Introductory Circuit Concepts

Introduction:

This confluence page will act as a guide mainly for those who are wishing to learn more about circuits and understand the bigger picture of electronics as a whole. This article will be particularly helpful if you’re joining a design team(not just this one) and want to learn more about circuits without having much circuit experience, so I will try my best to explain this from scratch even for those who haven’t really taken circuit courses in high school. Especially if you’re someone in first year engineering(ECE/Mechatronics/Computer Science), this will serve as a very useful guide for you if you choose to go down the path of hardware. Before we begin, it’s best we define some terminology

Voltage :

Formally, this is defined as “the potential difference between two points, measured in Volts”. If you’re just starting out with circuits, this probably means nothing to you. Effectively, it’s like the “pressure” that pushes electricity. Electronic devices are designed to operate at specific voltage ranges, so over-voltage and under-voltage conditions should be avoided.

Current:

This is the movement of electrons, and electrons are the charge carriers of a circuit. Current has some amplitude(some number strength), and some direction. Note that we denote conventional current flow to be in the opposite direction of electron flow(this is simply a standard). Current in simple terms, states the number of electrons travelling per second.

Voltage vs Current

Most people have trouble envisioning what voltage is since we can’t observe it with our eyes. Electricity flows as a current, imagine it like a flow of water in a river. Water will flow from places with a higher water height to a lower water height, because the higher water height means the water has more potential energy relative to the lower one(this is the analogy for electric potential). The actual flow of water particles is equivalent to explaining current

Resistance and Ohm’s Law

Resistance simply describes how difficult it is for electricity to flow, hence the name, it “resists” current. Picture a water pipe with a pump that’s pumping at some pressure. As a pipe grows smaller, all that water has to flow through a smaller area. This means resistance increases, and it becomes more difficult for the water to flow, but at the same time the strength of that flow increases. The same holds vice versa. If a pipe grows larger, water flows more readily but the strength of flow decreases. Same idea applies to electricity, and mathematically we just say that according to Ohm’s Law :

V = I x R

Power

As electrons flow through conductors and into some electrical load, that circuit will dissipate some power. Recall from Physics that Power is the rate that Energy/Work is done. This makes sense, as electrons have some potential energy to move some unit charge(that's the definition of electrical potential), so that means there is some work done to move that charge. Mathematically,

P = V x I

Or if you want to rearrange using Ohm’s Law, using only current and resistance

P = I² x R

P = V² / R

Kirchoff's Current/Voltage Laws

Recall that Electrical Current relates to the flow of charges) and Electric Potential(Voltage) relates to energy. Using this information, we can analyse circuits

Kirchoff’s Voltage Laws essentially states that the sum of voltages is always 0, this is a reference to conservation of energy. Energy is never destroyed, but simply transformed into different forms.

Kirchoff’s Current Law states that the sums of current of a Node is always 0. Effectively, it just means “Current in = Current out”, conceptually this makes sense due to conservation of charge

Digital and Analog Circuits : A typical electronic circuit

Typically, we saw a lot of different types of circuits, and you probably see the terms “analog and digital circuits” thrown around a lot. The motivation of a circuit or a system is to process information or energy. Processing information usually includes : Information Translation, Storage or Computation.

The following table highlights the major differences between analog circuits and digital circuits :

Parameter	Analog Circuit	Digital Circuit

Parameter	Analog Circuit	Digital Circuit
Definition	Circuit that processes analog signals	Circuit that processes digital signals, defined by voltage levels(0’s and 1’s Binary)
Input Signal	Input is a continuous time signal/analog signal	Input is a discrete time signal(happens at discrete intervals)
Output Signal	Produces Analog Signals	Outputs digital signals
Components	Uses Resistors/Inductors/Capacitors	Uses Logic Gates(CMOS/TTL usually)
Conversion	Often doesn’t require signal conversion	Often requires ADC(Analog Digital Converter) or DAC(Digital Analog Converter) to interface
Noise Immunity	More susceptible to noise	More immune(not completely immune)
Power Consumption	Generally consumes more power	Relatively little power consumption
Form of Information Storage	Stores information in the form of waves	Information stored in binary(data bits)
Logical Operations	Relatively complex to perform efficiently	Logical operations are fundamental and easy(AND, OR, NAND, XOR