| How much noise can we put up with?
The 10-finger system that we use is called a ‘denary’ or ‘decimal’
system. We have seen that a 5 V supply would accommodate a
10-digit counting system if each digit was separated by 0.5 V or, using
the more modern choice of 3.3 V, the digits would be separated by
only 0.33 V.
Question: Using a 5 V supply and a denary system, what is the highest noise voltage that can be tolerated?
Answer: Each digit is separated by only 5 V/10 = 0.5 V.
The number 6 for example would have a value of 3 V and the number
7 would be represented by 3.5 V. If the noise voltage were to increase
the 3 V to over 3.25 V, the number is likely to be misread as 7. The
highest acceptable noise level would therefore be 0.25 V. This is not
very high and errors would be common. If we used a supply voltage of
3.3 V, the situation would get even worse.
So why don’t we just increase the operating voltage to say, 10 V, or
100 V? The higher the supply voltage the less likely it is that electrical
noise would be a problem. This is true but the effect of increasing the
supply would be to require thicker insulation and would increase the
physical size of the microprocessor and reduce its speed.
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