Introduction to Electronic Circuits

Problem 1 (15 points): (Solving time ~10min)

A. Solve the circuit above and find 𝑣𝑥 and 𝑖𝑥. (5 points)
B. Is the 1mA current source, dissipating or generating power? What is power dissipated/generated by the 1mA current source? (5 points)
C. Is the 1V voltage source, dissipating or generating power? What is the power dissipated/generated by the 1V voltage source? (5 points)

Problem 2 (15 points): (Solving time ~10min)
You are required to design a surge protection circuit as shown below using semiconductor diodes with VD,ON = 1V and current handling of 10mA.
A. Draw the schematic of the surge protection circuit that ensures the output voltage (Vout) always lie between -1V and +2V, irrespective of the input voltage (Vin). (Note: The circuit “N” should only have diodes. It has no DC voltage sources.) (10 points)
B. For -5V< Vin < +5V, choose the minimum value of Rs such that the current through the diodes does not exceed their current handling. (5 points)

Problem 3 (15 points): (Solving time ~10min)

Above schematic shows a capacitor-coupled attenuator circuit. Assume C1 and C2 are very large and does not effect the small signal gain at AC frequencies. Both diodes D1 and D2 are semiconductor diodes with following properties.
Diode D1: Saturation current, Is = 2uA, non-ideality factor, 𝜂 = 1.5. (Assume Vt = 25mV)
Diode D2: Saturation current, Is = 1uA, non-ideality factor, 𝜂 = 1.5. (Assume Vt = 25mV) A. Assuming Io is positive, draw the small signal equivalent circuit and express the small signal resistances of the diodes D1 (rd1) and diode D2 (rd2) as a function of current Io. (5 points)
B. Plot the small signal gain (𝑣𝑜𝑢𝑡/𝑣𝑖𝑛) as a function of Io. Assume Io varying between 0 and 2mA. (4 points)
C. What is the small signal gain when Io = 0.5mA, 1mA, and 1.5mA. (6 points)

Problem 4 (15 points): (Solving time ~10min)

Find Io, V1, V2, V3, and V4. (3 points each)
Note: In the final answer, all transistors are in saturation region.

Problem 5 (15 points): (Solving time ~10min)

Assume transistors M1, M2, M3 are in biased in saturation, and transconductances of the transistors M1, M2, and M3 are gm1, gm2, and gm3 respectively. Ignore channel length modulation, i.e., λ = 0 for all transistors.
A. Calculate the small signal gain (𝑣𝑜𝑢𝑡/𝑣𝑖𝑛) in terms of gm1, gm2, gm3 and RL. (10 points)
B. For a given biasing point, gm1 = 1mS, gm2=0.5mS, gm3 = 1mS, and RL = 2KΩ, and small signal input, 𝑣𝑖𝑛 = 0.1sin(100t)-0.3cos(200t), where t represents time. Calculate the average power dissipated in load resistor RL due to this small signal input. (5 points)
Hint: Rms value of A*sin(ωt) is A/ .

Problem 6 (25 points): (Solving time ~20min)
NMOS: µn = 400 cm2/V⋅s, Cox = 4x10-7 F/cm2, Vthn = 1 V, λn = 0.1 PMOS: µp = 100 cm2/V⋅s, Cox = 4x10-7 F/cm2, Vthp = -1 V, λp = 0.2 For the amplifier circuit shown below, assume:
• Iref = 0.2mA,
• (W/L)1 = 1m/0.5m, (W/L)2 = 5m/0.5m, (W/L)3 = 5m/0.5m,
• Rin = 10KΩ, and RL = 5 KΩ.
• All capacitors C1, C2 and C3 are very large and their effect is negligible in small signal circuit.
A. Calculate value of IDS of M3. (4 points)
B. Calculate gm1, gm2 and gm3. (6 points)
C. Calculate value of R1 such that small signal gain is not effected by R1. (When A<A = B). (5 points) D. Calculate value of Rf such that small signal gain is not effected by Rf. (When A