--- title: "Establishing requirements for circuit design" subject: "Instrumentation II" chapter: 7 key: "semester_5/instrumentation_ii:req-to-design" source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/req-to-design site: BCT Engineering --- # Establishing requirements for circuit design Instrumentation II · Chapter 7: Circuit Design - Asked in: 2074 Chaitra, 4 marks; 2073 Shrawan, 6 marks; 2070 Chaitra, 6 marks; 2068 Chaitra, 6 marks (asked 4 times) - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/req-to-design - Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-7 ## Question Establishing requirements is the most difficult part of circuit design. Explain the procedure of establishing requirements and converting them into a circuit design. ## Short answer Requirements are established by identifying stakeholders, defining functions and measurable specifications, and resolving conflicts. This leads to an agreed specification. Conversion to a circuit involves block diagram, component selection, detailed schematic, simulation, prototype, test, and PCB layout with reviews. ## Answer Requirements are difficult because customers describe needs vaguely, needs conflict, and later changes are costly. Good requirements are complete, unambiguous, measurable, testable and traceable. The circuit design is built from them step by step. #### Establishing requirements 1. **Identify the stakeholders** (customer, user, manufacturer, maintenance, regulator) and collect needs by interview, questionnaires, studying existing products and observation. 2. **Define the function:** what the system must do, inputs and outputs (signals, ranges), and operating modes. 3. **Define the specifications** in measurable numbers: accuracy, resolution, speed/bandwidth, power, supply, size, weight, cost, operating temperature, humidity. 4. **Define constraints:** standards (EMC, safety), environment, reliability (MTBF), maintainability, availability of parts, time and budget. 5. **Separate "must" from "nice to have"**, resolve conflicts, and agree with the customer on a written requirement specification (SRS) with acceptance tests. #### Converting to a circuit design ```text Requirements -> Specification -> Block diagram -> Component selection -> Detailed schematic -> Simulation -> Prototype -> Test -> PCB ``` 1. **Block diagram (architecture):** divide the function into blocks (sensor, signal conditioning, ADC, processor, display, power) and define the interfaces. 2. **Trade-offs:** choose among alternatives (microcontroller vs discrete logic, analog vs digital) by cost, performance, power and risk. 3. **Component selection:** select parts that satisfy the specification with margin (tolerance, temperature, derating, availability). 4. **Detailed design:** schematic, calculations for every block (gain, filter, power budget), worst-case analysis. 5. **Simulation and prototype:** verify with SPICE, build a breadboard/prototype, and test against each requirement. 6. **Layout, review and documentation:** PCB design with noise rules, design review, final test and a traceability matrix showing that each requirement is met. Reviews with the customer at each stage reduce rework. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the first step in establishing requirements? A. Select the PCB layout B. Order components C. Run a prototype D. Identify stakeholders and collect their needs Answer: D. Customers, users and others are consulted by interviews, questionnaires and observation. (Key point: First step) 2. How should specifications be written? A. Vague, general terms B. Only as cost estimates C. In measurable numbers such as accuracy, speed, power and temperature D. Only as software features Answer: C. Good requirements are measurable and testable. (Key point: Specifications) 3. Which order of the design flow is correct? A. Schematic, requirements, PCB, test B. Requirements, specification, block diagram, component selection, schematic, simulation, prototype, test, PCB C. Prototype, requirements, block diagram D. PCB, schematic, specification Answer: B. The design proceeds from requirements down to PCB. (Key point: Design flow) 4. What does a traceability matrix show? A. That each requirement is met by the design B. Component prices only C. Layer count of PCB D. Operator names Answer: A. It links requirements to design and test evidence. (Key point: Traceability) ## Related in Instrumentation II - [Technical dilemmas in circuit design](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Adesign-dilemmas) — Instrumentation II, chapter 7 - [High speed circuit design guidelines](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ahigh-speed-guidelines) — Instrumentation II, chapter 7, asked 3× - [USB to RS-232 adapter design](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Ausb-rs232-adapter) — Instrumentation II, chapter 3 ## Related in other subjects - [Most economical span, double circuit line](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aeconomic-span-double-circuit) — Transmission and Distribution System Design, chapter 4, asked 6× - [Most economical span, 180 km single circuit](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aeconomic-span-180km-single-circuit) — Transmission and Distribution System Design, chapter 4 - [VIP latrine: working and design procedure](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Avip-latrine-working-design) — Sanitary Engineering, chapter 9, asked 2× - [Design procedure of steel purlin](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Apurlin-design-procedure) — Design of Steel and Timber Structure, chapter 8, asked 2×