Digital Integrated Circuits
Digital integrated circuits are small, inexpensive and efficient, allowing the creation of complex electronic systems. They can perform tasks, such as signal amplification and data processing, that were previously performed by individual components.
After synthesis and verification, the gate-level netlist is transformed into physical layout, which includes floorplanning methods to ensure that all blocks and pads meet their design goals. Then, routing automation scripts and software are used to connect each element.
ICs are small electronic circuits that contain buck switching regulator numerous components such as transistors, diodes, memory, capacitors and logic gates. They operate with individual voltage levels and are typically used in linear (analog) or digital systems that utilize Boolean algebra.
Integrated circuits have the advantage of being smaller than other types of electronic devices. They are used in a wide range of electronics, including automotive controls, computers, MP3, toasters and microwaves. Military equipment, aeroplanes and space crafts also rely on them.
ICs were first invented by Jack Kilby at Texas Instruments in 1958. He used germanium to construct his prototype. Today’s ICs consist of millions or billions of components all made from the same piece of silicon shaped like reliable pipes, or wafers. Each component is positioned and connected to its neighbours on the chip through a process of doping certain areas of the wafer. Two main technologies for the manufacture of ICs are TTL and CMOS. Both have different characteristics, and each is used in specific applications. The CMOS circuits are designed to be simpler and consume less power than the TTL.
Logic gates are the basic building blocks of a digital circuit. They take one or more bits of input and give a bit as an output based on Boolean logic. The output can be either a 1 or a 0. The relationship between the input and output is described by a binary number called a truth table for each gate type. There are seven basic gates: AND, OR, XOR, NOT, NAND and NOR. Each has its own graphic symbol and truth table.
The basic logic gate functions can be combined into larger circuits using combinations and sequential type gates. They can also be arranged in latching circuits that hold the gate output in a given state. A combination of such gates can be used to store a multiple-bit value in a storage device called a flip-flop.
There are also programmable logic devices that perform the same function as machines based on logic gates, but can be reprogrammed without changing the wiring. They are also often known by the abbreviation PLD (Programmable Logic Device). They operate much faster than standard TTL digital logic gates and can tolerate more noise on their inputs.
The heart of any digital IC is a transistor. It performs two essential tasks: amplifier and switch. In the former, a small change in the input current or voltage changes the output current and voltage and thus amplifies the strength of the signal. In the latter, a change in the input current or voltage changes the state of the transistor and thus either turns the signal “on” or “off”.
Silicon (Si) is not naturally a conductor of electricity (it falls somewhere between a real metal like copper and an insulator such as plastic). However, a chemical process called doping enables the semiconductor to gain free electrons that carry electric currents.
The outer layers of the semiconductor are called the drain and source. The central layer is power management called the gate. A small voltage applied to the gate permits a large current to flow between the drain and source, amplification the input signal. A larger voltage at the gate blocks the current and thus turns the signal “off”. The three terminals of a transistor are called the emitter, base and collector. The simplest configuration is the N-P-N transistor which has one N-type semiconductor material between two P-types.
Capacitors are electrical devices that store energy and quickly release it. They have two metal plates separated by a non-conducting substance, called a dielectric. The dielectric can be anything from mica to porcelain to Teflon. The plates are connected to terminal wires that connect them to other parts of the circuit.
The plate on one end of the capacitor receives electrons from a battery, which gives it an overall negative charge. As the number of electrons on the first plate grows, they repel the like charges on the other plate, causing it to become positively charged. The large mass of negatively charged electronics sucked into the plates makes them a very powerful electric source, and they are often used to power other electronic components.
A capacitor’s ability to hold charges, known as capacitance, depends on its shape and size. The bigger it is, the more charges it can hold. The capacitance is also affected by the type and thickness of the dielectric. It can range from less than a microfarad (millionths of a farad) to 2 kilofarads, the value of which opens up new technological possibilities such as regenerative braking in electric cars and industrial electrical motors and computer memory backup during power loss.
Memory is the ability to retain and recall information over time. A computer’s internal memory, called RAM (random access memory), is a digital IC that stores data and programs for quick retrieval. Other digital ICs that work with memory are flip-flops, counters and shift registers, which are used to build sequential logic circuits that react to current input values and previous stored states.
The complexity of digital ICs varies greatly, from simple 8-bit microcontrollers such as the ATmega328 in the pcDuino and Arduino to complex multi-core microprocessors that organize all activity within the system. These ICs pack thousands, millions and sometimes even billions of transistors on a single chip. To handle the massive amounts of current they produce, designers add metal trunks of power, called power rails, that take away from available routing area on the IC.
Linear integrated circuits excel at applications that require analog signal processing, such as amplification and filtering, while digital integrated circuits are best at logic operations and digital signals. Programmable ICs, such as FPGAs and CPLDs, are able to implement custom logic functions, making them useful for prototyping and constructing reconfigurable digital circuits.