Digital Signal Processing

IS54B Chipset Overview

The following text is from Chapter 1 of the TCS320IS54B Chipset User's Guide. To order the complete version, follow the link at the bottom of this page.

Description

The TCS320IS54B chip set consists of the following:

• One read-only memory (ROM) coded TI C5X-80 digital signal processor (DSP)
• One TLV320AC3X or TCM320AC3X voice-band audio processor (VBAP™) for the audio codec
• One TCM4300 advanced radio frequency (RF) cellular telephone interface circuit (ARCTIC™) for RF baseband conversions and DSP to microprocessor communications

Functions

The chip set implements the following functions:

• /4-shifted differential quarternary phase-shift keyed (DQPSK) modem and equalizer
• Vector sum excited linear predictive (VSELP) speech codec
• Error correction decoding associated with speech and control channels
• Analog-mode signal processing
• Transmit and receive
• Voice privacy masking for IS-54B compatibility implemented with acoustic echo canceller

Features

The IS-54B chip set includes the following features:

• Compatibility with the TIA IS-54B dual-mode cellular standard for North America
• Bit error rate (BER) performance execeeding IS-54B/IS-55 requirements
• VSELP segmented signal-to-noise ratio (SNR) performance exceeding IS-85 requirements
• Low power consumption with separate power controls for external circuits
• General purpose microcontroller (henceforth abbreviated as C) interface ensuring compatibility with many microcontrollers
• Baseband in-phase (I) and quadrature (Q) frequency modulation (FM) transmitter eliminates FM voltage controlled oscillator (VCO)
• Wide band data (WBD) demodulator with interface to microcontroller
• Full complement of RF controls:
  • Automatic frequency control (AFC)
  • Automatic gain control (AGC)
  • Transmitter (TX) power level
  • Receive signal strength input (RSSI)/battery analog-to-digital (A/D) converter
• Speaker and microphone drivers with programmable volume setting
• Voice privacy (Rev B)
• Calibration for RF/intermediate frequency (IF) interface compatibility

IS-54B Telephone

An IS-54B telephone consists of the following major subsystems:

• RF module
• TI baseband chip set (TCS320IS54B)
• Microcontroller
• User interface

The TCS320IS54B chip set consists of three devices (C5X-80, VBAP, and ARCTIC) that form the core of the baseband signal process. The C5X-80, VBAP, and ARCTIC devices minimize both power consumption and the number of interconnections needed for the manufacture of portable, cost-competitive, compact dual-mode cellular telephones.

Figure 1-1 shows a high level block diagram of a typical IS-54B telephone using the TCS320IS54B chip set.

RF Module

The RF module consists of a receiver and a transmitter. The functions of the receiver are:

• Amplification
• Down conversion
• Gain control
• FM demodulator
• In-phase/quadrature (I/Q) demodulator
• RSSI

The functions of the transmitter are:

• I/Q baseband input (both analog and digital mode)
• Up conversion
• Transmit power control
• Power amplifier
• Duplexer

TI Baseband Chip Set

TI baseband chip set consists of these three devices:

• VBAP
• TI C5X-80 DSP
• ARCTIC

VBAP

The VBAP is a complete audio interface device. Its main functions are:

• 13-bit linear A/D and digital-to-analog (D/A) conversion
• On-chip filtering
• Microphone mute
• Output amplification with programmable volume control
• Interface to microphone, speaker and TI C5X-80 DSP

C5X-80

TI C5X-80 DSP performs the modem functions in both analog and digital modes as well as the speech processing. The main functions are:

• FM voice transmission and reception
• Forward control channel (FOCC), reverse control channel (RECC), forward voice channel (FVC), reverse voice channel (RVC), supervisory audio tone (SAT), signalling tone (ST), dual-tone multifrequency (DTMF)
• Voice privacy masking
• Fast associated control channel (FACCH) and slow associated control channel (SACCH) encoding and decoding
• /4 shifted DQPSK decoding and demodulation
• Robust channel equalization
• Provision for external AGC, AFC, and power-level control signals
• Synchronization and chip set timing control during digital mode
• Interfacing to the VBAP and ARCTIC devices
• VSELP voice coding/decoding
• Channel codec and interleaving for speech

ARCTIC

ARCTIC performs the RF-baseband conversions with the associated filtering in both analog and digital modes. It is also an interface chip between the RF section, C5X-80 DSP, and the microcontroller. The main functions are to:

• Receive filtering and A/D conversions in both analog and digital modes
• Transmit filtering and D/A conversion in analog mode
• Perform /4 DQPSK modulation and filtering in digital mode
• Control the RF unit: TX power amplifer (PA) power control, AFC, AGC, synthesizer, etc.
• Manage the power control interface for the chip set
• Generate the system clock for the chip set
• Demodulate wide-band data for analog mode operation
• Provide DSP-to-microcontroller communications

The TCS320IS54B chip set addresses power reduction in standby mode directly by putting the DSP inIDLE2 mode and the VBAP in full sleep mode and partially turning off the ARCTIC device. With the microcontroller in idle mode and the RF/IF front-end circuitry operational, you can effectively perform the standby mode functions at very low power and hence increase the standby mode battery time.

Microcontroller

The microcontroller is responsible for:

• Layer 1 interface and layers 2, 3 microcontroller functions
• Power management
• User interface
• Control of baseband chip set and RF deck

User Interface

The user interface consists of the following:

• Keypad
• Display
• Audio interface
  • Microphone
  • Speaker

Literature