Extra exam: circuit components
Semiconductors, logic ICs, optoelectronics, piezoelectric devices and toroids. 62 questions, 10 at a time, starting with ones you haven't seen.
Rules to remember10 key circuit components rulesShow the rules
- A silicon junction starts conducting at roughly 0.6 to 0.7 V, so a base-emitter voltage in that range shows the transistor is biased on. (p. 61)
- Alpha is the common-base current gain, and the frequency where it falls to about 0.7 of its low-frequency value is called the alpha cutoff frequency. (p. 61)
- Hysteresis gives a comparator two slightly different switching thresholds, so small noise near the threshold cannot make the output chatter. (p. 64)
- Tri-state logic outputs can be 0, 1, or a high-impedance off state, which lets several devices share a common bus. (p. 64)
- A CMOS input switches near half the supply voltage, so noise must swing roughly half the supply before it changes the logic state. (p. 65)
- One side of the piezoelectric effect is that a material physically deforms when a voltage is applied across it. (p. 66)
- Most MMICs are designed with 50-ohm inputs and outputs to match common coax and test equipment. (p. 69)
- A good low-noise UHF preamp adds very little noise, and a noise figure around 0.5 dB is typical. (p. 69)
- An optoisolator passes the control signal as light, so the low-voltage control circuit stays electrically isolated from the 120 VAC circuit. (p. 71)
- A fully lit silicon solar cell produces about 0.5 volt with no load, which is why panels connect many cells in series. (p. 72)
Taken from the explanations to checked practice questions; page numbers link to the official handbook.
Sample circuit components questions
1.What happens when the level of a comparator's input signal crosses the threshold voltage?
- AThe feedback loop becomes unstable
- BThe IC input can be damaged
- CThe comparator changes its output state
- DThe reference level appears at the output
Show the answer
✓ C. The comparator changes its output state
A comparator's output switches state whenever its input crosses the threshold voltage.
2.Which of the following is a common use of a Schottky diode?
- AAs a VHF/UHF mixer or detector
- BAs a variable capacitance in an automatic frequency control circuit
- CIn power supplies as a constant voltage reference
- DIn oscillator circuits as the negative resistance element
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✓ A. As a VHF/UHF mixer or detector
Schottky diodes switch very quickly because they have little stored charge, which makes them good VHF/UHF mixers and detectors.
3.What is the beta of a bipolar junction transistor?
- AThe change in collector current with respect to the change in base current
- BThe breakdown voltage of the base-to-collector junction
- CThe frequency at which the current gain is reduced to 0.707
- DThe switching speed
Show the answer
✓ A. The change in collector current with respect to the change in base current
Beta is the common-emitter current gain: how much the collector current changes for a given change in base current.
4.What is a depletion-mode field-effect transistor (FET)?
- AAn FET for which holes are the majority carriers
- BAn FET that exhibits very high electron mobility due to a lack of holes in the N-type material
- CAn FET that exhibits a current flow between source and drain when no gate voltage is applied
- DAn FET that has no current flow between source and drain when no gate voltage is applied
Show the answer
✓ C. An FET that exhibits a current flow between source and drain when no gate voltage is applied
A depletion-mode FET has a built-in channel, so current flows from source to drain with zero gate voltage; gate bias is used to reduce it.