ARL-June 2017 Page 1 ASSIGNMENT #1 for FULL-TIME Students – JUNE 2017 ANALOG AND DIGITAL ELECTRONICS 201CDE 1. Write the node-voltage equations in phasor domain (π‘—πœ”) for the circuit shown in Figure 1 using the labels shown, incorporating the ideal OPAMP model so that the equations are solvable, but do not solve. 10 Marks Figure 1 2. Design an OPAMP differential amplifier with: a. A gain of 67 and a minimum input resistance of 22 kΩ for each input. 5 Marks b. For an OPAMP with CMRR = 67 with a maximum common-mode signal of 0.08V, find the differential input signal for which the differential-mode output is greater than 90 times the common-mode output. 5 Marks ARL-June 2017 Page 2 Verify your results using MULTISIM and explain your results using several different waveforms. 10 Marks 3. Design an operational amplifier circuit that performs the mathematical operation of differentiation – the circuit produces a voltage which is directly proportional to the input voltage’s rate-ofchange with respect to time. 5 Marks a. Explain fully the operation of the circuit and derive its input/output characteristic equation. 10 Marks b. Using MULTISIM show the performance of the circuit when the input was impressed with the following waveforms. i. Square Wave ii. Triangular Wave iii. Sine Wave 10 Marks c. The designed circuit may be susceptible to instability and noise. Propose a modification to the circuit so that the overall closed loop gain is not much affected by high frequencies. 5 Marks 4. An oscillator is the basic element of all AC signal sources and generates sinusoidal signals of known frequency and amplitude. It is one of the basic and useful instruments used in electrical and electronic measurement. Oscillators are used in many electronics circuits and systems providing the central clock signal that controls the sequential operation of the entire system. a. Describe the operation of an OPAMP-based oscillator using the concept of a basic oscillator feedback circuit. Your description must include all pertinent equations relating the overall closed loop gain and the open-loop and feedback gain 10 Marks ARL-June 2017 Page 3 b. Figure 2 shows the complete schematic diagram of a variable frequency Colpitts Oscillator. Use the MULTISIM platform to simulate the operation of this oscillator as you vary the values of the inductor, 𝐿, from 1πœ‡π» to 62π‘šπ». What is the gain of the oscillator? 3 Marks i. Tabulate the output frequencies versus the various inductor values. 7 Marks ii. Show the output waveforms as displayed on the oscilloscope for ten selected frequencies. 10 Marks iii. Show the output waveforms as displayed on the spectrum analyzer of the output amplitude versus frequency. 10 Marks Figure 2: Complete schematic diagram of a Colpitts Oscillator