dual power supply in differential amplifier

Discussion in 'General Electronics Chat' started by sachin_dukra, Mar 9, 2006.

  1. sachin_dukra

    Thread Starter New Member

    Mar 9, 2006
    why do we use dual power supply for differential amplifier and why not single?

    and also

    why don't we use voltage divide bias for didderential amplifier?
  2. paultwang

    Well-Known Member

    Mar 8, 2006
    For diff amps without current mirrors, a resistive current source is needed to properly bias the emitter (for BJT). To meet the requirement of common mode gain, the resistance, and therefore the voltage is often not the same as the supply voltage towards the collector (for BJT).

    What do you mean by voltage divider bias?
  3. pebe

    AAC Fanatic!

    Oct 11, 2004
    A single power supply can be used for a differential opamp provided that the input potentials allow the input transistors to be correctly biased. In the case of AC waveforms that can be capacitively coupled to the input, a potential voltage divider can be used for biasing.

    Many opamps using FETs can work with inputs down to the -ve supply rail.