UNIVERSITY OF CALIFORNIA College of Engineering Department of Electrical Engineering and Computer Sciences EECS 145L: Electronic Transducer Laboratory FINAL EXAMINATION Fall 2013 You have three hours to work on the exam, which is to be taken closed book. Calculators are OK, equation sheet provided. You will not receive full credit if you do not show your work. Use back side of sheet if necessary. Total points = 200 out of 1000 for the course. 1 (50 max) 2 (60 max) 3 (42 max) 4 (48 max) TOTAL (200 max) COURSE GRADE SUMMARY LAB REPORTS: [5 short reports (lowest grade dropped) - 25 points max each] [5 full reports (lowest grade dropped) - 100 points max each] 4 5 6 11 12 13 14 #8 #9 #10 LONG LAB REPORTS (400 max) SHORT LAB REPORTS LAB PARTICIPATION (100 max) (100 max) COURSE LETTER GRADE MID-TERM #1 (100 max) MID-TERM #2 (100 max) FINAL EXAM (200 max) TOTAL COURSE GRADE (1000 max) December 18, 2013 page 1 S. Derenzo
PROBLEM 1 (50 points) 1.1 (10 points) List 4 essential characteristics of the instrumentation amplifier 1.2 (10 points) Describe the thermistor and how it works December 18, 2013 page 2 S. Derenzo
1.3 (10 points) Describe the PIN photodiode and how it works 1.4 (10 points) Describe the Peltier heat pump and how it works 1.5 (10 points) Describe the metal film strain gauge and how it works December 18, 2013 page 3 S. Derenzo
Problem 2 (60 points) Design a system for the amplification and analog filtering of EEG (brain-wave) data, given that The electrical signals (V 1 and V 2 ) are taken from two skin electrodes placed on the head (a third ground electrode is placed on the neck). The wires from the skin electrodes to your system are approximately 1 m long. The 60 Hz electromagnetic interference received by one wire is 100 mv p-p (peak-to-peak) and by the other wire is 110 mv p-p. The desired differential EEG signal has an amplitude of 50 µv p-p and is in the 0.5 to 30-Hz frequency band. Electrode drift produces a differential voltage V ED2 V ED1 of 1 mv p-p in the 0 Hz to 0.1 Hz frequency range, and can be ignored at frequencies above this range. The EMG background amplitude V EMG2 V EMG1 from the head muscles is 100 µv p-p and is in the 100-Hz to 3-kHz band. To summarize the voltages present on the two wires: V 1 = V ED1 + V EEG1 + V EMG1 + (0.050 volts) sin(2πtf 0 ) (f 0 = 60 Hz) V 2 = V ED2 + V EEG2 + V EMG2 + (0.055 volts) sin(2πtf 0 ) You wish to see the differential EEG signal V EEG2 V EEG1 undistorted (variations in gain less than 10% from 0.5 to 30 Hz) and reduce all other backgrounds to below 2% of the EEG signal. The available instrumentation amplifiers have a gain limit of 1000 and a gain-bandwidth of 10 6. Your system should amplify the EEG signal to 5 volts p-p and be able to drive a 10 kω load. 2.1 (10 points) Using the grid below, show the magnitude of V2 V1 as a function of frequency before amplification and filtering. Label all signals and backgrounds. 1,000 100 10 1 0.1 0.01 0.001 0.01 0.1 1 10 100 1,000 10,000 Frequency (Hz) December 18, 2013 page 4 S. Derenzo
2.2 (10 points) Sketch a block diagram of your system, showing all essential components and signal lines \ 2.3 (15 points) Plot the differential voltage gain V out /(V 2 V 1 ) of your system after amplification and filtering, using the grid below. (You may use the voltage ratio or db for the vertical axis.) 0.01 0.1 1 10 100 1,000 10,000 Frequency (Hz) December 18, 2013 page 5 S. Derenzo
2.4 (15 points) Describe your analog filtering in terms of filtering elements, number of poles, and approximate location of corner frequencies. 2.5 (10 points) What is the maximum common mode gain that the instrumentation amplifier can have at 60 Hz? December 18, 2013 page 6 S. Derenzo
PROBLEM 3 (42 points) Analyze a laser communication system for sending information across long distances. (1) The maximum output of the laser into the beam is 1 watt of photons (2) The laser emits at a wavelength of 1240 nm. (Hint: E=1240/λ) (2) The laser beam transmits binary coded information (on/off) (3) The beam is a cone with an opening angle of 10 3 radians. (Hint: radian = arc/radius) (4) A PIN photodiode is used in photovoltaic mode to detect the light and a 100 MΩ resistor is used to convert the diode photocurrent into a voltage. (5) The voltage across the 100 MΩ resistor is amplified with an amplifier having a voltage gain of 10 and a gain-bandwidth product of 10 6. (6) The photodiode is circular with a diameter of 1 mm and its quantum efficiency is 80%. (7) Ignore any background due to sunlight 3.1 (8 points) What fraction of the beam is received by the PIN photodiode at a distance D = 1000 meters? 3.2 (8 points) With the laser beam on (1 watt), at what distance does the amplifier produce a signal of 1 V? December 18, 2013 page 7 S. Derenzo
3.3 (8 points) At room temperature, what is the Johnson noise rms of the 1 MΩ resistor at the output of the amplifier? 3.4 (10 points) For this system, what is the maximum distance that will result in a bit error rate less than 1.97 x 10 9? (Hint: The probability of exceeding 6 standard deviations is 1.97 x 10 9 ) 3.5 (8 points) How would the answer to section 2.4 change if a 10 cm diameter lens were used to focus the laser beam onto the PIN photodiode? December 18, 2013 page 8 S. Derenzo
PROBLEM 4 (48 points) Design a weather station for sensing the following four quantities and producing analog signals with the required amplitudes: (a) Air temperature (b) Barometric pressure (c) Wind direction (d) Wind speed For each section, think about the sensors used in the EECS145L course and sketch your designs in block diagram form. Your designs will be graded on the basis of Meeting the design requirements Sufficient detail so that a skilled technician could build your design. Avoidance of unnecessary complexity (keep it simple) 4.1 (12 points) Design a circuit that uses a solid-state temperature sensor (1 µa/k) to measure the air temperature over the range from 50 C to 50 C and converts it into an analog signal from 5V to + 5V. December 18, 2013 page 9 S. Derenzo
4.2 (12 points) Design a circuit that uses two 100 Ω metal film strain gauges (gauge factor G S = 2) to measure the barometric pressure over the range from 700 to 800 mm Hg and converts it into an analog signal from 0 V to + 10 V. Assume that L/L = 10 4 per mm Hg. 4.3 (12 points) Design a circuit that uses a one-turn rotary potentiometer (spiral resistor with 3 leads) to measure the wind direction over 360 and convers it into an analog signal from 0 V to + 10 V. December 18, 2013 page 10 S. Derenzo
4.4 (12 points) Design a circuit that uses four 100-Ω strain gauges (gauge factor G S = 2) to measure the wind speed over the range from 0 to 200 km/hr and converts it into an analog signal from 0 V to + 10 V. Assume that L/L = 10 5 per km/hr. December 18, 2013 page 11 S. Derenzo