current mirror?

Discussion in 'Homework Help' started by rsashwinkumar, Jan 1, 2012.

  1. rsashwinkumar

    Thread Starter New Member

    Feb 15, 2011
    In a current mirror (using BJTs), what happens if the emitter area of the transistor(drawing the mirrored current), is twice that of the diode-connected transistor(carrying the reference current) ??

    Plz explain me...
  2. Adjuster

    Well-Known Member

    Dec 26, 2010
    If this is a basic current mirror with no added resistors, there is a simple answer which should be obvious given a bit of thought. To be more exact, you might want to think a bit about base currents, but the difference should not be much if the transistors have reasonable gains and have not saturated.

    If the circuit includes any emitter resistors, as are sometimes used to desensitise the circuit to spreads in Vbe, it will be easiest if they too are scaled so that the resistance varies inversely to area, if not this becomes a much harder problem.