PBL38640-2 Ericsson, PBL38640-2 Datasheet - Page 10

• Manufacturer Part Number: PBL38640-2
• Description: Subscriber Line Interface Circuit
• Manufacturer: Ericsson

Figure 9. Simplified ac transmission circuit.
10
Functional Description
and Applications Infor-
mation
Transmission
General
A simplified ac model of the transmission
circuits is shown in figure 9. Circuit
analysis yields:
where:
V
G
V
E
I
R
R
Z
PBL 386 40/2
L
L
TX
TR
L
F
P
2-4S
V
V
Z
TR
TX
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.
T
TR
= E
G
V
Z
+
V
-
V
RX
RX
2 4
TR
L
TX
Z
L
- I
S
RING
L
TIP
· Z
+
-
E
Z
I
RSN
TR
I
L
L
L
L
R
R
(
F
F
2
RINGX
R
TIPX
R
R
F
P
P
PBL 386 40/2
2
R
P
R
HP
)
(1)
(2)
(3)
+
-
G
2-4S
Z
Z
V
Note that the SLICs two-wire to four-wire
gain, G
between two fix values. Refer to the
datasheets for values on G
Two-Wire Impedance
To calculate Z
sented to the two-wire line by the SLIC
including the fuse and protection
resistors R
From (1) and (2):
Thus with Z
known:
Two-Wire to Four-Wire Gain
From (1) and (2) with V
G
Z
Z
T
RX
RSN
RX
TR
T
2 4
V
I
L
determines the SLIC TIPX to
RINGX impedance at voice
frequencies.
controls four- to two-wire gain.
is the analog ground referenced
receive signal.
is the receive summing node
current to metallic loop current
gain = 200.
RX
/
I
I
2-4S
L
RSN
L
RSN
V
V
= 0.
RSN
TX
TR
, is user programmable
F
VTX
RSN
TR
and R
Z
G
,
TR
T
G
Z
2 4
T
Z
, the impedance pre-
2 4
RSN
RX
RSN
S
P
, let:
, G
S
Z
(
Z
T
G
2-4S
+
-
+
-
V
V
RX
Z
TX
TR
RX
2
2 4
R
T
, R
= 0:
F
/
2-4S
S
P
2
and R
RSN
R
.
2
F
2
R
R
P
F
2
F
R
2
P
R
)
P
Four-Wire to Two-Wire Gain
From (1), (2) and (3) with E
For applications where
Z
be equal to Z
simplifies 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
to V
of the combination CODEC/filter ampli-
fier. As can be seen from the expression
for the four-wire to four-wire gain a
voltage proportional to V
V
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
calculated from:
G
R
Z
G
G
T
R
TX
B
V
4 2
TX
Z
/(
4 4
Z
Z
4 2
Z
. This voltage is converted by R
TX
TX
RX
RX
T
RX
T
RSN
Z
Z
is injected into the summing node
R
RX
T
·G
V
V
TX
V
V
V
Z
TR
RX
Z
TX
RX
RSN
Z
RX
RSN
2-4S
B
Z
T
T
Z
V
V
RX
G
Z
RSN
T
) + 2R
L
RX
TX
T
2 4
the expression for G
0
G
G
(
G
2 4
B
E
2
S
2 4
2 4
G
L
a current proportional
G
F
2 4
(
S
2 4
+ 2R
1
S
Z
S
0
L
(
Z
Z
(
S
)
S
(
L
L
RX
Z
Z
P
L
2
(
L
is chosen to
R
is returned to
Z
B
L
L
2
L
F
= 0:
= 0:
can be
R
2
2
F
R
R
2
F
2
R
F
4-4
2
R
F
R
TX
4-2
P
,
P
2
)
2
R
to a
2
)
R
R
P
P
P
)
)
)