The IC Revolution: Microelectronics
In the early days of electronic circuits, components like vacuum tubes and transistors were individual devices mounted on a metal chassis or printed circuit boards. Then, in 1959, two researchers, Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor (who were working independently), started the microelectronics revolution by developing the first integrated circuit.
They discovered how to combine or integrate several transistors and resistors and connect them to form a circuit, all on the same small chip of silicon. Today, very complex electronic systems --like microprocessors containing millions of transistors -- can fit on a single inch-square silicon chip. These integrated circuits are what make modern-day computers possible.
You may have heard the term chip, especially when the subject of computer hardware comes up. A chip is a tiny piece of silicon, usually around one centimeter square. A chip may be a single transistor (a piece of silicon that amplifies electrical signals or serves as an on/off switch in computer applications). It can also be an integrated circuit composed of many interconnected transistors. Chips are encapsulated in a hermetically sealed plastic or ceramic enclosure called a package. Sometimes people refer to the whole package as a chip, but the chip is actually inside the package.
There are two basic types of integrated circuit -- monolithic and hybrid. Monolithic ICs include the entire circuit on a single silicon chip. They can range in complexity from just a few transistors to millions of transistors on a computer microprocessor chip. A hybrid IC has a circuit with several chips enclosed in a single package. The chips in a hybrid IC may be a combination of transistors, resistors, capacitors and monolithic IC chips.
A printed circuit board, or PCB, holds an electronic circuit together. The completed PCB with components attached is a printed circuit board assembly, or PCBA. A multilayer PCB may have as many as 10 stacked PCBs. Electroplated copper conductors passing through holes called vias connect the individual PCBs, which forms a three-dimensional electronic circuit.
The most important elements in an electronic circuit are the transistors. Diodes are tiny chips of silicon that act as valves to allow current flow in only one direction. Other electronic components are passive elements like resistors and capacitors. Resistors offer a specified amount of resistance to current, and capacitors store electric charge. The third basic passive circuit element is the inductor, which stores energy in the form of a magnetic field. Microelectronic circuits very rarely use inductors, but they are common in larger power circuits.
Most circuits are designed using computer-aided design programs, or CAD. Many of the circuits used in digital computers are extremely complex and use millions of transistors, so CADs are the only practical way to design them. The circuit designer starts with a general specification for the functioning of the circuit, and the CAD program lays out the complex pattern of interconnections.
The etching of the metal interconnection pattern on a PCB or IC chip uses an etch-resistant masking layer to define the circuit pattern. The exposed metal is etched away, leaving the pattern of connecting metal between components.
Why is AC used in electronic circuits?
In electronic circuits, the distances and currents are very small, so why use AC? First of all, the currents and voltages in these circuits represent constantly changing phenomena, so the electrical representations, or analogs, are also constantly changing. The second reason is that radio waves (like those used by TVs, microwaves and cell phones) are high-frequency AC signals. The frequencies used for all types of wireless communication has steady advanced over the years, from the kilohertz (kHz) range in the early days of radio to the megahertz (MHz) and gigahertz (GHz) range today.
Electronic circuits use DC to provide power for the transistors and other components in electronic systems. A rectifier circuit converts AC power to DC from the AC line voltage.
For more information about circuits, take a look at the links on the next page.