A little question on Lock-in Amplifiers

Discussion in 'General Electronics Chat' started by richiechen, Sep 11, 2012.

  1. richiechen

    Thread Starter Member

    Jan 1, 2012
    Hi Everyone, I am trying to get a 1kHz small signal from buries of noises. And a lock-in amplifier has been chosen. I have some questions on using lock-in Amps.

    1. The last stage of a lock-in amplifier is a low-pass filter or an integrator. What is the exact difference of using these two components?

    Could I say that the integrator is more accurate, since the output is measured by counting time needed to discharge the capacitor (you can visit http://cappels.org/dproj/syncdet/syncdet.html for more information), which means the result is time-averaged.

    If I use a low-pass filter, the result is just measured by, say ADC instantly. Could the measured result represent the real value? Or may I ask, if the lock-in amplifier is trading time for accuracy, what is the minimum time required to measure a 1kHz signal accurately?

    2. The amplifier will mix a synchronized signal with the measured signal. Could I just use switches? What are the differences of mixing signal with sine wave or with pulses?

    Thank you very much. Any idea will be highly appreciated. :))
  2. MrChips


    Oct 2, 2009
    A low-pass filter is an integrator.

    You can use a switch. Some lock-in amplifiers are designed using reed relays operating at the lock-in frequency.
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    This may help understanding more about lock-in amps
    richiechen likes this.
  4. richiechen

    Thread Starter Member

    Jan 1, 2012
    Sorry I was not specific enough,
    integrator way: The output it connected with a capacitor first for 999cycles and then discharge the capacitor. The time costed to discharge the capacitor indicates the amplitude desired.
    Low-pass filter way: Connect the ADC with the output of low pass filter directly.

    Which is better? And what is the time requirement for using the low-pass filter way?

    Thank you very much