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  1. A

    Meaning of Sigma in Laplace transform

    I am really looking for the answers to this question. Hope someone could make it clear.
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    I How inversion layer shields electric field?

    This question is somewhat relating to electronics but I think it fits better with physics. The leccture here (slide 13) shows that the gate to body capacitance (Cgb) in linear region is 0. However, there is no explanation at all. I tried to find the explanation from the reference book and got...
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    A Fixed effective charge in flat band voltage

    I am having a hard time understanding flat band voltage in MOS capacitor. Please see the picture below about MOS capacitor. Q0 is a fixed effective charge at the surface between oxide and semiconductor and it is positive here. The voltage across the oxide caused by the fixed charge ψox =...
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    Archived The drift and diffusion currents under equilibrium

    Thank you! Could you explain about unrealistic phenomenon here? Why is there a charge accumulation? I don't see how is each side of equation 2.61 can be zero. For the right hand side part, the total current always flows from p to n and in the left hand side the total current always flows from p...
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    Why LC tank only oscillates at resonant frequency?

    I simulated the oscillator. If Vdd is step voltage then the oscillator oscillates but if Vdd is constant then it doesn't oscillate. Could you explain why?
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    Why LC tank only oscillates at resonant frequency?

    Hi, the resistances are same (not exactly because tolerance)
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    Why LC tank only oscillates at resonant frequency?

    Thanks for the detailed answer. I have some problems understanding the oscillator. The first one relating to the boldfaced part above. I don't get what you meant here. Second problem is that how can the oscillation start up? Two transistors are exactly the same, so which one will be ON first...
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    Why LC tank only oscillates at resonant frequency?

    Hi, I read that that circuit can be converted to LC tank circuit using negative resistance of these mos transistors. So I think they are equivalent.
  9. A

    Why LC tank only oscillates at resonant frequency?

    So, could you explain why this cross coupled oscillator below oscillate? It is only connected with a DC voltage source.
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    Why LC tank only oscillates at resonant frequency?

    Thanks a lot! I have one more question. Assume I have an ideal parallel LC and it is connected permanently with an ideal constant voltage source. Does the LC tank oscillate with a sinusoidal waveform? I am confused because it is connected with a constant voltage source?
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    Why LC tank only oscillates at resonant frequency?

    I am wondering why LC tank only oscillates at resonant frequency not other frequencies? Is there a physics explanation for that?
  12. A

    Confusion about a point and a line

    Yes, I searched a lot but still feel confused. I am doing some integrals and really curious. That makes sense. Is there an direct explanation to this even philosophy?
  13. A

    Confusion about a point and a line

    A point has no dimension and a line, which has dimension, is made from points together. How does something without dimension create something with dimension? I can't really make any sense of it. Could you share your opinions?
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    Conditions for Laplace and its inverse transform to exist

    Thank you, SteamKing and AlephZero. SteamKing: I didn't express it clearly. My question is why in circuit analysis using Laplace (for example, the analysis given in the link), the author didn't consider about the existence of Laplace Transform and Inverse Laplace Transform before applying to...
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    Conditions for Laplace and its inverse transform to exist

    Sorry for the link. I don't know why it doesn't work when I click in that link directly. Could you go to the first result in Google below? https://www.google.com.vn/#q=http:%2F%2Fpeople.seas.harvard.edu%2F~jones%2Fes154%2Flectures%2Flecture_0%2FLaplace%2Flaplace.html Here is the pdf version...
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    Conditions for Laplace and its inverse transform to exist

    Thank you. For example, in the RLC circuit from this page below, how could you know that Laplace transform and its inverse transform exist before using them? In that example, I see that the author used Laplace and inverse transforms without considering the conditions for these transforms to...
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    Conditions for Laplace and its inverse transform to exist

    I usually see that Laplace transform is used a lot in circuit analysis. I am wondering why can we know for sure that the Laplace and its inverse transform always exists in these cases. Thank you.
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    Why can't energy change abruptly?

    Now, I just read that the voltage across an ideal inductor and the current through an ideal capacitor can change abruptly.
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    What is the difference in mechanisms in which IB1 and IB2 are formed?

    iB1: holes in Base move from Base to Emitter This is same as electrons from emitter, recombining with holes in Base to become valance electrons and they continue move to B. iB2: electrons from emitters recombining with holes in Base and continue move to B I don't see any difference. Please help.
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    Can anyone tell me how the hole will move after this?

    I would like to ask some more questions. In pure semiconductor, thermal energy will create electron-hole pairs all the time. If there is not recombination ( I mean electrons go from conduction band to valance band) then the current will continue forever and the pure semiconductor will become a...
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    Boost-Flyback converter

    I am reading about Boost-Flyback converter and this is a bit confusing. Could you explain the role of D1 and C1 here? The lecture says that "D1 and C1deliver to the output the energy stored in the transformer leakage inductance Ld." I can't understand what is meant here. And could you explain...
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    Approximation formula proof

    Thank you all. I think you misread the question a bit. The expression on the right hand side of the equation is e^{-\frac{t}{τ}} with τ = τ_1 + τ_2.
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    Shared contacted diffusion in layout

    Thank you. I am learning about analog design. Hope you could help!
  24. A

    Output states of a CMOS gate

    Thank you. That was a bit confusing.
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    Shared contacted diffusion in layout

    I am confused about shared contacted diffusion in CMOS layout. Is it possible to use shared contacted diffusion for two nMOS transistors with different widths? BTW, two nMOS and pMOS transistors are never shared contacted diffusion, right?
  26. A

    Output states of a CMOS gate

    Please help me with the question in the picture about pull-up and pull-down networks.
  27. A

    Approximation formula proof

    Thank you. However, that doesn't solve the problem. What need to be proved is different.
  28. A

    Approximation formula proof

    Hi. Please help me prove the approximation formula below given in my book. This is not homework question. Thanks.
  29. A

    2:4 decoder solution confusion

    Thanks. I see no difference in functioning between my solution and the key in the book. I also can derive the circuit given in the solution. However, I can't figure out why the author used the key solution not the one I get above.
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    2:4 decoder solution confusion

    Hi. I understand all possible conditions. I didn't draw Y1, Y2, Y3 because they are same in terms of implementation. My confusion about Y0. I am wondering why the author used that solution not mine.
  31. A

    2:4 decoder solution confusion

    Hi. I am confused a bit about the solution for 2:4 decoder in the picture below. Please help me with the question in the figure. Thanks.
  32. A

    Use of inductor in a receiver

    I always wonder why the LC tank resonates at the resonant frequency not other frequencies. It would be great if you could explain it.
  33. A

    Hi, At present, I am learning about Switched-mode power supply and Lo

    I meant the books teaching how to design SMPS using CMOS technology. I think something similar to this one: http://www.vrg.utoronto.ca/~ngwt/Publications/POWER%20ELECTRONICS%20-%20International%20Symposium/Integrated%20Power%20Stages.pdf
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    Hi, At present, I am learning about Switched-mode power supply and Lo

    Thank you. I have the first book while reading your post a long time ago. I understood more about inductors and capacitors. However, it doesn't use CMOS in SMPS. About LDO, I wanted to get advice from experts first.
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    Hi, At present, I am learning about Switched-mode power supply and Lo

    Hi, At present, I am learning about Switched-mode power supply and Low drop out regulator using CMOS. Could anyone suggest some good books about this? The main problem here is "using CMOS". Thanks.
  36. A

    Signal flow graph for two-port network

    Thank you. I thought I figured it out. My confusion was from why the left diagram is equal to the right one in Figure 2.4. I was told that node a2 doesn't depend on the input bs and therefore to change from left diagram to the right one all I need is to calculate b2 as a function of bs.
  37. A

    Signal flow graph for two-port network

    Hi, this is part of an application note entitled "Low-Noise Amplifier Stability Concept to Practical Considerations" from Maxim. Could you help me with the question in the picture? Thanks. Source: http://www.maximintegrated.com/app-notes/index.mvp/id/1849...
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    Does NFmin in cascode LNA depend on the negative feedback inductance?

    No, I am designing a LNA not a homework. I read some books and papers saying that NFmin in two cases are equal. However, I would like to understand clearly why and read a decent proof. Do you have ideal how to prove that? Thanks.
  39. A

    Does NFmin in cascode LNA depend on the negative feedback inductance?

    Hi, This is a cascode LNA. Please help me with the question in picture. Thank you.
  40. A

    Help explain the capacitance definition in Spice

    Hi, In Spice, the capacitance between two points x, y is defined as follows: Cxy = - dQx / dVy for x != y Cxx = dQx/dVx Could anyone help me explain why it is defined like that? I know that C = dQ/dV but the formula above seems strange to me. Is my understanding below correct? Cxy =...
  41. A

    Zin of a circuit with independent sources

    Hi, This is not a homework question. I need to calculate input impedance for a LNA and this is part of it. How do you calculate input impedance, Zin, for the circuit below? I tried by applying an input voltage, V1, and calculate Iin. Input impedance will be V1/Iin. However, the expression...
  42. A

    Transistor Base/Collector Current mystery

    Well, got it completely. Thanks, cabraham. Could you help me with the question in this thread? https://www.physicsforums.com/showthread.php?t=722855
  43. A

    Some basic doubts regarding transistors characteristics

    Can you explain why it creates IB not IE? I don't see how these electrons and holes go out of base to constitute IB.
  44. A

    Does energy of the signal lose after going through the filter?

    Hi, This is not a homework, just a problem that I can't figure out. Please help. Assuming that I have a low pass filter with cutting frequency, fc and a signal with many different frequencies (with some below fc and some above fc) is applied to the input of the filter. As we know, the...
  45. A

    Help understanding about wavelength

    I don't understand why the waveform in all wavelength are all sinusoidal. What shape of wave in space if the signal generated at transmitter is not sinusoidal? And then how we can definition wavelength in this case?
  46. A

    Help understanding about wavelength

    Thank you, I wanted to know that to confirm my understanding about how wave propagating in space. For example, there is a sinusoidal voltage source at transmitter and speed of propagation for the wave is v (m/s), the direction in which the wave moves is z. Say, at t=0, the voltage at the source...
  47. A

    Help understanding about wavelength

    Hi, I want to ask one question about wavelength. Here is a picture defining wavelength. To get a sinusoidal wave in space, we have to use a sinusoidal voltage source at transmitter, right? I mean if there is a sinusoidal voltage source at the transmitter to create a sinusoidal wave in space.
  48. A

    Why can't energy change abruptly?

    Now, I can't find out anything but I can't generalise it. Yes, but in my mind :)
  49. A

    Why can't energy change abruptly?

    Hi, I want to ask your help about energy. Why can't energy change abruptly? If energy E changes abruptly then power P = dE/dt = ∞. I would like to know why this is impossible? I know that energy has to be conserved and they can only change from one form to the other. But why this process...
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