PBL38620/2SOT Просмотр технического описания (PDF) - Ericsson
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PBL38620/2SOT Datasheet PDF : 16 Pages
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PBL 386 20/2
+
TIP
ZL
VTR
ZTR
+
EL
-
-
RING
TIPX
RF RP
RF RP
RINGX
+
RHP
G 2-4S
-
IL
VTX
IL
ZT
+
VTX
-
ZRX
RSN
+
I L /αRSN
VRX
-
PBL 386 20/2
Figure 9. Simplified ac transmission circuit.
Functional Description
and Applications Informa-
tion
Transmission
αRSN is the receive summing node current
to metallic loop current gain = 200.
Note that the SLICs two-wire to four-wire
gain, G2-4S, is user programmable between
two fix values. Refer to the datasheets for
values on G2-4S.
General
A simplified ac model of the transmission
circuits is shown in figure 9. Circuit analysis
yields:
VTR
=
VTX
G2 − 4S
+ IL
⋅ (2RF
+ 2RP )
(1)
VTX + VRX = IL
ZT ZRX αRSN
(2)
VTR = EL - IL · ZL
(3)
where:
VTX is a ground referenced version of the
ac metallic voltage between the TIPX
and RINGX terminals.
G2-4S is the programmable SLIC two-wire
to four-wire gain (transmit direction).
See note below.
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.
RP is part of the SLIC protection.
ZL is the line impedance.
ZT determines the SLIC TIPX to RINGX
impedance at voice frequencies.
ZRX controls four- to two-wire gain.
VRX is the analog ground referenced
receive signal.
Two-Wire Impedance
To calculate ZTR, the impedance presented
to the two-wire line by the SLIC including
the fuse and protection resistors RF and RP
let:
VRX = 0.
From (1) and (2):
ZTR
=
ZT
αRSN ⋅ G 2− 4S
+
2RF
+
2RP
Thus with ZTR, αRSN, G2-4S, RP and RF known:
ZT = αRSN ⋅ G2− 4S ⋅ (Z TR − 2RF − 2RP )
Two-Wire to Four-Wire Gain
From (1) and (2) with VRX = 0:
G2− 4
=
VTX
VTR
=
ZT / αRSN
ZT
αRSN ⋅ G2 − 4S
+
2RF
+
2RP
Four-Wire to Two-Wire Gain
From (1), (2) and (3) with EL = 0:
G4 −2
=
VTR
VRX
=
−
ZT
ZRX
⋅
ZT
αRSN
ZL
+ G2 − 4S ⋅ ( ZL
+
2RF
+ 2RP)
For applications where
ZT/(αRSN·G2-4S) + 2RF + 2RP is chosen to be
equal to ZL the expression for G4-2 simplifies
to:
G4 −2
= − ZT
ZRX
⋅1
2G2 − 4S
Four-Wire to Four-Wire Gain
From (1), (2) and (3) with EL = 0:
G4 −4
=
VTX
VRX
=
− ZT
ZRX
⋅
G 2− 4S ⋅ ( ZL + 2RF + 2RP)
ZT
αRSN
+ G2 −4 S ⋅ ( ZL
+ 2RF
+
2RP )
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 ZB a current proportional to
VRX is injected into the summing node of the
combination CODEC/filter amplifier. As
can be seen from the expression for the
four-wire to four-wire gain a voltage propor-
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:
VTX
RTX
+
VRX
ZB
= 0(EL
= 0)
The four-wire to four-wire gain, G4-4, includes
the required phase shift and thus the
balance network ZB can be calculated from:
ZB
=
−RTX
⋅
VRX
VTX
=
R TX
⋅
ZRX
ZT
⋅
ZT
α RSN
+ G2 −4 S ⋅ (ZL
+
G2 −4 S ⋅ (ZL + 2RF
2RF + 2RP )
+ 2RP )
When choosing RTX, make sure the output
load of the VTX terminal is >20 kΩ.
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
used together with programmable CODEC/
filters. The programmable CODEC/filter
allows for system controller adjustment of
10
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