Feature: Sensors
Firstly, industrial robots are an
application where position sensors are expected to operate continuously; any maintenance downtime adds cost and inconvenience. The solder joints of a circuit board are a common failure- point, so it makes sense to reduce component count by replacing discrete components and standard ICs with a single, very rugged package. In this way the electronics are afforded greater protection from environmental factors such as chemical attack and vibration, and assembly of the PCB becomes simpler. In addition, the size of the PCB
is reduced, leading to a smaller and lighter encoder that offers improved dynamics, and is able to serve new applications. Some customers also value the protection an ASIC affords for their IP, as monolithically-integrated circuits are far more difficult to reverse engineer than a collection of standard parts wired together and easily accessible. What’s more, an ASIC brings
output. It may also recognise features such as reference marks being passed, or overspeed conditions, generating immediate interrupts toward the host system. Interface electronics provide a bidirectional data path between CPU and host, and a stable power supply voltage.
Increased integration When an encoder is first prototyped, these separate components appear as several off-the-shelf ICs, each typically supported by discrete capacitors and resistors. When production volumes are very low, and the design does not care about class-leading performance, this may be the optimum solution. In most other cases, the cost of developing an ASIC is justified since developers can integrate many functionalities into a single package. The benefits of using ASICs can
be dramatic:
opportunity to reduce the cost of parts. Systems built from off-the- shelf components are frequently over-engineered, as standard parts are designed and sold with maximum versatility in mind. Swindon Silicon Systems, for instance, assesses its customers’ designs and identifies opportunities to squeeze costs out of them: Is that CPU really necessary, if we could synthesise hard-coded logic for a fraction of the price? Is that dual-channel ADC used to capacity? For high-volume products, the cost of the ASIC’s development is offset by a smaller bill of materials and simplified assembly. Trough ASIC design, customers can
invest in performance where it matters. In position sensors this might be a non-linearity specification, equating to accuracy at different scale points. It could equally be an aggressive target on low- frequency noise, which cannot be easily averaged away. Tis is where working with an experienced ASIC partner yields benefits: the entire signal path can be optimised and simulated to the finest
detail, using proven IP and expertise. For example, ‘chopping’ may mitigate troublesome flicker noise, or temperature measurement may be used to compensate for voltage reference drift. The best ASIC partners serve as consultants from the outset, understanding the system, recognising where a custom IC design can unlock improvements, and guiding the customer as they write their specification.
ASIC development A company should consider whether a project is ready to benefit from a custom ASIC as soon as a prototype exists. At this point, a supplier like Swindon Silicon Systems will assess whether a custom solution is for them, and identify the best possible system partitioning. It is common, but not always necessary, for a supplier to undertake a four- to eight-week feasibility study to inform these conclusions and arrive at a detailed proposition and costing. Te supplier will then develop the chip, spliting the design into analogue and digital blocks. At this stage, many customers benefit from receiving a detailed behavioural model, in VHDL for example, to allow co-simulation with the rest of their system. Beyond this, the work is firmly in the
supplier’s hands, and no more input is required from the customer, other than periodic reviews to demonstrate the growing maturity of the design and its verification. The timescale of the entire process from specification to silicon will depend on the complexity. But, in every case, it is essential to work with an ASIC supplier who can own all aspects of the project, from the initial consultancy to the ongoing supply of qualified production parts. Position sensors underpin modern
industry and continue to evolve in their performance and technology. Te sensor electronics are a key part of this evolution, having direct influence on speed, accuracy and overall form-factor. Whilst off-the- shelf components suit some applications, manufacturers looking to truly differentiate their products must take the next step and explore the benefits offered by a custom IC.
www.electronicsworld.co.uk April 2022 17
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