Suitability For Use With Low-voltage Electronics
In the electronics industry, and particularly in portable and mobile devices, there is a continuing tendency to lower the supply voltage in order to save power and reduce unwanted emitted radiation. A low supply voltage, however, causes problems with signaling because it reduces the noise immunity. Differential signaling helps to reduce these problems because, for a given supply voltage, it gives twice the noise immunity of a single-ended system.
To see why, consider a single-ended digital system with supply voltage . The high logic level is and the low logic level is 0 V. The difference between the two levels is therefore . Now consider a differential system with the same supply voltage. The voltage difference in the high state, where one wire is at and the other at 0 V, is . The voltage difference in the low state, where the voltages on the wires are exchanged, is . The difference between high and low logic levels is therefore . This is twice the difference of the single-ended system. Supposing that the voltage noise on one wire is uncorrelated to the noise on the other one, the result is that it takes twice as much noise to cause an error with the differential system as with the single-ended system. In other words, the noise immunity is doubled.
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