MLX71120

300 to 930MHz

FSK/FM/ASK Receiver

39010 71120

Page 13 of 31

Data Sheet

Rev. 008

Jun/12

1.15 Data Output and Noise Cancellation Filter

The data output pin DTAO delivers the demodulated data signal which can be further processed by a noise

cancellation filter (NCF). The NCF can be disabled if pin CINT is connected to ground. In this case the

multiplexer (MUX) connects the receiver output DTAO directly to the data slicer output.

Fig. 8:

Data output and noise filter

RZ

NRZ

R

R

t

6

6

min

6

-

10

5

.

7

10

15

10

15

CF3

−

−

⋅

=

⋅

=

⋅

⋅

=

The NCF can also operate as a muting circuit.

So if the RF input signal is below sensitivity level (or if no

RF signal is applied) then the data output will go to a constant DC level (either HIGH or LOW). This can be

achieved by setting the bandwidth of the preceding data filter (sec 1.13) about 10 times higher than the

bandwidth of the NCF. Further the data filter cutoff frequency must be higher than the data rate, so the noise

pulses are shorter than the shortest data pulse. Otherwise, the NCF will not be able to distinguish between

noise and data pulses.

Having the NCF activated is a good means for reducing the computing power of the microcontroller that fol-

lows the receiver IC for further data processing.

In contrast to conventional muting (or squelch) circuits, this topology does not need the RSSI signal for level

indication. The filtering process is done by means of an analogue integrator. The cut-off frequency of the

the maximum data rate. Below table provides some recommendations..

During receiver start-up a sequencer checks if pin CINT is connected to a capacitor or to ground. The maxi-

noise cancellation filter is activated.

0.6

1.2

12

1.2

2.4

6.8

1.6

3.2

4.7

2.4

4.8

3.3

3.3

6.6

2.2

4.8

9.6

1.5

6.0

12

1.2

In shutdown mode pin DTAO is set to Hi-Z state.

CF3

data slicer

output

CINT

NCF

noise cancellation filter

MUX

DTAO