EMI and Crosstalk in Integrated Circuits

Key Takeaways

• Signal integrity is lowered when the signal in an IC experiences electromagnetic interference or crosstalk. 

• Crosstalk in an IC can cause signal propagation delay, signal propagation failure, pulse distortions, and emissions.

• EMI and crosstalk are responsible for poor signal integrity and high noise margins in ICs. 

Signal integrity is greatly affected by electromagnetic interference and crosstalk

Signal integrity in integrated circuits (ICs) is the ability to propagate the signal from its source to a destination without distortion. In integrated circuits, signal integrity is greatly affected by power supply noise, delays, overshoots, electromagnetic interference (EMI), and crosstalk. The crosstalk in ICs is a type of electromagnetic interference between two signals propagating adjacently. As the EMI and crosstalk in an integrated circuit increases, the system experiences glitches, errors, and timing problems. Let’s explore signal integrity in ICs and how EMI and crosstalk affect this integrity.  

Signal Integrity in ICs

Signal integrity maintains the original signal over time without any distortion. The signal integrity in ICs greatly affects the timing and quality of the signal. In high-speed digital systems utilizing ICs, the timing is important, as every action depends on it. When the signal integrity is compromised, the signal fails to reach the destination at the supposed time. The quality of the signal will be poor at the receiving end compared to the transmitting end when the signal integrity is low. The signal integrity is affected by electromagnetic interference and crosstalk.

EMI and Crosstalk in ICs

EMI

Process integration, complexity in circuits, and higher switching speeds challenge the electromagnetic compatibility of ICs. Electromagnetic radiations generated by ICs interfere with the normal functioning of ICs. Conducted emissions are also present in integrated circuits. The interference in ICs resulting from physical contact are due to conducted emissions, which are typically under 30MHz frequency. Electromagnetic radiations or radio frequency emissions are usually above 30 MHz frequency.

A reduction in the power supply voltage and more interfaces are two major factors that cause EMI generation in ICs. Metal lines or metal interconnects, which are essential for reliable and high-speed data communication in integrated circuits, are also significant in inducing EMI in ICs. As the size and density of the die decrease with the reduced cross-sectional area of the metal interconnect, the parasitic effect becomes dominant in the interconnect and makes ICs more vulnerable to electromagnetic interference. 

Crosstalk

Crosstalk is the phenomenon in which the signal transmitted through one interconnect creates undesired effects on its neighboring interconnect. The signal in one interconnect influences the voltage waveform of neighboring interconnects. The interconnect carrying the signal (which creates crosstalk) is called the aggressor and the adjacent interconnect (which suffers from crosstalk) is called the victim. The effect of crosstalk is significant in high-speed integrated circuits and can lead to failure. 

Mechanisms Causing EMI and Crosstalk 

There are two mechanisms that can cause EMI and crosstalk in ICs:

1. Mutual inductance between the interconnects in ICs. When a varying current flows through an interconnect, it produces a varying magnetic field around it. The varying magnetic field can either radiate electromagnetic energy in the form of radio frequency (RF) emissions or it can couple with the adjacent interconnects. RF emissions are responsible for EMI and the coupling of the magnetic field creates crosstalk. 

2. Mutual capacitance between the adjacent interconnect can lead to EMI and crosstalk interference in ICs. The voltage in an interconnect produces an electric field around it. When the electric field associated with the interconnect varies, it either radiates electromagnetic energy as RF emissions or is capacitively coupled to the adjacent interconnects. 

Issues in ICs Due to EMI and Crosstalk

EMI problems in ICs are undesirable and have several consequences. EMI can emit direct radiations from the IC surface. The antenna effect of the conductors in the ICs due to the current flow through it aggravates electromagnetic radiations. EMI in ICs results in conducting noises to the signaling ports. The data and clock signals in the IC can lose synchronization in the presence of EMI, which can lead to the misalignment of clock information and poor data integrity. The power line conducting high-frequency noise signals in ICs is one of the challenging issues resulting from EMI.

The crosstalk in ICs can be between the interconnects, bonding wires, power pins, or signal pins. Crosstalk in an IC can cause signal propagation delays, signal propagation failures, pulse distortions, and emissions. There can also be excessive overshooting and undershooting due to crosstalk.

EMI and crosstalk are responsible for poor signal integrity and high noise margins in ICs. As the size of ICs continues to shrink, it will become increasingly important to mitigate EMI and crosstalk issues. Cadence offers tools that can help mitigate EMI and crosstalk in ICs.

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