Circuit Representation
Table of Contents
When we build and design circuits, we use various tools (such as notation, units, symbols, and more) to come up with a circuit representation. This begins with creating a block diagram, which is a high-level overview of what the circuit accomplishes, then a schematic, which designs the circuits to do this, then a layout, which describes how the physical components are to be placed to make the circuits, and finally an assembly, which assembles the layout into a physical circuit (often a printed circuit board or PCB).
1. Notation
1.1. Units
Here are some common units° that are used in circuits:
| Dimension | Unit | Symbol |
|---|---|---|
| Charge | coulomb | \(\text{C}\) |
| Voltage | volt | \(\text{V}\) |
| Current | amp | \(\text{A}\) |
| Resistance | ohm | \(\Omega\) |
| Capacitance | farad | \(\text{F}\) |
| Inductance | henry | \(\text{H}\) |
| Power | watt | \(\text{W}\) |
| Frequency | hertz | \(\text{Hz}\) |
Prefixes are also used to denote multiples and submultiples of units:
| Prefix | Symbol | Magnitude |
|---|---|---|
| peta | \(\text{P}\) | \(10^{15}\) |
| tera | \(\text{T}\) | \(10^{12}\) |
| giga | \(\text{G}\) | \(10^9\) |
| mega | \(\text{M}\) | \(10^6\) |
| kilo | \(\text{k}\) | \(10^3\) |
| milli | \(\text{m}\) | \(10^{-3}\) |
| micro | \(\mu\) | \(10^{-6}\) |
| nano | \(\text{n}\) | \(10^{-9}\) |
| pico | \(\text{p}\) | \(10^{-12}\) |
| femta | \(\text{f}\) | \(10^{-15}\) |
1.2. Typeset
Symbols with lowercase and uppercase generally have the following meanings:
- A lowercase letter represents the general case (e.g. \(i\), current, may or may not be time-varying)
- A lowercase letter followed by \((t)\) to emphasize time (e.g. \(i(t)\) is time-varying current)
- An uppercase letter if the quantity is not time-varying (e.g. \(I\) is current of a constant value)
2. Architecture
2.1. Components
Circuits are created using components, which are represented on schematics using abstracted symbols:
| Component | Description | Symbol |
|---|---|---|
| Resistor (R) | US style | |
| Resistor (R) | EU style | |
| Capacitor (C) | Non-polarized | |
| Capacitor (C) | Polarized | |
| Capacitor (C) | Polarized (electrolytic) | |
| Inductor (L) | Coil | |
| DC Source | Battery/voltage source | |
| AC Source | Sinusoidal source | |
| LED | Light emitting diode | |
| Switch | SPST (single throw) |
2.2. Terminology
The following is a diagram of the terminology used in a schematic:
