The University of Sydney Page 1

AERO2705Space Engineering 1Week 7The University of Sydney

PresenterMr. Warwick HolmesExecutive Director Space Engineering

School of Aerospace, Mechanical and Mechatronic Engineering

The University of Sydney Page 2

Analogue vs Digital electronicsWhat’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 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 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 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 ↔ HeaterRF communication: RF receiver (LNR) ↔ RF TransmitterRotational motion: Gyroscope ↔ Reaction wheelForce/Pressure: Strain gauge ↔ SolenoidOptical/ Light: Star tracker, sun sensor ↔ Laser, LEDPosition: Potentiometer, encoder ↔ Stepper motorMagnetic: Magnetometer ↔ Magnetorquer

– All acquisition, processing and control by electrical systems.

The University of Sydney Page 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 analogcircuits 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 7

https://www.slideshare.net/El-Rayes/build-your-own-labElectronic basics

The University of Sydney Page 8

Electrical component breadboard for circuit testing

The University of Sydney Page 9

Breadboard layout

Power rails runvertically for +5v+3.3v and GND

Circuit connectionsRun horizontallyjoining 5 “holes” together into a slot.

DIP “dual in line”circuits made to straddle “the ravine”Or “bridge”

The University of Sydney Page 10

Typical breadboard application

The University of Sydney Page 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 12

Power supplies, ACDC ….. thunderstruck?

The University of Sydney Page 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 14

Connecting resistors

Resistors connected in series

Resistors connected in parallel

Resistor colour codes for Ω

The University of Sydney Page 15

Capacitors

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 V0cos(ωt), the displacement current can be expressed as:

A capacitor is a passive two-terminal component that stores electrical energy in an electric field

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 16

Capacitors

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 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 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 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.

– https://www.onsemi.com/pub/Collateral/MC14504B-D.PDF

The University of Sydney Page 19

– Tutorial how to use a 555 timer– https://www.youtube.com/watch?v=stN-ZzHfiO4

555 Timer, Clock, Oscillator chip The heart beat of a digital circuit

The University of Sydney Page 20

555 Timer, Clock, Oscillator chip The heart beat of a digital circuit

The University of Sydney Page 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 22

The ubiquitous 741 Op-amp (operational amplifier)

The University of Sydney Page 23

The ubiquitous 741 op-amp – equivalent circuit

The University of Sydney Page 24

A discrete component 741 op-amp

The University of Sydney Page 25

741 Op-amp schematic representationhttp://www.ti.com/product/lm741Specification sheet

The University of Sydney Page 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 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 28

Active Low pass Filter with Amplification

The frequency response of the circuit is the same as the RC filter, but the amplitude is increased by the pass band gain, AF of the amplifier.

• AF = 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 voltage gain is given by feedback resistor (R2) divided by input resistor (R1)

The University of Sydney Page 29

Active Low pass Filter with Amplification

The Active Low Pass Filter has a constant gain AF from 0Hz to the high frequency cut-off point, ƒC. At ƒC the gain is 0.707AF, and after ƒC 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 30

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

Rinput = 10 kΩCap = 100 nF

gives fc = 159 Hz

Active Low pass Filter with Amplification

The University of Sydney Page 31

Electrical Circuit interfacing

– Input Interfacing Circuits– http://www.electronics-tutorials.ws/io/input-interfacing-

circuits.html

– Good site for electronic design and implementation:http://sound.whsites.net/articles.htm

– Build your own electronics labhttps://www.slideshare.net/El-Rayes/build-your-own-lab

The University of Sydney Page 32

Which is more precise, Which is more accurate?

DVM - Rarely do people ask what is the sampling rate?What is the lsb quantization for the DVM digital measurementWhen do you need more than 0.1v resolution or accuracy?What is the absolute accuracy of the digital measurement?

Four decimal places in the DVM implies it is more accurate than the analogue meter.