Schematic Design Basics

Schematic Design is the foundational step in the electronic circuit design process. It involves creating a graphical representation of the circuit, which shows how components are electrically connected. The schematic serves as a blueprint for PCB design and aids in troubleshooting and documentation.

Key Elements of a Schematic

  • Symbols: Graphical representations of components, such as resistors, capacitors, and ICs.
  • Nets: Lines connecting component pins to indicate electrical connections.
  • Designators: Unique identifiers for components (e.g., R1, C2, U3).
  • Power and Ground: Clearly marked connections for power (e.g., VCC) and ground (GND).
  • Annotations: Text labels for voltage levels, test points, or important notes.

Schematic Design Process

Define Circuit Requirements:

  • Create a block diagram for your design
  • Understand the design objectives and constraints, such as voltage levels, current requirements, and desired functionality.

Select Components:

  • Choose appropriate components (resistors, capacitors, ICs, etc.) based on specifications like operating voltage, tolerance, and power ratings.
  • Keep in mind the SAE rules when designing EV boards

Draw the Schematic:

  • Use an ISO A3 with metric units
  • Place components logically, connecting them with wires or nets to represent electrical connections.
  • Make things easy to read, you can use as many power and ground ports as you want
  • Use net names to avoid running connections all across the page

Add Supporting Elements:

  • Include labels, part numbers, and designators (e.g., R1, C1) for clarity.
    • Altium can automatically name components for you
    • Add comments with the component values to make things readable
  • Add decoupling capacitors, pull-up/pull-down resistors, and other necessary elements to ensure stability and functionality.

Simulate the Circuit (Analog circuits):

  • Use simulation tools to verify circuit behavior before moving to the PCB design phase.
    • LTSpice is recommended for this
  • Can be used to sanity check parts of digital boards like power supplies.

Review and Validate:

  • Perform a thorough review to check for missing or incorrect connections, unconnected pins, and design rule violations.
  • Altium can also be configured to check some of these things, check their documentation page for more details.

Best Practices for Schematic Design

Logical Component Placement:

  • Arrange components logically
  • Group related components together for easier understanding.
  • Make the groups easily understandable.

Clear Connections:

  • Avoid overlapping wires or crossing nets unnecessarily.
  • Use labels for shared connections instead of long wires.
  • Use multiple sheets for larger designs.

Hierarchical Design:

  • For complex circuits, divide the schematic into smaller sections or modules.
  • Use hierarchical blocks to represent subsystems.

Use Standard Symbols:

  • Follow industry standards for component symbols to maintain consistency and clarity.
  • Keep the symbols consistent.

Documentation:

  • Add detailed annotations, including voltage levels, pin functions, and reference part numbers.
  • Add important distinctions for frequencies or circuit gain.

Design for Debugging:

  • Include test points and connectors to facilitate troubleshooting.

Common Mistakes to Avoid

  • Missing or incorrect connections between components.
  • Floating pins (unconnected pins that should be connected to power, ground, or other signals).
  • Using the wrong symbol for a component.
  • Forgetting decoupling capacitors near ICs.
  • Not assigning unique designators to components.

Next Steps

Transition to PCB Design:

  • Use the schematic as a basis to place components and route traces on the PCB.
  • PCB Design

Simulate and Test:

  • If necessary, simulate the circuit using EDA tools to validate the design.

External Resources