Receiver Section; Transmitter Section - Motorola MTP700 Detailed Service Manual

TRANSCEIVER 400 MHz

Receiver Section

The receiver section includes the following main components:
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The Receiver Path implements an Automatic Gain Control (AGC). It is required to main-
tain good receiver linearity over a wide range of incoming signals and to prevent clipping
of high level signals.
The First Intermediate frequency (IF) circuit consists of the Mixer, IF Filter, and WPIC.
The First IF is down converted to baseband using an analog mixer (high-side injection)
located in the WPIC. An external second LO synthesizer IC is used to generate the
required 219.3 MHz signal, which is further divided by two to 109.65 MHz before being
applied to the mixer.
The WPIC performs the following functions:
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Transmitter Section

The transmitter circuitry includes a linear class AB Power Amplifier (PA) for the linear
modulation of the MTP700. Also included is a cartesian feedback loop to enhance the
transmitter linearity and hence reducing splattering in the adjacent channels.
The transmitter path consists of forward and feedback paths. The forward path includes
the WPIC for digital-to-analog conversion of the transmit baseband signal, the LNODCT
(Low Noise Offset Direct Conversion Transmitter) IC, Balun, Attenuator and Power
Amplifier. The feedback path includes the directional coupler, attenuator and LNODCT
(Low Noise Offset Direct Conversion Transmitter) IC.
The linearized power from the PA goes through the isolator which provides the isolation
between the antenna and the PA. The signal then passes through the antenna switch and
a lowpass Harmonic Filter to provide additional filtering to remove far out unwanted sig-
nals.
MTP700 Portable Radio / Detailed Service Manual
Antenna Switch
Limiter
Pre-selection Filter
Low Noise Amplifier (LNA)
Post-selection Filter
Mixer
IF Filter
Balun
WPIC
Carries out amplification and quadrature down conversion of the signal into base-
band.
Performs IF AGC.
Converts the baseband analog signal into digital I & Q formats.
Synthesizes the receive and transmit data (i.e. Sigma-Delta) clock.
Transmits the received data to the DSP.
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