Digital Section; Transmitter Path; Receiver Path - Motorola ST7000 Basic Service Manual

2.3.1

Digital Section

The digital section is based on a Dual Core System On a Chip (SoC) processor, a low-power
Applications processor with dual core architecture based on Advanced RISC Machine (ARM)
application core and Digital Signal Processor (DSP) core with floating point.
The dual-core architecture of the Dual Core Processor SoC provides benefits of both DSP and
Reduced Instruction Set Computing (RISC) technologies.
The DSP performs modulation and de-modulation functions for the radio. It also performs Forward
Error Correction and other correction algorithms for overcoming channel errors and Algebraic Code
Excited Linear Prediction (ACELP) speech coding. It carries out linear 16-bit analog to digital
conversions, audio filtering, and level amplification for the microphone audio input and the received
audio output.
The power and audio section is based on the Power Management IC and includes power supplies,
audio routing, microphone, and earpiece amplifiers. An external audio power amplifier is used for the
loudspeaker.
2.3.2

Transmitter Path

The transmitter circuitry includes a linear class AB Power Amplifier (PA) for the linear modulation of the
terminal. It includes a Cartesian Loop to enhance its transmitter linearity and reduce splattering power
into adjacent channels.
The transmitter path consists of a Cartesian Loop that contains forward and feedback paths. The
forward path includes the following items.
• Tx Power Control Integrated Circuit
• Balanced-Unbalanced Converter (BALUN)
• Attenuator
• Power Amplifier
• Coupler
• Antenna Switch
The loop feedback path includes the following items.
• Tx Power Control Integrated Circuit
• BALUN
• Attenuator
• Directional Coupler
2.3.3

Receiver Path

The receiver section in the radio is based on the DCR (Direct Conversion) technology. The main
concept of this technology is down converting of the RF signal directly into a base band signal,
skipping the intermediate stage of IF signal.
The receiver path includes the following items.
• Duplexer
• Antenna Switch
• RF Switches
MN002952A01-AH
Chapter 2: Overview
29