Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while typing up your telephone line, and a nice lady's voice announced "You've Got
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Remember the Basics?
Answers to RF Cafe Quiz #22
All RF Cafe Quizzes make great fodder for
employment interviews for technicians or engineers - particularly those who are
fresh out of school or are relatively new to the work world. Come to think of it,
they would make equally excellent study material for the same persons who are going
to be interviewed for a job. Bonne chance, Viel Glück, がんばろう,
buena suerte, удачи, in bocca al lupo, 행운을 빕니다,
ádh mór, בהצלחה, lykke til, 祝你好運.
Well, you know what I mean: Good luck!
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Cafe Quiz #22
This quiz challenges your recollection of the basics.
1. How much power is dissipated by the
ideal 10 μH inductor in the circuit to the right?
d) 0 mW
Ideal reactive components
(inductors and capacitors) do not dissipate power - only resistive components dissipate power. Ideal inductors and
capacitors store and release energy in the form of magnetic and electric fields, respectively, with 100%
efficiency (no losses). Real-life inductors and capacitors have a resistive property (the ratio of which is
referred to as "Q", or quality factor), so they do actually dissipate some power.
2. How much current flows through
the guy at the right?
d) 0 A
Since there is not a complete path, current cannot flow through the
3. In the figure for Q2, what voltage would be measured
between the guy's
hand and ground?
c) 0 V
The voltage supply as shown has no established ground reference, so any
place you connect a resistive (< ∞) path sets the ground (0 V) point. Even a high impedance input voltmeter has a
finite resistance so it would set the ground reference, although it might take a while for any residual charge to
4. What is the name of the newly fabricated 4th type of passive
Memristors - a contraction of "memory resistors" - are passive two-terminal circuit
elements that exhibit a fixed a functional relationship between the time integrals of current and voltage. The
property is called memristance. The existence of
memristors was predicted in
1971 in paper published by Professor Leon Chua, of UC Berkeley.
5. What is the
significance of a component's self-resonant frequency?
b) It is the frequency about which its reactance
changes numerical sign (+ to -, or - to +)
Due to the non-ideal characteristics of capacitors and
inductors, there are parasitic elements in series and parallel in the complete equivalent circuit models.
have inductive properties in series that, together with the intended capacitance, create a point of frequency
resonance where the impedance is purely resistive. Below the self-resonant frequency (SRF), the capacitor measures
as a capacitor (a negative reactance) and above the SRF, it measures as an inductor (a positive reactance).
parasitic capacitance in parallel that causes them to measure as inductive (+) below the SRF, and capacitive (-)
6. Which type of filter is called "maximally flat" in amplitude response?
filters have a transfer function that is numerically optimized to produce the maximum rate of rejection out of
band while producing no amplitude ripple in the passband. It turns out to be a very simple equation.
7. What is the approximate melting point of common lead-free solder (e.g.,
b) 220 °C (~430 °F)
Use of lead-free solder was mandated by global insistence on conforming to
practices that reduce the amount of heavy metals (e.g.; lead) in waste products. Lead from solder in electronics
represents a very small percentage of overall lead in the world (compared to batteries, x-ray shielding, plumbing,
etc.), but it was an easy target. Lead solders like the common 60Sn/40Pb compound melt at much lower temperatures
(~190°C = 370 °F) than lead-free types. SnAg3.0Cu0.5 (~220 °C = 430 °F) is the mix
JEITA for reflow while
iNEMI recommends SnAg3.9Cu0.6 (~ same
melting point as SnAg3.0Cu0.5). The down side is that the higher melting temperatures
require much more energy usage, so while pollutants in landfills go down, pollutants in the atmosphere go up
Pb-Free Solder: Today's Stuff Too Energy-Inefficient).
8. What is the gain of the opamp
The gain for an inverting configuration opamp is:
G = - Rfeedback/Rinput
9. What is the gain of the opamp
The gain for a non-inverting configuration opamp is:
G = 1 + Rfeedback/Rinput
10. Which type of transistor is
shown to the right ?
a) Enhancement Mode N-Channel MOSFET
A simple tip for interpreting the symbol
for a MOSFET is that the arrow tip always points to the N-type material (true for all semiconductors), and the
broken line for the channel suggests that is needs to be completed (enhanced) to permit current flow.