Read Panasonic KX-TCD951EB / KX-TCD955EC Service Manual online
32
KX-TCD951EB/KX-TCD955EC
Fig. 28
1.6 AUDIO PATH - TX AUDIO (SEE Fig. 28)
Balanced audio from the microphone (TP40 and TP41) enters the BBIC at pins 61 and 63. A balanced bias voltage for
the (“electret” type) microphone is supplied by the BBIC from pins 60 and 64 via R31 and R32. This supply is
de-coupled by R22, R27, C21, C28, and C22. RF de-coupling of the microphone signal is provided by R27, C25, R28,
C26, R24, R25, and C20.
The microphone audio signals are coupled to the BBIC via C22 and C23, which provide some high pass filtering.
In the BBIC audio passes through the gain-controlled microphone amplifier, into the ADC part of the codec, where it is
sampled and turned into digital data. The burst mode controller then processes this raw data (called the B-field)
performing encryption and scrambling, adding the various other fields that go together to produce the GAP standard
D E C T frame, assigning to a time slot and channel etc. The data then passes through the gaussian filter to emerge on
pin 20 as T R A D AT.
1.7 AUDIO PATH - RX AUDIO (SEE Fig. 28)
Audio from the receiver R E C D AT (TP54) enters the BBIC on pin 18 and passes through the clock recovery circuit. The
burst mode controller separates out the B-field data, and performs de-encryption and de-scrambling as required. It
then goes to the DAC part of the codec where data is turned back into analogue audio. The audio signal is
amplified by the gain-controlled earpiece amplifier, and balanced audio is output on pins 65 and 66, and fed to the
earpiece (TP31 and TP32). The leads feeding the earpiece are RF de-coupled by C15 to R22, C17, C16, R23, and
C18. C19 provides low pass filtering.
Circuit Diagram
DAC
CODEC
ADC
B.M.C.
GAUSS FILTER
RSSI ADC
CLOCK/DATA
RECOVERY
RECOVERY
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