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  1. LvW

    Bode plot of RC circuit

    Via internet there are hundreds of knowledge sources regarding your question. Why didn`t you try to find an answer by yourself?
  2. LvW

    I need some help with analyzing an opamp

    Sometimes it is recommended to check if such a transfer function is in accordance with the drawing. For example: For s=jw=0 the capcitor values must not play any role. However, setting s=0 in your expression for H(s) we have H(w=0)=R2C2/R1C1. So - something must be wrong. Can you find the error?
  3. LvW

    I need some help with analyzing an opamp

    "So to draw the bode plot, I figured I'd have to start with the transfer function." The BODE plot of a filter is a plot of the transfer functions magnitude and phase vs. frequency (log scale). And the transfer function is H(jw)=Vout/Vin (not: Vin/Vout). Where is your transfer function?
  4. LvW

    Very large gm (transconductance) values

    May I ask you: Which book? To me, the figure together with the given "explanation" looks a bit weird. Examples: * gm is "very high" (what does this mean)? * basic gain is "high" (??). That`s all? No gain expression? * I suppose the resistance "r" in the circuit is identical to rs=1/gm ? * The...
  5. LvW

    LTSpice phase angle of RC circuit, why is phase angle increasing with frequency?

    OK - agreed.
  6. LvW

    LTSpice phase angle of RC circuit, why is phase angle increasing with frequency?

    Daniel - here is another recommendation: Without any math, a so-called "vector diagram" can visualize the phase relations between all voltages and the current. Because in your example, both elements are in series, you start with the current vector and add the voltage vectors for the resistor (in...
  7. LvW

    Frequency dependent resistor in PSpice

    Perhaps, this is not what the OP (Bala_01) needs - but there is a very versatile active circuit called "Frequency-Dependent Negative Resistor (FDNR) " consisting of two opamps. Such a device is extensively used in active filters and harmonic oscillators. It is a special version of the universal...
  8. LvW

    LTSpice phase angle of RC circuit, why is phase angle increasing with frequency?

    Without any algebra: You have plottet the output voltage across the capacitor versus the constant input voltage. As you know, the voltage across a capacitor will lag the corresponding current through the device by 90 deg. On the other hand, for rising frequencies the current through the whole...
  9. LvW

    opamcircuit output

    All the given information are useless (infinite gain, input/output impedances, offset,...) if you do not understrand the principle of negative feedback. Start with feedback theory.
  10. LvW

    opamcircuit output

    The polarity of the 2nd opamp is false. You have provided POSITIVE feedback.
  11. LvW

    opamcircuit output

    The correct answer was given already to you. You now have the task to verify it.
  12. LvW

    opamcircuit output

    Just a short hint: Because you have two input voltages, it is recommended to use two separate calculations (one for each input): Application of the superposition theorem.
  13. LvW

    Phase shift oscillator help

    OK - agreed.
  14. LvW

    2nd order circuit's bode plot

    The plot shows the loop gain (magnitude and phase). The stability criterion requires to determine the phase difference between the actual loop phase at the "cross-over frequency" (magnitude 0dB) and zero phase. This difference must be positive (for a stable closed-loop) and, hence , is called...
  15. LvW

    Phase shift oscillator help

    Hi Electrician - back from a one-week vacation (with some time to recall our loop gain problem) I like to reply to your contribution as follows: I think your explanation cannot show why Ratchs derivation could not give the correct results. At first - the Barkhausen criterion reqires Aß=1, which...
  16. LvW

    Please help! Amplifier design problem

    Only three resistors? Resistors with given values - and the factors are also given? Sounds a bit strange.
  17. LvW

    Phase shift oscillator help

    The electrician - I think, what you have done in your relatively long calculation is simply to make use of Im{T(s)}=Im{H(s)*A}=Im(H(s)=0 (because we can assume that A is fixed and constant value). The function H(s) is a third-order highpass (three bufferd CR sections). This is the normal and...
  18. LvW

    Phase shift oscillator help

    May I tell you about an error I have made some time ago? Somewhere within a relatively long sequence of calculations there was a term SQRT(1E4-1E3) - and I realized that the final result was wrong. But where is the error? It took me several hours to see that the SQRT was not "1E4/1E3=10" but...
  19. LvW

    Phase shift oscillator help

    Ratch - sorry, but you are not on the right track in this case. General (preliminary) remark: If for any oscillator the frequency determining components are given (as in our case) there are still two unknowns to be determined: (1) The oscillation frequency wo and (2) the required gain A of the...
  20. LvW

    Phase shift oscillator help

    No - I don`t know any "trick". I am afraid, you have to apply one of the classical methods (equations for node voltages or sequence of loaded voltage dividers,..) . It is a bit involved, indeed...
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