0300. The output voltage 5V_TX
is fixed to 5 volts and is mainly used in the transmitter section.
3V3_DIG Voltage Follower Q0305
Transistor Q0305 is configured as voltage follower and gets its input voltage from the 5 volt regulator
U0303. The output voltage 3V3_DIG is set to 3.3 volts by the reference voltage 3V3_FN from
U5321. Diode D0303 compensates the base to emitter voltage drop of Q0305. The voltage is used
for the optional UART connected to J0570.
3V_DIG Linear Regulator U0305
Regulator U0305 gets its input voltage from the 5 volt regulator U0303. The output voltage 3V_DIG
is set to 3 volts with resistors R0320 and R0317 and is mainly used in the controller section.
1.8 V Linear Regulator U0306
Regulator U0306 gets its input voltage from the 5 volt regulator U0303. The output voltage 1.8V is
set to 1.8 volts with resistors R0319 and R0318 and is used in the controller section.
4.6V VSF Voltage
The fractional N synthesizer U5331 creates the 4.6 volts super filter voltage (VSF). This voltage is
used for the main VCO.
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