I/O Interfaces & Buses
Why do high-speed serial links use differential signaling, sending opposite signals on two wires?
- ATwo wires always double the amount of data sent
- BIf one wire breaks, the other alone carries the data at the same speed
- CNoise picked up equally on both wires cancels when the difference is taken, so small swings can be sent fast and reliably
Show answer and explanation
Answer: C. Noise picked up equally on both wires cancels when the difference is taken, so small swings can be sent fast and reliably
In differential signaling, 0 and 1 are represented by the voltage difference between two wires. External noise couples almost equally onto the two closely routed wires, so it cancels when the difference is taken. This allows swings of only a few hundred millivolts, reducing the time and power needed to change voltage and enabling high speed. Because the two currents flow in opposite directions, electromagnetic emissions are also small.
- A. Two wires carry one signal, so throughput does not double.
- B. One wire alone cannot be received as a differential signal.
- C. Correct. It also emits less noise.