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A Brief Introduction to Analog and Digital Signals
2022-06-15 | By Maker.io Staff
With the abundance of development boards and platforms to choose from, many makers experience the digital domain in which signals typically switch between two discrete, well-defined states: high and low. However, there’s an entirely different domain, namely the analog domain, where signals can take any value in a specific range, leaving an infinite number of states that each encode different information. This article provides a brief overview of analog signals and discusses vital differences between the analog and digital domains.
Understanding Signals in Electrical Engineering
In electronics, a signal is a quantity (such as a voltage level) that varies over time and encodes some information (for example, a temperature reading). Typically, two devices exchange such signals to communicate with each other. For example, a signal could encode audio data coming from a microphone, a video signals your computer sends to your monitor, or, broken down even further, single bits that a standard logic gate integrated circuit (IC) transmits to a microcontroller (MCU). These signals can be analog or digital. While analog signals can take infinitely many states between given voltage levels, binary digital signals take one of two well-defined states (namely HIGH and LOW).
This figure outlines the difference between analog and digital signals.
Note that the digital signal never quite reaches 0V or 5V. However, that is typically not a problem, as digital electronic devices (for example, logic ICs) usually have upper and lower threshold regions in which they assume a signal to be HIGH or LOW. In the following example, the lower threshold is 1.35V, and the circuit considers any input below that value to be LOW. Similarly, the device assumes every value above the upper threshold of 3.15V to be HIGH, given a supply voltage of 4.5V. As a result, values between the two threshold regions are invalid, and the chip’s behavior is often undefined or non-deterministic for inputs that fall between the two areas.
This table contains the recommended operating conditions of the SN74HC163 counter IC. The green box highlights the high-level threshold, and the red box marks the low-level threshold values of this device.
While the analog signal in the example above is still limited to values between 0V and 5V, it can take an infinite number of values within that range. Digital signals, on the other hand, can only take a finite number of states. In a binary digital signal, those values are HIGH and LOW. The analog signal from above can be 0.00001V, 2.5V, 0.1243, 4.9999V, and so on. Often, tiny changes in the voltage level of an analog signal of a few millivolts can have dramatic effects, depending on what the signal encodes.
Analog vs. Digital Signals - Some Key Differences
While many beginners primarily work with digital circuits, their first encounter with electrical engineering often involves purely analog circuits. Such circuits comprise simple components, such as resistors, capacitors, diodes, OPAMPs, inductors, and transistors, which are all inherently analog. Examples of analog circuits include simple things like two resistors forming a voltage divider and a simple blink circuit that uses two transistors and capacitors. However, more complex examples include radio receivers to modems.
While analog circuits can implement very elegant and cost-effective solutions for everyday problems, they are typically more challenging to design. Planning non-trivial analog circuits requires experience, knowledge, and complex mathematical calculations. In contrast, digital circuits are often easier to build and troubleshoot, as many ICs were designed to implement tasks originally done by analog circuits in a simple-to-use package.
Analog circuits are often more susceptible to electrical noise, while digital circuits are often more expensive than their purely analog counterparts. It’s also important to mention that digital circuits are often synchronous. They require a common clock signal that tells each part in the circuit to perform its next task. Analog circuits, on the other hand, are usually asynchronous, which means they react to changes in input signals immediately.
Conclusion
Although you may typically work with digital electronics, it’s important to understand what analog signals are and how they compare to digital signals.
Analog circuits that operate on analog signals can be very elegant and fast. However, designers often require significant knowledge and experience to design reliable and error-free analog circuits. Digital circuits and signals are typically easier to work with and troubleshoot than their analog counterparts. However, digital circuits are often more expensive to design and implement, and analog circuits are more susceptible to electrical noise.
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