Dsp; Base-Band Circuit; Rs-232C Circuit; Power Supply Circuit - Kenwood TKR-750 Service Manual

TKR-750

5-6. DSP

The DSP circuit filters transmit/receive audio signal and
encode/decodes signaling (QT, DQT). This circuit consists of
IC618, IC612, IC613, IC614, IC603, IC606, IC608, IC610,
IC616, and IC619.
The receive signal DET is converted from analog to digital
by IC614 with a sampling frequency of 16.128kHz. The digi-
tized audio signal is sent to DSP IC618 to process the signal-
ing signal and audio signal. The processed digital audio signal
is fed to CODEC IC613, converted from digital to analog, and
the analog signal is output from pin 16 (AOUTR). Then, the
audio signal is amplified by IC619 (B/2), passes through the
IC619 (A/2) low-pass filter, and goes to an electronic volume
IC615.
The transmit audio signal coming from IC605 is amplified
by IC610, fed to pin 3 (AINL) of CODEC IC614, and converted
from analog to digital at a sampling frequency of 16.128kHz.
The digitized transmit audio signal is AGC-processed, pre-
emphasized and filtered at 300Hz to 3kHz by DSP IC618, and
the resulting signal is fed back to CODEC IC614, and con-
verted from digital to analog, and the analog signal is output
from pin 15 (AOUTL). The transmit signal from AOUTL is
amplified by IC616 (B/2), passes through the IC616 (A/2) low-
pass filter, and goes to the IC611 (A/2) summing amplifier.
IC613 is a counter IC and the clock required for the
CODEC and DSP is generated by dividing the 16.515MHz
clock signal produced by DSP IC618.
IC603 and IC606 are interface IC between the CPU oper-
ated at 5.0V and the DSP operated at 3.3V.
16
CIRCUIT DESCRIPTION
IC614 : AK4550VT
RX detected signal
2
(AINR)
RD
TX modulation signal
3
Local Mic
(AINL)
TA
[Frequency response]
RX
TX
REPEAT
Fig. 10 An audio signal course and the frequency characteristic

5-7. Base-Band Circuit

The base-band circuit switches between the modulation
signal to the transmitter circuit, and remote audio and adjusts
their levels. This circuit consists of IC605, IC607, IC611,
IC615, and IC617.
Modulation inputs include local microphone input, low-
speed data (LSD), high-speed data (HSD), external audio in-
put (TA), and external data input (TD), and demodulation out-
puts include receive audio output (RA), and receive data out-
put (RD).
The multiplexer (IC605) changes signals, the electronic
volume (IC615) adjusts the level, and the operational ampli-
fier (IC607, IC611, IC617) amplifiers and sums signals.

5-8. RS-232C Circuit

The RS-232C circuit connects the RS-232C serial port of a
personal computer directly to this model to perform FPU op-
eration. The FPU operation can also be performed by con-
necting a programming cable (KPG-46) to the local micro-
phone on the front panel. But, if the D-sub connector on the
rear panel is used, the programming cable is not required.
The 232C driver IC (IC620) changes the TTL-232C level. The
firmware can only be rewritten with the local microphone on
the front panel.

5-9. Power Supply Circuit

The power supply circuit generates power to operate the
CPU, DSP, flash ROM, bi-directional buffer, and base-band
circuit. This circuit consists of IC624, IC625, IC626, IC627,
IC628, and IC630.
CODEC IC
16
RX
(AOUTR)
REPEAT
15
TX (AOUTL)
TD
300Hz 3kHz
(De-emphasis)
(Pre-emphasis)
(300Hz~3kHz Flat)
RA
RX audio
amp.
TX VCO
(Modulation
circuit)