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AG2120 Fiches technique(PDF) 5 Page - List of Unclassifed Manufacturers

No de pièce AG2120
Description  FULLY FEATURED PSTN INTERFACE
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V2.0 October 2002
Advance Data Sheet
© Silver Telecom 2002
Page 5
Ag2120
F U L L Y F E ATUR E D P S TN I N TE RF ACE
2.0
Line Interfacing
The Ag2120
line interface provides a flexible and
robust interface to the telephone line.
It has been
designed to meet regulatory standards whilst providing
a space and power efficient solution.
2.1
D.C. Termination.
Any equipment terminating a telephone line must
present the correct d.c. resistance to the line.
This
ensures that the correct current flows to be able to
detect the off hook condition, avoids excessive power
dissipation in the Subscriber Line Interface (SLIC) and
the Subscriber’s equipment, and minimises the size of
power supply needed to drive the SLIC.
The
Ag2120
has
been
designed
to
meet
the
requirements of many network operators. This is done
by making the d.c. characteristic adjustable. These are
controlled by connecting the DM pins on the line side of
the circuit. Table 1 shows how these are connected.
Table 1 Set Up of the DM Pins
Market
DMa
DMb
North America
(EIA 464, Resistive)
Connect together through
390K resistor
Europe (CTR21)
Connect together through
390K resistor
Far East
Connect together through
390K resistor
2.2
Signalling and Loop Status.
The Ag2120 provides facilities to monitor and control
the telephone line. This allows the device to be used
with a variety of loop signalling schemes and minimises
the
number
of
external
components
needed
to
implement a complete line interface.
In order to implement ground start applications please
contact Silver Telecom or our local representative.
2.2.1 The On-Board Loop Switch
The Ag2120 implements the loop start protocol when
initiating and answering a call.
This means that a
switch must be closed to allow loop current to flow,
signalling to the SLIC that the terminating equipment
has gone “off-hook”. This has been done historically
by a relay.
The Ag2120 uses an integral optically
isolated switch to do this, eliminating the need for an
external relay, so space and cost is saved for the user.
The on-board Loop Switch is controlled by the LSC pin.
A logic 1 applied to the pin closes the loop switch. This
is done when the terminating equipment wishes to
begin a call or in response to the reception of the
ringing signal. The LSC pin can be controlled by the
output drive pins of a Codec or from a micro controller
device.
Once the Loop Switch has been closed confirmation
that loop current is flowing is provided by the LC pin.
This can be used for fault detection and for call clear
detection.
2.2.2 Ringing Detection and Sensitivity.
The terminal equipment must be capable of detecting
and responding to an incoming call in the same way as
a telephone set.
The termination circuitry must,
therefore, detect the presence of the ringing signal.
The Ag2120 provides an output, RS, which indicates
the presence of ringing by switching from a logic 1 to
logic 0.
The RS output will toggle at the ringing
frequency. A capacitor to ground can also be added if
ringing cadence is needed rather than the ringing
frequency.
The sensitivity to ringing is set internally to 22V
RMS
when V
CC is +5V, or 14VRMS when VCC is +3.3V.
2.2.3 Reversal Detect
The reversal of the battery polarity is used as a
signalling technique.
The Ag2120 can detect this
condition and provides an output on the F/R pin,
whether in the on-hook or off-hook state.
One example of this type of signalling is in Caller Line
ID in the United Kingdom, where a battery polarity
reversal precedes the transmission of data before the
ringing signal is applied to the line. Another example is
in some systems in the US where a reversal is used to
indicate far end answer.
3.0 The 2-4 Wire (Hybrid) Conversion.
The Ag2120 transmits and receives balanced 2-wire
analog signals at the Tip and Ring connections. These
are converted to a ground referenced output at V
OUT
and from a ground referenced signal at V
IN.
V
OUT and VIN are normally connected to a Codec (via
d.c. blocking capacitors) for conversion to and from a
Pulse Code Modulated (PCM) stream.
3.1 Transmit and Receive Gain.
The gain in both the transmit and receive directions is
set at 0dB. Any gain adjustments can be made using
the Codec functionality. This is either by hardware or
software depending upon the Codec used.


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