User Guide

Technical Documentation
NHD–4
System Module
P.A.M.S
Page 4–16
Original 11/97
Audio Block
The block consists of audio codec with some peripheral components. The
codec includes microphone and earpiece amplifier and all the necessary
switches for routing. The controlling of the codec is done by the MCU. The
PCM–data comes from and goes to DSPs.
The code converts analog voice to digital samples that can be processed
by the DSP. It also accepts DSP processed speech, converts it to analog
and transmits the output to the handset or hands free speaker. The
codec communicates linear coded data with the DSP over a dedicated
serial port. The master clock of the codec is synchronized with the RF
VCTCXO and generated by the CDSB ASIC. Codec set up and DTMF
tone generation are controlled by the microprocessor via a second serial
port.
Transmitter Functional Description
The transmitter stages are as follows:
 The CDAGCT ASIC
 The Variable Attenuator
 Two SAW filters
 Three BJT driver amplifiers
 The GaAs FET power amplifier
 The Detector circuit
 The Isolator
 The Duplexer