avalanche photo diode amplifier know how

Discussion in 'General Electronics Chat' started by donut, Dec 7, 2012.

  1. donut

    Thread Starter Member

    May 23, 2012
    Using a APD (Avalanche Photo Diode). See attached datasheet.

    The spec sheet provides pretty good insight into how the IC works but I still have a few questions that I need help with answering.

    1) What type of signal does this IC receive. Infra Red?

    2)The spec says that the output is in the form of differential voltage pulsed signals. What does this actually mean? Mirror images of the signal, Like a +1v and a-1V? Why create differential signals?

    3)The spec says that IC needs positive bias voltage? What does this actually mean? How do you create a bias voltage? Why does one have to generate bias voltage in the first place?

    Please advise.
  2. crutschow


    Mar 14, 2008
    1) The spectral response on the first page of the spec shows that the sensitivity peaks at around 875nm wavelength of light (in the near infrared) but it will respond to visible light with less sensitivity.

    2) Differential signals are used to minimize noise pickup and to drive high speed differential lines. The spec says the amp's differential output is 600mVpp with a 2mA p-p input. It doesn't say but I expect this output voltages are DC offset by around 1/2 the supply voltage since there is no negative supply to generate negative output voltages.

    3) The IC needs a plus 4.5V to 11V for the amplifier and a plus 100 to 240V for the detector bias (through a 390kΩ nominal resistor). These voltages are needed to power the circuit. It is called a bias voltage since it draws very little current. You create the voltages with a power supply.