PBL38772/1 데이터 시트보기 (PDF) - Ericsson
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PBL38772/1 Datasheet PDF : 24 Pages
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PBL 387 72
+
TIP
ZL
VTR
ZTR
+
EL
-
-
RING
TIPX
RF
HP
RF
RINGX
RHP
+
-G2-4S
IL
VTX
IL
ZT
+
VTX
-
PBL 387 72
ZRX
I L /αRSN
RSN
+
VRX
-
Figure 9. Simplified AC model of PBL 387 72/1.
Transmission
General
A simplified ac model of the transmission circuit is shown in
figure 9. Circuit analysis yields:
VTR =
VTX
G2-4S
+ IL × 2RF
(1)
IL = VTX + VRX
(2)
αRSN ZT
ZRX
VTR = EL - IL × ZL
(3)
where:
VTX
VTR
EL
IL
RF
G2-4S
ZL
ZRX
ZT
VRX
αRSN
RHP
is the ground referenced ac voltage at the VTX terminal.
is the ac metallic voltage between tip and ring.
is the line open circuit ac metallic voltage.
is the ac metallic current.
is a line over voltage protection resistor.
is the SLIC two-wire to four-wire gain (transmit
direction) with a nominal value of 0.5.
is the total line impedance
controls four- to two-wire gain.
determines the SLIC TIPX to RINGX ac impedance for
signals at voice frequencies.
is the analog ground referenced receive signal.
is the receive summing node current to metallic loop
current gain. αRSN = 400
internal resistor, approx. 400 kΩ
Two-Wire Impedance
To calculate ZTR, the impedance presented to the
two-wire line by the SLIC including the line protection
resistors RF , let VRX =0.
From (1) and (2):
ZTR
=
αRSN
ZT
× G2-4S
+ 2RF
(4)
Thus with ZTR, G2-4S, αRSN and RF known:
ZT = αRSN × G2-4S × (ZTR - 2RF)
(5)
Two-Wire to Four-Wire Gain
From (1) and (2) with VRX =0:
G2-4
=
VTX
VTR
=
ZT/α RSN
α
RSN
ZT
× G2-4S
+2RF
(6)
Four-Wire to Two-Wire Gain
From (1), (2) and (3) with EL = 0:
G4-2 =
VTR
VRX
=-
ZT × 1 ×
ZRX G2-4S
ZL
ZT
αRSN × G2-4S
(7)
+ ZL + 2RF
For applications where
ZT
αRSN ×
G2-4S
+2RF
=
ZL
the expression for G4-2 simplifies to:
G4-2
=
-
ZT
ZRX
×
2
1
× G2-4S
(8)
12
EN/LZT 146 136 R1A © Ericsson Microelectronics, December 2001
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