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参数资料
| 型号： | PBL38630-2 |
| 厂商： | ERICSSON |
| 英文描述： | Subscriber Line Interface Circuit |
| 中文描述： | 用户线接口电路 |
| 文件页数： | 11/16页 |
| 文件大小： | 134K |
| 代理商： | PBL38630-2 |
PBL 386 30/2
11
When choosing R
, make sure the output
load of the VTX terminal is >20 k
.
If calculation of the Z
formula above
yields a balance network containing an
inductor, an alternate method is recom-
mended. Contact Ericsson Microelectron-
ics for assistance.
The PBL 386 30/2 SLIC may also be
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.
Thus longitudinal disturbances will ap-
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.
The SLIC longitudinal impedance per
wire, Z
and Z
, appears as typically
20
to longitudinal disturbances. It should
be noted that longitudinal currents may
exceed the dc loop current without disturb-
ing the vf transmission.
Capacitors C
TC
and C
RC
The capacitors designated C
and C
RC
in figure 11, connected between TIPX
and ground as well as between RINGX
and ground, can be used for RFI filtering.
The recommended value for C
and C
RC
is 2200 pF. Higher capacitance values
may be used, but care must be taken to
prevent degradation of either longitudinal
balance or return loss. C
and C
contribute to a metallic impedance of
1/(
π
f
C
) = 1/(
π
f
C
RC
), a TIPX to ground
impedance of 1/(2
π
f
C
) and a RINGX
to ground impedance of 1/(2
π
f
C
RC
).
Figure 9. Hybrid function.
AC - DC Separation Capacitor, C
HP
The high pass filter capacitor connected
between terminals HP and TIPX provides
the separation of the ac signal from the dc
part. C
positions the low end frequency
response break point of the ac loop in the
SLIC. Refer to table 1 for recommended
values of C
.
Example: A C
value of 150 nF will posi-
tion the low end frequency response 3dB
break point of the ac loop at 1,8 Hz (f
)
according to f
3dB
= 1/(2
π
R
HP
C
HP
) where
R
HP
= 600 k
.
High-Pass Transmit Filter
The capacitor C
in figure 11 connected
between the VTX output and the CODEC/
filter forms, together with R
and/or the
input impedance of a programmable
CODEC/filter, a high-pass RC filter. It is
recommended to position the 3 dB break
point of this filter between 30 and 80 Hz to
get a faster response for the dc steps that
may occur at DTMF signalling.
Capacitor C
LP
The capacitor C
, which connects between
the terminals CLP and VBAT, positions
together with the resistive loop feed resis-
tor R
(see section Battery Feed), the high
end frequency break point of the low pass
filter in the dc loop in the SLIC. C
together
with R
SG
, C
HP
and Z
T
(see section Two-Wire
Impedance) forms the total two wire output
impedance of the SLIC. The choise of
these programmable components have an
influence on the power supply rejection
ratio (PSRR) from VBAT to the two wire
side at sub-audio frequencies. At these
frequencies capacitor C
also influences
the transversal to longitudinal balance in
the SLIC. Table 1 suggests suitable values
on C
for different feeding characteristics.
Typical values of the transversal to longitu-
dinal balance (T-L bal.) at 200Hz is given in
table 1 for the chosen values on C
LP
.
R
Feed
R
SG
C
LP
T-L bal. C
HP
@200Hz
[dB]
-46
-46
-43
-36
[
]
2
50
2
200
2
400
2
800
[k
]
0
60,4
147
301
[nF]
150
100
47
22
[nF]
47
150
150
150
Table 1. R
, C
and C
values for differ-
ent feeding characteristics.
V
T
Combination
CODEC/Filter
R
TX
R
FB
Z
B
Z
RX
Z
T
VTX
RSN
V
RX
PBL
386 30/2
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