Codec And Audio Circuitry - Tait TM8235 Service Manual

3.5

CODEC and Audio Circuitry

Introduction
A/D and D/A
Conversion
Device IC203
Device IC205
Device IC204
Base-band CODEC
Voice-band CODEC
Auxiliary CODEC
Audio Circuitry
TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
For a block diagram of the CODEC and audio circuitry, refer to
The analog-to-digital conversion and digital-to-analog conversion is
performed by the devices IC203, IC204 and IC205.
IC203 is an eight-channel DAC that provides control of transmitter biasing,
front-end AGC, front-end tuning, and the output of analog RSSI signals.
The digital input data are fed to IC203 in synchronous serial form. Three of
the DAC channels are not used.
IC205 contains two CODECs. One is used by the FCL. The second is used
for auxiliary audio (input) and VCO modulation (output). The digital
section communicates with this device via a four-wire synchronous serial
interface.
IC204 contains base-band, voice-band and auxiliary CODECs and some
analog signal conditioning. The reference voltage (nominally 1.2V) for
these CODECs is provided internally by IC204 but is decoupled externally
by C228.
The base-band CODEC handles the I and Q outputs (
balls) of the receiver's second IF stage. The analog signals are
QRXN
differential and biased at 1.2V nominally. The digital section communicates
with this CODEC via a two-wire synchronous serial interface (
balls). The digital-to-analog conversion section of the base-band
BSOFS
CODEC is not used.
The voice-band CODEC handles the microphone and speaker signals.
The digital section communicates with this CODEC via a three-wire
synchronous serial interface (
voice-band filtering, pre-amplification and volume control.
The auxiliary CODEC handles transmitter power control, receiver gain
control, auxiliary audio output and general analog monitoring functions.
The digital section communicates with this CODEC via a three-wire
synchronous serial interface (
receiver gain control (
voltage conversion is performed by R238. The full-scale output of 1.2V is
amplified by IC201 to approximately 3V as required by the receiver.
The audio circuitry performs four functions:
output of audio signal for speaker
input of microphone audio signal
input of auxiliary audio signal
output of auxiliary audio signal.
, and
VSFS VSDO
, and
ASFS ASDI ASDO
ball) is a current output type. Current-to-
IDACOUT
Figure
, ,
IRXP IRXN QRXP
BSDO
balls). IC204 also contains
VSDI
balls). The DAC used for
Circuit Descriptions
3.7.
and
and
77