GATE Technical: ELECTRONICS COMM. ENGG. - EC questions with solutions

Q1. Common Data for Questions 48 and 49: With 10 V dc connected at port A in the linear nonreciprocal two-port network shown below, the following were observed: (i) 1 Ω connected at port B draws a current of 3 A (ii) 2.5 Ω connected at port B draws a current of 2 A With 10 V dc connected at port A, the current drawn by 7 Ω connected at port B is

1. 3/7 A
2. 5/7 A
3. 1 A
4. 9/A

Answer: 1 A

Using I=E/(R+R0): 3=E/(1+R0) and 2=E/(2.5+R0) give R0=2 ohm and E=9 V. For R=7: I=9/(7+2)=1 A, not 5/7 A.

Q2. Common Data for Questions 50 and 51: In the three dimensional view of a silicon n-channel MOS transistor shown below, δ = 20 nm. The transistor is of width 1 μm. The depletion width formed at every p-n junction is 10 nm. The relative permittivities of Si and SiO2, respectively, are 11.7 and 3.9, and ε0 = 8.9 × 10⁻¹² F/m. The gate-source overlap capacitance is approximately

1. 0.7 fF
2. 0.7 pF
3. 0.35 fF
4. 0.24 pF

Answer: 0.7 fF

The correct option is right because the gate-source overlap capacitance can be calculated using the formula that incorporates the dimensions of the transistor, the permittivities of the materials involved, and the depletion width. Given the provided values, the calculation yields approximately 0.7 fF.