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6.3. Speakerphone (SEE BLOCK DIAGRAM Fig.18 and SCHEMATIC
DIAGRAM [BASE UNIT])
The extra circuitry for the TCD953/958 speakerphone circuit comprises a microphone, a speaker, a speakerphone codec IC10 and
a speaker amplifier IC14.However, note that the majority of the speakerphone functionality is contained within the existing BBIC
IC101. This includes the switching between microphone and speaker path, echo suppression and cancelling, etc. The
speakerphone codec IC10 only provides analogue-to-digital conversion and digital-to-analogue conversion.
a speaker amplifier IC14.However, note that the majority of the speakerphone functionality is contained within the existing BBIC
IC101. This includes the switching between microphone and speaker path, echo suppression and cancelling, etc. The
speakerphone codec IC10 only provides analogue-to-digital conversion and digital-to-analogue conversion.
A bi-directional serial data link is provided between the speakerphone codec IC10 and the BBIC IC101. The 8.0 kHz strobe signal
STRO from IC101 pin 39 (TP46) is a synchronising pulse for this data link, and the 2.3 MHz clock ICLK from IC101 pin 44 (TP47)
is the clock for the serial data link, and is also the sampling clock for the analogue-to-digital converter (ADC) and digital-to-analogue
converter (DAC) in the speakerphone codec IC10.
STRO from IC101 pin 39 (TP46) is a synchronising pulse for this data link, and the 2.3 MHz clock ICLK from IC101 pin 44 (TP47)
is the clock for the serial data link, and is also the sampling clock for the analogue-to-digital converter (ADC) and digital-to-analogue
converter (DAC) in the speakerphone codec IC10.
The DC supply to the speakerphone codec IC10 pin 6, is a 3.1V supply, derived from the regulator IC6 (TP185). The DC supply
to the speakerphone amplifier IC14 pin 6, is a 6.4V supply, derived from the regulator IC5 (TP109).
to the speakerphone amplifier IC14 pin 6, is a 6.4V supply, derived from the regulator IC5 (TP109).
6.3.1. Path from Telephone Line to Speaker
Audio from the telephone line passes via the normal signal path of J1 tel-line connector (TP13 and TP14), D8 bridge rectifier
(TP45), T3/T5 current limiter (TP50), T8 hookswitch (TP55), and R41 (TP123), to BBIC IC101 pin 58 (TP121).In the BBIC it is
converted from an analogue audio signal into digital data in the BBIC´s internal codec. Additionally, the speakerphone switching
and echo suppression functions are contained within the BBIC.An eight level speaker volume control is provided, and the
functionality for this is also contained within the BBIC.The digital data is sent from the BBIC IC101 pin 46 to IC10 speakerphone
codec pin 10 (TP25), via the serial data link. In the speakerphone codec IC10, the data is converted back to analogue audio, and
fed from IC10 pin 5 (TP178) and to the speaker amplifier IC14 pin 4 (TP179). The audio signal is amplified in IC14, and the push-
pull audio output is sent from IC14 pins 5 and 8 to the speaker (TP101) and (TP102).
(TP45), T3/T5 current limiter (TP50), T8 hookswitch (TP55), and R41 (TP123), to BBIC IC101 pin 58 (TP121).In the BBIC it is
converted from an analogue audio signal into digital data in the BBIC´s internal codec. Additionally, the speakerphone switching
and echo suppression functions are contained within the BBIC.An eight level speaker volume control is provided, and the
functionality for this is also contained within the BBIC.The digital data is sent from the BBIC IC101 pin 46 to IC10 speakerphone
codec pin 10 (TP25), via the serial data link. In the speakerphone codec IC10, the data is converted back to analogue audio, and
fed from IC10 pin 5 (TP178) and to the speaker amplifier IC14 pin 4 (TP179). The audio signal is amplified in IC14, and the push-
pull audio output is sent from IC14 pins 5 and 8 to the speaker (TP101) and (TP102).
6.3.2. Path from Microphone to Telephone Line
DC bias for the microphone is provided from the BBIC IC101 pin 57 (TP170) (positive bias) and pin 51 (TP171) (negative bias). The
bias is fed to the microphone via R89 and R82 (positive bias) and R90 and R83 (negative bias). The balanced audio signal from
the microphone is fed to the speakerphone codec IC10 pins 19 and 18 via R82 (TP172), R87, R99, and R83 (TP173), R88, and
R100.
bias is fed to the microphone via R89 and R82 (positive bias) and R90 and R83 (negative bias). The balanced audio signal from
the microphone is fed to the speakerphone codec IC10 pins 19 and 18 via R82 (TP172), R87, R99, and R83 (TP173), R88, and
R100.
The analogue signal is converted into a digital signal in the speakerphone codec (IC10), and the digital signal on IC10 pin 11
(TP37), is fed via the serial data link to the BBIC IC101 pin 45. The speakerphone switching and echo suppression functions are
contained within the BBIC. The digital data is converted again into an analogue signal in the BBIC´s internal codec.
(TP37), is fed via the serial data link to the BBIC IC101 pin 45. The speakerphone switching and echo suppression functions are
contained within the BBIC. The digital data is converted again into an analogue signal in the BBIC´s internal codec.
The analogue signal is fed from IC101 pin 63 (TP119), via T13 audio amplifier (TP55), T8 hookswitch (TP50), T3/T5 current limiter
(TP45), D8 bridge rectifier, to J1 tel. line connector (TP13 and TP14), and out to the telephone line.
(TP45), D8 bridge rectifier, to J1 tel. line connector (TP13 and TP14), and out to the telephone line.
6.4. Keyboard
The TCD953 is fitted with a keyboard which provides the user with comprehensive speakerphone facilities, and includes a full
numeric keypad for dialling out.The keyboard is mounted on a separate pcb (2AP board), and is connected to the main pcb via J3
connector.
numeric keypad for dialling out.The keyboard is mounted on a separate pcb (2AP board), and is connected to the main pcb via J3
connector.
Additional circuitry for the keyboard comprise a tri-state latch (IC9) and tri-state buffer (IC8), both mounted on the main
pcb.Keyboard scan pulses and LED drive signals are fed from the BBIC address/data bus to the keyboard via latch IC9 and
connector J3.Key press information from the keyboard is fed via J3 and the tri-state buffer IC8 to the BBIC address/data bus
pcb.Keyboard scan pulses and LED drive signals are fed from the BBIC address/data bus to the keyboard via latch IC9 and
connector J3.Key press information from the keyboard is fed via J3 and the tri-state buffer IC8 to the BBIC address/data bus
The DC supply to IC8 pin20, and IC9 pin 20, is a 3.1V supply, derived from the regulator IC6 (TP185).
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KX-TCD958RUC
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