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  1. LvW

    Calculate Op Amp Gain

    Yes - of course, this is correct. But this result was given in general form in post#7 already: A = [1 + ( (R1 + R2) / R3)] * (R2+R3)/(R1+R2+R3) Harald: How can you say that R1 has "no influence"?
  2. LvW

    Calculate Op Amp Gain

    The voltage at the opamp output is of "no concern"?? I rather think, we have an active device (called opamp) which has a low-resistive voltage output and it is THIS output only which provides voltage feedback! The only difference to the classical non-inverting circuit is that we do not further...
  3. LvW

    Active Filter Design

    Clarification: It doesn`t reduce frequencies. Instead, it is correct to say "...it reduces the amplitudes of higher frequency componenets..."
  4. LvW

    Active Filter Design

    Yes - as OBWO549 has recommended - use C2=2*C1 and make a rescaling of the components. Fore example: R1=R2=1100 Ohms and C1=10nF, C2=20nF. However, please realize that the used opamp (741) has a slew rate that does not fulfill the requirements for a 10kHz cut-off frequency. You need a better...
  5. LvW

    BP filter design

    ...."between 40 and 80 MHz " normally means: Passband between 40 and 80 MHz. In this case, however, you cannot eliminate any 80 MHz peak. Please, solve this contradictory specification. In general, you can design a bandpass with a real zero at 80 MHz (Chebyshev invers or elliptical response)...
  6. LvW

    Frequency Generation Without An Oscillator Ckt:multisim Simulation

    Remember the oscillation condition: The loop gain (the gain around the complete feedback loop) must be unity - unity magnitude AND zero phase - for ONE SINGLE frequency only!.
  7. LvW

    beginner struggling with a opamp

    What is the meaning of "so much"? Theoretically, the maximum gain will be (1+R7/R8).
  8. LvW

    basic electronics question: types of oscillators

    As Harald has pointed out - there are some fundamental differences. For this reason - some authors (and I strongly support them) apply the term "oscillator" to harmonic (linear) oscillators with a sinusoidal output only (Frequency in Hertz). All devices producing squarewaves should be called...
  9. LvW

    Transistor Base, Emitter, Collector -Voltage Question

    From the physical point of view - there is nothing like a "turn-on voltage" between base and emitter. The relation between the collector current and the controlling base-emitter voltage Vbe is an exponenetial function (Shockley equation): Ic=Is*exp[(Vbe/Vt)-1] . From this, you can see that there...
  10. LvW

    Common emitter amplifier

    Wikipedia is not he bible. Several examples can reveal wiki`s errors. I think, phase inversion are identical to a 180deg phase shift for sinusoidal (periodic) signals only. However, ther are also non-periodic applications.
  11. LvW

    Help me calculate output impedance

    I think, everything is OK (except "beta+1" instead of "beta") if we consider Rs to be the effective (resulting) source resistance at the base node.
  12. LvW

    Help me calculate output impedance

    In the link which was given by Steve (post #5), you will find the following expression: This is the output resistance without the external ohmic resistor RE. This can be writte as rout=rbe/beta +Rs/beta. We knbow that rbe/beta=1/gm=Vt/Ic. Hence, rout=1/gm +Rs/beta. (I have explained this...
  13. LvW

    Help me calculate output impedance

    Ratch - I think, your equations are not easy to read.(and to understand) * Why don`t you distinguish between static (R) and differential (r) resistances ? * In the transfer function, what is rs (with respect to the given circuit)? * T=1 for rs=0 ? * I doubt if your expression for rout is correct...
  14. LvW

    Help me calculate output impedance

    At first, using approximations one should know if such a simplification is allowed or not. The explaining text (right from the transistor) gives an expression fo the output impedance which is a rough approximation. The correct formula is: r(out)=RE||[1/gm + Rsource/(1+beta)] With...
  15. LvW

    Second order filter - quadratic formula and standard normalized form

    Ratch - is this question directed to me? Are you saying that a second-order function (always) has TWO corner frequencies? It has (for Qp>0.5) two poles (conjugate-complex) and ONE SINGLE corner frequeny. Or did I misunderstood your reply?
  16. LvW

    Help with Phase locked loops (PLL) what does phase mean here?

    For my opinion, it is best to forget this formula. It is just a general expression which should serve as an additional explanation for the sentence before. Unfortunately the author has chosen the subscript "1" which is also used in the first line (formula for u1(t). Another subscript (like "x")...
  17. LvW

    Second order filter - quadratic formula and standard normalized form

    Jonathan - why do you think that you would have two corner frequencies? Just because you have found two roots? That`s not logical. Corner frequencies are defined for the magnitude response of a second order filter. Now - you have to distinguish between two cases: (a) Two REAL roots (poles of...
  18. LvW

    Class A amp with NPN BC547 transistor

    You are "making a simple amplifier". May I ask you if you have DESIGNED the shown circuit (calculation of parts values based on some requirements like quiescent current?). This would be the first - and necessary - step. Otherwise, you cannot understand any malfunction.
  19. LvW

    Common gate amplifier gain

    Have you ever hears about the "drain current"? Such a current needs a voltage source.
  20. LvW

    Common gate amplifier gain

    Perrhaps it makes sense to use a supply voltage?
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