Guidelines for Drawing Schematics

A well-drawn schematic is more than just a collection of connected components—it communicates your design intent clearly to others and to yourself. Whether you’re using pen and paper, CAD software, or LTspice, following these guidelines will make your schematics easier to understand, debug, and build from.

• These guidelines are helpful when drawing a schematic by hand or using LTSpice or any other tool.

• Ask yourself: “Does this schematic help or hinder someone unfamiliar with the schematic to understand it?” If your schematic makes people work to understand it, reorganize and simplify until it communicates clearly at a glance.

Signal Flow and Orientation¶

Signal flow from left to right: The primary input signal should enter from the left side of the schematic and progress toward the output on the right. This mirrors the direction we read text and how most people intuitively understand signal processing flow.

• Input on the left: Place input connectors and signal sources on the left edge

• Output on the right: Place output connectors and loads on the right edge

• Processing stages in between: Arrange amplification stages, filters, and other functional blocks in logical sequence from left to right

This convention helps making it clear how the signal path flows through your circuit and helps readers understand the circuit’s purpose at a glance.

Power Supply Rails¶

Positive supply on top, ground at bottom, negative supply (if present) below that:

• Place the positive power rail at the top of the schematic

• Place the ground rail at the bottom (and/or use multiple GND segments with GND symbols)

• If using dual supplies (e.g., ±15 V), place the negative rail at the bottom and ground in between

• This arrangement matches standard conventions used in textbooks and industry

Benefits:

• Reduces visual clutter by keeping power distribution organized

• Makes it easier to spot missing connections or power issues

• Helps readers quickly identify the power architecture

Minimizing Wire Crossings¶

Excessive wire crossings make schematics difficult to read and prone to interpretation errors. Reduce them by:

Thoughtful component placement:

• Group related components together (e.g., all resistors in a bias network, all capacitors in a filter stage)

• Place high-impedance nodes (op-amp inputs, gate terminals) away from high-current paths

• Arrange components to avoid forcing wires into awkward routing

Use multiple layers or segments:

• Break large schematics into functional blocks, each occupying its own region

• Draw each block cleanly, then connect blocks together with minimal crossings

• If crossings are unavoidable, use a junction symbol (dot or bridge) where wires actually connect, and ensure non-connected crossings are clearly distinguished

Common routing strategies:

• Route power and ground on dedicated paths (often relegated to top and bottom of the drawing)

• Route signal paths in the middle

• Use vertical and horizontal segments to maintain alignment and clarity

Wire Connections and Crossings¶

Indicating connected wires:

• When two wires form an intentional connection, place a dot or junction symbol at the intersection point

• This dot indicates electrical continuity at that node

• Without the dot, crossing wires are assumed to be not connected and simply pass over each other

Best practice:

• Minimize situations where wires cross without connecting

• If crossings are necessary, make it visually clear whether they are connected (dot present) or not (no dot)

• Consider rerouting wires, using two T-junctions or using global node labels to avoid ambiguous crossings

Component Alignment and Aesthetics¶

Align components on a grid: Use consistent spacing and alignment to create a clean, professional appearance.

• Align component leads vertically or horizontally

• Space components evenly to avoid crowding

• Leave adequate space around each component for labeling and future modifications

Consistent component orientation:

• Orient resistors and capacitors horizontally or vertically, not at arbitrary angles

• Place op-amp symbols with inputs on the left and output on the right (standard convention)

• Align polarized components (capacitors, diodes) consistently

Avoid cluttered regions:

• Leave whitespace around complex sections to improve readability

• Don’t pack components so tightly that labels overlap

• Use separate schematic pages for different functional blocks if necessary (e.g., one page for power supply, one for amplifier, one for filters)

Labeling and Annotation¶

Clear component designators:

• Use standard designators: R for resistors, C for capacitors, L for inductors, U for integrated circuits, etc.

• Number components sequentially (R1, R2, R3... or U1, U2...)

• Use consistent numbering throughout your design

Value and reference labels:

• Show all component values clearly, use SI prefixes (e.g., “10kΩ” for resistors, “100µF” for capacitors)

• Label voltage nodes with meaningful names (V_out, V_bias, GND, etc.) rather than generic numbers

Global Connectors

• Note that voltage nodes with the same label are assumed to be implicitly connected, even without a wire between them. Such implicit connections work in LTSpice netlists

• Strategic use of global connectors can greatly improve the readability and maintainability of a schematic

Reference designators on schematic:

• Place the component designator (e.g., “R5”) near the component for easy identification

• Use a consistent position relative to each component (e.g., always above resistors)

• Ensure labels don’t obscure the circuit topology

Block Diagrams and Hierarchical Schematics¶

Schematics can also be structured hierarchically, with a top block diagram schematic and sub-schematics that implement each block. See for example Figure 4. This high-level view helps readers quickly understand how the major subsystems connect before diving into detailed component schematics.

Block diagrams:

• Show the major functional blocks and how they connect at a high level

• Use simple rectangles or blocks to represent each subsystem

• Clearly indicate signal flow and power distribution between blocks

Hierarchical schematics:

• Create a top-level schematic showing blocks and their interconnections

• Create detailed schematics for each block, showing all components within that block

• Use hierarchical sheet references to link detailed schematics to top-level blocks

• Hierararchical schematics are also supported in design and simulation tools. For example, in LTspice, you can use sub-circuits (.subckt) to organize complex designs

Benefits:

• Simplifies understanding of large, complex circuits

• A partionining of a bigger schematic into blocks may facilitate team collaboration—different team members can work on different blocks

• Enables reuse—well-designed blocks can be used in multiple projects