Technical dilemmas in circuit design

Circuit design is a set of compromises, because improving one property usually worsens another.

Common technical dilemmas

• Speed vs power: faster circuits need higher clock/currents, which increases power and heat.
• Speed vs noise/EMI: faster edges give better timing but more crosstalk, ringing and radiation.
• Cost vs performance/quality: better components and more precision cost more.
• Accuracy/resolution vs speed: a high-resolution ADC is slower.
• Size vs heat and routing: miniaturised designs have thermal and coupling problems.
• Reliability vs complexity: redundancy and features add parts that can themselves fail.
• Flexibility vs efficiency: programmable (software) solutions are flexible but slower and costlier in power than dedicated hardware.
• Time-to-market vs testing, and hardware vs software implementation.
• Analog vs digital and standard vs custom parts (availability, lifetime support).

Reaching an optimal solution

1. Capture the customer's priorities and measurable specifications; classify them as must-have, important, and nice-to-have, and agree on the margins.
2. Generate alternatives (several architectures/components).
3. Evaluate trade-offs by calculation and simulation; use a weighted decision matrix scoring each option against the weighted requirements (cost, power, speed, reliability, size, availability).
4. Prototype and test the critical risk areas early.
5. Optimise iteratively, relax the less important requirement to meet the key one, and negotiate with the customer using data (e.g. "20 percent more cost gives 2x reliability").
6. Review and document the decisions, and keep design margins (derating, tolerance).