Given the specification of a system Develop a working system

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Earl Shelton
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Team of engineers who build a system need: An

Decomposition Function transformation from

2 Team of engineers who build a system need: An abstraction of the system An unambiguous communication medium A way to describe the subsystems Inputs Outputs Behavior Functional Decomposition Function transformation from inputs to outputs Decomposition reduce to constituent parts 2

3 By the end of this chapter, you should: Understand the differences between bottomup and top-down design. Know what functional decomposition is and how to apply it. Be able to apply functional decomposition to different problem domains. Understand the concept of coupling and cohesion, and how they impact design. 3

4 Given constituent parts Develop a working system Build modules to accomplish specific tasks Integrate modules together into working system For example Given a supply AND, OR and NOT gates. Build a computer Pros Leads to efficient subsystem Cons Complexity is difficult to manage Little thought to designing reusable modules Redesign cycles 4

5 Given the specification of a system Develop a working system Divide the problem into abstract modules Reiterate until constituent parts are reached Pros Highly predictable design cycle Efficient division of labor Cons More time spent in planning 5

6 Recursively divide and conquer Split a module into several submodules Define the input, output, and behavior Stop when you reach realizable components Determine Level 0 functional requirements N=1 Determine architecture and functional requirements for modules at Level N At the detailed design level? Yes DONE No N=N+1 6

7 The design process is iterative Upfront time saves redesign time later Submodules should have similar complexity Precise input, output, and behavior specifications Look for innovation Don t decompose ad infinitium Use suitable abstraction to describe submodules 7

8 Look at how it has been done before Use existing technology Keep it simple Communicate results 8

9 The system must Accept an audio input signal source with a maximum input voltage of 0.5V peak. Have adjustable volume control between zero volume and the maximum volume level. Deliver a maximum of 50W to an 8Ω speaker. Be powered by a standard 120V 60Hz AC outlet. 9

10 audio input signal power, 120 VAC Audio Power Amplifier audio output signal 10

11 Module Inputs Outputs Functionality Audio Power Amplifier Audio input signal: 0.5V peak. Power: 120 volts AC rms, 60Hz. User volume control: variable control. Audio output signal:?v peak value. Amplify the input signal to produce a 50W maximum output signal. The amplification should have variable user control. The output volume should be variable between no volume and a maximum volume level. The peak value of the audio output voltage is determined from the system requirements on power gain. Vpeak= (8Ω*50W)=20V 11

12 Audio Amplifier Design audio input signal voltage buffered amplified input Buffer Amplifier High Gain Amplifier signal Power Output Stage audio output signal DC voltages Power Supply power, 120 VAC 12

13 Module Buffer Amplifier Inputs - Audio input signal: 0.5V peak. - Power: ± 25V DC. Outputs - Audio signal: 0.5V peak. Functionality Buffer the input signal and provide unity voltage gain. It should have an input resistance >1MΩ and an output resistance <100Ω. The system must produce a ±25V AC output signal to satisfy the Level 0 requirements, so supply values that exceed that are required to power the electronics. The output resistance are educated quesses, based on knowledge of what is achievable with the technology. The exact resistance requirements are refined later on the basis of the overall design. 13

14 Module High Gain Amplifier Inputs - Audio input signal: 0.5V peak. - User volume control: variable control. - Power: ± 25V DC Outputs - Audio signal: 20V peak. Functionality Provide an adjustable voltage gain, between 1 and 40. It should have an input resistance >100kΩ and an output resistance <100Ω. The gain of 40 is determined from the overall system power gain: 20 V/0.5 V. The output resistance are educated quesses. 14

15 Module Power Output Stage Inputs - Audio input signal: 20V peak. - Power: ± 25V DC Outputs - Audio signal: 20V peak at up to 2.5 A. Functionality Provide unity voltage gain with output current as required by a resistive load of up to 2.5A. It should have an input resistance >1MΩ and an output resistance <1Ω. For the power output stage, it is clear that 20 V peak needs to be delivered. The current needed to drive the speaker is: I=20/8 = 2.5 A. 15

16 Module Power Supply Inputs V AC rms Outputs - Audio signal: 25V DC with up to 3.0 A of current with a regulation of <1%. Functionality Convert AC wall output voltage to positive and negative DC output voltages, and provide enough current to drive all amplifiers. The power supply needs to deliver h± 25 V DC, while the 3.0 A current capability was selected to supply the 2.5 A needed for the peak output requirement plus the current needed to power the other amplifiers stages. For cascaded amplifier stages, the overall voltage gain is given by the product of gains multiplied by the voltage divider losses between stages: Voltage gain = [100k/(100k+100)][1M/(1M+100)] 40 16

17 Output 120 V AC Rectified DC DC V AC Transformer Rectifier Voltage Smoothing Filter Regulator(s) Voltage 17

18 Electronics Design Digital Design Software Design See the book for more in-depth examples 18

19 The system must Measure temperature between 0 and 200 C. Have an accuracy of 0.4% of full scale. Display the temperature digitally, including one digit beyond the decimal point. Be powered by a standard 120V 60Hz AC outlet. Use an RTD (thermal resistive device) that has an accuracy of 0.55 C over the range. The resistance of the RTD varies linearly with temperature from 100Ω at 0 C to 178Ω at 200 C. 19

20 Ambient Temperature Power, 120 VAC Digital Thermometer Digital Temperature Display 20

21 Module Digital Thermometer Inputs - Ambient temperature: C. - Power: 120V AC power. Outputs - Digital temperature display: A four digit display, including one digit beyond the decimal point. Functionality Displays temperature on digital readout with an accuracy of 0.4% of full scale. ATD current converter could be used, integrated circuit temperature-sensing packages could be considered, and microcontroller-based solutions are feasible as well. The overall accuracy that the system must achieve is 0.4%, and that translates into 0.8 C of allowable error for the 200 C range. 21

22 b 0 BCD 0 Ambient Temperature Temperature Conversion Unit V T Analog to Digital Converter b 1... b N-1 Binary Coded Decimal (BCD) Conversion Unit BCD 1 BCD 2 BCD 3 7-Segment LED Driver +/- x V DC Power, 120 VAC Power Supply, 22

23 Module Temperature Conversion Unit Inputs - Ambient temperature: C. - Power:?V DC (to power the electronics). Outputs - V T : temperature proportional voltage. V T = αt, and Functionality ranges from? to?v. Produces an output voltage that is linearly proportional to temperature. It must achieve an accuracy of?%. The voltage necessary to power the electronics is not known. The output voltage range and accuracy are unknown. The RTD will introduce up to 0.55 C of error and electronics will introduce additional error (exact amount is unknown). An educated guess is that max error allowed for temp. unit is 0.6 C (this means that electronics would introduce no more than 0.05 C and RTD introduces 0.55 C of error). 23

24 Module A/D Converter Inputs - V T : voltage proportional to temperature that ranges from? to?v. - Power:?V DC. Outputs - b N-1 -b 0 :?-bit binary representation of V T. Functionality Converts analog input to binary digital output. Two unknowns the range of input voltage and number of bits. The number of bits affects accuracy. The number of bits is calculated from the max. allowable error that the A/D can introduce (0.2 C), the number of discrete intervals, and the temp. range: Max error = range/num. intervals = 200 C/2 N 0.2 C N 9.97 bits. Voltage range usually is fixed for a particular IC solution. 24

25 Module BCD Conversion Unit Inputs - 10-bit binary number: Represents the range C. - Power:?V DC. Outputs - BCD 0 : 4-bit BCD representation of tenths digit. Functionality - - BCD 3 : 4-bit BCD representation of hundreds digit. Converts the 10-bit binary number to BCD representation. 25

26 Module Seven-Segment LED Driver Inputs - BCD 0 : 4-bit BCD representation of tenths digit. - - BCD 3 : 4-bit BCD representation of hundreds digit. - Power:?V DC Outputs - Four 7-segment driver lines. Functionality Converts the BCD for each digit into outputs that turn on LEDs in seven-segment package to display temperature. 26

27 Module Power Supply Inputs V AC rms. Outputs - ±? V DC with up to? ma of current. - Regulation of?% Functionality Converts AC wall output voltage to positive and negative DC output voltages, with enough current to drive all circuit subsystems. 27

28 How would you determine the unknown details in the previous 2 slides? 28

29 What is coupling? How much coupling is there in the modules in the Level 1 of the previous amplifier example? Phenomena of highly coupled systems A failure in 1 module propagates Difficult to redesign 1 module Phenomena of low coupled systems Discourages reutilization of a module 29

30 What is cohesion? Phenomena of highly cohesive systems Easy to test modules independently Simple (non-existent) control interface Phenomena of low cohesive systems Less reuse of modules 30

31 Design Level 0 Present a single module block diagram with inputs and outputs identified. Present the functional requirements: inputs, outputs, and functionality. Design Level 1 Present the Level 1 diagram (system architecture) with all modules and interconnections shown. Describe the theory of operation. This should explain how the modules work together to achieve the functional objectives. Present the functional requirements for each module at this level. Design Level N (for N>1) Repeat the process from design Level 1 as necessary. Design Alternatives Describe the different alternatives that were considered, the tradeoffs, and the rationale for the choices made. This should be based upon concept evaluation methods in Chapter 4. 31

32 Design approach: top-down and bottom-up Functional Decomposition Iterative decomposition Input, output, and function Applicable to many problem domains Coupling interconnectedness of modules Cohesion focus of modules 32

Introduction (concepts and definitions)

Introduction (concepts and definitions) Objectives: Introduction (digital system design concepts and definitions). Advantages and drawbacks of digital techniques compared with analog. Digital Abstraction. Synchronous and Asynchronous Systems.