Sage-Tips

What happens when pmos and NMOS interchange with one another in CMOS?

When pmos and nmos are interchanged in CMOS inverter it gives a buffer with weak output states. If again the PMOS transistor be from Vcc down so when its input goes low it passes and pulls the output high opposite to the NMOS one be at ground so when input goes high then output goes low.

What happens when NMOS is connected to VDD?

If we connect the buck of nMOS to VDD, the PN junction between source-to-buck and drain-to-buck will forward biased, and there will be a very large current flow between source to buck and drain to buck, which is not allowed. The reason for pMOS is the same.

What will happen if pmos are connected in pull down network and NMOS are connected in pull up network?

If input is One for an inverter in CMOS, N transistor will be drive the output to Zero as pull down. If PMOS is used to pull down with source as VSS output will be at By and similarly, NMOS gives VDD minus one threshold as output if source connected to VDD.

Why is it that the NMOS is always connected to VSS?

Because the voltage between the Ground and the Source in the NMOS transistor has to be positive, so the logical choice is to connect the Source to the ground. In PMOS, the voltage between the Gate and the Source has to be negative, so you connect the Source to VDD. Refer to this video for details.

When NMOS is off and PMOS transistor is on in CMOS logic design then output will be?

The CMOS inverter consists of the NMOS and the PMOS field-effect transistors connected in one below the other. PMOS will be shorted and output will be High.

How NAND gate can be realized with PMOS and NMOS?

For the design of ‘n’ input NAND or NOR gate: In case of NAND gate, 3 pMOS will be connected in parallel and 3 nMOS will be connected in series, and other way around in case of 3 input NOR gate. The same pattern will continue even if for more than 3 inputs.

Why is NMOS connected to ground and PMOS to VDD?

Because Drain and Souce same type semiconductor, substrate is opposite type. Substrate produce diode with source and drain and we can bloke this diode by Source-Substrate connection else this diode conduct and mos dont work.

When NMOS and PMOS transistors are in off condition?

Explanation: In CMOS logic circuit, the switching operation occurs because N-MOS transistor turns ON, and p-MOS transistor turns OFF for input ‘1’ and N-MOS transistor turns OFF, and p-MOS transistor turns ON for input ‘0’.

Why do we need both PMOS and NMOS transistors to implement a pass gate?

Therefore, connecting an NMOS transistor with a PMOS transistor in parallel provides a single bilateral switch which offers efficient output drive capability for CMOS logic gates controlled by a single input logic level.

Why NMOS output should be charged to VDD-Vth?

Hence, the output should get charged to Vdd. But due to threshold voltage effect, nMOS is not capable of passing Vdd/ good logical 1 at the output. Hence, the output will be Vdd-Vth.When logic 0 is applied as input, nMOS transistor turns OFF and PMOS transistor turns ON. Hence, the output should get discharged to ground level.

What is the passing voltage of NMOS and PMOS?

Therefore, Passing of 1 (VDD) from Drain to Source is poor for NMOS. On the other hand, if the PMOS source is connected to VDD, and the input (gate voltage) is LOW, and the output (connected to drain) can go up to VDD. Passing of 1 is well for PMOS.

Can a PMOS be connected to VDD?

On the other hand, if the PMOS source is connected to VDD, and the input (gate voltage) is LOW, and the output (connected to drain) can go up to VDD. Passing of 1 is well for PMOS.

What is the function of MOSFET in NMOS?

MOSFET is a symmetrical device that means source and drain can be interchanged (if body is not short circuited to any of the drain or source). For an NMOS to pass VDD (logic 1) from input node to output node gate should be logic 1 . And the node out gets gradually charged from 0 towards VDD .