Transmitter Circuits; Logic Circuits - Motorola StarTAC 3000 Service Manual

StarTAC 3000
frequency error, using the received signal as
the frequency reference. The logic section
monitors the Frequency Error signal and
reprograms the reference oscillator until the
frequency error signal changes state. The
AFC circuit is always functional during call
processing, but is not functional in manual
test mode servicing level.
The RX Audio and data signals are routed
through the SNAP
processing. Depending on the option used,
RX audio signals can be sent to the PACER
IC or to other external connections such as
the earpiece speaker, external accessory
connector, or headset jack.

Transmitter Circuits

Transmit audio enters the SNAP IC either
from a internal microphone, external acces-
sory connector, or headset jack.
TX audio can contain voice audio, high-
speed data, low speed data, DTMF, SAT and
ST. (Low speed data including DST and
DSAT for NAMPS operation)
The TX audio is processed and/or generated
by the SNAP IC, and then is routed to be
modulated on
824-849 MHz TX VCO for direct conversion
transmit. The 800 MHz transmit signal is
amplified by the Dual GaAs RF IC and a
separate GaAs FET device before being
filtered, and then sent to a FET RF switch
that routes RF to the antenna or external
port.
The high-efficiency GaAs PA stages require
a negative bias voltage. A 0 to -3.5V negative
voltage potential is contained in the PA area
for this purpose. The PAC IC controls
biasing to the GaAs PA FET stages for
proper operation.
The directional coupler samples the PA
output. This sample is converted to a DC
Power Detect voltage which is fed to the
SNAP IC.
IC for internal
the transmitter's
The SNAP IC compares the Power Detect
voltage to a reference voltage and sends a
Power Control signal back to the PA. The
Power Control voltage adjusts the PA gain
to achieve the desired power output.
The SNAP IC also performs the following
functions:
• Enables the alert ringer and vibrator (if
installed).
• On/Off control functions for receiver,
transmitter, and synthesizer circuitry.
• Audio conditioning,
processing as well as SAT, DTMF, ST and
data detection/transmission.
• Divides 4.2 MHz clock to 3.84 MHz and
2.1 MHz for
micro-processors, and 160 kHz for the
PACER IC.
The SNAP IC Phase Mod signal is routed to
the ANGUSS IC for low speed data trans-
missions when in NAMPS operation. The
Frequency Mod output from the SNAP IC
contains all other summed TX audio infor-
mation to be modulated on the transmitter.

Logic Circuits

The StarTAC's Audio-Logic section consists
primarily of:
• Microprocessor —execute
provide most control and logic flow
processes. The processor uses Serial
Peripheral Interface (SPI) to pass control
data to other IC's.
• PACER IC —regulates supplies to logic and
RF circuits,
functions. Also contains audio driver
circuitry for RX audio and alert ringer.
• SNAP IC —See "Transmitter Circuits" for
description.
• Memory —256K EPROM for storage for
executable software, and 8K EEPROM for
storage of repertory information.
4
routing,
main and display
software
power on/off control
6/29/98
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