MOS Family-PMOS and NMOS

NMOS devices are formed in

• a) p-type substrate of high doping level

• b) n-type substrate of low doping level

• c) p-type substrate of moderate doping level

• d) n-type substrate of high doping level

Answer explanation

nMOS devices are formed in a p-type substrate of moderate doping level. nMOS devices have higher mobility and is cheaper.

Source and drain in nMOS device are isolated by

• a) a single diode

• b) two diodes

• c) three diodes

• d) four diodes

Answer explanation

: The source and drain regions are formed by diffusing n-type impurity, it gives rise to depletion region which extend in more lightly doped p-region. Thus Source and drain in a nMOS device are isolated by two diodes.

In depletion mode, source and drain are connected by

• a) insulating channel

• b) conducing channel

• c) Vdd

• d) Vss

Answer explanation

In depletion mode, source and drain are connected by conducting channel but the channel can be closed by applying suitable negative voltage to the gate.

The condition for non saturated region is

• a) Vds = Vgs – Vt

• b) Vgs lesser than Vt

• c) Vds lesser than Vgs – Vt

• d) Vds greater than Vgs – Vt

Answer explanation

The condition for non saturated region is Vds lesser Vgs – Vt. In non saturation region MOSFET acts as voltage source. Varying Vds will provide significant change in drain current.

In enhancement mode, device is in ---------------------condition

• a) conducting

• b) non conducting

• c) partially conducting

• d) insulating

Answer explanation

In enhancement mode, the decive is in non conducting condition. For n-type FET, threshold voltage is positive and p-type threshold voltage is negative.

The condition for non conducting mode is

• a) Vds lesser than Vgs

• b) Vgs lesser than Vds

• c) Vgs = Vds = 0

• d) Vgs = Vds = Vs = 0

Answer explanation

In enhancement mode the device is in non conducting mode, and its condition is Vds = Vgs = Vs = 0.

nMOS is

• a) donor doped

• b) acceptor doped

• c) all of the mentioned

• d) none of the mentioned

Answer explanation

nMOS transistors are acceptor doped. Acceptor is a dopant which when added forms p-type region. Some of the accpetors are silicon, boron, aluminium etc

MOS transistor structure is`

• a) symmetrical

• b) non symmetrical

• c) semi symmetrical

• d) pseudo symmetrical

Answer explanation

MOS transistor structure is completely symmetrical with respect to source and drain

pMOS is

• a) donor doped

• b) acceptor doped

• c) all of the mentioned

• d) none of the mentioned

Answer explanation

nMOS is acceptor doped and pMOS is donor doped devices. Acceptor doped forms p-type region and donor doped forms n-type region

Inversion layer in enhancement mode consists of excess of

• a) positive carriers

• b) negative carriers

• c) both in equal quantity

• d) neutral carriers

Answer explanation

Inversion layer in enhancement mode consists of excess of negative carriers that is electron