gsm noise on tsop1738

[m3r]

hi
When the phone rings alongside the tsop1738 , there's a lot of noise in the output but there is no noise in normal mode.
How can I remove outgoing noise?
I used the datasheet circuit for driving tsop1738.

 

[betwixt]

Most of the noise will be RF pickup causing the biasing in the TSOP's internal amplifier to change and create a shift in it's output. You can try shielding it, you may have noticed that many IR receivers in commercial equipment are housed in metal cans with a small window for that very reason. You also try adding additional filtering DIRECTLY across the supply pins. A ceramic 1nF capacitor with legs as short as possible and as close as possible may help to reduce supply borne noise. Remember that at frequencies used by GSM equipment, even short wires act as receive antennas.

Brian.

 

[m3r]

Most of the noise will be RF pickup causing the biasing in the TSOP's internal amplifier to change and create a shift in it's output. You can try shielding it, you may have noticed that many IR receivers in commercial equipment are housed in metal cans with a small window for that very reason. You also try adding additional filtering DIRECTLY across the supply pins. A ceramic 1nF capacitor with legs as short as possible and as close as possible may help to reduce supply borne noise. Remember that at frequencies used by GSM equipment, even short wires act as receive antennas.

Brian.

thanks
I use vs1838 that has a metal body and is connected to the ground.


I put the 1nf capacitor on the power supply but did not change output

 

[betwixt]

OK, so that is already covered.
Next question: is it actually causing a problem or is it just noise you are observing. The reason I ask is because your measuring equipment (oscilloscope I presume) will have probes that inject RF from the GSM source.

The other thing you can try is to add a small ceramic capacitor directly from the TSOP output to it's ground pin. This time you should use a lower value, maybe 100pF so it doesn't distort the output waveform. If you do the same at the other end of the track/wire, across the input of the following circuit it might also help.

Brian.

 

[KlausST]

Hi,

How do you measure it.
Mybe you just see noise couling on the scope probe.
You easily can verify this by connecting both probe_signal and probe_gnd to the PCB_GND.

Klaus

 

[m3r]

OK, so that is already covered.
Next question: is it actually causing a problem or is it just noise you are observing. The reason I ask is because your measuring equipment (oscilloscope I presume) will have probes that inject RF from the GSM source.

The other thing you can try is to add a small ceramic capacitor directly from the TSOP output to it's ground pin. This time you should use a lower value, maybe 100pF so it doesn't distort the output waveform. If you do the same at the other end of the track/wire, across the input of the following circuit it might also help.

Brian.

no measuring equipment connect to output pin or other pin!!
i used 80pf on output pin but GSM noise still exist

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Hi,

How do you measure it.
Mybe you just see noise couling on the scope probe.
You easily can verify this by connecting both probe_signal and probe_gnd to the PCB_GND.

Klaus

hi
connect output pin to external interrupt micro pin.

 

[FvM]

i used 80pf on output pin but GSM noise still exist

Show the layout of power supply bypass and 80 pF capacitor. Without respective low inductance wiring, the capacitors are useless at GSM frequency.