It isn’t exactly “news” that today’s world is a very much high-speed, digitally interconnected one. It is a world built on electronic systems that are expected to transmit data quickly, reliably, and with minimal disruption.
This brings us to the subject of signal integrity, or “SI”. This term refers to the quality and reliability of an electrical signal as it travels through connection paths such as connectors, cables, and printed circuit boards (PCBs).
For professionals involved in designing systems for 5G infrastructure, automotive electronics, industrial automation, or high-performance computing, signal integrity is a hugely important concept.
This is becoming even more the case in an era of ever faster and more compact designs that depend on high-quality signal connectors and cable assemblies.
What Is Signal Integrity?
Signal integrity refers to how well an electrical signal’s original characteristics, such as voltage levels, timing, and shape, are preserved throughout its journey from transmitter to receiver.
Across such applications as telecommunications, aerospace systems, and consumer technology, it is of critical importance to maintain strong signal performance.
Ideally, then, the signal received should match the signal that was sent. In practice, however, a signal might be altered during transmission by a combination of electrical and physical factors.
Poor signal integrity can lead to issues such as:
- Bit errors
- Jitter
- Signal attenuation
- Crosstalk
- Reflections
Problems like these can bring about system failures, compromised performance, or non-compliance with standards.
As far as high-speed applications like Ethernet networking, USB-C systems, radio frequency (RF) communications, medical devices, and data centres are concerned, such issues are particularly urgent and significant.
There are certain sectors, and situations, in which nothing less than excellent signal integrity will suffice.
Key Factors Affecting Signal Integrity in Cables
Cables are the backbone of any connection. However, there are various physical and electrical properties that can affect their preservation of signals.
Examples of these are set out below.
- Dielectric materials: the insulation around conductors can have implications for capacitance and signal speed.
- Conductor quality and size: resistance and skin-effect losses can be minimised, for instance, when high-purity copper with appropriate gauge is used.
- Shielding: when shielding is effective, it can go a long way to driving down electromagnetic interference (EMI) and crosstalk.
- Length and impedance matching: attenuation generally increases with cable length and operating frequency. Reflections can be minimised when consistent characteristic impedance is maintained.
- Frequency and data rate: at higher frequencies, losses go up dramatically as a result of skin effect and dielectric absorption.
Connectors Play a Critical Role in Signal Integrity
As central as cables are to signal integrity, it is also true that even the best cable’s performance can be hindered if a poor-quality connector is used to terminate it.
High-speed signal connectors are designed specifically with high-frequency or high-speed digital signals in mind. However, they do need particular scrutiny as far as the optimisation of signal integrity is concerned.
Below are some of the challenges that can frequently arise with connectors.
- Impedance discontinuities. Changes in geometry, such as to pin-to-ground spacing or dielectric interfaces, can cause reflections. This is why high-quality signal connectors are crucial for maintaining tight impedance control across the mated pair.
- Contact resistance and oxidation. Gold-plated or other noble metal contacts help lower resistance and corrosion. This can be an especially crucial priority for installations in coastal or industrial environments.
- Crosstalk and EMI. Where compact multi-pin connectors are used, such as in backplanes or modular systems, it is necessary for excellent isolation to be achieved between channels.
- Mating cycles and mechanical stability. In transport and aerospace applications, vibration can be a particularly widespread problem. Where vibration does arise, it can cause the gradual degradation of contacts.
When engineers are looking to choose the right signal connectors for a particular project or installation, they will need to carefully assess such factors as compliance with relevant standards, environmental ratings, and backward compatibility.
Signal Integrity: A Fundamental Consideration, Not A Mere ‘Nice to Have’
As we have addressed in this article, from the perspective of various electronic and communication systems during the 2020s, signal integrity is a central and critical factor.
Connectors and cables are no longer the simple and passive components they might have once been widely presumed to be. Instead, they are now all-important elements that exert a direct and profound influence on performance, reliability, and efficiency.
