PBL38620-2 Ericsson, PBL38620-2 Datasheet - Page 10

• Manufacturer Part Number: PBL38620-2
• Description: Subscriber Line Interface Circuit
• Manufacturer: Ericsson

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