IR receiver output noise when there is no signal input

[lhlblue]

i use an IR preamplifier IC(including I-V converter, preamplifier, AGC amplifier, bandpass filter, demodulator, shaper. etc) and a PIN diode to build an IR receiver. but when i power up, there are some spurious pulses at the OUT pin (NO IR signal present), and the width of the spurious pulse is about 200us~300us, very strange.
does anyone meet this problem before?

i doubt the spurious pulses come from power noise, so i add a 100ohm resistor and a 1uF capacitor to filter the powe noise, but it doesnot work. or it comes from the ground noise, but how to deal with the ground noise?

in the IR preamplifier datasheet, it said that, the connection between diode and INPUT pin should be as short as possible and carefully be shielded. what is the meaning of 'carefully be shielded'? how to shield it well for me?

the width of the spurious pulse is about 200us~300us, so maybe it obeys some rule, or it may come from some fixed reason. but i don't know what it is.

so, can anyone give me some related suggestions? thanks.

 

[Y.SAI SARASWATHI]

As you are dealing with ic it is very sensitive to external operating temperature and noise(it should not be beyond the value as specified in data sheet)this might be a reason.
carefully be shielded implies that interconnect wire should be insulated(metal contact taken out from the insulated wire should not be exposed to external environment)

 

[lhlblue]

As you are dealing with ic it is very sensitive to external operating temperature and noise(it should not be beyond the value as specified in data sheet)this might be a reason.
carefully be shielded implies that interconnect wire should be insulated(metal contact taken out from the insulated wire should not be exposed to external environment)

thanks.
i have checked for my circuit, the interconnect wire is insulated, and the tempreture has little effect on my receiver noise, the spurious pulse.
so, any other reasons? such as, ground shielding. how to make a good ground shielding? or EMI interference?

 

[ard]

Why reinvent the wheel? Why dont you use a simple 3 pin tsop ir module?

 

[lhlblue]

Why reinvent the wheel? Why dont you use a simple 3 pin tsop ir module?

i need two diodes to detect in different direction, but tsop has only one diode inside.
any other ideas?

what caused the spurious pulses at OUT pin?

besides, i used tsop753xx in another project, but it has spurious pulse also when there is no input IR signal. i don't know why.

 

[ard]

The tsop has a fairly wide angle of response. Plus, you could use 2 in parallel, as their outputs are internally pulled high with a high resistor.

The tsops do need a 100 ohm resistor in series with the supply, and a 10uf across its vcc a.d ground. That should take care of the spurious outputs.

 

[lhlblue]

The tsop has a fairly wide angle of response. Plus, you could use 2 in parallel, as their outputs are internally pulled high with a high resistor.

The tsops do need a 100 ohm resistor in series with the supply, and a 10uf across its vcc a.d ground. That should take care of the spurious outputs.

as i said above, i used tsop753xx in another project, but it has spurious pulse also when there is no input IR signal, even i add a 100ohm+10uF filter between vcc and gnd.

and due to some special reason, i must use the discrete solution: a preamplifier IC plus two photodiodes (for two opposite direction). so, how to remove the spurious pulse when there is no IR signal input?
and what caused the spurious pulses at OUT pin? substrate coupling? EMI interference? or power noise?
i need more explanation.
thanks.

 

[crutschow]

The cause of the spurious pulses cannot be determined from your description. It could be from any number of things. You will have to track that down yourself by following the pulses through the circuit to see where they might originate.
Do you totally block the input of the IR sensor from all light?
Is there some possible nearby source of RF interference?
What is the frequency of the pulses?

 

[schmitt trigger]

The cause of the spurious pulses cannot be determined from your description. It could be from any number of things. You will have to track that down yourself by following the pulses through the circuit to see where they might originate.
Do you totally block the input of the IR sensor from all light?
Is there some possible nearby source of RF interference?
What is the frequency of the pulses?

Many, many years ago, before the integrated IR receivers were available, I distinctly remember that the IR receiver's circuitry were shielded inside a metal box (with openings for the IR light, of course).

Even when the very first "modules" came along, they had a small shield. Removing the shield (I did that) would cause all sorts of spurious response, most likely from RFI.

 

[ard]

The spurious signals might be caused by stray ir components in the ambient. To rule out this possibility, just ground the input and check the output.

 

[Y.SAI SARASWATHI]

thanks.
i have checked for my circuit, the interconnect wire is insulated, and the tempreture has little effect on my receiver noise, the spurious pulse.
so, any other reasons? such as, ground shielding. how to make a good ground shielding? or EMI interference?

Instead of leaving input terminal open try to short circuit it to ground and once again check the output.
(Is that spurious pulse is badly affecting your output even you have connected an input?)

 

[lhlblue]

The cause of the spurious pulses cannot be determined from your description. It could be from any number of things. You will have to track that down yourself by following the pulses through the circuit to see where they might originate.
Do you totally block the input of the IR sensor from all light?
Is there some possible nearby source of RF interference?
What is the frequency of the pulses?

the power system (220V power) to generate VCC may be a RF interference, but i must use it to generate the VCC of IR IC.

besides, the width of spurious pulse is about 200us~300us, but is a demodulated signal, i don't know the interference frequency, because it is inside the chip(not a pad or a port outside).

thanks.

- - - Updated - - -

Many, many years ago, before the integrated IR receivers were available, I distinctly remember that the IR receiver's circuitry were shielded inside a metal box (with openings for the IR light, of course).

Even when the very first "modules" came along, they had a small shield. Removing the shield (I did that) would cause all sorts of spurious response, most likely from RFI.

so, do you mean that the spurious pulses are due to RFI/EMI interference? but i have tried to shield it using a ion box, but it has no effect. how can i shield it well?

- - - Updated - - -

The spurious signals might be caused by stray ir components in the ambient. To rule out this possibility, just ground the input and check the output.

do you mean that, it is caused by the stray capacitor or inductor nearby? if i ground the input, the I-V opamp will saturate, and no IR signal will be received.

- - - Updated - - -

Instead of leaving input terminal open try to short circuit it to ground and once again check the output.
(Is that spurious pulse is badly affecting your output even you have connected an input?)

if i ground the input, the I-V opamp will saturate, and no IR signal will be received. but i tried to connect a pull down resistor (1M/100K/1K/100), but it has no abvious effect.
when i connect a photodiode in the input Pin, the spurious pulse is still the same as i didn't connect the photodiode. so the spurious may come from the IC inside or the ambient.

- - - Updated - - -

there is a 100khz oscillator inside the IR preamplifier IC, so can this oscillator cause the spurious pulse?

 

[lhlblue]

everyone, what is the cause of the spurious pulse? can it be power noise, RFI interference, substrate coupling, or others?
waiting for more advice.
thanks.

 

[Y.SAI SARASWATHI]

Can you post a snap shot of your complete circuit?

 

[lhlblue]

Can you post a snap shot of your complete circuit?

the circuit is just like the picture, the microcontroller is not connected, OUT is connected by a 5pF capacitor.
thanks.

 

[Y.SAI SARASWATHI]

Try to add a stray capacitance at the output terminal and check the output once again without giving input signal.

 

[lhlblue]

Try to add a stray capacitance at the output terminal and check the output once again without giving input signal.

i have tried that, when i add a stray cap from 1pF~1nF, the result is the same as i didn't add the stray cap.
any other ideas?

 

[lhlblue]

Try to add a stray capacitance at the output terminal and check the output once again without giving input signal.

can it be caused by the OUTPUT pad coupling?

 

[lhlblue]

i find it is related to RFI/EMI. that is, maybe there is one or more antenna in the board (input pin or power pin), but i don't know how to avoid the antenna effect.
i tried to shield it with a metal box, but have no effect at all.
i need more ideas here.
thanks all.

 

[Y.SAI SARASWATHI]

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