A. low electric field
B. high electric field
C. low magnetic field
D. high magnetic field
Answer: B
The saturation of drain current with an increasing drain to source voltage is caused by velocity saturation which occurs in a high electric field in the channel.
142. Knee voltage is the boundary between
A. active region and saturation region
B. linear and non-linear region
C. linear and saturation region
D. linear and cutoff region
Answer: C
The boundary between the linear and saturation regions defined by Vds=Vgs-Vt is referred to as the ‘knee voltage’.
141. Depletion mode MESFET operates as
A. reverse biased
B. forward biased
C. both reverse and forward biased
D. none of the mentioned
Answer: A
Depletion mode MESFET operates as reverse biased (Vt is lesser than Vgs) and enhancement mode MESFET operates as forward biased.
142. Pinch-off voltage is equal to
A. built-in potential
B. applied voltage
C. sum of built-in potential and applied voltage
D. difference between built-in potential and applied voltage
Answer: C
Pinch-off voltage is the total voltage, both built-in potential and applied voltage necessary to completely deplete the channel of mobile charge carriers.
143. Pinch-off voltage is a function of
A. channel depth
B. channel thickness
C. channel length
D. channel density
Answer: B
Pinch-off voltage is a function of both channel thickness ‘a’ and concentration density Nd and it is always positive.
144. The threshold voltage is sensitive to
A. channel length
B. channel depth
C. doping density
D. doping of the channel layer
Answer: D
The threshold voltage Vt is very sensitive to both the channel thickness ‘a’ and the doping of the channel layer.
145. The dynamic switching energy must exceed the capacitive load.
A. true
B. false
Answer: A
In logic structure, the dynamic switching energy must exceed the energy stored in the capacitive load.
146. To keep dynamic switching energy small
A. logic voltage swing must be large
B. logic current swing must be large
C. logic voltage swing must be small
D. logic current swing must be small
Answer: C
To keep dynamic switching energy small, the logic voltage swing must be kept small. This requires proper control over threshold voltages.
147. The standard deviation of threshold voltage should be ______ of logic voltage swing.
A. less than 5%
B. more than 5%
C. less than 10%
D. more than 10%
Answer: A
To achieve proper control over the threshold voltage, the standard deviation of the threshold voltage should be maintained at less than 5% of the logic voltage swing.
148. In D-MESFET, the voltage swing is less than 1V.
A. true
B. false
Answer: B
In D-MESFET, the logic voltage swing can be larger than 1V which means tolerance to higher threshold voltage variation can be accommodated.
149. Threshold voltage is ________ on implant depth.
A. proportionally dependent
B. inversely proportionally dependent
C. exponentially dependent
D. logarithmically dependent
Answer: C
The threshold voltage is exponentially dependent on implant depth and there is a need for proper control of channel thickness.
150. The drain current is independent of
A. Vgs
B. Vds
C. Vt
D. Vs
Answer: A
The drain current saturates at the same drain to source voltage Vds and is independent of the gate to source voltage Vgs.
151. Impurity concentration should be
A. greater than 20%
B. lesser than 20%
C. greater than 10%
D. lesser than 10%
Answer: B
The channel thickness should be controlled within 20 Armstrong and the change in impurity concentration should be less than 20%.
152. The threshold voltage is independent of pinch-off voltage.
A. true
B. false
Answer: B
The threshold voltage is dependent upon pinch-off voltage Vpo and barrier potential and this is given as the difference between the two.
153. Pinch-off voltage is ______ to channel concentration density.
A. directly related
B. inversely related
C. exponentially related
D. is not related
Answer: A
Pinch-off voltage is directly related to the effective channel concentration density Nd.
“Pinch-off” refers to the threshold voltage below which the transistor turns off.
The pinch-off voltage is the value of Vds when the drain current reaches a constant saturation value.
154. Gain of MESFET is _______ to transconductance.
A. directly proportional
B. indirectly proportional
C. exponentially dependent
D. does not depend on
Answer: A
The gain of the MESFET is directly dependent on the transconductance and output conductance of the device.
155. Transconductance gives the relationship of
A. Ids and Vds
B. Vds and Vgs
C. Ids and Vgs
D. Ids and d
Answer: C
Transconductance describes the relationship between the output current Ids and the input control voltage Vgs.
156. Output conductance gives the slope of linear characteristics.
A. true
B. false
Answer: B
Output conductance is also used to measure the gain of MESFET and it gives the slope of output characteristics.
157. The transconductance value in cut off region is
A. Vds
B. 1
C. cannot be determined
D. 0
Answer: D
The transconductance value for the cut-off region is 0 and it is the relationship between Ids and Vgs.
158. GaAs device has
A. high bandwidth
B. high transconductance
C. low gate capacitance
D. all of the mentioned
Answer: D
GaAs devices have high transconductance, very low gate capacitance, high gain, and high bandwidth.
159. Transconductance is not influenced by transistor size.
A. true
B. false
Answer: B
Transconductance is independent of process and slightly influenced by the transistor size. In GaAs transconductance is both process and size-dependent.
160. Switching speed does not depend on
A. gate length
B. gate voltage
C. carrier mobility
D. doping level
Answer: D
The switching speed of the device depends on gate length, gate voltage, and carrier mobility in the channel but does not depend on the doping level.
