Panasonic KX-TC1868B / KX-TC1871B / KX-TC1872B Service Manual ▷ View online
13.10. DSP (Digital Speech/Signal Processing) Circuit
General Description:
(IC501, IC751) is a digital speakerphone/speech/signal processing system that implements all the functions of speech
compression, record and playback, and memory management required in a digital telephone answering machine.
The DSP system is fully controlled by a host processor IC501. The host processor provides activation and control of all that
functions, such as speech Recording, Playback, Tone detecting and Line monitoring.
(IC501, IC751) is a digital speakerphone/speech/signal processing system that implements all the functions of speech
compression, record and playback, and memory management required in a digital telephone answering machine.
The DSP system is fully controlled by a host processor IC501. The host processor provides activation and control of all that
functions, such as speech Recording, Playback, Tone detecting and Line monitoring.
The DSP system comprises of following.
— a Host Processor.
— a Host Processor.
— a Digital Signal Processor which includes the firmware implemented functions.
— a FLASH MEMORY (IC751), which is used for stored voice messages and synthesized voice.
•
Voice Message Recording
The DSP system use a proprietary speech compression technique to record and store voice message in FLASH MEMORY
(IC751).
An error correction algorithm is used to enable playback of these messages from the FLASH MEMORY (IC751).
The DSP system use a proprietary speech compression technique to record and store voice message in FLASH MEMORY
(IC751).
An error correction algorithm is used to enable playback of these messages from the FLASH MEMORY (IC751).
•
DTMF Detection
The DTMF detection is implemented by the DSP system in software. The DTMF detection is performed during Record,
Playback, and Line Monitoring modes of operation.
The DTMF detection is implemented by the DSP system in software. The DTMF detection is performed during Record,
Playback, and Line Monitoring modes of operation.
•
Synthesized Voice
The DSP implements synthesized Voice, utilizing the built in speech detector and an FLASH MEMORY (IC751), which stored
the vocabulary.
The DSP implements synthesized Voice, utilizing the built in speech detector and an FLASH MEMORY (IC751), which stored
the vocabulary.
•
Caller ID and Call Waiting CID demodulation
The DSP implements monitor and demodulate the FSK signals that provide CID information from the Central Office.
The DSP implements monitor and demodulate the FSK signals that provide CID information from the Central Office.
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KX-TC1868B / KX-TC1871B / KX-TC1872B
13.11. Greeting Recording Circuit
Circuit Operation:
MIC
MIC
→
C724
→
C725
→
C726
→
R726
→
pin 47 of IC501.
13.12. Greeting Play Back Circuit
Circuit Operation:
pin36 of IC501
pin36 of IC501
→
R431
→
C432
→
C433
→
Telephone Line.
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KX-TC1868B / KX-TC1871B / KX-TC1872B
13.13. ICM Recording Circuit
Circuit Operation:
Telephone Line
Telephone Line
→
Q131
→
C463
→
R448
→
C442
→
R464
→
C441
→
pin 32 and 33 of IC501.
13.14. ICM Play Circuit
Circuit Operation:
pins 32 and 33 of IC501
pins 32 and 33 of IC501
→
Speaker.
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KX-TC1868B / KX-TC1871B / KX-TC1872B
13.15. Telephone Line Interface
Circuit Operation:
l
ANSWER
In the idle mode, Q121 is open to cut the DC loop current and decrease the ring load. When ring voltage appears at the Tip (T)
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
T
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
T
→
L101
→
R103
→
C103
→
Q101
→
IC501 pin 64.
When the CPU (DSP) detects a ring signal, Q121 turns on, thus providing an off-hook condition (active DC current flow through the
circuit) and the following signal flow is for the voice signal.
T
circuit) and the following signal flow is for the voice signal.
T
→
D101
→
Q121
→
Q131
→
R138
→
C140
→
D101
→
L102
→
PO101
→
R
l
ON HOOK
Q121 is open, Q121 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-hook
condition.
condition.
l
SPECIFICATIONS
In the on-hook state (idle), the current flows between the telephone line and the unit is as follows:
T
T
→
L101
→
R103
→
C103
→
R106
→
C104
→
R104
→
L102
→
PO101
→
R.
The DC component is blocked by C103, C104: thereby providing an on-hook condition.
The AC interface impedance is over 47 k
The AC interface impedance is over 47 k
Ω
; thus, satisfying the telephone company requirements.
13.16. Intercom Mode
1. When the base unit LOCATOR/INTERCOM button is pressed, a call monitor signal (intercom sound) is output from pins 32 and
33 of IC501. Thus a monitor tone is heard from the speaker.
2. At the same time, flashing of the IN USE/CHARGE (LED541) is obtained from pin 65 of IC501. This status is called "Intercom
stand-by".
3. The receiving signal flows:
RF
→
pin 32 and 33 of IC501
→
SP
4. The transmission signal flows:
MIC
→
C724
→
C725
→
C726
→
R726
→
pin 47 of IC501
→
RF
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KX-TC1868B / KX-TC1871B / KX-TC1872B
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