How to increase npn transistor effective input resistance and reduce gain

Discussion in 'Analog & Mixed-Signal Design' started by JumpingElephant, May 2, 2019.

  1. JumpingElephant

    Thread Starter New Member

    May 2, 2019
    Idea is that for some application like automatic gain control and regeneration it is useful to be able not just to reduce gain, but also increase input resistance of a transistor, so that signal is not wasted in voltage divider or similar methods of gain reduction.

    So far i see one way of using another transistor that works as variable resistance near our main transistor's base
    i suspect it is also possible by varying resistance near emitter by the same method with second transistor, may be its even simpler.

    is there any simpler method to achieve the same result? preferably using simple components (passives L,R,C, or simple like diodes)
    (to increase input resistance of a transistor using a voltage control signal from other part of a circuit. gradually so that delicate feedback is possible)

    in particular npn bipolar transistor in low voltage(~3v), low current(~1ma), high frequency(~10mhz), signal circuits
    codewords for search: automatic gain control, agc, automatic regeneration control, arc, automatic volume control, avc, controlled gain
  2. danadak

    Distinguished Member

    Mar 10, 2018