Audio; Function Description; Tx-Audio - Benefon DRAGON TDP70WN Service Manual

The µCBIC circuit has a continuous power supply and the 32 kHz clock crystal
runs constantly. Not even the RESET line stops the clock. If the power supply
has dropped too low, the clock will need to be reset with the radio buttons (from
the menu).

5.2 AUDIO

5.2.1 Function Description

The audio module is comprised of the following functions:
1. TX-audio signal handling
2. RX-audio signal handling
3. Fii signal handling
4. FFSK modem
5. DTMF generator/receiver
6. Signal level detectors
7. Compander
8. Expander
9. Buzzer
The audio functions are mainly located in a single circuit AK2339. This chip
from AKM is controlled by a serialbus. It is possible to shut down parts of the
circuit, one block at a time to minimise power consumption.

5.2.2 TX-audio

The input from the microphone is fed to the audio circuit I7 pin 61, which is an
operational amplifier (AMP1) inverting input. The operational amplifier gain is
set by resistors R87 and R89. The amplifier is connected as a low pass filter.
After the amplifier is the microphone switch and then summing junction of MIC
input signal, EXTMIC input signal and transmit DTMF signal. VR1 is a
programmable amplifier, which sets the microphone signal (sensitivity) to the
correct level. After VR1 comes band-pass filter for transmitting the voice signal.
A special scrambler circuit I9 can be mounted between the pins 57/58 and 59
of I7. This device is optional and it is controlled also by the serial interface
circuit. TXDET is the transmit voice signal detection circuit which works as a
full wave rectifier. Next comes ATT1 which is an attenuate circuit to set the
transmit signal level in the HF-mode. COMP is the compressor circuit.
Compress the transmitting signal amplitude with square root law. It can be
bypassed. The linearity is adjustable by the control register CVR. Next is VR2,
4Z2200GB.fm
Product: TDP70WN /
5.9.2000
OC2285 Processor/Audio/RF
7