U4311B Datasheet, PDF (9/14 Pages) TEMIC Semiconductors – Low-current Superhet Remote Control Receiver

TELEFUNKEN Semiconductors
U4311B
0.005
1400
0.004
0.003
0.002
0.001
0
15
95 10333
Output
1300
1200
1100
1000
Input
20
25
30
35
Time ( ms )
Figure 20. Time domain response of 2 kHz Bessel low pass data filter
900
800
40
100
100 dBmV
80
70 dBmV
60
40
50 dBmV
20
30 dBmV
0
6
95 10332
8
10
12
14
16
IF frequency ( MHz )
Figure 21. IF-frequency response
0
–10
–20
Data Recovering Filter
The test circuit in figures 23 and 26 includes an example
of a data recovering filter realized with the components
R₁, R₂, C₁, C₂, C₃. It is of a second order Bessel type with
low pass characteristic, a 3 dB cut-off frequency of 2 kHz
and an additional high pass characteristic for suppressing
dc and low frequency ac components. Simulation of time
domain and frequency response is drawn in figures 20 and
22. This filter gives a typical application of a 1 kBaud
Manchester code amplitude modulated transmission.
The capacitor C₂ is responsible for the high pass cut-off
frequency. For a correct pulse response this high pass cut-
off frequency should be as low as possible. Figure 20
shows the transient response and the influence of the dc
component. The first pulses might be wrong if the high
pass cut-off frequency is too low. For this reason some
burst bits must be transmitted before the real data trans-
mission starts. On the other hand, if the cut-off frequency
is too high, you might get in trouble with roof shaping of
the rectangle pulses at the operational amplifier output.
–30
–40
0.01
0.1
1
10
100
95 10334
Frequency ( kHz )
Figure 22. Frequency response of 2 kHz Bessel
low pass data filter
The low pass cut-off frequency and the maximum trans-
impedance V_out/I_in are distinguished by the further
external elements. Careful design of the data filter gives
optimized transmission range. For designing other filter
parameters look for filter design handbooks or programs
or request TEMIC TELEFUNKEN microelectronic
GmbH for support. Some proposals can be found in the
application notes ANT012, ANT013 and ANT015.
Rev. A1: 23.06.1995
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