Feature: IoT
Figure 1: Isolated LVDS interface with ADN4651 and ADuM5000
(differential) on the receiver side, which among other things, yields very low electromagnetic interference (EMI) and extremely fast switching speeds. LVDS interfaces are often used in control and regulating
systems where large data volumes must be sent between circuits or between short cable lengths. They are also used for synchronisation of components in an application by distributing the clock signals to the respective components. Analogue front ends (AFEs) in industrial measurement applications and control systems count among the typical applications for LVDS. However, they are also commonly used for realisation of digital interfaces between multiple data nodes and in the transmission of video signals, for example via HDMI. Another aspect that should not be neglected is the galvanic
isolation that LVDS circuits provide. Hence, they are also used where isolation of communication interfaces, such as in electronic circuits or backplanes, is required. Backplanes are circuit boards with multiple connectors for accommodating various add-on board modules, allowing for easy plug- and-play extension of the base system to include additional assemblies. However, add-on modules are often subject to large voltage transients because in many applications they are in direct contact with components connected to the power distribution grid. The add-on modules are accordingly vulnerable to external events such as lightning strikes.
Electrostatic discharge caused by human contact or internal capacitors that are suddenly charged, charged with reverse polarity or discharged when the add-on modules are plugged or unplugged, can also lead to high transients. Thus, a safely- isolated interface is indispensable. Otherwise, the connected assemblies could easily be damaged or users endangered if voltage transients occur. Functionally-isolated communication interfaces are also
favourable for industrial measuring instruments because isolated interfaces offer a floating ground, for example, between analogue-to-digital converters (ADC) and microcontrollers. This allows the measured signals to be isolated from influencing or being influenced by the rest of the device.
Realising LVDS interfaces A variety of products for realising isolated LVDS interfaces are already on the market. Analog Devices offers a very efficient and reliable solution with its isolated LVDS family consisting of ADN4650, ADN4651 and ADN4652, which supports data rates of up to 600Mbps and simultaneously also corresponds to the standard values of non-isolated LVDS interfaces. In comparison, standard digital isolators can reach just 150Mbps. Very-high data rates, despite existing isolation, are possible thanks to the iCoupler technology, which involves microelectromechanical systems (MEMS)
www.electronicsworld.co.uk November/December 2020 31
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