Motorola MTM800 User Manual page 56

4.1 - 22
RX Path
The receiver feeds the digital output signal via the baseband port (BBP) to the DSP which performs
the functions of digital demodulation, ACELP speech de-compression, and audio filtering. After
processing, the DSP feeds the signal via the serial audio port (SAP) to the CODEC FL0200.
The CODEC converts the digital audio format to an analog signal. One of the CODEC's analog
output signals is amplified by U0206-1 and then fed to the RX_AUDIO pin on the 20 pin accessory
connector J0400.
The second output signal from the CODEC is fed to the programmable potentiometer U0204 which
attenuates the analog signal according to the terminal mode of operation or the setting of the
volume control.
The multiplexer U0201 selects between the signal from the potentiometer or the signal SP_AUDIO
from the 40 pin expansion head connector J500 and routes the audio to the audio power amplifier
(PA) U0205 and the amplifier U0206-2.
The amplified audio from U0206-2 is available on the HANDSET_AUDIO pins on the 20 pin
accessory connector J0400 and the 40 pin expansion head connector J0500.
The audio PA has one inverted and one non-inverted output that produces the differential audio
output signals SPEAKER+ and SPEAKER-.
Both signals are available on the 20 pin accessory connector J0400 and the 12 pin Enhanced
Control Head connector J0550.
RTC
The real time clock (RTC) IC U0100 supplies the controller with 32.768kHz clock. When the terminal
is powered off, the RTC is supplied by a 5.1V supply URTC which derives from A+ via the zener
diode VR0325.
After the terminal has been switched on, the IC is supplied from 3V_DIG and URTC is internally
disconnected from the IC supply. When the terminal is disconnected from FLT_A+, the RTC
continues to work for approx.10 minutes.
TEMP_SENSE and BATTERY_VOLTAGE MUX
The controller alternately senses the battery voltage and the temperature on a dedicated input. The
temperature information TEMP_SENSE is generated by the temperature sensor U5501 which is
located close to the PA.
The battery voltage information derives from FLT_A+ via R0312 and R0313. These signals are input
to the analog multiplexer U0104. With the PWM_ADC_SEL line, the controller selects which signal
is routed to the comparator U0103-1.
The comparator compares the voltage from the multiplexer and the filtered (R0115 and C0113)
pulse width modulated signal PWM_ADC_REF from the controller.
This PWM signal is adjusted by the controller until the comparator output changes its state. Thus the
voltage either battery or temp sense can be determined.
GPS connector J0600
On this connector an optional GPS module electrically interfaces to the terminal. Two voltages,
3V_DIG and a protected SWB+, are available to supply the GPS circuitry. The GPS module
THEORY OF OPERATION (TRANSCEIVER)