Photo diode circuit not receiving signals continuously?

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karthickb3e

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Hi all,

I assembled the photodiode op-amp circuit as shown in the below ......



my emitted signal is 4khz.. The circuit not receives the emitted signal continuously..
i shown the my received signal in the following images...







there is some gap between the emitted signal... please help what is the problem how to solve this????
 

You have biased the opamp (non-inverting input) at zero volts and the most negative supply on the opamp is zero volts. So, the output cannot go below zero. I am not sure what you were expecting. Try biasing the opamp non-inverting input above zero volts.

Keith.
 

Maby yo try adding dc source on noninverting side input of 3.3v/2.
 

Another basic problem is operating the photo diode AC coupled - which restrict it to photo element mode, although zero biased current source would be much more sensitive. In addition, the AC current sourced to the amplifier will be half-wave rectified according to the chosen OP bias, as already explained. By removing the capacitor, the waveform should be shown completely, but with a DC bias according to the constant light intensity.

If you want to place an AC-coupling before the amplifier, the photo diode should have a DC bias as well.
 

thanks to all for the reply.....

1.) i try biasing to the non inverting terminal... it works ,,, but the pulse not as like the emitted pulse.... i need the exact pulse( zero to high) .. i change the C1 value to 100nF..to get exact pulse................... is it affect its response??? please clarify ...!


2.) and also which of the following configuration will work with high speed(response) and more efficient and less noise and why????
Fig 1:


Fig 2:


Fig 3:
 

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i think figure two is good enough.
because it has negative biasing.so it can conduct very fast and respond quickly.
but i dont know about the noise.
the noise may come..!!!!!!!!!!!!!
 

Unfortunately, all four schematics are ignoring the basic requirements of photo diode operation. They only differ by subsidiary details. :sad:

The circuits will give some response, but are slow and insensitive. Their AC gain will strongly depend on DC light level.

Please refer to the simple input stage circuit linked by dselec as a starting point or provide an equivalent DC path for the photo current.
 

i cant get it with the diagram , you said. i'm using AC signal. if i give that signal to the circuit you mention/ refer only DC output came. not AC output.
i need to place capacitor in front of the amplifier right....?
and also if i connect non inverting terminal to ground means , the output signal is not proper . as i shown in the first image...
what can i do for this...?
 

As previously said, the problem is with photo diode operation, not the amplifier.
 


Some cells need a bias and or parallel resistor to close the cell circuit so just add 10k resistor in series like the link shows and see what happens ,remember it is a light cell you need to let the electrons from the cell pass thru resistor and back to cell its really a dc cell that its dc value changes as light changes so all dc sources need a resistor and u will get your signal on the resistor and the changes will pass thru cap as ac.
https://www.google.co.il/imgres?q=b...03&vpy=325&hovh=185&hovw=272&biw=1280&bih=820
 
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