Codec And Audio Circuitry - Tait TM9100 Service Manual

3.5

CODEC and Audio Circuitry

For a block diagram of the CODEC and audio circuitry, refer to
Introduction
The analog-to-digital conversion and digital-to-analog conversion is
A/D and D/A
Conversion
performed by the devices IC203, IC204 and IC205.
IC203 is an eight-channel DAC that provides control of transmitter biasing,
Device IC203
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
Device IC205
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
Device IC204
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 (
Base-band CODEC
QRXN
differential and biased at 1.2V nominally. The digital section communicates
with this CODEC via a two-wire synchronous serial interface (
BSOFS
CODEC is not used.
The voice-band CODEC handles the microphone and speaker signals.
Voice-band CODEC
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
Auxiliary CODEC
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:
Audio Circuitry
76 Circuit Descriptions
balls) of the receiver's second IF stage. The analog signals are
balls). The digital-to-analog conversion section of the base-band
IDACOUT
output of audio signal for speaker
input of microphone audio signal
input of auxiliary audio signal
output of auxiliary audio signal
, and balls). IC204 also contains
VSFS VSDO VSDI
, and balls). The DAC used for
ASFS ASDI ASDO
ball) is a current output type. Current-to-
© Tait Electronics Limited August 2005
Figure 3.5.
, , and
IRXP IRXN QRXP
and
BSDO
TM9100 Service Manual