TELEFUNKEN Semiconductors

U4313B

Rev. A1: 23.06.1995

9 (14)

15

20

25

30

35

0

0.001

0.002

0.003

0.004

0.005

Time ( ms )

40

95 10333

800

900

1000

1100

1200

1400

1300

Output

Input

Figure 20. Time domain response of 2 kHz Bessel low pass data filter

6

8

10

12

14

0

20

40

60

80

100

IF frequency ( MHz )

16

95 10332

100 dB

mV

70 dB

mV

50 dB

mV

30 dB

mV

Figure 21. IF-frequency response

0.01

0.1

1

10

–40

–20

–10

0

Frequency ( kHz )

100

95 10334

–30

Figure 22. Frequency response of 2 kHz Bessel

low pass 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

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.

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.

The low pass cut-off frequency and the maximum trans-

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.