low voltage amplification

Discussion in 'General Electronics Chat' started by ispymalik, Mar 28, 2011.

  1. ispymalik

    Thread Starter Member

    Apr 7, 2008
    I always see amplifiers with 1+ V input ranges to be amplified.
    How is a extremely low voltage signal like uV or nV amplified?
    Wouldnt offset voltage on op amps be to large and smuther the signal?
  2. JDT

    Well-Known Member

    Feb 12, 2009
    Yes, but the offset voltage can be nulled out. Measuring very low value DC voltages is difficult though.
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
    In some applications the DC content of the signal is unimportant, so that the offset problem reduces to making sure that the correct DC working point is obtained.

    Where really low DC voltages do require to be measured, precision amplifiers can get offsets down to well below 1mV. Here is an example: http://www.national.com/ds/LM/LMP7721.pdf

    Beyond that, special techniques like chopper stabilisation or auto-zero are required in order to reduce the effective offset voltage. The chopper method uses low-offset analogue switching techniques to convert the DC input to a series of pulses before amplification, whereas the auto-zero method periodically calibrates out the DC offset.

    http://focus.ti.com/lit/ds/symlink/tlc2652a.pdf http://focus.ti.com/lit/ds/symlink/opa333.pdf