Lesson 14 Flashcards – Transistors and Digital Logic 1

What is a transistor?

A small electronic device made from semiconductor material that can amplify a signal or act like a switch.

In digital logic, what does a transistor being ON represent?

ON means current flows, which we treat as a 1.

In digital logic, what does a transistor being OFF represent?

OFF means no current flows, which we treat as a 0.

What is a semiconductor?

A material that is not a full conductor and not a full insulator. Its conductivity can be changed using doping.

What does doping do to a semiconductor?

It adds small amounts of other chemicals to change electrical properties, creating N-type or P-type regions.

What is an N-type region?

A doped semiconductor region with extra electrons (negative charge carriers).

What is a P-type region?

A doped semiconductor region with holes (missing electrons that behave like positive charge carriers).

What are the three terminals of a BJT transistor?

Emitter, Base, and Collector.

For an NPN transistor, what happens when a small current flows into the base?

It allows a larger current to flow from collector to emitter (the transistor turns ON).

How can you conceptually build an AND gate using transistors?

Use two switching devices in series so current only reaches the output when both inputs are ON.

How can you conceptually build an OR gate using transistors?

Use two switching paths in parallel so current reaches the output when either input is ON.

What does a NOT gate do?

It flips the input: 1 becomes 0, and 0 becomes 1.

What is a truth table?

A table that lists all possible input combinations and the resulting output for each combination.

How many rows are in a truth table with n inputs?

2^n rows.

How many input combinations exist for a 2-input logic circuit?

4 combinations.

How many input combinations exist for a 3-input logic circuit?

8 combinations.

Why does transistor count matter in engineering?

More transistors increases chip area, energy use, and cost.