how to get started with differential Amplifier

Discussion in 'The Projects Forum' started by circuitBoy818, Dec 13, 2013.

  1. circuitBoy818

    Thread Starter New Member

    Dec 13, 2013
    Hi everyone.
    I'm trying to design a differential amplifier for one of my projects.
    The specs require that it would be completely discrete. The other requinment is that it needs to work for up to 5Mhz.

    I'm just stuck and i don't know how to get started. For example when i took class on electronics, the Beta and Cpi and all those stuff were given and i just needed to find the resistor values. Lets say that im going to use the 2n222 transistor. How do i get started and, any formulas, techniques or first few steps would be very helpfull.

    P.s is this the right diagram to go with or should this be modified?
  2. LvW

    Active Member

    Jun 13, 2013
    Hi Circuitboy,

    the circuit diagram - in principle - looks OK, however it also depends on some of your requirements.
    To start the design you must know what the circuit is required to do!

    * Power supply: Any requirements? Double or split supply? This has influence on the base dc voltages (base biasing still missing); Which values?
    * Gain requirements: You must discriminate between differential gain and common mode gain. It is the main purpose of such an amplifier to attenuate common mode signals - and this may require a third transistor in the common emitter leg (acting as a current source). No gain requirements?
    * Do you know the corresponding formulas for the gain expressions?
  3. abhaymv


    Aug 6, 2011
    If you want to get a good grasp of the concepts, I recommend reading 'Microelectronic Circuits' by Sedra and Smith. This book has a chapter dedicated to Differential and Multistage amplifiers -both FET and BJT. The section on frequency response is likely to help you, even if it is explained in terms of MOSFET.
  4. crutschow


    Mar 14, 2008
    Is a differential output for this (sounds like homework) project acceptable?