Description
Page 29 of 290
Line cards
Description
Analog line interface units
Once the 8-bit digital voice signal has been received by the analog line card,
it must be converted back into an analog signal, filtered, converted from a
4-wire transmission path to a 2-wire transmission path, and driven onto the
analog telephone line. Figure 10 shows a typical example of the logic that
performs these functions. Each part of the analog line interface unit is
discussed in the following section.
Figure 10
Typical analog line interface unit block diagram
CODEC
2-wire
to
4-wire
conversion
Line
interface
and
protection
Message
waiting
Variable gain
filters
Impedance
matching
transformer
Balancing Network
Tip
Ring
DS-30X or
SL-1 network
loop
Message
waiting
circuit
–150V dc
553-6153
Message
waiting
Ringing
circuit
Ring voltage
Ringing
Off-hook
detector
Off-hook
Tx PCM
Rx PCM
Summary of Contents for NT1R20
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