TK-2140
10
Fig. 14 Decode
IC500
AF IC
IC303
BPF
IC300
AMP
IC306
LPF
IC301
DTMF
DECODE
DCK,SD,STD
LSD
IN
HSD
IN
IC307
CPU
IC312
IC500
XOUT
OSC1
PD
11
3
95
IC201
BPF
DT
,CK,CE
CIRCUIT DESCRIPTION
Fig. 13 Encode
SUM
SUM
IC305 (1/2)
SUM
1
LSD
OUT
HSD
OUT
IC309
CPU
O5
O2
O3
O6
I2
I1
I5
IC307
D/A (ADJ)
VCO
MD
RX Audio
MIC IN
IC500
2
LPF
IC304
I6
I3
VCXO
X1
MB
AF
AMP
IC305 (2/2)
O1 BUFF
AMP
IC302
7-2. Decode
●
Low-speed data (QT,DQT,LTR)
The demodulated signal from the IF IC (IC200) is amplified
by IC300 (2/2) and passes through a low-pass filter (IC306) to
remove audio components. The signal is input to pin 95 of the
CPU.
The CPU digitizes this signal, performs processing such as
DC restoration, and decodes the signal.
●
High-speed data (DTMF)
The DTMF input signal from the IF IC (IC200) is amplified
by IC300 (2/2) and goes to IC301, the DTMF decoder. The
decoded information is then processed by the CPU. During
transmission and standby, the DTMF IC is set to the power
down mode when the PD terminal is High. When the line is
busy, the PD terminal becomes Low, the power down mode is
canceled and decoding is carried out.
●
High-speed data (2 tone)
The demodulated signal from the IF IC (IC200) is amplified
by IC300 (2/2) and passes through an audio processor (IC500)
and band-pass filter IC303 (1/2) and IC 201 (1/2) to remove a
low-speed data. The CPU digitizes this signal, performs
processing such as DC restoration, and decodes the signal.
●
MSK (ESN)
The MSK input signal from the IF IC is amplified by IC300
(1/ 2) and goes to pin 5 of IC500. The signal is demodulated
by MSK demodulator in IC500. The demodulated data goes to
the CPU for processing.
7. Signalling Circuit
7-1. Encode
●
Low-speed data (QT,DQT,LTR)
Low-speed data is output from pin 1 of the CPU. The signal
passes through a low-pass CR filter, and goes to the summing
amplifier (IC305 1/2). The signal is mixed with the audio signal
and goes to the VCO and VCXO (X1) modulation input after
passing through the D/A converter (IC307) for BAL adjustment.
●
High-speed data (DTMF)
High-speed data is output from pin 2 of the CPU. The signal
passes through a low-pass filter consisting of IC304, and
provides a TX DTMF tone and a RX DTMF tone. TX DTMF
deviation making an adjustment by microprocessor is passed
through the D/A convertor (IC307) and then applied to the audio
processor (IC500).
The signal is mixed with the audio signal and goes to the
VCO and VCXO. The RX DTMF tone is passed a summing
amplifier (IC305 2/2). The D/A converter (IC307) for audio
control, audio power amplifier and then to the speaker.
●
MSK (ESN)
ESN utilizes 1200bps MSK signal. MSK signal is output from
pin 6 of IC500. The signal passes through the D/A converter
(IC307) for the MSK deviation adjustment. and is routed to the
VCO. When encoding MSK, the microphone input signal is
muted.
