-------------------------------------------ELECTRONICS HOMEWORK HELP---------------------------

Phy415 Scientific Electronics Final Quiz

Assigned: May 01, 2012 (Prof. Sajstein Alam)

Due: May 11, 2012

Full Points = 5 x 5 = 100 points

No consultations or Cheating Allowed. The exam will take about 3 to 4 hours. You will be able to get a good score only if you understand the course materials.

Question 1: (DAC) 20 points

Explain how this digital-to-analog converter (DAC) circuit is supposed to function:

Please give a clear explanation. What is the current flowing through the R1 and R4 resistors,

when the switches U1 and U4 are closed?

Question 2 (Op-Amps) 20 points

a) What current flows into “-“input terminal of the op-amp?

b) What is the voltage difference between V- V+ ?

c) Consider V1 = 2mV and Rin = 1 K . Now calculate the input current from this branch into the virtual ground X.

d) Consider V2 = 4mV and Rin = 2 K . Now calculate the input current from this branch into the virtual ground X.

e) Consider V3 = 6mV and Rin = 3 K . Now calculate the input current from this branch into the virtual ground X.

f) What is total current flowing into X?

g) What is IF flowing through the feedback resistor RF?

h) Show in a couple of lines that Vout = - IF RF.

i) Write the complete formula for Vout in terms of input V1, V2, and V3? Assume RF = 20 K .

j) Calculate Vout?

Problem 3 (Digital Logic) 20 points

a) Draw the diagram for the Boolean expression: (A.B).(C+D+E)

b) Draw the diagram for the Boolean

expression: (C+D+E .

c) Combine the above expressions to get the diagram for the Boolean expression:

(A.B).(C+D+E) + (C+D+E). . Use the C, D and E inputs once only.

d) Evaluate the expression (A.B).(C+D+E) for A=1, B=1, and C=0, D=1 and E=1.

e) Evaluate the expression (C+D+E for C=0, D=1 and E=1, and F=1 and G=0.

f) Now evaluate the complete expression given in c for the values of the input in the above two questions.

Problem 4 (Combinational Logic)

What is a Demulitplexer?

Below give the truth table of the demulitplexer?

Show for a and b = 0 and 0, A is selected.

Show for a and b = 1 and 1, D is selected.

How many inputs like a and b are needed if we are demuliplexing eight outputs from A, B, … G, H.

Problem 5 (Oscillator) 20 points

a) Suppose the switch is first connected to A. The capacitors start charging till what time?

b) What is the maximum voltage to which the capacitor will charge?

c) Now the Switch is flipped to B. Describe what will happen?

d) How does the capacitor start charging back?

e) So the capacitor keeps charging and discharging. Will this go on forever?

f) What is the inductive reactance in the circuit if L = 100 mH? Assume a frequency of 200 Hz for the next three questions.

g) What is the capacitive reactance in the circuit if C = 20 pF?

h) What is the condition for getting a resonance?

i) Calculate the resonance frequency for the circuit above?

j) How do you increase the resonant frequency of the circuit?