Kenwood TKR-740 Service Manual page 39

5.3 DSP circuit
The DSP circuit filters transmitter/receiver audio signals
and decodes signalling (QT, DQT). This circuit consists of IC30,
IC24, IC27, IC22, IC31, IC34, and IC25. The receiver signal
DET is converted from analog to digital by codec IC27 w ith a
sampling frequency of 16.128 kHz. The digitized audio signal
is sent to DSP IC30 to process the signalling signal and audio
signal. The processed digital audio signal is fed to codec IC27,
converted from digital to analog, and the analog signal is output
from pin 12 (Vout R). Then, the audio signal is amplified by
IC34 (B/2), passes through the IC34 (A/2) low -pass filter, and
goes to multiplexer IC37.
The transmitter audio signal coming from pin 13 of IC29 is
CIRCUIT DESCRIPTION
amplified by IC22 (B/2), fed to pin 6 (Vin R) of codec IC27, and
converted from analog to digital at a sampling frequency of
16.128 kHz. The digitized transmitter audio signal is AGC-
processed, pre-emphasized and filtered at 300 Hz to 3 kHz by
DSP IC30, and the resulting signal is fed back to codec IC27,
converted from digital to analog, and the analog signal is output
from pin 15 (Vout L). The transmit signal from Vout L is
amplified by IC34 (B/2), passes through the IC34 (A/2) low -
pass filter, and goes to the IC12 (A/2) summing amplifier. IC24
is a counter IC and the clock required for the codec and DSP is
generated by dividing the 16.515M Hz clock signal produced
by DSP IC30.
Fig.23 DSP circuit
TKR-740
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