Lower frequency response of a BJT common emmitter amplifier

Discussion in 'Homework Help' started by student_technician, Jan 16, 2015.

  1. student_technician

    Thread Starter New Member

    Dec 28, 2014
    Stuck on a Lab question that reads:
    What Change would you make to the circuit to lower the frequency response in the CE amplifier in fig 10-1 by a factor of five?

    pics are coming

  2. WBahn


    Mar 31, 2012
    If you want people to look at your images, you might consider scaling them to something rational. With a bit of effort, I'm guessing you can get them under 100 kB each and have them still readable.
  3. crutschow


    Mar 14, 2008
    You determine which parts of the circuit contribute to the low frequency rolloff and then modify them to give the desired lower frequency response.
    Do you know what determines the low frequency response of that circuit?
    (Hint: There are three possible contributions).
  4. MrAl

    Well-Known Member

    Jun 17, 2014

    Here is a reduced image size version. All three on one page takes less than any one of those original images :)
    I would have went even smaller but the circuit lines get distorted.
  5. Veracohr

    Well-Known Member

    Jan 3, 2011
    And another hint (student technichian): one of your pages tells you how to calculate that low frequency response.
  6. shteii01

    AAC Fanatic!

    Feb 19, 2010
    I aint going to bother downloading 1.6 MB pics.
    The old rule of thumb is to keep pictures under 300 kB. I think it goes back to dial-up days.
  7. WBahn


    Mar 31, 2012
    I suspect it was even smaller back then. Even with a 57.6kb/s modem, and assuming every bit transferred is data, a 300KB file would taken nearly 45 seconds to download and I suspect that, in practice, it would have usually been well over a minute. Granted, people expected things to take longer and so maybe that was considered reasonable. I did very little with BBs back then, so I really don't know. I sure to remember accessing the school's system with my first computer that had a 300/1200 baud modem and there were only a few lines that could accept a 1200 baud connection, so when you got one you camped on it and did everything you could before surrendering it. It just seems unimaginable how "fast" that connection seemed when you consider that the same 300 KB image (which I would have never considered downloading given that my computer had 768KB of RAM and mass storage consisted of two 360KB floppies) that we now routinely expect to load in a fraction of a second would have taken over half an hour!
  8. Yakima


    Jan 23, 2012
    Student technician, the capacitors in your CE circuit are the factors to consider in determining its frequency response. There are three. Just analyze the effect of varying the capacitance of each one and the answer should come clear to you. Do you have the equations for the 3dB roll off point for each node? I mean for each capacitor: one at the base, the other at the emitter and one at the collector? If you don't, I'll help you figure them out and then you should be able to determine the solution. Let me know if you're still interested.