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NMOS is built with n-type source and drain and a p-type substrate, while PMOS is built with p-type source and drain and a n-type substrate. In a NMOS, carriers are electrons, while in a PMOS, carriers are holes. When a high voltage is applied to the gate, NMOS will conduct, while PMOS will not. Furthermore, when a low voltage is applied in the gate, NMOS will not conduct and PMOS will conduct. NMOS are considered to be faster than PMOS, since the carriers in NMOS, which are electrons, travel twice as fast as holes, which are the carriers in PMOS. But PMOS devices are more immune to noise than NMOS devices. Furthermore, NMOS ICs would be smaller than PMOS ICs (that give the same functionality), since the NMOS can provide one-half of the impedance provided by a PMOS (which has the same geometry and operating conditions).
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Why Pmos transistor is usually larger than Nmos transistor in layout?
Due to differences in carrier mobility between P and N type semiconductor, for similarly doped channels the channel of a PMOS FET will be a bit wider than the channel of an NMOS FET so that they both have identical channel resistance. To make the channel wider the PMOS FET will take a larger chip area.
Is cmos a combination of both nmos and pmos?
yes
What happens if you interchange pmos and nmos in a cmos inverter?
it becomes a buffer
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Frequently Asked Questions - Electronics Engg. 1. Insights of an inverter. Explain the working? 2. Insights of a 2 input NOR gate. Explain the working? 3. Insights of a 2 input NAND gate. Explain the working? 4. Implement F= not (AB+CD) using CMOS gates? 5. Insights of a pass gate. Explain the working? 6. Why do we need both PMOS and NMOS transistors to implement a pass gate? 7. What does the above code synthesize to? 8. Cross section of a PMOS transistor? 9. Cross section of an NMOS transistor? 10. What is a D-latch? Write the VHDL Code for it? 11. Differences between D-Latch and D flip-flop? 12. Implement D flip-flop with a couple of latches? Write a VHDL Code for a D flip-flop? 13. What is latchup? Explain the methods used to prevent it? 14. What is charge sharing? 15. While using logic design, explain the various steps that r followed to obtain the desirable design in a well defined manner? 16. Why is OOPS called OOPS? (C++) 17. What is a linked list? 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What are the Disadvantages of cmos over pmos and nmos?
CMOS and NMOS are two logic families. As the name itself indicates, CMOS is complementary Metal Oxide Semiconductor technology. It uses both PMOS and NMOS transistors for design. Whereas, NMOS logic family uses only NMOS FETs for design.
What is the use of pseudo nMOS gates in digital design?
These circuits use nMOS for implementation of a whole gate + one pMOS which is connected between positive supply and nMOS.
Why Pmos transistor is usually larger than Nmos transistor in layout?
Due to differences in carrier mobility between P and N type semiconductor, for similarly doped channels the channel of a PMOS FET will be a bit wider than the channel of an NMOS FET so that they both have identical channel resistance. To make the channel wider the PMOS FET will take a larger chip area.
Is cmos a combination of both nmos and pmos?
yes
What is difference between inverter and buffer?
if you connect Nmos and Pmos other way around then it act as buffer
What happens if you interchange pmos and nmos in a cmos inverter?
it becomes a buffer
What happens if you change pmos to nmos and nmos to pmos in cmos?
It will act like a buffer but not the exact buffer. Since nmos conduct logic 1 weakly and pmos conduct logic 0 weakly, the output ranges from vdd-vtn to vtp. For eg. If you apply 5v then the op will be 4.3 not the complete 5v. If you apply 0v then output will be 0.7v not 0 v. Hope this works
What are sleep transistors?
A rest transistor is either a pMOS or nMOS high VT transistor and is utilized as a change to close off force supplies to parts of a configuration in standby mode. The pMOS rest transistor is utilized to switch VDD supply and henceforth is known as a "header switch."
What type of doping have the drain and the source of a PMOS transistor?
PMOS - (drain + source) = p-type doping NMOS - (drain + source) = n-type doping :)
What are the blocks in logic gates?
The blocks in a logic gate depends on the logic family we use.A logic gate is designed using a specific logic family. The logic families can be DTL, TTL, CMOS etc.The blocks are different for different logic families.The various blocks in various logic families are:Diode logic: diodes and resistorsDTL logic : diodes and resistorsTTL logic : transistors and resistorsNMOS logic: only NMOS FETsPMOS logic: Only PMOS FETsCMOS logic: Both NMOS and PMOS FETsBiCMOS Logic: both transistors and FETs.
Which mos needs logic '1' on its gate terminal to get ON?
It is NMOS FET. PMOS works in a reverse way.
Why the resistance of PMOS is greater than NMOS?
because pmos has low mobility . the inverter threshold voltage can be shifted to the middle and the inverter is more symmetrical in terms of transistor times.
