Square wave is analog or digital signal?

Answer 1

This question has become the point of much heated debate here on WikiAnswers, and I will attempt to pare down the answers to its simplest form while keeping all valid viewpoints intact. Any further debate should be put in the "Discussion" area.

The Case For Digital: With a few exceptions, a square wave in it's theoretical form will most likely be used in digital applications.

A square wave may be "analog" during the time it is in transition from one stable state to another, and "digital" when it is in one state or the opposite state (i.e., voltage level), according to the type of digital inputs stimulated, but a transition is not an analog state function in the context of computers or digital logic. A square wave has two states hi and low and the transition from hi to low can be switched up to gigahertz (GHz) frequencies. Test equipment manufacturers are able to generate square wave signals well above 100GHz. Function generators have the square wave signal where the transition can be controlled. Practically all digital circuits utilize these states as "1" and "0" (or true and false) that computers use to make decision at the machine language level. Furthermore all modern computer uses this signalling scheme. But digital signals (1's and 0's) are not necessarily "square" waves, strictly speaking. A clock circuit generates a square wave that is used as a timing reference for the address, data, and control circuits.

The Case For Analog: All theoretical waveforms look great on paper, but it is impossible to produce any perfect waveform. Therefore, all waveforms (including square waves) are inherently analog.

By Fourier Analysis, a square wave is actually an infinite series of the summation of sine waves, in this case the odd harmonics divided by N. As a result, a square wave can actually be considered an analog signal. Looking at this another way, no pulse driver, conductor, or transmission line is perfect, so the rise and fall time of a square wave are not instantaneous, meaning that the series is not really infinite so, again, the square wave is analog, although quite complicated, but still analog. We call it digital because we sense it with discriminators that decide the "value" of the wave based on some thresholds with appropriate hysteresis.

The Case For Sanity: A wave form is not inherently digital or analog. "Digital" and "analog" are arbitrary words used to describe an application of waveforms. In other words, all digital signals are square waves, but not all square waves are digital.

A square wave is usually used in digital applications, but is also used in audio applications for a "distorted" guitar or vocal effect. A sine wave can become a square wave if the input signal on an amplifier is too great for the power of the circuit to amplify, "clipping" the high and low portions of the sine wave.

A square wave can be considered an analog or a digital signal. A perfect square wave (not possible to generate based on Fourier Analysis) would not in general be considered an analog signal because it only has two values, defeating the point of analog (in many cases, but not all). One can make a square wave oscillator to use as an alarm - different frequencies were used to convey different information. A square wave was simple to create, thus my reason for using as opposed to a sine wave (this is an example of an analog use of square waves - the information is not stored in the two values of the wave, but in the "infinite frequency range made available by the extra circuitry to change frequencies."

This point is moot, really, because it is the nature of the data (being analog or digital) that truly is important, and defines whether the wave should be catagorized as "analog" or "digital".

Oh-So-Clever Analogy: A wrench is the perfect tool for fixing trucks, but if I use the wrench to fix a desk, that doesn't make the desk a truck. In short, the application defines the state, but does not limit the tool.

Answer 2

analog