EECE 310 Exam 2, Fall 2007

EECE 310 – Electronics – Quiz 2 – Fall 2007-2008 - Page 1 of 6 American University of Beirut Department of Electrical and Computer Engineering EECE 310 – Electronics Quiz 2 – December 7, 2007 Closed Book – No Programmable Calculators 90 minutes Penalty is 5 to 1 Name: _________________________________ ID number: _________________ Use ni ≈ 1.25×1010 / cm3 Dp = 12 cm2/s, Dn= 34 cm2/s μp = 470 cm2/V.s, μn = 1333 cm2/V.s. q = 1.6×10-19 C k = 1.38×10-23 J/K 1 μm = 10-4 cm VT ≈ 25 mV (when T is not specified) ▬▬▬▬▬▬▬▬ 1. The electron and hole concentrations in a semiconductor material are as shown in the figure below. The direction of current flow is in the: a) negative x direction for holes, positive x direction for electrons b) positive x direction for holes, positive x direction for electrons c) negative x direction for holes, negative x direction for electrons d) positive x direction for holes, negative x direction for electrons e) none of the above 2. In Problem 1, the magnitude of the total current (in μA) when L = 2.5 μm and A = 1 μm2 is: a) 10.3 b) 31 c) 20.7 d) 15.5 e) 12.4 Questions 1 to 4 are not included in Fall 2008-2009 Quiz 2 EECE 310 – Electronics – Quiz 2 – Fall 2007-2008 - Page 2 of 6 ▬▬▬▬▬▬▬▬ 3. A PN junction diode is formed by doping the P type at a density NA = 4×1016 cm-3 and the N type at a density ND = 5×1017 cm-3. Find the minority concentration in the N-type material (in cm-3). a) 390.6 b) 260.4 c) 520.8 d) 223.2 e) 312.5 4. Find the potential barrier (in V) at T = 273 K, when the doping density of acceptors is increased to 7×1016 cm-3. a) 0.758 b) 0.769 c) 0.778 d) 0.785 e) 0.792 ▬▬▬▬▬▬▬▬ 5. An N-channel MOSFET with k’ = 100 μA/V2 is biased in the triode (linear) region. The drain current is 1 mA at an overdrive voltage of 0.6 V. When VOV increases to 0.8 V, with constant VDS, the drain current increases to 1.9 mA. Find the value of VDS (in V). a) 0.89 b) 0.84 c) 0.63 d) 0.76 e) 0.4 6. Find the value of (W/L) for the MOSFET in the previous problem. a) 72.8 b) 62.5 c) 55.7 d) 59.6 e) 65.8 ▬▬▬▬▬▬▬▬ 7. A P-channel MOSFET is biased at VGS = –3, VDS = –1, and has a threshold voltage Vt = –1 V. Find its region of operation. a) Saturation b) Not enough data to decide c) Triode (linear) d) Cut-off e) None of the above ▬▬▬▬▬▬▬▬ 8. In the circuit shown in Figure A, find the value of VDD (in V) that will place the MOSFET at the edge of saturation (i.e. at the intersection between triode and saturation). Assume RD = 6 KΩ, and for the MOSFET: k’(W/L) = 0.5 mA/V2 and Vt = 0.7 V. RD VDD 3 V Figure A a) 10.2 b) 11.6 c) 8.91 d) 6.27 e) 7.59 EECE 310 – Electronics – Quiz 2 – Fall 2007-2008 - Page 3 of 6 9. In the circuit shown in Figure A, assume VDD = 12 and RD = 5 KΩ. For the MOSFET: k’(W/L) = 0.5 mA/V2, Vt = 0.8 V, and λ = 0.03 V–1. Find the value of VDS (in V) for the MOSFET. a) 3.89 b) 2.81 c) 6.25 d) 5.04 e) 7.55 10. Find the value of gm (in mA/V) for the MOSFET in Problem 9. a) 1.67 b) 1.47 c) 0.81 d) 1.04 e) 1.26 11. Find the value of ro (in KΩ) for the MOSFET in Problem 9. a) 45.9 b) 34.4 c) 27.5 d) 22.9 e) 19.7 ▬▬▬▬▬▬▬▬ 12. Consider the two-stage amplifier shown below. What should be the value of G (in mA/V) to get an overall voltage gain vo/vs of 750? 20K 10K 50K 40K vs + + vi + - vo + - io ii v2 + - 30 v2 G vi 40K 30K a) 2 b) 2.5 c) 3 d) 1 e) 1.5 13. Find the overall current gain, in the circuit of Problem 12, io/ii, when the 40K load is replaced by a short circuit. Assume that G = 7 mA/V. a) 20250 b) 15750 c) 11250 d) 13500 e) 18000 ▬▬▬▬▬▬▬▬ Consider the MOSFET amplifier shown in Figure B. The capacitors are very large. vs + vo + - VDD 27K 56K 3.3K 47K 22K vi + - Figure B EECE 310 – Electronics – Quiz 2 – Fall 2007-2008 - Page 4 of 6 14. The MOSFET is biased such that gm = 0.85 mA/V and ro = 100 KΩ. Find the small-signal voltage gain of the amplifier (vo/vi). a) –9.7 b) –7.6 c) –8.1 d) –8.6 e) –9.2 15. Assume that the gain from gate to drain vo/vi is –10. What should be the DC voltage at the drain (in V) in order to have a signal swing of +/– 2 V at the drain, while keeping the MOSFET in saturation? The transistor is biased at VOV = 0.7 V. Neglect signal distortion. a) 3.1 b) 3.3 c) 2.7 d) 2.9 e) 2.5 16. Find the input resistance (in KΩ) of the amplifier shown in Figure B. a) 56 b) 68 c) 82 d) 39 e) 47 ▬▬▬▬▬▬▬▬ To analyze the circuit shown below, we use the MOSFET characteristics shown in Figure C. The iD – vDS curves correspond to the following values of VGS: 1.2, 1.7, 2.2, 2.7, and 3.2 V. The three points shown on the plot have the following coordinates (3.3 V , 3.26 mA), (3.3 V , 5.10 mA), and (4.5 V , 5.36 mA) Assume that VDD is 5 V and RD = 1 KΩ. EECE 310 – Electronics – Quiz 2 – Fall 2007-2008 - Page 5 of 6 iD (mA) 0 1 2 3 4 5 1 2 3 4 5 6 vDS(V) Figure C 17. Find the drain current (in mA) at the operating (Q) point of the MOSFET when VGS = 2.2 V. a) 1.8 b) 3.1 c) 3.6 d) 0.8 e) 0.3 18. Determine the value of λ (in V-1) for the MOSFET. a) 0.05 b) 0.07 c) 0.03 d) 0.02 e) 0.01 19. Determine the value of Vt (in V) for the MOSFET. a) 1.3 b) 1.1 c) 0.7 d) 0.9 e) 0.5 20. What is the region of operation of the MOSFET if VGS is raised to 3.2 V? a) Linear b) Saturation c) Cut-off d) Not enough data to decide ▬▬▬▬▬▬▬▬ In the circuit shown below, VDD is 9 V. The resistor values are RD = 3.3 KΩ, RS = 2.2 KΩ, and RG = 470 KΩ. EECE 310 – Electronics – Quiz 2 – Fall 2007-2008 - Page 6 of 6 21. Find the voltage at the gate of the MOSFET. a) VDD/2 b) 0 c) VDD d) –VDD e) none of the above 22. Find VDS (in V) if ID = 1 mA. a) 4.5 b) 6.5 c) 8.5 d) 10.5 e) 12.5 23. Find ID (in mA) when the MOSFET parameters are k’(W/L) = 1 mA/V2 and Vt = 1.2 V. a) 1.78 b) 2.52 c) 1.06 d) 1.42 e) 2.15 ▬▬▬▬▬▬▬▬ 24. The threshold voltage of an N-channel MOSFET increases from 0.8 to 1.1 V when the source-to-body voltage (VSB) increases from 0 to 3 V. Find the value of γ (in V1/2) for this transistor. Assume that 2φf = 0.6 V. a) 0.445 b) 0.623 c) 0.356 d) 0.267 e) 0.534 ▬▬▬▬▬▬▬▬ 25. In the circuit shown below, VIN is a very small voltage. Find the minimum VG (in V) such that the circuit attenuates VIN by not more than 5%. Assume RL = 150 Ω. For the MOSFET: k’(W/L) = 1 mA/V2 and Vt = 0.8 V. VG VIN VOUT RL a) 1.22 b) 1.85 c) 1.15 d) 1.33 e) 1.50