What are the main advantages of MOS transistor

Introduction to MOS tube
MOS tubes are metal oxide semiconductor field effect transistors, or metal insulator semiconductors. The source and drain of MOS transistor can be switched. They are n-type regions formed in p-type backgate. In most cases, the two regions are the same, and even if the two ends are switched, the performance of the device will not be affected. Such devices are considered symmetrical.
Application advantages of MOS transistor
MOSFET was first implemented successfully by D. kahng and Martin Atalla of Bell lab in 1960. The operating principle of this element is very different from that of bipolar junction transistor (BJT) invented by William Shockley and others in 1947. Because of its low manufacturing cost, small area and high integration, it is widely used in large integrated circuits In the field of large-scale integrated circuits (LSI) or very large-scale integrated circuits (VLSI), it is far more important than BJT.
Due to the gradual improvement of the performance of MOSFET components, in addition to the traditional applications in digital signal processing such as microprocessors and microcontrollers, more and more analog signal processing integrated circuits can be realized by MOSFET. These applications are introduced below.
Digital circuit
The progress of digital technology, such as the continuous improvement of microprocessor operation efficiency, has brought more power to the in-depth research and development of a new generation of MOSFET, which also makes the operation speed of MOSFET itself faster and faster, almost becoming the fastest of various semiconductor active components. The main success of MOSFET in digital signal processing comes from the invention of CMOS logic circuit. The greatest advantage of this structure is theory There will be no static power loss on the, and the current will pass only when the logic gate is switched. The most basic member of the CMOS logic gate is the CMOS inverter, and the basic operation of all CMOS logic gates is the same as the inverter. There must be only one transistor (NMOS or PMOS) at the same time In the conduction state, the other must be the cut-off state, which makes there is no direct conduction path from the power supply end to the grounding end, which not only greatly saves the consumption of current or power, but also reduces the heating capacity of the integrated circuit.
Another advantage of MOSFET in digital circuit application is that for direct current (DC) signal, the gate terminal impedance of MOSFET is infinite (equivalent to open circuit) In other words, in theory, there will be no current flowing from the gate terminal of the MOSFET to the ground point in the circuit, but the gate is completely controlled by the voltage. This makes the MOSFET more power-saving and easier to drive compared with their main competitor BJT. In CMOS logic circuits, in addition to the driver responsible for driving off chip load In addition, the logic gate of each stage only faces the gate of the same MOSFET, so it is less necessary to consider the driving force of the logic gate itself. In contrast, the logic circuit of BJT (such as the most common TTL) Without these advantages, the infinite gate input resistance of MOSFET also has other advantages for circuit design engineers, such as less need to consider the loading effect of logic gate output.
Analog circuit
For some time, MOSFET was not the first choice for analog circuit design engineers, because analog circuit design paid attention to performance parameters, such as transistor transduction Or in terms of the driving force of current, MOSFET is not as suitable for the needs of analog circuits as BJT. However, with the continuous evolution of MOSFET technology, today's CMOS technology can also meet the specifications and requirements of many analog circuits. In addition, MOSFET does not have some fatal disadvantages of BJT due to its structure, such as thermal runaway In addition, the voltage controlled resistance characteristics of MOSFET in the linear region can also be used to replace the traditional polysilicon resistor in integrated circuits, or the MOS capacitor itself can be used to replace the commonly used polysilicon insulator polysilicon capacitor, and even show inductor under appropriate circuit control In other words, in addition to playing the role of the original transistor, MOSFET can also be used as a passive device widely used in analog circuits. This advantage makes the implementation of analog circuits with MOSFET not only meet the requirements of specifications, but also effectively reduce the area of the chip and reduce the production cost.
With the progress of semiconductor manufacturing technology, the demand for integrating more functions into a single chip is also greatly increased. At this time, another advantage of designing analog circuits with MOSFET also emerges. In order to reduce the cost of printed circuit board (PCB) In order to reduce the number of integrated circuits used, reduce the packaging cost and reduce the volume of the system, many originally independent analog chips and digital chips are integrated into the same chip. MOSFET originally has great competitive advantages in digital integrated circuits. After MOSFET is also widely used in analog integrated circuits, the difficulty of integrating these two circuits with different functions is also significant In addition, some mixed signal circuits, such as analog-to-digital converter (ADC), can also use MOSFET technology to design products with better performance.
There is also a process technology that integrates the respective advantages of MOSFET and BJT: BiCMOS (bipolar CMOS) is also becoming more and more popular. BJT components are still superior to general CMOS in driving high current, and have some advantages in reliability, such as not easy to be "electrostatic discharge" (ESD) Therefore, many integrated circuit products that require complex noise signal processing and strong current driving capability will be fabricated using BiCMOS technology.

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