Digital Electronics |
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What is Digital ElectronicsA description of what we mean by digital electronics is, strangely, best approached from a description of what it is not. It is not analogue. Analogue electronics are designed and used to process analogue signals. An analogue signal is a fluctuating voltage which can have any numerical value. i.e it may be tiny fractions of a volt or it may be hundreds of volts. It may be a constant voltage or rapidly changing. The key feature that separates it from digital electronics is this ability to assume any value within a continuous range. In many ways this is a more true reflection of the real world than digital signals. If you consider the amplification of a singers voice via a microphone it is obvious that the resulting signal from the microphone will have a voltage continuously varying in amplitude from the quietest to the loudest note. The processing of this signal must take account of this to accurately reproduce it when amplified. In sharp contrast to this is digital electronics. A digital signal can only have one of two possible values. The exact value of these voltages depends on the particular type of digital circuit but one of the most common systems uses +5 volts and 0 volts. In this system the +5v is referred to as the digital High (or simply HI) and the 0v as digital Low (or LO). At first glance this may seem a little restrictive. After all what real world signals can be represented (and then processed) by two states, except perhaps a simple switch which is either on or off ? The true power of digital representation becomes apparent when we start to consider patterns of these two states rather than just the one. If you take two signals , each capable of being either HI or LO then the combination can have four different patterns i.e. LO LO, LO HI, HI LO, HI HI. By considering the pattern rather than just the individual signal we have increased the range of what can be represented from two to four. Similarly we can use three digital signals to represent a range of 8 and four signals for a range of 16. More generally, if we use N signals we can represent 2 ^{N} possible patterns.Lets give these patterns a name. Conventionally we use the BINARY number system to name these patterns of HI and LO, although you should be aware that this is not always the case. Below you can see a table of the first few binary number patterns. The HI is represented as '1' and the LO as '0' |
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Number Represented | Binary Pattern | ||||||||

0 | 00 | ||||||||

1 | 01 | ||||||||

2 | 10 | ||||||||

3 | 11 | ||||||||

Using patterns of these "two state" signals we are getting back to the ability that analogue signals have in representing a bigger range of values. However, representing real world signals using these discrete values is a bit like using an approximation. It gives you roughly what you had but not exactly. If we take the
example of the singer and the amplified microphone and assume the microphone signal varied from, say, 0.1 volts to 3.2 volts, then we could use 5 digital signals to represent each 0.1 volt level (i.e. 32 different binary patterns). We could then process this and generate bigger numbers which could be used to generate correspondingly larger voltages (i.e amplification). The only thing wrong with this is quality. We would be ignoring, or actually rounding off, the intermediate values
of signal between these discrete values. Trust me on this; the singer would not sound so good. If however we had used 32 digital signals then the RESOLUTION of the representation would be much better and, in fact , you would probably not be able to distinguish the resultant amplified signal from the analogue processed type. The binary representation of real world signals is important, but , by no means, the only use of digital electronics. In the next section we will look at the use of these BINARY patterns to represent numbers which are manipulated as numbers without any requirement to represent an analogue signal. We will also show how these HI/LO patterns can be used to represent the logical decision making process we all take for granted. |
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. Digital Logic . |
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