Integrated Circuits

Table of Contents

What is an Integrated Circuit?

An integrated circuit, also known as a microelectronic circuit or microchip, is the result of an assembly of active components and passive components. Examples of active components are transistors and diodes and examples of passive components are capacitors and resistors. The interconnections between these devices are built on a thin substrate of a semiconductor material, which is often silicon. The result is the integrated circuit which may be anywhere between a couple square centimeters or a few square millimeters large. The active and passive components are not easily seen as they are normally microscopically small [1].

Types

Analog vs. Digital Circuits

Analog circuits, also known as linear circuits, are some of the simplest integrated circuits and have few components. They are mainly used to send signals to an environment or collect signals from an environment. One such example is the use of a microphone. The microphone will convert sound waves to varying voltages and the analog circuit will do something useful with this, like amplifying of filtering the sound. Another use of analog circuits is when a temperature sensor shows a change in temperature, the analog circuit turns on a heater once the temperature has passed a certain threshold [3].

On the other hand, digital circuits are circuits that are designed to only accept voltages of certain values. They include binary circuits, which can be used to express Boolean algebra and use transistors as switches.

Microprocessor Circuits

These are the most complicated kinds of integrated circuits. They are made up of billions of transistors that have been created as thousands of individual circuits. Each of these smaller circuits has its own logic function, and the entire microprocessor circuit is built of these logic gates synchronized with one another. The director in the microprocessor is called the clock (a signal that alternates quickly between two logic states). Every logic gate in the microprocessor executes some function when the clock changes state. Microprocessors also contain some circuits known as registers that are memory locations. There are many types of registers; permanent, temporary, program counter, stack point and the memory address register. Permanent registers hold the preprogrammed instructions for operations, such as addition. Temporary registers store in numbers to be operated on and the result. The program contains the address in memory of the next instruction, the stack pointer contains the address of the last instruction in the stack, and the memory address register contains the address of the data to be worked on or where the result (data that has been processed) should be stored. Microprocessors are powerful and can perform billions of operations per second. They are used in computers, televisions, cars, and more [1]. 

Memory Circuits

Since microprocessors often have to store more data than what can be held in a couple of registers, this information is passed to memory circuits. These memory circuits are made of arrays of parallel circuits that use voltage states to store information. Memory can also store the temporary sequence of instructions (also known as the program) that is used for the microprocessor. One challenge in the industry is to continually reduce the size of memory circuits in order to pack more information or storage into a smaller amount of space. Furthermore, normally smaller components reduce the cost, making memory circuits less expensive [1].

Design

Analog Design

Analog circuits take an infinitely variable real-world voltage or current and modify it in some useful way. This includes amplification, comparison, mixing, separation, examination for values, or manipulation. For this design of an analog circuit, the choice of each component, size, placement, and connection is very important. Unique decisions have great consequences. For example, decisions like whether one resistor should be parallel or perpendicular or whether a wire should lie on top of another will have a great impact on performance. Every detail affects the performance.

Back when integrated circuits were significantly simpler, component values could be calculated by hand. A specific amplification value (also known as gain) of an amplifier could be calculated from the ratio of two resistors. The current could then be determined using the resistor value required for the gain and the supply voltage that was used. When designs became more complex, laboratory measurements were used to characterize the devices. Graphs were drawn of the characteristics and referred to for calculations. As characterization was improved for the physics of the devices, complex equations that took subtle effects into account were developed. There are some parasitic components (unwanted effects) that have been discovered to be inherent in the way some devices are built. As circuitry became small, these unwanted effects became more problematic as the transistors run at higher frequencies. These effects can be accounted for with very complex equations and computers now do these calculations [1].

Digital Design

Digital circuits involve millions of times as many components as analog circuits. Most of the design work is done by copying or reusing the same circuit functions and using software that contains libraries of pre-structured components. The design and layout of an analog circuit is much more time consuming, innovative, and demanding than that of a digital one. Digital design focuses on different skills from analog design [1].

Mixed-Signal Design

This is a design that contains both analog and digital circuity (also known as mixed-signal chips), special simulators are necessary. They employ the same simplifying idea as digital ones to model entire circuits rather than individual transistors. The simulators are primarily designed to speed up simulations on the analog side of a mixed-signal chip. The difficulty lies in making sure the analog part of the circuit simulation is accurate. Since every analog circuit is different, it requires more work [1].

References

[1] “Integrated Circuit,” Britannica. [Online]. Available: https://www.britannica.com/technology/integrated-circuit/Microprocessor-circuits. [Accessed: 18-Feb-2021].

[2] "Integrated Circuit- The miniaturizing aid for electronics," ELE Times. [Online]. Available: https://www.eletimes.com/integrated-circuit-the-miniaturizing-aid-for-electronics. [Accessed: 04-Mar-2021].

[3] "Difference between Analog and Digital circuits," School Electronic. [Online]. Available: https://www.schoolelectronic.com/2012/01/difference-between-analog-and-digital.html. [Accessed: 04-Mar-2021].

[4] "Modern Nonmechanical Memory," All About Circuits. [Online]. Available: https://www.allaboutcircuits.com/textbook/digital/chpt-15/modern-nonmechanical-memory/ [Accessed: 04-Mar-2021].