AERO2705 Space Engineering 1 Week 7 The University of Sydney

Transcription

1 AERO2705 Space Engineering 1 Week 7 The University of Sydney Presenter Mr. Warwick Holmes Executive Director Space Engineering School of Aerospace, Mechanical and Mechatronic Engineering The University of Sydney Page 1

2 Analogue vs Digital electronics What s the difference? Digital electronics dominates the world or does it? PC, internet, MP3, DTV, DVD s, JPG, 4G-mob everything's digital, Digital circuit design requires almost no knowledge of analogue electronics, true? this is dangerous analogue effects are everywhere! In fact, all digital electronics are analogue!. but very fast analogue (e.g. Schmidt trigger, or open loop op-amp) All signals within a microprocessor or any digital device are in fact analogue voltages, currents, with frequency and phase relationships. digital circuits are vulnerable to analogue inductance, resistance and capacitance effects on all signals. The speed or bandwidth of a digital system is determined by transistor switching times (turning on and off) and the physical distance a signal travels between one subsystem and another. These are analogue constraints which determine the performance of digital systems. What limits a processor speed up to 4.0 GHz? The University of Sydney Page 2

3 We actually live in an Analogue World In nature everything is analogue noise, voltage, current are all analogue, no truly natural digital system exists except at the quantum (atomic & subatomic) scale (Heisenberg uncertainty etc.) Digital signals and processing removes analogue ambiguities. Minimizes uncertainty associated with noise and stochastic systems. Ironically as time and technology progresses, digital systems are now designed to mimic analogue systems. (D/A converters, fuzzy logic random noise generators, pseudo random systems) The design of analogue circuitry is based on the time domain, with the fundamental concepts of voltage, current, frequency and phase. Digital circuits are constrained by analogue design issues eg: * Nr. of external gates driven from a single logic output * Bandwidth and switching frequency of logic gates * Power supply must have correct voltage and supply current The University of Sydney Page 3

4 Digital Analogue limitations Digital circuit performance limitations are fundamentally driven by analogue circuit electrical principals. However, clever and complex integrated circuit design has significantly simplified the limitations of simple lumped element analogue components such as inductors, capacitors and active transistor amplifier circuits, filters, etc. Discrete components (capacitors, inductors, transistors, FET s ) have been replaced by well designed integrated circuits that replace discrete components as electrical functional blocks. Circuit design is no longer focused on individual analogue or active component level. A video of how to connect and interface circuits designed using complex principles of integrated circuits replacing discrete equivalent circuits. The University of Sydney Page 4

5 Sensors and Actuators in Spacecraft All electronic systems are processing/managing Inputs & Outputs (Sensor = Inputs) [PROCESSOR] (Output = Actuators) Transducers convert energy of one kind into electrical energy, which can be processed, conditioned or controlled for output. Example of spacecraft Sensor/Inputs and Output/Actuators: Temperature: Thermistor, thermocouple Heater RF communication: RF receiver (LNR) RF Transmitter Rotational motion: Gyroscope Reaction wheel Force/Pressure: Strain gauge Solenoid Optical/ Light: Star tracker, sun sensor Laser, LED Position: Potentiometer, encoder Stepper motor Magnetic: Magnetometer Magnetorquer All acquisition, processing and control by electrical systems. The University of Sydney Page 5

6 Integrated Circuit families IC types include TTL, ECL, CMOS CMOS technology is used in microprocessors, microcontrollers, static RAM, digital logic circuits. Also used for several analog circuits such as image sensors (CMOS sensor) and highly integrated transceivers e.g. within Mobile phones. TTL has much greater heat generation due to quiescent current for off logic states CMOS uses complementary pairs of N type and P type differential pairs in logic states CMOS devices are high noise immunity and low static power consumption. Since one transistor of the pair is always off. The University of Sydney Page 6

7 Electronic basics The University of Sydney Page 7

8 Electrical component breadboard for circuit testing The University of Sydney Page 8

9 Breadboard layout Power rails run vertically for +5v +3.3v and GND Circuit connections Run horizontally joining 5 holes together into a slot. DIP dual in line circuits made to straddle the ravine Or bridge The University of Sydney Page 9

10 Typical breadboard application The University of Sydney Page 10

11 Circuit testing/development with Breadboards Greatest benefit are that connections are solderless, allows rapid changes of circuit layout without PCB re-fabrication. Ideal interface to microprocessors like Arduino, Raspberry Pi. Used to temporarily build an electronic circuit, mimicking the component layout based on a schematic diagram of a PCB. Allows rapid exchange of resistors, capacitors, transistors, switches, relays, sensors, and motors to modify or adapt a circuit design, and monitoring electrical connections. Operates well for low and medium-high frequency operation but generally not >10MHz or GHz. Physical dimensions of the board in terms of capacitive coupling, inductance and noise. Not suitable for Surface Mount Technology (SMT) too small. Biggest problem are accidental dis-connections. The University of Sydney Page 11

12 Power supplies, ACDC.. thunderstruck? The University of Sydney Page 12

13 Resistors. Obey Ohm s law used to reduce current flow, adjust signal levels, divide voltages, bias active elements and terminate transmission lines. Obeys Ohm s Law: Electric Voltage is the product of electric current times resistance. V = I x R The University of Sydney Page 13

14 Connecting resistors Resistors connected in series Resistors connected in parallel Resistor colour codes for Ω The University of Sydney Page 14

15 Capacitors A capacitor is a passive two-terminal component that stores electrical energy in an electric field When connected to a sinusoidal voltage source this causes a phase shifted current to flow through it. In the case that the voltage source is V 0 cos(ωt), the displacement current can be expressed as: The current of the capacitor may be expressed in the form of cosines to show that current leads the voltage by 90 The University of Sydney Page 15

16 Capacitors Capacitors connected in Parallel Capacitors connected in a parallel add up their combined charge according to the individual effective charge on each of the capacitor plates. The total capacitance is simply the sum of all capacitors (or plates) in parallel. Capacitors connected in Series Capacitors connected in series add the reciprocal values of all the capacitors then reciprocate to get the total effective value. The series acts as a capacitor smaller than any of its individual components. The University of Sydney Page 16

17 Modern day electrical engineering! Modern day electrical engineering focuses on high level functionally complex Integrate Circuit (IC) interfacing. Schematic block level electrical functional design is effectively implemented in discrete integrated circuits to create highly complex equipment with relatively little circuitry. Electrical circuit design is trending toward more and more complex functionality integrated into a single monolithic chip. design principles are now focused on correct interfacing not fundamental design from first principles of discrete electrical components. Interface data sheets compress technical requirements of electrical connection into 2-3 pages for a massively complex integrated electrical circuit The University of Sydney Page 17

18 Example of IC circuit interface data sheet HEX level shifter for TTL to CMOS logic voltage levels Converts 6 binary data bits from TTL logic voltage levels to CMOS logic voltage levels CMOS circuits have different input and output (0,1) signals levels than TTL logic. CMOS gates operating at a power supply voltage of 5 volts, Low logic state voltages range between 0.0 volts to 1.5 volts High logic state voltages range between 3.5 volts to 5 volts. TTL gates operating at a power supply voltage of 5 volts Low logic state voltages range from 0.0 volts to 0.8 volts High logic state voltages range between 2.0 volts to 5 volts. The University of Sydney Page 18

19 555 Timer, Clock, Oscillator chip The heart beat of a digital circuit Tutorial how to use a 555 timer The University of Sydney Page 19

20 555 Timer, Clock, Oscillator chip The heart beat of a digital circuit The University of Sydney Page 20

21 Important to protect circuits from excessive voltages, noise, spikes (particularly digital circuits) which can easily be damaged by unregulated voltage disturbances. The University of Sydney Page 21

22 The ubiquitous 741 Op-amp (operational amplifier) The University of Sydney Page 22

23 The ubiquitous 741 op-amp equivalent circuit The University of Sydney Page 23

24 A discrete component 741 op-amp The University of Sydney Page 24

25 741 Op-amp schematic representation Specification sheet The University of Sydney Page 25

26 Effect of Noise in digital modulation Noise causes multiple zero crossings of input signal. These are interpreted as multiple 1 0 transitions. The University of Sydney Page 26

27 Filters implemented by 741 Op amp The advantage of this configuration is that the op-amps high input impedance prevents excessive loading on the filters output while its low output impedance prevents the filters cut-off frequency point from being affected by changes in the impedance of the load. The University of Sydney Page 27

28 Active Low pass Filter with Amplification The voltage gain is given by feedback resistor (R 2 ) divided by input resistor (R 1 ) The frequency response of the circuit is the same as the RC filter, but the amplitude is increased by the pass band gain, A F of the amplifier. A F = the pass band gain of the filter, (1 + R2/R1) ƒ = the frequency of the input signal in Hertz, (Hz) ƒc = the cut-off frequency in Hertz, (Hz) The University of Sydney Page 28

29 Active Low pass Filter with Amplification The Active Low Pass Filter has a constant gain A F from 0Hz to the high frequency cut-off point, ƒ C. At ƒ C the gain is 0.707A F, and after ƒ C it decreases at a constant rate as the frequency increases. When the frequency is increased tenfold (one decade), the voltage gain is reduced by a factor of 10. The gain decreases 20dB (= 20log 10) for every factor of 10 increase in frequency. The University of Sydney Page 29

30 Active Low pass Filter with Amplification Design a non-inverting active low pass filter circuit that has a gain of ten at low frequencies, a high frequency cut-off or corner frequency of 159Hz and an input impedance of 10KΩ. Choose: Resistor values R1 = 1kΩ Resistor values R2 = 9kΩ R input = 10 kω Cap = 100 nf gives f c = 159 Hz The University of Sydney Page 30

31 Electrical Circuit interfacing Input Interfacing Circuits Good site for electronic design and implementation: Build your own electronics lab The University of Sydney Page 31

32 Which is more precise, Which is more accurate? Four decimal places in the DVM implies it is more accurate than the analogue meter. DVM - Rarely do people ask what is the sampling rate? What is the lsb quantization for the DVM digital measurement When do you need more than 0.1v resolution or accuracy? What is the absolute accuracy of the digital measurement? The University of Sydney Page 32