Search results

Search Forums New Posts
  1. LvW

    How a BJT Transistor works (base current version)

    Steve, what shall I answer? You know of my opinion: It has no "limitations", but it simply does not reflect the reality and it does not simplify anything (as I have shown in my former answer). It is even worse - it directs a beginner to a wrong direction so that he cannot explain and understand...
  2. LvW

    How a BJT Transistor works (base current version)

    OK - I will check. OK - but in this case I must ask : Why in the title of your text the phrase "base current version" ?
  3. LvW

    How a BJT Transistor works (base current version)

    For my opinion - both (as well as). In your contribution you are referring to Horowitz/Hill page 64. But one should consider that on page 62 the authors speak about a "very simple introductory transistor model" only. (Comment: A model does not necessarily reflect the main physical properties; it...
  4. LvW

    How a BJT Transistor works (base current version)

    May I add one remark (because mentioning LvW in this thread): For my opinion, it helps to make clear if "the method" is applied (a) for explaining the function of the BJT or (b) for designing a BJT-based amplifier. (By the way: I think, mixing both items during relevant discussions always...
  5. LvW

    The BJT as an Amplifier homework question

    Roy - for calculation of the signal output voltage you need to know the gain. It shouldn`t be aproblem for you to find the gain formula for a common-emitter amplifier without emitter degeneration (because you didn`t mention any external emitter resistor RE). It`s really a simple formula that...
  6. LvW

    Calculating gain in this op amp stage

    1.) Although the opamp input resistances are neglected during calculations, there is a small DC current into both input terminals. And it is the task of R114 to develop a small DC voltage (caused by the small DC input current into the non-inv. terminal). This DC voltage should be approximately...
  7. LvW

    Calculating gain in this op amp stage

    This circuit is one of the classical second-order active lowpass filters: Lowpass with multi-feedback in MFB topology. Googling these keywords will give you a lot of information and hints how to find the transfer functiuon ("gain") of the circuit. The resistor R114 is not so important - it just...
  8. LvW

    Op amp help (multisim)

    Chris - I am somewhat surprised about your response. Why so harsh? In post#2 I have kindly asked you to redraw the diagram (without any response). I suppose, all of us have to do also something else than to participate in this forum. And therefore, I think, also the questioners should be aware...
  9. LvW

    instrumentation amplifier

    It would be much easier to help you if you could us all relevant information: * input signal * general gain formula used and required/expected gain value * output signal * Which kind of analysis? * mentioning of observed discrepancies
  10. LvW

    Op amp help (multisim)

    An easy circuit to read makes for an easy circuit to diagnose when it doesn't work properly Yes, yes, yes... I must confess that I am not motivated enough (even to lazy) to start analyzing such a confusing wiring.
  11. LvW

    Op amp help (multisim)

    One of the reasons I dislike Multisim is that the various "instruments" partly hide the real circuit. Please, can you redraw the whole assembly and make it somewhat clearer?
  12. LvW

    op-amp help

    My recommendation is to start a google search for "instrumentation amp". You will find a great number of related documents and circuits. Because you certainly will need a high-resistive unit you, most probably, will arrive at a circuit with three opamps. This is the classical instrumentation...
  13. LvW

    Best circuit simulator

    What is a "good" simulator? (What is a "good" amplifier?). I think, such a question cannot be answered. When you are looking for a circuit simulator you should - at first - clarify: *What is the main purpose of such a simulation program? *Simulation in the time or frequency domain (Transient or...
  14. LvW

    what is this Circuit ?

    Adam - just two comments to your last contribution: 1.) It is a classical 2nd-order lowpass topology with two feedback pathes (called very often: Multi-Feedback MFB). 2.) As you and me have discoverd - it has a parts combination (dimensioning) which is extremly "weird" because the dc gain is...
  15. LvW

    what is this Circuit ?

    Well - no problem. I will try to upload a pdf file showing the simulation circuit.
  16. LvW

    what is this Circuit ?

    Adam - what do you expect from this posting? I have entered the given circuit diagram into my simulation program, that`s all.
  17. LvW

    what is this Circuit ?

    What does this mean? 18.5 kHz input signal?
  18. LvW

    what is this Circuit ?

    My simulation (real opamp model LM741, +/-5V supply) gives a dc gain of -75dB and a peaking of app. 20 dB at zhe pole frequency (1.5 kHz)
  19. LvW

    what is this Circuit ?

    This time constant, of course, is part of the 2nd order filter. The rest of the circuit (you call it "opamp part") is only a first order circuit.
  20. LvW

    what is this Circuit ?

    In linear electronics opamps are used because they provide a low-resistive voltage output. Hence, in the circuit under discussion (a well-known 2nd order active filter topology) the circuit´s output, of course, is the opamp output terminal. However, I agree with Adam´s recent comment: I also...
Top