PBL 386 30/2
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 recom-
mended. Contact Ericsson Microelectron-
ics for assistance.
The PBL 386 30/2 SLIC may also be
usedtogetherwithprogrammableCODEC/
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.
R
FB
R
TX
VTX
V
T
PBL
386 30/2
Z
Z
Combination
CODEC/Filter
V
T
B
Z
RX
RX
RSN
Figure 9. Hybrid function.
Longitudinal Impedance
AC - DC Separation Capacitor, CHP
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
smalllongitudinalvoltageexcursions,leav-
ing metallic voltages well within the SLIC
common mode range.
The SLIC longitudinal impedance per
wire, ZLoT and ZLoR, appears as typically
20Ω to longitudinal disturbances. It should
be noted that longitudinal currents may
exceed the dc loop current without disturb-
ing the vf transmission.
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 CLP also influences
the transversal to longitudinal balance in
the SLIC. Table 1 suggests suitable values
on CLP 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 CLP.
The high pass filter capacitor connected
between terminals HP and TIPX provides
the separation of the ac signal from the dc
part. CHP positions the low end frequency
response break point of the ac loop in the
SLIC. Refer to table 1 for recommended
values of CHP.
Example: A CHP value of 150 nF will posi-
tion the low end frequency response 3dB
break point of the ac loop at 1,8 Hz (f3dB
according to f3dB = 1/(2 π RHP CHP) where
HP = 600 kΩ.
)
R
RFeed
RSG
CLP
T-L bal. CHP
@200Hz
High-Pass Transmit Filter
The capacitor CTX in figure 11 connected
between the VTX output and the CODEC/
filter forms, together with RTX 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.
Capacitors CTC and CRC
[Ω]
[kΩ]
[nF]
[dB]
[nF]
The capacitors designated CTC and CRC
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 CTC and CRC
is 2200 pF. Higher capacitance values
may be used, but care must be taken to
prevent degradation of either longitudinal
balance or return loss. CTC and CRC
contribute to a metallic impedance of
1/(π f CTC) = 1/(π f CRC), a TIPX to ground
impedance of 1/(2 π f CTC) and a RINGX
to ground impedance of 1/(2 π f CRC).
2 50
0
150
100
47
-46
-46
-43
-36
47
2 200
2 400
2 800
60,4
147
301
150
150
150
22
Table 1. RSG , CLP and CHP values for differ-
ent feeding characteristics.
Capacitor CLP
ThecapacitorCLP,whichconnectsbetween
the terminals CLP and VBAT, positions
together with the resistive loop feed resis-
tor RSG (see section Battery Feed), the high
end frequency break point of the low pass
filter in the dc loop in the SLIC. CLP together
withRSG, CHP andZT (seesectionTwo-Wire
11
ERICSSON [ ERICSSON ]
