
V2.0 October 2002
Advance Data Sheet
Silver Telecom 2002
Page 6
Ag2120
FULLY FEATURED PSTN INTERFACE
eg.
2-wire
Impedance
Z
T
Z
C
Network
Balance
Impedance
Z
b1
Z
b2
Z
b3
C3
Notes
1
600
300
47K
600
100K
0R
---
---
USA Short Line,
Far East, Middle East
2
CTR21
TBA
TBA
CTR21
TBA
TBA
TBA
TBA
Europe
3
600
300
TBA
AT&T
compromise
TBA
TBA
TBA
TBA
USA Long Line
3.2 The 2 Wire Impedance
The input impedance, Z
IN
, of the Ag2120 can be
programmed. This is achieved by connecting an
impedance matching network between Z
and Z
.
This network is the line impedance to be matched
minus 300
. For example to match 600
, fit a 300
resistor. Other common line impedances, and the
corresponding programming components are listed in
Table 2.
In addition to the programming network, an impedance,
Z
, must be fitted between ZT2 and Zb to provide
frequency compensation.
An alternative method of programming the 2 wire
impedance is to choose a codec where the internal
filter characteristics can be programmed to provide the
correct matching. In order to generate the filter
coefficients a model of the Ag2120 must be used. This
file, in .CIR format is available on request from Silver
Telecom or one of our representatives.
Full details on how the Codec is programmed must be
obtained from the Codec manufacturer.
3.3
Network Balance Impedance
The setting of the network balance impedance is very
similar to that of the 2 wire impedance. Again this can
be done by programming of the Codec, using the .CIR
file, or it can be done by hardware components.
3.4
On-Hook Reception
The need to provide the facility for data exchange
On-Hook is becoming increasingly common, whether
for Caller Line I.D. or for telemetry purposes. The
For 600
application:
R1 = 390K
Zb1 = 100K
Zb2 = 0R
Zb3 = NF
ZT = 300R
ZC = 47k
C1, C2 = 100nF
C3 = NF
Table 2: Line and Network Balance Impedance Examples
Figure 4: Line Impedance and Network Balance Components
V
CC
R1
Z
b1
C1
C2
Ag2120
V
IN
V
OUT
RS
LC
LSC
RING
TIP
DMa
V
CC
Z
b
DMb
GND
GND
Silver
T E L E C O M
Codec
C3
Z
b2
GND
F/R
Z
b3
Z
T
Z
C
Z
T1
Z
T2
GATE
ANODE
CATHODE