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  1. LvW

    buffer circuit before rlc

    Yes - correct. On the other hand, for my opinion, if we speak about a voltage or current source we ALWAYS mean a constant voltage resp. current source, don´t we? Remember, for example, the classical abbreviations VCVS, VCCS. I don´t think so. Does a battery deliver a certain current -...
  2. LvW

    Op Amp Stability

    Hi Adam, I am sorry but there a many comments/corrections from my side in addition to the two remarks I have posted already. And since you have asked for comments... Well, here it comes: 1.) Main Parameters * Beta: I think it would be useful to define the resistors R1 and R2 using a ref. to...
  3. LvW

    buffer circuit before rlc

    A low-impedance source is called "voltage source". A current source has a very large internal source resistance.
  4. LvW

    How can I set a frequency in a Wien bridge oscillator

    I think, the method as proposed in the referenced paper is very useful - in particular for fine tuning of the oscillator. That means, when the required tuning range is not too large (e.g. less than 10...20%).
  5. LvW

    Op Amp Stability

    Adam - please, give me one or two days more, OK?
  6. LvW

    How can I set a frequency in a Wien bridge oscillator

    It depends on the sign of the temperature coefficients. Your goal must be to LOWER the gain (which at t=0 must be larger than "3") for rising amplitudes leading to rising temperatures.. That means either R2 must be INCREASED (light bulb) or R1 must be DECREASED (NTC thermistor).
  7. LvW

    Op Amp Stability

    Hi Adam, since you have mentioned to welcome constructive criticism - I like to comment on two points: 1.) Quote: "It is high because you normally close the loop with feedback which stabilises the op-amp" I think, such a statement can be misleading because it is the feedback that may cause the...
  8. LvW

    How can I set a frequency in a Wien bridge oscillator

    What is the problem? When 2*Pi*Fo=1/RC you can choose either R or C as you like and compute the remaining value correspondingly. However, as mentioned already by duke37, the disadvantage of the WIEN-type oscillator is that you have to vary two elements (R or C) at the same time (because the...
  9. LvW

    How can I set a frequency in a Wien bridge oscillator

    The WIEN oscillator consists of a NON-INVERTING amplifier and a simple RC-bandpass. It is easy to show that the center frequency of the bandpass (with zero phase shift) is at wo=1/RC. This zero phase shift is the reason we need a non-inv. amplifier with a nominal gain of "3" because the...
  10. LvW

    harmonics and fundamental frequency

    No problem. Although I'm not so very young anymore, my sense of humor is not lost.
  11. LvW

    harmonics and fundamental frequency

    Yes - and sometimes even SUBHARMONICS belong to a composite sound signal we appreciate.
  12. LvW

    harmonics and fundamental frequency

    Ohh - I have another exception from this rule: I am sure you have heard about Schroedinger´s cat. Nice explanation. (I hope you forgive my searching for counter examples - I am german too).
  13. LvW

    harmonics and fundamental frequency

    I think, A. Einstein (A German who was born in Ulm) can serve as a good counter-example: "Explain everything as simple as possible - but not simpler! As a good example for his methods I remember how he has explained some of his findings using a running train or an elevator. And Barkhausens...
  14. LvW

    harmonics and fundamental frequency

    Applying a (theoretically) "clean" sinusoidal signal to a non-linear transfer characteristic - and you are producing harmonics of the fundamental frequency. Remember, each transistor amplifier has such a non-linear characteristic and, therefore, the voltage swing is limited if you need a "good"...
  15. LvW

    Op-Amp Gain ?

    Yes - but tell your teacher that this answer is purely theoretical and has no practical relevance because the shown frequency response is by far not realistic. It leads to instability.
  16. LvW

    Op-Amp Gain ?

    The closed-loop gain Acl of the circuit (non-inverting) for low frequecies is Acl=1/Hf with Hf (feedback factor)=Ro/(Ro+Rf)=1/1001. Hence Acl=1001. This value applies as long as the open-lop gain Aol is much larger than Acl (identical to loop gain LG>>0 dB). For all frequencies above the...
  17. LvW

    What does impedance mean?

    There is nothing left to add to these excellent explanations above (post#2 and #4) except the following hint: Even in case the design of opamp circuits is based on the assumption of IDEAL opamp properties it is necessary to enable a dc input current (which, however, can be neglected during all...
  18. LvW

    Phase Shift Oscillator

    But how did we know that 1.732 identical to SQRT(3) ? Look at the following derivation (like the one for coupled RC sections in post#2): 1.) For three decoupled RC sections in series we have H(jw)=1/(1+jwRC)^3 2.) This can be expanded easily (polynominal of 3rd degree) and becaue we want...
  19. LvW

    Phase Shift Oscillator

    Do you want a simpler derivation for the frequency with 60deg phase lag (that means: Phase shift of -60deg)? Here it comes: * For a RC lowpass stage we have H(jw)=1/(1+jwRC) * Total phase shift PHI=PHI(numerator)-PHI(denominator) = 0 - PHI(d)=-PHI(d) PHI=-PHI(d) *...
  20. LvW

    Phase Shift Oscillator

    Yes - that´s the reason we have to consider the whole RC network as a whole (in contrast to the contribution in post#7). But it is to be noted that the CIRCUIT in Fig. 18-3 is wrong (missing dc feedback)
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