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  1. T

    Impedance of two stage amplifier

    Rough calculation of what? Overall voltage gain? Colin's comment was in reference to another problem the OP posed in post #9.
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    Impedance of two stage amplifier

    Or like saying that there are 39.37 inches in a meter, or that the speed of light is 299792458 meters per second. Where do these absurd values come from?
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    Open / Short circuit time constants for pole approximation

    Are you still interested in a reasonably full explanation?
  4. T

    Open / Short circuit time constants for pole approximation

    Your result doesn't appear to be correct. To make it easier to compare your solution with the book solution, put both over a common denominator: Your solution isn't the same as the book solution; it has an extra term, re*R'L, in the denominator.
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    Impedance of two stage amplifier

    The value of Vin doesn't matter when calculating Av, because its value cancels out when you divide Vout by Vin. So if Vin contains R1 as a factor, or any other factor that determines the value of Vin, that factor will not appear in Av.
  6. T

    Impedance of two stage amplifier

    Your expression for Av is slightly in error. You have: -R2||RL*beta/((beta+1)R3+r Pi+R1) The R1 in the denominator shouldn't be there. Also, you appear to have a numerical value for Av of 0.1355, but you must have used the correct value of .24 to calculate Ai Otherwise, it all looks good...
  7. T

    Impedance of two stage amplifier

    Finding the current gain, Ai, is not too hard if you can find the voltage gain, Av. The voltage and current at the input are related by Vin = Zin*Iin. The output voltage is given by Vout=Vin*Av which gives Vout = Iin*Zin*Av. The output voltage and output current are related by Vout =...
  8. T

    Impedance of two stage amplifier

    Given that the input is a current and the output is also shown as a current, I would have thought they wanted the current gain, Ai, rather than the voltage gain, Av. Which is it?
  9. T

    Impedance of two stage amplifier

    You're not carrying enough digits in your calculations. You got Av = -.007987. If I carry out the multiplication of all those terms with more digits I get: Some of your intermediate quantities also should have been calculated with more digits. If I do this I get: This is the correct...
  10. T

    Impedance of two stage amplifier

    You have R1 where you should have R6. This error carries through to the last expression.
  11. T

    Impedance of two stage amplifier

    Things are way worse than that. The 5k is not driving 400 ohms. It's driving 400 ohms in parallel with the input resistance at the source of the FET, which is a lot lower than 400 ohms. This whole amplifier is totally useless for anything other than an exercise problem.
  12. T

    Impedance of two stage amplifier

    It will work just fine, although it's more often used in RF work: https://en.wikipedia.org/wiki/Common_gate In the OP's circuit, the second stage actually has voltage gain greater than one, unlike the first stage.
  13. T

    Impedance of two stage amplifier

    Your life has been simplified by the fact that the two stages have identical DC conditions. It looks like you have calculated gm to be .018 A/V, and the output conductance ro of the FETs is ignored. Also, I assume that Rin2 is the resistance seen at the source of each FET. The resistance seen...
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    Can a clock pendulum be slowed down by adding a resistor to the PSB?

    Can you post a picture showing the inside of the clock body, with the pendulum mechanism in place? Do the various interchangeable pendulums weigh the same?
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    Wanted: Reference Wireless World magazines

    You probably don't still want this, but just for grins I checked my collection of WW. The article you asked about is in the March 1984 issue, titled "The parallel-fed voltage multiplier", by R.D. Purves and C. Prescott. It was to be used in a muscle stimulator.
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    How can I simplify the denominator of the Op Amp KVL formula?

    It's interesting to note that Equation 9.43, even though it's incorrect, has a limiting value for Go -> infinity which is the same as the correct expression for GoVd:
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    How can I simplify the denominator of the Op Amp KVL formula?

    I compare my solution derived from Figure 9.21c with yours and they are identical. I think your book has an error in Equation 9.43
  18. T

    How can I simplify the denominator of the Op Amp KVL formula?

    Before trying to get your denominator into the same form as Equation 9.43, you should make sure that all the rest of your algebra is correct. When I have two relatively complicated symbolic expressions that I need to test for equality, I use a modern symbolic algebra software to expand them...
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    ESR meters show different values

    Try measuring a much larger capacitor, such as 1000uF or 3300uF. The ESR should be much smaller; what do the two meters give you? Also, don't measure a small resistor by itself; connect it in series with the various capacitors and see if the measured ESR increases by the amount of the small...
  20. T

    Thevenins and nortons circuit help

    You might find it interesting to have a look at this: http://www.clever4hire.com/throwawaypic/home/weston-engineering-notes/engineering-notes/Weston2-5.pdf?attredirects=0 Look on page 6 under the heading "Wheatstone bridge--List of circuit equations".
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