RF, Digital and Analog Interconnect Considerations and Options for Design Engineers
The already booming world of commercial and industrial Internet of Things requires connecting many sensitive sensor modules, RF modules to antennas, and networked devices.
The latest smart appliances, data infrastructure, and wireless devices often require interconnect solutions that span the RF/microwave, digital, analog, and power domains. Due to the increased reliability demands and “smart” features of equipment in HVAC, industrial, and commercial applications, expectations of these diverse connections providing consistent and seamless operation is growing. However, no system or interconnect solution is invincible, and the increased pace of upgrades and replaced equipment creates a shortened timetable on the acquisitions of custom interconnect. Fortunately, certain interconnect suppliers have enhanced their supply chain and rapid manufacturing capability in order to provide urgent-need interconnect and component solutions with the ease of e-commerce transactions.
High Speed Digital and Signal Integrity
As the data rates for common consumer and commercial applications increase, and the need for improved isolation due to increased EMI, RF connectors and cables are being used for more high speed data applications. These applications include cable-to-board and board-to-board interconnect over short distances where the square wave signals are of such high data rates that the frequency content of the data streams reaches gigahertz to tens of gigahertz. Hence, connectors such as AFI board-to-board connectors up to 6 GHz, SMB surface mount and cable connectors up to 4 GHz, and SMP surface mount and cable connectors up to 40 GHz are becoming more common for digital signal processing (DSP) applications.
Routinely, these connectors are very high density and may need to be reconfigured regularly. As a consequence, snap on connectors with convenient surface mount technology (SMT) connectors or connector/cable assemblies are regularly used for routing many digital signal channels. Though not often rugged, RF interconnect for high speed digital applications requires reasonable isolation and electromagnetic interference (EMI) protection. Various sized cables are prevalent for these applications, as many systems require routing patterns with consistent delays among the signal paths.
4K/UHD TV Digital Broadcast and Machine Vision Applications
High speed digital cameras for machine vision applications and digital broadcast applications handling 4K/UHD quality video transmit many times more video data than previous technologies. Subsequently, the higher frequency content of these high data rate video signals suffers from attenuation to a much greater extent that lower data rate signals, and RF interconnect can be used to reduce the signal integrity degradation over long distances. Additionally, with these applications the interconnect is often bundled tightly or separated by a tight pitch, so interference and crosstalk is also a concern.
Typical RF interconnect for these applications are BNC to 4 GHz, high density BNC (HD-BNC) to 6 GHz, and DIN 1.0/2.3 to 10 GHz for bulkhead, PCB edge card, and top entry PCB mounting. Also, for these applications adapters to bridge between the different connector types are often needed.
The latest advances in connected car, smart car, and automotive infotainment systems include very sophisticated automotive control technologies and data driven connectivity. From massive fleet management systems to in-car-entertainment, both commercial and consumer industries are clamoring for more capable vehicle technology. Nevertheless, placing autonomous-driving grade GPS, high-speed wireless data, radar, sonar, driver monitoring systems, high-speed cameras, and a plethora of wired and wireless vehicle sensors places a large burden on the vehicles interconnect.
A major challenge with connectors and cables in these applications is the high-reliability and performance mix that is required, and mitigating the inevitable internal and external interference in order to maintain uninterrupted connections. These connections include high-speed data, analog, digital, RF, microwave, and millimeter-wave connections that are all necessary in meeting the most recent feature demands.
Aside from a demand for industry standard FAKRA connectors, MMCX/MCX, SMB, SMP, and potentially 1mm or other millimeter-wave coaxial connectors for millimeter-wave radar will be used more to connect the various wireless antenna technologies. Also, for routing high-speed data between various computers and sensors, including camera technologies, will likely be connected with RF connectors to reduce producing and receiving interference. To reduce electromagnetic-interference (EMI), 100 Ohm connectors with high EMI shielding and high temperature stability are becoming common to enable multiple digital transmission standards for displays and infotainment. For example, low voltage differential signaling (LVDS) and gigabit video interface (GVIF), USB, Ethernet, and IEEE 1394.
Industry 4.0, M2M, or IoT/IoE
In order to enable the onrush of connecting everything, many wireless sensor nodes and communication systems require a multitude of RF interconnect paths, internal and external to the systems. The already booming world of commercial and industrial Internet of Things (IoT/IIoT) requires connecting many sensitive sensor modules, RF modules to antennas, and between networked devices. Recent advances in phased-array, carrier aggregation, and multi-input multi-output technologies require several wireless and antenna technologies to be integrated in a very small space with many antenna-to-board and board-to-board connections.
Another area of concern for Industry 4.0 or machine-to-machine applications is having rugged factory grade interconnect that maintains low-cost and high performance, while being hardy to interference and EMI. SMA, TNC, and FAKRA adapters are current industry standards for reliable interconnect for data and RF applications. Nonetheless, to accommodate for much smaller board landing areas and great interconnect densities, MMCX, MCX, and SMB connector types are regularly used in applications where many connections need to be placed rapidly and reliably. MMCX, MCX, SMB connections also benefit operators and technicians with quick and efficient snap connections that can rapidly be reconfigured or troubleshot as required.
For much higher frequencies, precision SMA and SMP connectors may be used. Though relatively expensive, for high performance connections up to 26.5 GHz, 3.5mm RF connectors may be used, as they are also compatible with SMA connectors. Though rare outside of millimeter-wave applications, 2.92mm, 1.85mm, and 1mm coaxial RF connectors may be used instead of waveguide interconnect for frequencies from 40 GHz to 110 GHz. Depending upon the moisture, oil, debris ingress, and other environmental conditions for an application, various waveguide interconnect may be used, especially in precision sensing applications.
Military and Aerospace
Unlike many of the previous applications discussed, military/defense and aerospace applications require both high performance and extremely rugged interconnect that is capable of being both physically and environmentally stable in extreme conditions, and over long periods of time without service. For example, similar to smart car/autonomous car interconnect challenges military ground vehicles require mixed domain interconnect capability. But, with military applications, the EMI ruggedness and environmental requirements are much higher. RF connectors and cables in aerospace applications also require mechanical resilience specifications that far exceeds what is necessary in even military automotive systems.
Often, interconnect for defense and avionics applications experience much higher power levels at extreme temperatures and these interconnect must conform to military specifications and standards (MILSPEC).Type N, SMA, TNC, and 2.4mm RF connectors are often used in these applications, as well as FAKRA connectors. However, military grade connectors often require much more durable full crimp techniques and shrink wrapped connections for greater reliability and reduced VSWR.
Moisture and particle ingress ratings, IP67, IP68, and MIL-STD-348 RF connector interfaces are often required to meet military standards. Avionic applications also commonly require standards; MIL-C-39012, ARINC 600, and ARINC 404 are among the connector and cabling standards needed to survive the harsh installation and operation environments in these applications.
The wide range of selection and application specific demands of each interconnect design places substantial burden on the system, signal integrity, or integration designer for finding and sourcing compliant and quality interconnect. Additionally, the rate at which standard purchase orders are processed, custom manufacturing/assembly and shipping can lead to significant delays and elongation of design cycles or the fulfillment of customer orders. The majority of RF connector and cable suppliers are not readily equipped to fulfill quick turnaround orders, and often require substantial markups for any rushed services.
Fortunately, not all organizations in the RF/microwave industry are held back by the necessities of purchase orders, organizational delays on custom orders, or inexperienced rush shippers. Also, a few companies in the industry have even risen to the occasion, and provide convenient web-based tools that assist with custom cable assembly purchases, that introduce a seamlessly and delay-free acquisition process.
As the technological advancement and enhanced capability of RF/microwave technologies—as well as high speed digital data exchange—continues to proliferate every industrial and commercial application, the mix of connector and cable technologies will become ever more complex. The next generation of wireless, 5G, and the Internet of Things (IoT) is already contributing to higher data rates and greater need for high integrity interconnect, fueling the use of RF/microwave connectors and cabling in applications unfamiliar with such high frequency and performance needs.