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参数资料
| 型号： | PBL386212SHT |
| 厂商： | ERICSSON |
| 英文描述： | Subscriber Line Interface Circuit |
| 中文描述： | 用户线接口电路 |
| 文件页数： | 10/16页 |
| 文件大小： | 130K |
| 代理商： | PBL386212SHT |
PBL 386 21/2
10
Functional Description
and Applications Informa-
tion
Transmission
General
A simplified ac model of the transmission
circuits is shown in figure 8. Circuit analysis
yields:
(1)
(2)
V
TR
= E
L
- I
L
· Z
L
(3)
where:
is a ground referenced version of the
ac metallic voltage between the TIPX
and RINGX terminals.
G
2-4S
is the programmable SLIC two-wire
to four-wire gain (transmit direction).
See note below.
V
TR
is the ac metallic voltage between tip
and ring.
E
L
is the line open circuit ac metallic
voltage.
I
L
is the ac metallic current.
R
F
is a fuse resistor.
R
P
is part of the SLIC protection.
Z
L
is the line impedance.
Z
T
determines the SLIC TIPX to RINGX
impedance at voice frequencies.
Z
RX
controls four- to two-wire gain.
V
RX
is the analog ground referenced
receive signal.
V
TX
V
Z
V
Z
I
TX
T
RX
RX
L
RSN
+
=α
α
RSN
is the receive summing node current
to metallic loop current gain = 200.
Note that the SLICs two-wire to four-wire
gain, G
, is user programmable between
two fix values. Refer to the datasheets for
values on G
2-4S
.
Two-Wire Impedance
To calculate Z
, the impedance presented
to the two-wire line by the SLIC including
the fuse and protection resistors R
F
and R
P
let:
V
RX
= 0.
From (1) and (2):
Thus with Z
TR
,
α
RSN
, G
2-4S,
R
P
and R
F
known:
Two-Wire to Four-Wire Gain
From (1) and (2) with V
RX
= 0:
Four-Wire to Two-Wire Gain
From (1), (2) and (3) with E
L
= 0:
V
V
Z
Z
Z
RX
T
+
α
For applications where
Z
/(
α
·G
) + 2R
+ 2R
is chosen to be
equal to Z
L
the expression for G
4-2
simplifies
to:
Four-Wire to Four-Wire Gain
From (1), (2) and (3) with E
L
= 0:
Hybrid Function
The hybrid function can easily be
implemented utilizing the uncommitted
amplifier in conventional CODEC/filter
combinations. Please, refer to figure 9. Via
impedance Z
a current proportional to V
is injected into the summing node of the
combination CODEC/filter amplifier. As
can be seen from the expression for the
four-wire to four-wire gain a voltage propor-
tional to V
is returned to V
. This voltage
is converted by R
to a current flowing into
the same summing node. These currents
can be made to cancel by letting:
The four-wire to four-wire gain, G
, includes
the required phase shift and thus the
balance network Z
B
can be calculated from:
V
V
Z
G
RX
RSN
2 4
When choosing R
, make sure the output
load of the VTX terminal is >20 k
.
I
f calculation of the Z
formula above
yields a balance network containing an
inductor, an alternate method is
recommended. Contact Ericsson Micro-
electronics for assistance.
The PBL 386 21/2 SLIC may also be
used together with programmable CODEC/
filters. The programmable CODEC/filter
allows for system controller adjustment of
Figure 8. Simplified ac transmission circuit.
G
Z
Z
G
T
RX
S
4 2
2 4
1
2
=
V
R
V
Z
E
TX
TX
RX
B
L
+
=
=
0
0
(
)
PBL 386 21/2
+
-
+
-
VTX
RSN
I
L
/
α
RSN
TIPX
RINGX
+
-
E
L
-
+
TIP
RING
R
F
R
F
Z
TR
Z
T
V
TX
V
RX
-
Z
RX
I
L
I
L
R
HP
+
Z
L
V
TR
R
P
G
2-4S
R
P
V
V
G
I
R
R
TR
TX
S
L
F
P
=
+
+
2 4
2
2
(
)
Z
Z
G
R
R
TR
T
RSN
S
F
P
=
+
+
α
2 4
2
2
Z
G
Z
R
R
T
RSN
S
TR
F
P
=
α
2 4
2
2
(
)
G
Z
G
Z
R
R
TR
RX
T
L
RSN
S
L
F
P
4 2
2 4
2
2
=
=
+
+
(
)
G
V
V
Z
Z
G
R
R
TX
TR
T
RSN
T
RSN
S
F
P
2 4
2 4
2
2
=
=
+
+
/
α
α
G
V
V
Z
Z
G
Z
R
R
Z
G
Z
R
R
TX
RX
T
RX
S
L
F
P
T
RSN
S
L
F
P
4 4
2 4
2 4
2
2
2
2
=
=
+
+
+
+
+
(
)
(
)
α
Z
R
R
Z
Z
Z
R
R
G
Z
R
R
B
TX
RX
TX
TX
T
T
S
L
F
P
S
L
F
P
=
=
+
+
+
+
+
α
2 4
2
2
2
2
(
)
(
)
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