Signal transmission is very common in our daily lives, such as in mobile phones, televisions, and the internet.

Single-ended signal transmission is a type of signal transmission we use most of the time.

A single-ended signal refers to a signal transmitted using only one signal line. It sends the signal through a single conductor and is most commonly used in single-ended audio and video signals—for example, headphones are devices that receive single-ended signals. In a single-ended signal, the signal is encoded and transmitted using voltage or current relative to a reference level or ground. For instance, a voltage higher than the ground level may represent logic "1", while a voltage lower than the ground level may represent logic "0". This is single-ended signal transmission: simple, but highly susceptible to interference.

Suppose you are making a call in a noisy environment. The surrounding noise will interfere with your call, making it hard for the other person to hear you clearly. This is similar to how single-ended signal transmission is prone to interference, except that the interference in signal transmission is electromagnetic interference (EMI). How to solve this problem? The answer is to use differential signal transmission.

Differential signaling is a signal transmission technology characterized by transmitting two signals simultaneously over two wires. These two signals have the same amplitude but opposite phases—and they are the differential signals. So, what are the benefits of this approach? Please refer to the diagram below:

1. The "Sender" (transmitting end) uses two wires to transmit signals when sending signals over the line: the lower wire transmits the original signal, while the upper wire transmits the inverted signal.
2. During transmission, a noise signal ("Noise") occurs and superimposes itself on the signals of both the upper and lower wires. As can be seen, the signals in both wires exhibit the same fluctuation.
3. The "Receiver" (receiving end) determines whether the sender transmitted logic 0 or logic 1 by comparing the voltage difference between these two signals. (In digital communication, information is represented and transmitted in binary form, i.e., using combinations of 0s and 1s to represent different symbols or data.)

• Strong anti-interference capability: Interference noise is generally applied equally and simultaneously to the two differential signal wires, but the receiver only cares about the signal difference between these two wires. Therefore, noise has no impact on the logical meaning of the signal, achieving complete noise cancellation.

  Practical application: In high-speed data transmission, differential signals can effectively reduce signal distortion caused by external electromagnetic interference, ensuring data accuracy and integrity.

• Effective suppression of electromagnetic interference (EMI): Since the two differential signal wires are placed close together and have equal signal amplitudes, the coupled electromagnetic fields between each wire and the ground also have equal amplitudes. At the same time, their signal polarities are opposite, so their electromagnetic fields cancel each other out. Thus, differential signals cause less electromagnetic interference to the outside world.

  Practical application: Differential signals are widely used in communication and signal processing systems, especially in scenarios where electromagnetic radiation and interference need to be reduced—such as in automotive electronics and aerospace fields.

• Accurate timing positioning: The receiver of differential signals judges the logic 0/1 transition based on the point where the amplitude difference between the two wires changes from positive to negative (or vice versa). This method is more accurate than single-ended signals (which rely on threshold voltage judgment), as it is less affected by the ratio of threshold voltage to signal amplitude voltage. It is therefore more suitable for low-amplitude signals.

  Practical application: In high-speed data transmission and precision measurement, the accurate timing positioning of differential signals ensures data synchronization and accurate processing, improving system performance and stability.

1. Compared with single-ended signals, differential signals require two signal wires to transmit the same information. This means that when transmitting the same amount of data, differential signals need more signal wires, increasing the number of circuit connections and the demand for PCB (Printed Circuit Board) area.
2. Differential traces must be two wires with equal length, equal width, close proximity, and located on the same layer.
3. Risk of common-mode signal generation: If the differential signal design is improper, common-mode signals may be generated on the signal wires. Common-mode signals not only increase EMI issues but also may affect the transmission quality of differential signals.

Differential signals are widely used in various scenarios that require high-quality signal transmission and anti-interference capabilities. The following are some main application fields:

• Cable transmission: For example, common cables such as USB (Universal Serial Bus), HDMI (High-Definition Multimedia Interface), and Ethernet (used for network cables) all use differential signals. This enables better signal quality and stronger anti-interference capabilities.
• Audio equipment: Differential signals are widely used in signal transmission for professional audio equipment, as they can reduce noise and improve audio quality.
• Data communication: In high-speed data communication (e.g., in servers and network devices), differential signals can provide higher data transmission rates while reducing error rates.
• Medical equipment: In some medical devices that require high precision and high signal-to-noise ratio—such as electrocardiographs (ECGs) and electroencephalographs (EEGs)—differential signals are also widely used.
• Industrial control systems: In industrial environments, where electromagnetic interference is strong, differential signals are often used for communication between sensors and controllers to improve system reliability and stability.

These are the main application areas of differential signals, but they are not limited to these. Differential signals can be used in any scenario that requires high-quality signal transmission and anti-interference capabilities.

In summary, differential signaling is a highly effective signal transmission method. It has strong anti-interference capabilities, can effectively suppress electromagnetic interference, and offers accurate timing positioning. Although it has certain limitations in wiring, this does not affect its wide application in many fields.