Overview
An integrated circuit, or IC, combines many electronic components on one small piece of semiconductor. Transistors form the active elements, while diodes, resistive regions, capacitive structures, and layers of metal interconnection complete the circuit. The tiny semiconductor die is then mounted inside a package that provides pins or pads large enough to connect to a circuit board.
VRML Illustration
This original LearnTronics model shows a traditional 16-pin dual-inline integrated-circuit package. The package is much larger than the semiconductor die inside it.
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Digital and analog ICs
Integrated circuits are not all digital. An analog IC works with continuously varying voltages and currents; examples include operational amplifiers, voltage regulators, audio amplifiers, comparators, sensor interfaces, and oscillators. A digital IC represents information using discrete logic states, most commonly called 0 and 1.
Many modern devices are actually mixed-signal ICs containing both analog and digital circuitry. A microcontroller with an analog-to-digital converter is one familiar example.
Logic families
Functionally identical logic can be built with very different transistor technologies. Two families dominate the historical teaching of digital logic:
| Family | Basic construction | Why it matters |
|---|---|---|
| TTL | Bipolar junction transistors, historically with multi-emitter input structures. | Defined the classic 7400-series logic world and was extremely important in computers and control equipment. |
| CMOS | Complementary N-channel and P-channel MOSFETs. | Very low static power and enormous integration density made CMOS the dominant modern digital technology. |
The logic function—NAND, counter, decoder, flip-flop—can be the same while supply voltage, input thresholds, current, speed, power consumption, and electrical compatibility differ greatly.
Small-scale to very-large-scale integration
Early ICs contained only a handful of gates. As fabrication improved, designers moved through small-, medium-, large-, and very-large-scale integration. Today those old labels are mostly historical, but they help explain the progression from a package containing four NAND gates to a processor containing billions of transistors.
Off-the-shelf logic is still useful
Classic logic ICs remain valuable because many jobs do not require a processor. A single inexpensive chip can invert a signal, debounce a switch, count pulses, select one of several inputs, latch a state, shift data, divide a clock, or translate between logic families.
Continue through these pages
The Basics page introduces logic levels, truth tables, pins, supply connections, and safe handling. Inside an IC explains fabrication and packaging. Logic & Gates introduces Boolean functions. Separate pages compare TTL and CMOS, followed by Families & Interfacing. Combinational and Sequential logic organize ICs by function, while Common ICs surveys useful 74xx and 4000-series devices. Memory & PLDs and Timing & Signal Integrity expand the subject before History, Advanced, and To Computers.