pbl386141 ETC-unknow, pbl386141 Datasheet - Page 11

• Manufacturer Part Number: pbl386141
• Description: Pbl 386 14/1 Subscriber Line Interface Circuit
• Manufacturer: ETC-unknow

Hybrid Function
The hybrid function can easily be imple-
mented utilizing the uncommitted amplifier
in conventional CODEC/filter combinations.
Please, refer to figure 10. Via impedance
Z
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 proportional to V
is returned to V
by R
summing node. These currents can be
made to cancel by letting:
cludes the required phase shift and thus
the balance network Z
from:
output load of the VTX terminal is (R
in Figure 14) > 20 k .
yields a balance network containing an
inductor, an alternate method is recom-
mended.
Figure 10. Hybrid function.
B
V
R
The four-wire to four-wire gain, G
Z
- R
When choosing R
If calculation of the Z
a current proportional to V
TX
B
TX
= - R
TX
TX
+
•
to a current flowing into the same
V
Z
Z
Z
RX
B
TX
RX
T
= 0 (E
•
•
V
V
TX
RX
TX
. This voltage is converted
RSN
Z
=
L
T
= 0)
G
TX
- G
2-4S
, make sure the
386 14/1
B
2-4S
can be calculated
•
B
( Z
formula above
PBL
•
( Z
L
RX
+ 2R
L
is injected
+ 2R
F
)
VTX
RSN
4-4
TX
F
, in-
)
//R
RX
T
Z
used together with programmable CODEC/
filters. The programmable CODEC/filter
allows for system controller adjustment of
hybrid balance to accommodate different
line impedances without change of hard-
ware. In addition, the transmit and receive
gain may be adjusted. Please, refer to the
programmable CODEC/filter data sheets
for design information.
Longitudinal Impedance
A feed back loop counteracts longitudinal
voltages at the two-wire port by injecting
longitudinal currents in opposing phase.
pear as longitudinal currents and the TIPX
and RINGX terminals will experience very
small longitudinal voltage excursions, leav-
ing metallic voltages well within the SLIC
common mode range.
Z
longitudinal disturbances. It should be not-
ed that longitudinal currents may exceed
the dc loop current without disturbing the vf
transmission.
Capacitors C
If RFI filtering is needed, the capacitors
designated C
nected between TIPX and ground as well
as between RINGX and ground, may be
mounted.
junction with suitable series impedances
T
LoT
The PBL 386 14/1 SLIC may also be
Thus longitudinal disturbances will ap-
The SLIC longitudinal impedance per wire,
C
TC
and Z
R
Z
and C
TX
RX
LoR
RC
, appears as typically 20
Z
TC
TC
B
work as RFI filters in con-
and C
and C
RC
RC
in figure 13, con-
Combination
CODEC/Filter
to
(i.e. resistances, inductances). Resistors
R
inductances can be added to form a sec-
ond order filter. Current-compensated in-
ductors are suitable since they suppress
common-mode signals with minimum influ-
ence on return loss. Recommended values
for C
values impose smaller degradation on re-
turn loss and longitudinal balance, but also
attenuate radio frequencies to a smaller
extent. The influence on the impedance
loop must also be taken into consideration
when programming the CODEC. C
C
1/(
impedance of 1/(2
ground impedance of 1/(2
AC - DC Separation Capacitor, C
The high pass filter capacitor connected
between terminals HP and RINGX p r o -
vides the separation of the ac and dc
signals. C
cy response break point of the ac loop in the
SLIC. Refer to table 1 for recommended
value of C
position the low end frequency response
3dB break point of the ac loop at 13 Hz (f
according to f
R
F1
RC
HP
Example: A C
•
and R
contribute to a metallic impedance of
= 180 k .
f
•
TC
C
V
V
TC
RX
T
and C
) = 1/(
HP
F2
HP
.
positions the low end frequen-
may be sufficient, but series
RC
3dB
HP
•
f
= 1/(2
•
• •
are below 1 nF. Lower
C
value of 68 nF will
RC
PBL 386 14/1
f
•
C
), a TIPX to ground
TC
• •
) and a RINGX to
• •
R
HP
f
•
C
•
C
RC
HP
).
) where
HP
TC
and
3dB
11
)