[HCRA] Amateur Radio Quiz: The Transistor, Our Three-Legged Friend

[KB1NWH]

Amateur Radio Quiz: The Transistor, Our Three-Legged Friend


By H. Ward Silver, N0AX
ARRL Contributing Editor 
n0ax at arrl.org 

January 04, 2010

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What piece of active equipment in the ham shack doesn't have a transistor in
it somewhere? Could you troubleshoot that equipment? While transistors are
nearly ubiquitous, we often don't understand their inner workings as well as
we might like. Here are some sharp questions to put an edge on your
solid-state know-how.

  _____  

1) What parameter is used to specify the current gain of a bipolar
transistor in a common emitter configuration?
a. Alpha (A)
b. Beta (B)
c. Mu (M)
d. Rho (P)

2) Adding impurities to a pure semiconductor, creating p-type or n-type
material is called:
a. Peaking
b. Passivating
c. Stagger tuning
d. Doping

3) In the acronym "MOSFET," "MOS" stands for
a. Metal Oxide Semiconductor
b. Metal On Sapphire
c. Metal Over Silicon
d. Metallic Organic Source

4) In a transistor fails from excessive voltage, which is the most likely
cause of failure?
a. Thermal runaway
b. Miller effect
c. Avalanche breakdown
d. Parasitic oscillation

5) What is the term that describes FET gate bias reaching the point at which
current flow from drain to source stops?
a. Pinch-off
b. Punch-through
c. Charge starvation
d. Saturation

6) True or False: To cause current to flow in an NPN transistor, electrons
must flow into the base terminal.

7) True or False: In an FET, increasing device temperature causes drain
current to decrease.

8) True or False: Bipolar transistors for RF power amplifiers require
impedance matching to drive a 50 Ω load because their collector impedance is
very low.

9) Match the bipolar and field-effect terminals that have similar functions:
a) Emitter     d) Drain
b) Base          e) Source
c) Collector    f) Gate

10) Which parameter specifies the maximum voltage that a bipolar transistor
can withstand from the collector to emitter with the base terminal open?
a. BVCEO
b. BVEBO
c. PDISS
d. IDSS

11) Which instrument is used to determine the linear region for a
transistor?
a. Network analyzer
b. Octopus
c. Curve tracer
d. Beta tester

12) In a bipolar transistor, the charge carriers are
a. electrons and positrons.
b. electrons and holes.
c. monopoles.
d. torts and writs.

Bonus: Which type of transistor was invented first -- bipolar or
field-effect?

 

Answers

1. b
2. d -- The "dopants" are elements whose atoms have one more or one less
electron than those of the semiconductor in their outer shell.
3. a -- The gate of the MOSFET is a deposit of metal on a layer of
insulating silicon oxide over the underlying source-drain channel.
4. c -- The avalanche is of electrons that are driven across the
transistor's internal potential barriers, causing current to flow unchecked
through the transistor.
5. a -- Viewed in cross-section through the source-drain channel, gate bias
gradually reduces the area through which current flows, eventually reducing
it to zero, as in pinching off water flow through a hose.
6. False -- Conventional current (the flow of positive charge) flows into
the NPN base, but electronic current (the flow of electrons) must flow out
of the base.
7. True -- Because channel resistance increases with temperature, reducing
current, this helps prevent the thermal runaway effect present in bipolar
transistors.
8. True -- Sometimes the output impedance of a large transistor can be a
fraction of an ohm!
9. a-e, b-f, c-d
10. a -- "BV" stands for breakdown voltage, "CE" stands for
collector-to-emitter and "O' stands for remaining terminal open, which is
the base.
11. c -- Curve tracers present a graph of many combinations of current and
voltage through a device.
12. b -- See also the answer to questions 2 and 6.

Bonus: Field-effect devices based on copper-oxide were first described in
the 1920s and 1930s, while the bipolar device was invented in 1948. The
bipolar device proved practical to fabricate, though, and became widely
used.

Author's Note: The Wikipedia entries for the bipolar
<http://en.wikipedia.org/wiki/Bipolar_transistor>  transistor and
field-effect <http://en.wikipedia.org/wiki/Field_effect_transistor>
transistor go into considerable detail about the transistor's functions. You
can also learn more about circuit design with transistors in The ARRL
<http://www.arrl.org/news/stories/2009/10/01/11102/?nc=1>  Handbook for
Radio Communications.