Bipolar Transistors (Art of Electronics, Ch. 2)

84 flashcards by Chris R.

What is a bipolar junction transistor (BJT), in one sentence?
What are the three terminals of a BJT called?
State the transistor's "polarity" rule for an npn transistor.
State the transistor's "junctions" rule.
State the transistor's "current amplifier" rule (the beta relationship).
What does beta (hFE) typically range over for a given transistor type, and why does that matter for design?
What are the three operating regions of a BJT, and what distinguishes each?
Roughly what's the base-emitter voltage drop of a conducting silicon BJT?
Why isn't collector current best thought of as forward conduction of the base-collector diode?
How do you use a BJT as a switch (basic recipe)?
Why should you drive a switch's base current well beyond what IC/beta would predict ("overdriving")?
Why put a diode across an inductive load (e.g. a relay coil, motor, solenoid) driven by a transistor switch?
When should you add a diode in series with (or reverse-biased across, to ground) a switch's collector?
Which BJT polarity switches a load's "low side" to ground, and which switches the "high side" to a positive rail?
What is a Schmitt trigger, and why is it useful?
What is an emitter follower, and why is it called that?
What's the approximate voltage gain of an emitter follower, and why isn't it exactly 1?
If an emitter follower has no voltage gain, what's the point of it?
Emitter follower input impedance, looking into the base?
Emitter follower output impedance, looking into the emitter?
Why can an npn emitter follower only source current into a grounded load, not sink it?
How do you fix an emitter follower's inability to swing symmetrically (two approaches)?
Rule of thumb for biasing an emitter follower's base voltage divider?
Why must there always be a DC path to the base of a follower (or any transistor amplifier)?
Name a few applications where a current source (rather than a voltage source) is needed.
What does the simplest resistor-based current source approximation require, and what's its drawback?
Basic transistor current source: formula for IC in terms of VB and RE?
What makes a transistor current source much better than a plain resistor-to-voltage source?
What determines a current source's "compliance range"?
"Source" vs. "sink" — what do these terms mean, and which polarity of transistor typically does which?
What is a common-emitter amplifier, at the simplest level?
Common-emitter amplifier voltage gain formula, with an emitter resistor (emitter degeneration)?
What is "emitter degeneration," and what three benefits does it bring?
Why is a grounded-emitter amplifier (RE = 0) generally a bad idea outside of a feedback loop?
What is transconductance (gm), and its formula/units?
What is the intrinsic emitter resistance re, and its approximate formula at room temperature?
What does the Ebers-Moll equation relate?
Rule of thumb: how much must VBE increase to raise IC by a factor of 10 (one decade)?
Rule of thumb: roughly how much does IC change per mV change in VBE?
Why is treating the BJT as a "transconductance device" (VBE→IC) more accurate than the simple current-amplifier (IB→IC) model?
What is the Early effect, and what does the Early voltage VA characterize?
What happens to VBE (at fixed IC) as temperature rises — rough tempco?
What's the simplest reliable way to bias a common-emitter amplifier for stable gain despite beta variation and temperature drift?
What's "dc feedback" biasing, and how does it stabilize the quiescent point?
How does using a matched transistor help bias a common-emitter (or emitter-follower) stage?
Why is voltage-divider biasing better than sizing a base resistor from an assumed beta value?
What is a current mirror, in one sentence?
What property must the two transistors in a basic current mirror share, and why?
What limits the accuracy of a simple two-transistor current mirror?
How do emitter resistors improve a current mirror, and why?
What is a Wilson current mirror, and what does it fix that the basic mirror doesn't?
What is a differential amplifier used for?
What's the difference between a "common-mode" and a "differential" (normal-mode) input signal?
What does CMRR measure, and how is it usually expressed?
Basic differential pair gain formula (single-ended output, emitter resistors RE)?
How does replacing the tail resistor with a current source improve a differential amplifier?
How does adding a current-mirror active load boost a differential pair's gain?
Why is a differential amplifier a good choice for a precision DC amplifier, even with a single-ended (one input grounded) input?
How is a differential amplifier used as a comparator?
What is a push-pull output stage, and what problem does it solve?
What is "crossover distortion," and what causes it?
How do you reduce crossover distortion in a push-pull stage?
What's the difference between class-A, class-B, and class-AB operation?
What is a Darlington pair, and what's its effective beta?
What are two drawbacks of the Darlington connection?
What is a Sziklai (complementary Darlington) connection, and how does it differ from a true Darlington?
Why is the Sziklai connection often preferred over the Darlington for output stages?
What is the Miller effect?
Why does the Miller effect matter for high-speed/wideband circuit design?
Name a few circuit techniques that avoid or defeat the Miller effect.
What is the cascode configuration, and how does it defeat the Miller effect?
What is "bootstrapping," in the context of a transistor bias network?
What effect does bootstrapping a collector load resistor have on a common-emitter stage?
What does negative feedback do to an amplifier's gain, at the simplest level?
Closed-loop gain formula in terms of open-loop gain A and feedback fraction B?
What is "loop gain," and why does a large loop gain matter?
What are the main benefits negative feedback brings to an amplifier?
How does negative feedback affect input impedance: series (voltage) feedback vs. shunt (current) feedback?
How does negative feedback affect output impedance, depending on what's sampled at the output?
Why can too much lagging phase shift in a feedback loop turn negative feedback into oscillation?
In a simple zener-based regulated supply improved with an emitter-follower buffer, what does the follower do for the zener?
In a thermistor-based temperature controller comparing a thermistor bridge to a fixed reference divider with a differential amplifier, why use a ratio (bridge-style) comparison rather than comparing the thermistor voltage directly to a fixed voltage?
Why does a "seat-belt buzzer" style logic circuit combine diodes (for OR-gate logic) with transistors (as switches)?
Big picture: what are the core transistor circuit "topologies" this chapter builds almost everything from?