11.3.2. Telephone Line Interface
11.3.2.1. Circuit operation
· On hook
Q101 is open, Q101 is connected as to cut DC loop current and cut the voice signal.
· Off hook
Q101 turns on thus providing an off-hook condition (active DC current flow through the circuit) and the following signal flow id
for the DC loop current. T → POS101 → D101 → Q101 → Q108 → R124 → D106 → D101 → R
· The receiving signal flows:
TEL line → POS101 → Q101 → C113 → R125 → C108 → Q109 → Q405 → Q406 → Speaker
· The transmission signal flows
Mic → Q421 → Q424 → C435 → R437 → Q108 → POS101 → Tel Line
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KX-T2373MXW
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