La Trobe University Department Of Electronic Engineering Ele2emi 2007 Assignment

La Trobe University Department of Electronic Engineering ELE2EMI 2007 Assignment 2 Due: 2 pm, Monday 24 September 2006

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Question 1. (Sensors and Transducers) (a) Strain gauge: (i) What is another name for the sensitivity S of a strain gauge? (ii) Write the formula for S in terms of the resistance R and the length L of a conductive bar under longitudinal compression. (b) Thermistor: (i) Write the formula for the resistance R of a thermistor as a function of absolute temperature T, coefficient β, reference temperature T0 and reference resistance R0 . (ii) If a thermistor has a resistance of 200 kΩ at 300 K (kelvin), and a temperature coefficient β = 4000 K, then at what temperature is its resistance equal to 400 kΩ? (c) Thermocouple: In the Seebeck effect, a temperature gradient along a metal bar produces a potential between its ends. Question: What is the name of the converse effect whereby a potential applied between the junctions of two dissimilar metals generates a temperature difference between the junctions?

Question 2. (Basic Counters) (a) In the 74LS163 of the following diagram: (i) What are the functions of the control inputs labelled CLK, CLR, LD, ENP and ENT? (ii) If the output RCO is high, what are the values of QA, QB, QC and QD?

74LS163 CLR

1

16

VCC

rising CLK

2

15

RCO

A

3

14

QA

B

4

13

QB

C

5

12

QC

D

6

11

QD

ENP

7

10

ENT

GND

8

9

LD

(b) Using one 74LS163 combined with one or more logic gates, draw a counter circuit that produces the repeating sequence 3, 4, . . . , 9, 10. (c) Using as many 74LS163s as necessary, draw the circuit diagram for a twelve (12) bit counter.

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Question 3. (Schmitt Triggers) For the simple Schmitt trigger in the next diagram, assume that the maximum and minimum output voltages are +12V and -12V, and that R1 = 10kΩ and RF = 15kΩ. Vout

RF VCC = +12V

VCC R1 Vref

V1

Vout

V2

Vin

Vin VDD

VDD = −12V

Calculate the input voltages V1 and V2 at which the transitions occur.

Question 4. (Data Converters) (a) State the sampling theorem. (b) A twelve (12) bit Digital to Analog Converter (DAC) has a minimum voltage of zero volts (for the binary input zero) and a maximum voltage of 4.095 V (for a binary input of 1111 1111 1111). What binary input produces the output voltage 6.203 V? (c) Analog to Digital Converters: (i) How many clock pulses does it take for a 128-bit ramp ADC to perform a full scale conversion? (ii) Given a 4 GHz clock, how long will that conversion take? (iii) Using the same clock, how long will it take a 128-bit successive approximation ADC to do the same conversion? (iv) Using the same clock, how long would a 128-bit flash ADC would take? (v) Estimate the linear dimensions of a 128-bit flash ADC given current IC technology. [Hint: Suppose that the flash ADC is implemented on a single layer of silicon, and that each comparator (etc.) occupies an area of 1 micrometre (1µm = 10−6 m) square.]

Question 5. (Oscillators) (a) Define the term oscillator. (b) Closed Loop Gain: (i) Quote the formula for closed loop gain in an amplifier feedback circuit. (ii) Name the variables in that formula. (iii) Describe what those variables mean. (c) Wien bridge: (i) Draw a Wien bridge oscillator. (ii) In what frequency band is it useful? (iii) Quote the formula for its oscillation frequency, f0 . page 3 of 4

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Question 6. (Modulation) (a) AM versus FM: (i) Describe amplitude modulation (AM). (ii) Describe frequency modulation (FM). (b) FM modulation index: (i) Quote the formula for the modulation index m of an FM system. (ii) Name all the variables in that formula.

Question 7. (Pulse Generation) (a) Draw the block diagram of a pulse generator. (b) Sketch the pulse waveform from the lecture notes. (c) Define the following terms: (i) rise time, (ii) pulse width, (iii) overshoot, (iv) ringing. Author: Geoffrey Tobin: Tuesday 4 September 2007.

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