ECE 3043 Lecture Exam 1

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ECE 3043 Lecture Exam 1 September 18, 2020 Dr. Robinson

Lab Section

Name

Instructions.

• Plan to have time to scan and submit your work before the time expires.

• Print your name in the space above and at the top of all other pages in your quiz.

• When possible, express all answers as a decimal number, i.e. do not give an answer that involves fractions, square roots, symbols, etc.

• You Must Show Your Work to Receive Credit for an Answer. Include intermediate results. Clearly indicate the path to your solution.

• Write Answers in the Spaces Provided or Box Your Answers.

• Be Sure To Clearly Label Your Submitted Work.

• Open Lab Manual And Notes. Calculator Permitted. No software. Three Equally Weighted Problems.

• You Have 90 Minutes.

• You Are Not Permitted To Discuss This Exam With Anyone Until The Due Time Has Passed.

• All Work On This Exam Must Be Your Own.

1

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1. For the circuit shown, (a) Find the Thevenin equivalent circuit with respect to C1 in terms of the symbolic component values. Draw the overall equivalent circuit including the capacitor. (b) Find an expression for the current that flows through R2 from right to left at time t. (c) Let V1 = 5u(t), R1 = 3 kΩ, R2 = 1 kΩ, R3 = 3 kΩ, R4 = 1 kΩ, and C1 = 0.1 µF. Solve for the numerical value of the current that flows through R2 from right to left at time t = 200 µs.

2

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2. Determine the complex gain transfer function T̄ (s) = V out/V1 . for the circuit shown below and write it in the space provided. Specify it as a function of the complex frequency, s, and the symbols for the resistors and capacitor. Write it in standard form (a gain multipied by a ratio of polynomials in s having constant terms of 1) Determine the symbolic expressions and the numerical values of the pole and zero frequencies as well as the high and low frequency gains. On the attached graph, plot the asymptotic magnitude of the complex transfer function T̄ (jω) in decibels as a function of the frequency f of the source as f varies from 1 Hz to 1 MHz. When making the plot, use the numerical values given for the resistors and capacitors.

T̄ (s) =

T̄ (0) =

T̄ (∞) =

fp = 3

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fz =

4

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5 10

10

6

f (Hz) 1

10

2 10

10

3

4 10 dB T(jω)

5

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3. Answer the following. (a) An ammeter is used to measure the current through resistor R4 The ammeter reads 1.3314 mA. What is the input resistance of the meter? Is this an ideal meter? Explain.

(b) Design a circuit containing 1 ideal op amp, 1 10 kΩ potentiometer, and any additional resistors that has a gain that varies from −1 to −0.5 as the potentiometer is turned across its complete range. Draw a schematic of your design.

(c) In terms of the symbolic component values, what resistance would be measured across R7 by an ideal ohmmeter?

6

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Figure 1:

7

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