MIT 6.002 Circuits and Electronics, Spring 2007
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analog waves varies sinusoidally with time ie alternating current generated by roting coil of wire in a magnetic field.......... but digital waves are square waves generated by specific ic s such as ne 555 timer etc.....
analog signals are continuous and passes full data information and changes through the cycle whereas digital are discrete and some of the information is lost as it passes data at 1 and 0's format;we dont know whats going on b/w 1 and 0's.
analog signals have infinitely many values between any two points. Digital signals have finitley many values between any two points. Think of a circle versus an n-gon. As n approaches infinity the n-gon would approach a circle. In this way with sufficiently large values of n, the n-gon can be thought of as a digital representation of a circle. The circle of course would be analog.
Here is my attempt to answer your question, FauxShaux. Analog is that branch of electronics which deals with the synthesis, measurement and analysis of quantities that occur in the real world. Examples of analog quantities are sound, temperature, pressure, weight, luminance (how bright a light is), velocity, acceleration and so on. Oh, let's not forget voltage and current either! Often we cannot easily experience or understand analog quantities accurately with our senses. Here's why we call it "analog". An analog, in plain english, is the use of one quantity or thing to represent another quantity or thing. It is from this word that we get the word "analogy" meaning a rhetorical comparison used to illustrate a point. In electronics when we use an analog we use an electrical quantity to allow us to apprehend, or sense a physical quantity. For example, using an electric current through a photo-transistor to represent the relative brightness of a light source. Here's another one that follows from this same example: If we're going to measure the current that is passing through the photo-transistor we could use an amp meter connected in series with the transistor's output. That meter may indicate the current by causing a pointer to deflect to a certain point on a calibrated dial. The position of the needle on the dial then would be the analog of the current through the meter and transistor. Thus it would also be the analog of the relative brightness (luminance) of the light shining on the photo-transistor. Whew! lot's of zig-zags on that line weren't there? What does this have to do with signals and waves and all that? Real world physical phenomena, such as those mentioned above, tend to vary or change gradually and smoothly over time. The sun doesn't rise or set all at once, right? Therefore, when we use electronic circuits to convert these real world phenomena to electrical signals, those signals too, vary gradually and smoothly over time. Otherwise the signals would not be very accurate representations of the phenomena, would they? So this is what people mean when they talk about analog signals "varying continuously" and all that. To keep things simple, let's pretend for a minute that we've never heard of analog-to-digital converters or digital-to-analog converters. Digital electronics then, is that branch of electronics which deals with the direct representation of data as discrete (separate) quantities that can be evaluated as present/not present, yes/no or true/false. Digital signals then, are going to either on or off and not anywhere in between for very long. If you graph them by any means, such as looking at them in real time on an oscilloscope, they're going to look more or less like square waves i.e. they'll be ON (at one discrete voltage level for instance) for a period of time and when they change they will very rapidly change to OFF (another discrete, meaning separate and distinct, voltage level) and will then remain OFF until they are switched back to ON through some means or cause. Usually the ON state of a digital signal is represented by some positive voltage level and the OFF state by either no voltage or a negative voltage. Remember the part about representing data. Digital circuits are used to perform logic operations on data. Well, that's enough for now. I didn't mean to write a whole chapter, but it is a big distinction. I hope this helps you.
sinply put, analog instruments contain ballistics or components that change "analogously" with the changes of the outside world, when measuring, capturing or what have you. Digital devices, on the other hand represent these changes with "snapshots" of the changes, at a limited resolution, unlike the seemingly "unlimited resolution" of analog gear. The digital gear is always representing, in some kind of code, what is going on and there will always be a moment of hysteresis between the change of the real world and the digital device's ability to translate it into code. It will inherently be limited, but the resolution is increasing as the technology advances, blurring the line a bit. Analog timing is usually at the physical speed of circuitry, that is to say, usually the speed of electricity or light, so the capture/ballistics/processing is quite near instantaneous, as digital is not.
if amplitude of a signal can take any value in interval than it is analog suppose a closed interval [a,b] if a signal can take any value in this interval than it is analog in digital only discrete value of amplitudes are possible