Connect with us

feedback circuit analysis

Discussion in 'Electronics Homework Help' started by only6512, Feb 15, 2014.

Scroll to continue with content
  1. only6512

    only6512

    18
    0
    Feb 15, 2014
    Hello, everyone
    I have problem about the ratio of the Vout/I(in)
    as shown in the attachments

    the method i use:
    let the gate voltage of M2 be vx
    Vout/I(in)=Vout/vx*(vx/I in)

    I don't know how to figure out (vx/I in)
    does the small signal model include R(D1)?
    and the current through RD1 is?
    can any one help me?
     

    Attached Files:

    • 31.jpg
      31.jpg
      File size:
      10.5 KB
      Views:
      125
    • ??-1.jpg
      ??-1.jpg
      File size:
      4 KB
      Views:
      134
    Last edited: Feb 15, 2014
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,655
    2,696
    Nov 17, 2011
    Welcome to the forum.
    I'm sure we can guide you along your work.

    I assume that you are looking for the small signal solution, right? (By the way it's customary to use small letters to denote the small signal sloution, capital letters for the DC operating point).

    I'd go about solving the circuit as follows:


    - find the operating point (Iin=0A, note this is only the small signal current)
    - replace the transistors by their small signal models (see e.g. here). The parameters are defined by above operating point. The small signal model of the transistor does, of course, not include the external resistors. The small signal model of the circuit does include them.
    - solve for Vout=f(Iin) and calculate Vout/Vin.
     
  3. duke37

    duke37

    5,364
    772
    Jan 9, 2011
    A very strange circuit. Are you sure that the two RF resistors are connected to ground?
     
  4. only6512

    only6512

    18
    0
    Feb 15, 2014
    That's why i am confused
    the small signal model includes RD1
    but the textbook's answer to vout/ I in doesn't(shown in attachment 2)
    is it wrong?


     
  5. only6512

    only6512

    18
    0
    Feb 15, 2014
    yes.actually this circuit is used to calculate the closed loop gain with finite impedance
    of a feedback system
    the two "RF" are respectively "sense duplicate "and "return duplicate"
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-