Unit
- Design specification: Every circuit begins with a requirements document that lists input/output ranges, power budget, operating conditions, and performance targets. For example, an audio amplifier may specify 20 Hz to 20 kHz bandwidth with less than 1% total harmonic distortion at full output.
- System-level partitioning: The design is divided into functional blocks such as power supply, signal conditioning, processing, and output stages. Each block has its own constraints and interface requirements that must be compatible with neighboring blocks.
- Component selection and sourcing: Engineers choose components based on availability, cost, temperature range, and tolerances. Preferred parts often belong to standard families like 74HC logic or industrial-grade op-amps such as the LM358.
- Schematic capture: Using EDA tools like KiCad or Altium Designer, the circuit is drawn with symbols that represent real components. Net labels unify connections, and design rules check for unconnected pins or short circuits.
- Pre-simulation review: Before simulation, a peer review verifies that all connections match the specification and that no obvious errors exist. This step catches missing pull-up resistors, wrong voltage dividers, or illegal configurations.
- Simulation and analysis: Transient, AC, and DC sweep simulations verify circuit behavior under nominal and extreme conditions. SPICE engines like ngspice or LTspice provide accurate predictions of voltages, currents, and power dissipation.
- Layout and routing: The physical PCB layout places components to minimize parasitic inductance and keep sensitive traces short. Controlled impedance traces are used for high-speed signals, and power planes are split for analog and digital domains.
- Design rule check (DRC) and manufacturing: The layout is checked against manufacturer capabilities such as minimum trace width, clearance, and drill sizes. After verification, Gerber files are generated for PCB fabrication.
- Prototyping and validation: A prototype board is assembled and tested against the original specification. Measurements from oscilloscopes and spectrum analyzers are compared to simulation results to identify discrepancies and refine the design.
- Thermal management analysis: Power dissipation in components such as voltage regulators, power transistors, and resistors is calculated to ensure junction temperatures stay within safe limits. Heatsinks, thermal vias, or forced air cooling are specified when necessary. Thermal simulation using tools like SolidWorks or ANSYS can validate the design before fabrication.
- Signal integrity and EMI/EMC review: High-speed digital and sensitive analog signals require careful impedance matching, termination strategies, and shielding. The design is reviewed for potential electromagnetic interference sources such as switching noise or long parallel traces. Ferrite beads, decoupling capacitors, and ground planes are added to suppress emissions and meet regulatory standards.
System Architecture
Pattern: Top-down hierarchical design flow
Components:
- Requirements layer: Captures all functional and non-functional specifications in a document.
- Block diagram layer: High-level blocks with I/O definitions and power/ground connections.
- Schematic layer: Component symbols and netlist connectivity.
- Layout layer: Physical PCB with copper traces, vias, and component footprints.
Code Example
SPICE
* Simple RC low-pass filter simulation
V1 1 0 SIN(0 1 1k)
R1 1 2 1k
C1 2 0 0.1uF
.tran 0 5ms 0 1u
.plot tran V(2)
.endThis SPICE netlist defines a voltage source with a 1 kHz sine wave, a 1 kOhm resistor, and a 0.1 uF capacitor. The transient analysis plots the output voltage across the capacitor, showing the expected 3 dB cutoff at about 1.6 kHz.
Quick Revision
- The design flow proceeds from specification through simulation, layout, and prototyping.
- Each stage includes verification steps like peer review and design rule checks.
- SPICE simulation allows virtual testing of circuit behavior before building hardware.