U4311B-FS Datasheet, PDF (9/13 Pages) ATMEL Corporation – Low-Current Superhet Remote Control Receiver

U4311B-FS
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 lowpass 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
–30
–40
0.01
0.1
1
10
100
95 10334
Frequency ( kHz )
Figure 22. Frequency response of 2-kHz Bessel
lowpass data filter
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
lowpass characteristic, a 3-dB cut-off frequency of 2 kHz
and an additional highpass characteristic for suppressing
dc and low-frequency ac components. Simulation of time
domain and frequency response can be seen 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 highpass cut-off
frequency. in order to 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 highpass cut-off frequency is too low. For this reason,
some burst bits must be transmitted before the real data
transmission starts. On the other hand, if the cut-off fre-
quency is too high, roof shaping of the rectangle pulses at
the operational amplifier output might cause problems.
The lowpass 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
enables optimized transmission range. For designing
other filter parameters,please refer to filter design hand-
books/ programs or request Atmel Wireless &
Microcontrollers for support.
Rev. A3, 28-Sep-00
9 (13)