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photodiode amplifiers

ramya reddy
Prodigy 10 points


hello ,

First of all i need to design a detector using a photodiode for laser pulse radiation .  I  laser with pulse radiation of 1microseconds , which am able to to detect through a resistor of 1 kohm parallel to the photodiode . now the problem  is when i reverse bias the photodiode with - voltage of 10v to cathode i can see the pulse width of 1microsecond but it even shows when I  cover the laser , very strange results , am not at all sure whats happening . any information will be helpful 

  • 0
    TI__Guru 62356 points

    Hello Ramya,

    From what you say, I would guess that the laser "pulse" is coming in through the power supply. My guess is that the laser causes the supply to "droop" when the laser is on - or - the high-current pulses are capacitively coupling into your circuit from unshielded conductors.

    Are the "covered" pulses the same amplitude??

    Are you deriving any reference voltages off the same supply that sources the laser current?

    Is your receiver circuit unshielded? Is it close to the laser diode?

    If your supply is poorly regulated and/or bypassed, these "droops" on the supply can couple in through other parts of the circuit. Try placing a large bypass capacitor on the diode end of the bias resistor to ground. This should attenuate any supply noise and also eliminates resistor noise (using bias resistor and capacitor as a "R-C" filter).

    Look at anything that the laser circuit and the receiver share. The grounds for the diode circuit and the receiver should be separate.

    Is this a semiconductor or tube laser?

    How are you "covering" the laser? What wavelength is the laser? IR? UV? Red? Green? Some materials can be opaque at certain wavelengths (particularly IR).

    Regards,