Functional Description
2.5.3
S/T Interface Circuitry
2.5.3.1 S/T Interface Pre-Filter (PEB 2085 only)
In some applications it may be desirable to improve the signal-to-noise ratio of the received
S/T interface signal by filtering out undesirable frequency (usually high frequency)
components. This may be realized by an external pre-filter.
To simplify the implementation of this filter, an operational amplifier is integrated in the
PEB 2085, as shown in figure 46. By connecting an RC network between input SR2 and the
extra pin UFI an active RC filter of desired order can be realized (one example is shown in
figure 46).
RC Network Example
UFI
C1
UF1
SR2
RC
Network
_
+
A
SR2
SR1
R1
R2
A
C2
VSSA
10 nF
ITS02360
VSSA
ITS02359
Figure 46
Prefilter Connections and Example of 2nd Order RC Network
Following component values are recommended to give a 500 kHz cutoff, and 600 ns
(± 170 ns) propagation delay time:
R
C
C
1
= R
=
=
2
= 10 kΩ
13 pF
22.5 pF
1
2
Delay Compensation (PEB 2085 and PEB 2086)
To compensate for the extra delay introduced into the received signal by a filter, the sampling
of the receive signal can be delayed by programming bits TEM and PFS in the ADF1 register
as shown in table 5. Note that setting TEM to "1" and PFS to "0" has the effect of completely
disabling layer-1 functions, for test purposes (see section 2.7).
Semiconductor Group
84
INFINEON [ Infineon ]
