The unwanted coupling between signals in a circuit causes crosstalk interference.
Electrical coupling between wires is the cause of interchannel crosstalk interference in different communication channels.
Depending on the understandability of both interchannel and intrachannel crosstalk interference, the interference can be classified as either intelligible or unintelligible crosstalk interference.
Electronic circuits deal with different types of signals, and these signals differ in magnitude, frequency, and phase. Signals can be periodic, aperiodic, random, or deterministic in nature. A signal in an electronic circuit that is unintentional or unwanted is called noise, which is detrimental to circuit operation. Crosstalk interference is one type of noise commonly seen in electronic and communication circuits.
Crosstalk interference is capable of changing the behavior of intentional signals in the system and can be a cause of poor performance or failed operation. Mitigating crosstalk interference is of great importance for signal integrity and reliability in circuit operations. Let’s take a look at what causes different types of noise, including crosstalk interference.
Types of Noise
Noise can be classified into the following types:
Thermal or Johnson noise - When the circuit operating temperature is above absolute zero (-273°C), thermal noise is generated. It is caused by the random motion of electrons in the conductive path.
Shot noise - The noise generated in transistors and integrated circuits due to the random velocity of electron movements is called shot noise. The random velocity is caused by the external voltage applied to the device.
Partition noise - In devices with more than one electrode, such as valves and transistors, partition noise is commonly seen due to current division at the electrodes.
Intermodulation noise - Intermodulation noise is a spurious frequency signal observed in non-linear devices handling multiple signals. The frequency of intermodulation noise can be either inside or outside the frequency band of interest.
Flicker noise - Noise presence increases at low-frequencies and is called 1/f noise of excess noise. Flicker noise is sometimes known as low frequency (1/f) noise or excess noise.
Crosstalk interference - Coupling between the wanted and unwanted signals in a circuit causes crosstalk interference.
In crosstalk interference, energy gets coupled between two or more lines that are placed adjacent to each other. Some of the main reasons for crosstalk interference in circuits are:
- Electrical coupling between the transmission lines or conducting paths.
- The capacitive imbalance experienced between the wire pairs in cables.
- Poor control of frequency responses in analog systems.
- Defective filters or poor filter performance.
- Non-linear behavior of the system.
Crosstalk Interference in Communication Channels
Crosstalk interference is an undesirable phenomenon in communication channels. It happens when the signals from one line pick up with a signal in the neighboring line, and it can greatly affect the privacy of communications.
Crosstalk interference can be classified into two types:
Interchannel Crosstalk Interference
This type of crosstalk interference is experienced by two different communication channels. The electrical coupling between the wires is the cause of interchannel crosstalk interference in different communication channels. The non-linearities in the receiver system sometimes are a factor causing interchannel crosstalk interference in single communication channels.
Intrachannel Crosstalk Interference
Intrachannel crosstalk interference occurs when the crosstalk signal wavelength is the same as that of the intentional signal in the communication channel or when the difference in the wavelengths of the crosstalk signal and the desired signal falls within the receiver frequency band. Depending on the understandability of both interchannel and intrachannel crosstalk interference, the interference can be classified as intelligible or unintelligible crosstalk interference. Intrachannel crosstalk interference is otherwise known as intermodulation distortion or coherent crosstalk.
Regardless of the type, all crosstalk interference affects the reliability of electronic and communication systems. Designers should be cautious about crosstalk interference and follow several crosstalk mitigation techniques for their system’s design. The use of differential signaling schemes, high speed clock signals, guard traces, and solid return paths are some of the routing tips commonly used to reduce crosstalk in circuit boards. Cadence offers a suite of PCB design and analysis tools that help to retain the signal integrity of a system’s design by eliminating crosstalk, interference, and other noises.