LED optical power

Discussion in 'Homework Help' started by rajiv.ganti, Oct 16, 2012.

  1. rajiv.ganti

    Thread Starter New Member

    Jun 2, 2012
    2
    0
    Hello all,
    I am involved in one thesis task. I am using "FC300R-120" LED that has following characteristics:
    Max. forward current= 100mA
    forward voltage between 1.7v-2.3v
    and Datarate of 250Mbps.
    According to the specifications, the -3db optical power is achieved at 100MHz frequency at 20mA bias.
    Now my task is to use any simple circuit (for example: RC circuit) added infront of LED to increase this -3db optical power achieved at 135MHz or 150MHz instead of 100MHz.
    The curve should be linear.
    As per specification the above mentioned 100MHz -3db curve looks like the 1st graph that I attached below.
    And now, I should make a lump at 100MHz using this "simple circuit" so that the -3db falls at later frequency range. (I ve drawn the approximated circuit and attached as 2nd image.
    Can someone please help me/suggest me how to proceed with this?
     
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  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    You configure the RC as a high-pass filter that has a corner frequency of about a 100MHz. You place that in parallel with a resistor to provide a constant gain below 100MHz.
     
  3. rajiv.ganti

    Thread Starter New Member

    Jun 2, 2012
    2
    0
    I have a small query..I attached an image titled "01.jpg". If you open it, you can see two wave forms, one is the "small-signal frequency response" vs "capacitive load" and the circuit diagram is also included.
    I would like to know how does the resistor 'Rs' and capacitance 'Cl' effect the transfer function of the Op-Amp. In other words, I would like to know clearly the function of this resistor and capacitance.
     
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