PBL 386 20/2
For applications where
ZT/(αRSN·G2-4S) + 2RF +2RP is chosen to be
equaltoZL theexpressionforG4-2 simplifies
to:
TIPX
TIP
I
+
L
R
R
F
P
Z
L
Z
+
TR
VTX
V
TR
RHP
G
+
2-4S
ZT
1
-
+
E
-
G4−2 = −
L
ZRX 2G2− 4S
V
TX
R
R
F
P
-
I
L
RING
RINGX
-
Z
T
Four-Wire to Four-Wire Gain
From (1), (2) and (3) with EL = 0:
Z
RX
RSN
+
V
RX
I
/α
RSN
VTX
L
-
G4−4
=
=
PBL 386 20/2
VRX
ZT
−
G2− 4S (ZL + 2RF + 2RP)
+ G2−4S (ZL + 2RF + 2RP )
ZT
αRSN
ZRX
Figure 9. Simplified ac transmission circuit.
αRSN is the receive summing node current
Functional Description
andApplicationsInforma-
tion
to metallic loop current gain = 200.
Hybrid Function
Note that the SLICs two-wire to four-wire
gain, G2-4S, is user programmable between
two fix values. Refer to the datasheets for
The hybrid function can easily be
implemented utilizing the uncommitted
amplifier in conventional CODEC/filter
combinations. Please, refer to figure 10.
Via impedance ZB a current proportional to
VRX isinjectedintothesummingnodeofthe
combination CODEC/filter amplifier. As
can be seen from the expression for the
four-wiretofour-wiregainavoltagepropor-
tional to VRX is returned to VTX. This voltage
is converted by RTX to a current flowing into
the same summing node. These currents
can be made to cancel by letting:
values on G2-4S
.
Transmission
General
Two-Wire Impedance
A simplified ac model of the transmission
circuitsisshowninfigure9. Circuitanalysis
yields:
To calculate ZTR, the impedance presented
to the two-wire line by the SLIC including
the fuse and protection resistors RF and RP
let:
VTX
VTR
=
+ IL (2RF + 2RP )
(1)
VRX = 0.
G2− 4S
From (1) and (2):
VTX VRX
IL
+
=
(2)
(3)
ZT
ZRX
αRSN
VTX VRX
ZT
+
= 0(EL = 0)
ZTR
=
+ 2RF + 2RP
RTX
ZB
αRSN G2− 4S
VTR = EL - IL · ZL
where:
Thefour-wiretofour-wiregain,G4-4,includes
the required phase shift and thus the
balancenetworkZB canbecalculatedfrom:
Thus with ZTR, αRSN, G2-4S, RP and RF known:
ZT = αRSN G2− 4S (ZTR − 2RF − 2RP )
VTX is a ground referenced version of the
acmetallicvoltagebetweentheTIPX
and RINGX terminals.
G2-4S is the programmable SLIC two-wire
to four-wire gain (transmit direction).
See note below.
V
RX
Z
= −R
=
B
TX
V
TX
Two-Wire to Four-Wire Gain
Z
T
From (1) and (2) with VRX = 0:
+ G
(Z + 2R + 2R )
2−4S L F P
Z
α
RX
RSN
G
R
TX
Z
(Z + 2R + 2R )
L F P
T
2−4S
VTX
VTR
ZT / αRSN
G2− 4
=
=
VTR is the ac metallic voltage between tip
and ring.
ZT
αRSN G2− 4S
+ 2RF + 2RP
When choosing RTX, make sure the output
load of the VTX terminal is >20 kΩ.
EL
is the line open circuit ac metallic
voltage.
If calculation of the ZB formula above
yields a balance network containing an
inductor, an alternate method is re-
commended. Contact Ericsson Compo-
nents for assistance.
The PBL 386 20/2 SLIC may also be
usedtogetherwithprogrammableCODEC/
filters. The programmable CODEC/filter
allows for system controller adjustment of
Four-Wire to Two-Wire Gain
IL
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.
From (1), (2) and (3) with EL = 0:
RF
RP
ZL
ZT
VTR
G4−2
=
=
VRX
ZT
−
ZL
ZT
αRSN
ZRX
+ G2− 4S (ZL + 2RF + 2RP)
ZRX controls four- to two-wire gain.
VRX is the analog ground referenced
receive signal.
10
ERICSSON [ ERICSSON ]
