IR receiver output noise when there is no signal input

Y.SAI SARASWATHI said:

which type of antenna is that?is your circuit related to any communication system?

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no, it is not related to any communication system, but when i generate a 38khz modulated signal using a signal generator(a modulated current pulse to simulate the photo signal), even the connector of signal generator is not connected to the input pin of the receiver IC, the IC can still output the correct signal (demodulated IR signal) responding to the signal that the generator generated, so the input pin behaves an antenna.

You tell us about 200-300µS pulses, is this their duration(at what frequency) or their PRF (how wide are they), In your circuit diagram you show a .22 MF capacitor - is this a typo, it should be at least 10 MF. If you circuit can demodulate a signal from a signal generator that is not connected, you really must attend to the screening of it and all its associated leads.
Frank

chuckey said:

You tell us about 200-300µS pulses, is this their duration(at what frequency) or their PRF (how wide are they), In your circuit diagram you show a .22 MF capacitor - is this a typo, it should be at least 10 MF. If you circuit can demodulate a signal from a signal generator that is not connected, you really must attend to the screening of it and all its associated leads.
Frank

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thank you first. 200-300us is the duration of the output pulse, but it is a demodulated signal, so i don't know the interference frequency when un-demodulated. the 0.22MF capacitor is the power filter cap, even i add it to 10MF or 100MF, the spurious pulses are still the same, besides, what do you mean by 'you really must attend to the screening of it and all its associated leads', do you mean the signal genarator or the IC? but how to make a good screening in my case? and screening means shielding? i tried to cover my IC use a metal box, but have no effect.
thanks.

you need to post your circuit and also respond to post #10 without your circuit everyone is only guessing.
Your problem is almost certainly either spurious IR (sunlight - striplight - laptop display etc) or bad circuit design/build.
There is no reason for poor IR reception using modern components - I would certainly consider
using the integrated recievers as suggested if I were you - it will save you time -

123jack said:

you need to post your circuit and also respond to post #10 without your circuit everyone is only guessing.
Your problem is almost certainly either spurious IR (sunlight - striplight - laptop display etc) or bad circuit design/build.
There is no reason for poor IR reception using modern components - I would certainly consider
using the integrated recievers as suggested if I were you - it will save you time -

Click to expand...

i have post my circuit in #15, about #10, i have explained for that, if i connect input to ground, then the circuit will saturate, then none signal will be recepted, and output is always high.
thanks.

lhlblue said:

no, it is not related to any communication system, but when i generate a 38khz modulated signal using a signal generator(a modulated current pulse to simulate the photo signal), even the connector of signal generator is not connected to the input pin of the receiver IC, the IC can still output the correct signal (demodulated IR signal) responding to the signal that the generator generated, so the input pin behaves an antenna.

Click to expand...

How can it respond correctly even though input is not given ,input terminal will not have characteristics of antenna wright?

Y.SAI SARASWATHI said:

How can it respond correctly even though input is not given ,input terminal will not have characteristics of antenna wright?

Click to expand...

but it is the ral thing i observerd in my circuit test. so, it may be caused by the coupling between the signal generator connector and the input connecting wire (which connects input pin and the diode). if i put the signal generator connector away from the chip, then the antenna effect disappeard. maybe the circuit gain is very very large, so even a very small interference in the input pin, an output responds. i need more ideas.
thanks.