PBL38665-2 查看數據表（PDF） - Ericsson
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PBL38665-2 Datasheet PDF : 18 Pages
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PBL 386 65/2
Preliminary
+
TIP
ZL
VTR
ZTR
-
EL
-
+
RING
TIPX
RF
RF
RINGX
RHP
+
-G2-4S
IL
VTX
IL
ZT
+
VTX
-
PBL 386 65/2
ZRX
I L /αRSN
RSN
+
VRX
-
Figure 9. Simplified ac transmission circuit.
Functional Description and Applications
Information Transmission
General
A simplified ac model of the transmission
circuits is shown in figure 9. Circuit analysis
yields:
VTR =
VTX
G2-4S
- IL • 2RF
(1)
α VTX + VRX = IL
ZT ZRX
RSN
(2)
VTR = IL • ZL - EL
(3)
where:
VTX is a ground referenced version
of the ac metallic voltage
between the TIPX and RINGX
terminals.
VTR is the ac metallic voltage
between tip and ring.
EL is the line open circuit ac metallic
voltage.
IL is the ac metallic current.
RF is a fuse resistor.
G2-4S is the SLIC two-wire to four-
wire gain (transmit direction) with
a nominal value of -0.5.
(Phase shift 180°)
ZL is the line impedance.
ZT determines the SLIC TIPX to
RINGX impedance for signal in
the 0 - 20kHz frequency range.
ZRX controls four- to two-wire gain.
VRX is the analogue ground referenced
receive signal.
αRSN is the receive summing node
current to metallic loop current
gain. The nominal value of
αRSN =400
Two-Wire Impedance
To calculate ZTR, the impedance presented
to the two-wire line by the SLIC including
the fuse resistor RF, let VRX = 0.
From (1) and (2):
α ZTR =
ZT
G RSN • 2-4S
- 2RF
Thus with ZTR, G2-4S, αRSN, and RF known:
α ZT = RSN • G2-4S • (2RF - |ZTR|)
Two-Wire to Four-Wire Gain
From (1) and (2) with VRX = 0:
G2-4
=
VTX
VTR
=
ZT/αRSN
ZT
αRSN • G2-4S
- 2RF
Four-Wire to Two-Wire Gain
From (1), (2) and (3) with EL = 0:
G4-2
=
VTR
VRX
=
ZT •
ZRX
ZL
ZT
αRSN
-
G2-4S
•
(
ZL
+
2RF)
In applications where
2RF - α ZT/( RSN • G2-4S) is chosen to be
equal to ZL, the expression for G4-2 simpli-
fies to:
G4-2 = -
ZT
ZRX
•
1
2 • G2-4S
Four-Wire to Four-Wire Gain
From (1), (2) and (3) with EL = 0:
G4-4
=
VTX
VRX
=
ZZTRX•
G2-4S • ( ZL + 2RF)
ZT
αRSN
-
G2-4S
•
(
ZL
+
2RF)
10
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