Feature: Evalboards
New PoS terminals Te EMVCo 3.0 standard applies a comprehensive set of specifications covering both, analogue operations (the physical coupling between the card device and the terminal) and digital operations (the NFC protocol layer and payments application layer). Many of the changes to the standard’s specifications
implemented in moving from EMVCo version 2.6 to 3.0 were aimed at tightening regulation of the terminal radio’s behaviour to ensure interoperability with mobile phones and smart watches. Tis is because mobile communications devices provide a far inferior operating environment for an NFC radio compared with conventional payment cards. By requiring improved performance on the terminal side, EMVCo 3.0 compensates for the inferior NFC performance of the mobile device. Hence, the EMVCo 3.0 standard on its own raises the bar a PoS-
terminal developer must reach. Still, the difficulty is made even greater by the new trend in terminal design, which calls for much larger display screens. Following the lead set by the smartphone, the latest PoS
terminals feature a large display, which in many cases occupies the entire front of the device, and might also include touch- sensing functionality. Tis creates a substantially more difficult environment for an NFC radio: in this new design style, the antenna lies behind the display, so NFC signals from the card device must pass through the display assembly, which includes various metal components. Te display’s metal backplate in particular acts as a shield, greatly attenuating the NFC signals. NFC signals can also suffer from interference generated by the display controller, reducing the system’s signal-to-noise ratio. Te interference can also go the other way: an NFC controller can in some cases interfere with the display controller.
Simpler NFC antenna matching Te three RF issues that cause the greatest difficulty when developing conventional NFC transceivers are: • Antenna matching; • Wave shaping; • Regulation of the controller’s power output. Te Panthronics PTX100R evalboard kit provides simple
settings and an easy-to-use tool to make design of the matching network, configuration of wave-shaping operation and regulation of the PTX100R controller’s output straightforward. Underpinning the simple GUI that the evalboard provides is the PTX100R’s unique sine-wave architecture: this is more difficult to implement in silicon than a conventional NFC front-end’s square- wave architecture, but makes the PTX100R much easier for an OEM to implement in a device such as a PoS terminal. Te conventional square-wave output generates interference
in the form of multiple harmonic frequencies and, so, requires a complex EMC filter network made up of many external components. Te PTX100R’s sine-wave output creates no such harmonic interference, therefore it can be coupled directly to the antenna; see Figure 1. Tis benefits the design through reduced power losses, higher output power, avoidance of the large tolerances that create variances in performance across a population of production units, and, of course, reduced bill of materials. Another important benefit is in antenna matching: the
impedance of the PoS terminal’s antenna needs to be matched only to the impedance of the PTX100R and not that of the NFC front-end and the multiple components in the EMC filter. In addition, in a circuit that has an EMC filter, the designer will need to take account of the multiple resonant frequencies generated by the filter, whilst in the PTX100R-based circuit the only resonant frequency is that from the PTX100R itself.
Figure 2: The PTX100R evalboard’s intuitive GUI allows the developer to perform EMVCo tests
Figure 3: The PTX110R evalboard’s frequency response graph
www.electronicsworld.co.uk June 2021 21
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