What is the mathematical definition of the differential signal voltage in a differential pair?

Conditions

• There are two transmission lines and their corresponding reference planes.
• The driver outputs a positive-polarity signal and a negative-polarity signal.

Reasoning, step by step

1. Identify the positive-polarity signal voltage, denoted as $V_1$.
2. Identify the negative-polarity signal voltage, denoted as $V_2$.
3. Subtract $V_2$ from $V_1$ to obtain the differential signal voltage.
4. Express the result mathematically as $V_{diff} = V_1 - V_2$.

Example

In the video's simulation, the instructor observes the waveforms of $V_1$ and $V_2$. The differential signal $V_{diff}$ is plotted as their difference, showing an amplitude approximately twice that of the single-ended signals.

Common misconceptions

• Believing the differential signal is the sum of the two voltages.
• Assuming the differential signal is measured relative to the ground plane rather than between the two lines.

Watch the explanation

Explore next

• What is the definition of the common-mode signal?
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