Lock In Amplifiers

Discussion in 'General Electronics Chat' started by shahdeep, Aug 13, 2015.

  1. shahdeep

    Thread Starter New Member

    Aug 13, 2015
    3
    0
    Dear Users,
    I am working on EQE measurements and we have a lock in amplifier which uses voltages as input source. But the EQE setup that we have has DC modulated current. So I need to know what kind of circuit will be useful for my setup to have a linear voltage response to the change in DC current.
    Thank you in advance.
    K.R,
    DS
     
  2. Brainbox

    Member

    Nov 15, 2010
    25
    2
    For linear conversion from current to voltage You wil need a linear resistor to do the conversion and a capacitor to shift out the DC component.
    Most common resistors are linear.
    Btw; what is ment by EQE measurements ?
     
  3. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    631
    What is the impedance of your current source?
     
  4. shahdeep

    Thread Starter New Member

    Aug 13, 2015
    3
    0
    Hello,
    EQE: External Quantum Efficiency, used for solar cell measurements.
    I have not measured the impedance yet but my working range is 100uA to 50mA.
    Thank you once again.
     
  5. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    631
    If the output impedance is very high you can simply measure the voltage across a resistor as Brainbox suggested.

    If you run the solar cell into a dead short instead of a resistor you will be able to obtain consistent results regardless of the output impedance of the cell. A transimpedence is the classic way of accomplishing this. The voltage at the output is equal to I x R while the cell looks into a virtual short circuit.
    [​IMG]
    An op amp such as the SGS-Thompson Semiconductors L272M can supply more than the needed 50 ma.

    Bob Pease's take on it:
    http://electronicdesign.com/analog/whats-all-transimpedance-amplifier-stuff-anyhow-part-1
     
  6. shahdeep

    Thread Starter New Member

    Aug 13, 2015
    3
    0
    Thank you so much. I will read about it and let you know if anymore doubts.
    Thank you once again.
     
    Last edited: Aug 13, 2015
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