PPT CMOS.pptx
- 1. DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING FUNDAMENTALS OF CMOS PREPARED BY -
- 2. CMOS (Complementary Metal-Oxide Semiconductor) • CMOS is the semiconductor technology used in the transistors that are manufactured into most of today's computer microchips. • In CMOS technology, both kinds of transistors are used in a complementary way to form a current gate that forms an effective means of electrical control.
- 3. CMOS (Complementary Metal Oxide Semiconductor) • The main advantage of CMOS over NMOS and BIPOLAR technology is the much smaller power dissipation. • Unlike NMOS or BIPOLAR circuits, a Complementary MOS circuit has almost no static power dissipation. • Power is only dissipated in case the circuit actually switches. This allows integrating more CMOS gates on an IC than in NMOS or bipolar technology, resulting in much better performance. • Complementary Metal Oxide Semiconductor transistor consists of P-channel MOS (PMOS) and N-channel MOS (NMOS) transistor.
- 4. Schematic Symbol of NMOS and PMOS
- 5. NMOS • NMOS is built on a p-type substrate with n-type source and drain diffused on it. In NMOS, the majority of carriers are electrons. • When a high voltage is applied to the gate, the NMOS will conduct. • Similarly, when a low voltage is applied to the gate, NMOS will not conduct. • NMOS is considered to be faster than PMOS, since the carriers in NMOS, which are electrons, travel twice as fast as the holes.
- 7. PMOS • P- channel MOSFET consists of P-type Source and Drain diffused on an N-type substrate. • The majority of carriers are holes. When a high voltage is applied to the gate, the PMOS will not conduct. When a low voltage is applied to the gate, the PMOS will conduct. • Hence the PMOS devices are more immune to noise than NMOS devices.
- 8. CMOS Circuit
- 9. CMOS Working Principle • In CMOS technology, both N-type and P-type transistors are used to design logic functions. • The same signal which turns ON a transistor of one type is used to turn OFF a transistor of the other type. • This characteristic allows the design of logic devices using only simple switches, without the need for a pull-up resistor.
- 10. CMOS Function • If both p-type and n-type transistor have their gates connected to the same input, the p-type MOSFET will be ON when the n-type MOSFET is OFF, and vice-versa. • The networks are arranged such that one is ON and the other OFF for any input pattern as shown in the figure. • CMOS offers relatively high speed, low power dissipation, high noise margins in both states, and will operate over a wide range of source and input voltages (provided the source voltage is fixed).
- 11. CMOS Inverter
- 12. CMOS Inverter • The inverter circuit is as shown in the figure. It consists of PMOS and NMOS FET. The input A serves as the gate voltage for both transistors. • The NMOS transistor has input from Vss (ground) and the PMOS transistor has input from Vdd. • The terminal B is output. When a high voltage (~ Vdd) is given at input terminal (A) of the inverter, the PMOS becomes an open circuit, and NMOS switched OFF so the output will be pulled down to Vss.
- 13. CMOS Inverter • When a low-level voltage (<Vdd, ~0v) applied to the inverter, the NMOS switched OFF and PMOS switched ON. So the output becomes Vdd or the circuit is pulled up to Vdd. INPUT LOGIC INPUT OUTPUT LOGIC OUTPUT 0 V 0 VDD 1 VDD 1 0 V 0
- 14. CMOS Characteristics • The most important characteristics of CMOS are low static power utilization, huge noise immunity. When the single transistor from the pair of MOSFET transistor is switched OFF then the series combination uses significant power throughout switching among the two stated like ON & OFF. • As a result, these devices do not generate waste heat as compared with other types of logic circuits such as TTL or NMOS logic, which usually use some standing current even they don’t change their state. • These CMOS characteristics will allow for integrating logic functions with high density on an integrated circuit. Because of this, CMOS has become the most frequently used technology to be executed within VLSI chips.
- 15. Advantages of CMOS • It uses a single power supply like + VDD • These gates are very simple • Input impedance is high • CMOS logic uses less power whenever it is held in a set state • Power dissipation is negligible • Fan out is high • TTL compatibility • Stability of temperature • Noise immunity is good • Compact • Designing is very well • Robust mechanically
- 16. The disadvantages of CMOS • The cost will be increased once the processing steps increases, however, it can be resolved. • The packing density of CMOS is low as compared with NMOS. • MOS chips should be secured from getting static charges by placing the leads shorted otherwise; the static charges obtained within leads will damage the chip. This problem can be solved by including protective circuits or devices. • Another drawback of the CMOS inverter is that it utilizes two transistors as opposed to one NMOS to build an inverter, which means that the CMOS uses more space over the chip as compared with the NMOS. These drawbacks are small due to the progress within the CMOS technology.
- 17. CMOS Applications CMOS technology has been used for the following digital IC designs. • Computer memories, CPUs • Microprocessor designs • Flash memory chip designing • Used to design application-specific integrated circuits (ASICs).
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