Advent Instruments AI-5120, Руководство пользователя

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4. Technical Overview
4.1 Block Diagrams
The AI-5120 Telephone Line Monitor consists primarily of a high impedance voltage
amplifier connected to a digital signal processor via two analog-to-digital converters. By
sensing the voltage present on the telephone line, the signal processor is able to determine
the line state and perform measurements on various signals. The following figure shows
the major functional blocks of the AI-5120.
The voltage on the telephone line is measured by an amplifier presenting an input
impedance greater than 10 Mohm to ground for each of the tip and ring leads. The high
input impedance prevents the AI-5120 from affecting the signals present on the telephone
line in any significant manner. Following the amplifier, the signals are split into two
paths. Both signal paths continue through amplifier or buffer stages followed by analog-
to-digital conversion. However one of the signal paths is DC coupled while the other is
AC coupled. The DC coupled channel can accommodate a voltage range of +/- 300 volts
with a sample rate of approximately 1200 sample per second. This channel is primarily
used for detecting DC line conditions (on/off hook, line flash, line reversals) and ringing.
The second channel is AC coupled with a maximum voltage range of 10 volts peak-to-
peak and a much faster sampling rate of approximately 20,000 samples per second. The
AC coupled channel is used for performing DTMF, CAS/DTAS, and FSK detection
along with general purpose signal measurements.
Line
10M
RJ-11
Jack
DAC ADC
ADC
600
BNC Output
Speaker Output
Signal
Processing
DSP
Control &
Supervisory
Functions
USB
Port
RS-232
Port
Digital
In/Out
AC Coupled Channel
DAC
10M
RJ-11
Jack
DC Coupled Channel
Bypass
The digital samples from both AC and DC coupled channels are fed into the signal
processing block. It performs all of the detection and measurement for ringing, DTMF,
AI-5120 User Guide 13