Problem 1—The circuit below is one way to build an op-amp peak detector. The first op-amp compensates for the forward voltage drop of the diode, and the second op-amp buffers the voltage on the capacitor, isolating it from the load current.

Even if the op-amps are a FET-input type, leakage current through the diode can create an unacceptable voltage drop. Show how the addition of one diode and one resistor can eliminate this problem.

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Problem 2—Name some of the methods used to overcome the "skin effect."

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Problem 3—What is a good approximate formula for skin depth in a conductor such as copper or aluminum?

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Problem 4— The power-handling capacity of a coaxial cable is limited by what?

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Problem 5— Direct measurement of voltage and current is possible in a non-TEM (transverse electromagentic) transmission line. True or false?

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Problem 6—The conventional way to calculate the magnitude (length) of a vector is to take the square root of the sum of the squares of its components. On small processors, this can be difficult (especially the square root operation), so various approximations are used instead.

One approximation that works surprisingly well for 2-D vectors and complex numbers is to take the absolute values of the two components, compare them, and then add one-third of the smaller value to the larger value.

What is the maximum error using this method?

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Problem 7—Is there a similar formula that gives even better results?

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Problem 8—Suppose you have a microcontroller project that you want to power from a 6-V battery pack. The microcontroller can handle voltages up to 6 V, but the actual voltage of the pack can be as high as 6.25 V when it is freshly charged, so you decide to put a diode in series to reduce the voltage. Would it be better to use a Schottky diode (Vf = 0.3 V) or a regular silicon diode (Vf = 0.7 V) for this purpose?

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Published April 2003
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