ASICs in Industrial Control Systems

Carl Hudson is Business Development Manager at Swindon Silicon Systems

When we think of ASICs it is usually in the context of high volume applications like consumer electronics but, by combining expertise in design with modern foundry manufacturing technology, they can be a cost effective alternative to traditional electronic circuits in specialist low volume markets. One of the fastest growing is industrial control systems.

Industrial controllers cover many industries and come in many forms but they all carry out a similar function: they monitor a variable, compare the measured value with a desired value and adjust a controlled variable to reduce any discrepancy. This usually incorporates some sort of feedback loop with three term (proportional, integral and derivative) control. The signals generated by the sensors that carry out the monitoring function may be digital, but more often are analogue values of temperature, pressure, level or analytical quality, and these need to be conditioned and digitised to allow them to interface with the control systems. The nature of the sensors has changed too, as material science has allowed the development of CMOS sensing elements, which lend themselves to integration either on chip or in the same package. Industrial sensors, which are often located in confined and difficult environments, are typically in operation for many years and mixed signal (analogue and digital) ASICs offer a rugged and compact solution with the additional benefit of obsolescence protection, an important factor for lifetime maintenance and spares. Communication between the sensor and the controller can be any one of the many standard or proprietary protocols, either RF or wired. Data rates tend to be low, so the most common protocols are the Serial Peripheral interface, (SPI) or the Inter-Integrated Circuit (I2C), from networks such as Profibus and Profinet.

Today we can integrate substantial functionality into an ASIC, especially at the smaller 22nm and even 14nm CMOS geometries. However, these geometries are best suited for predominately digital designs so, for industrial mixed signal designs, geometries are usually in the 350nm – 110nm range. These can still achieve a high level of digital integration, including digital signal processors (DSPs) and microprocessors, and can also offer the flexibility needed for the analogue part of the design. The nature of sensing elements has also changed, with developments in material science making possible CMOS sensing elements which can be integrated either on chip or in the same package. Functional safety is a concept applicable to programmable electronic systems across all industrial sectors, and is fundamental to the enabling of complex technology used for safety-related systems and, increasingly, non-safety related systems. Safety is, clearly, vital to any industrial control system and, for a number of years SWINDON has been designing mixed signal ASICs to meet the requirements of the international safety standard IEC 61508 to ensure the necessary risk reduction required to achieve safety for the equipment.

In some cases, the solution is for a platform approach, where one design will be used in different scenarios within a product family. For example, a single controller can be used in combination with a variety of sensors for different physical or chemical parameters, and it will support many sensor interfaces and communication ports. It may also process information local to the sensor – that is fat client type architecture. There is always a balance between performance and costs and the key is to have clearly defined goals at the project outset. Figure 1 shows a typical example of a platform type of architecture.

This type of architecture can perform processing independently from the main controller and report back. Being generic it is able to interface with many different sensor types, and the controller communications can be wired or wireless.

The fabrication costs of ASICs have fallen year on year, making them attractive even for the relatively low annual volumes typical of instrumentation and control applications. Add to this benefits like optimised performance, obsolescence and IP protection and it is no surprise that mixed signal ASICs are changing the face of industrial controllers. However ASIC design is not simply a question of transferring an existing PCB design. ASIC design needs different techniques, and good system knowledge and design experience are vital if the project is to be a success. In many cases, this comes from an amalgamation of the ASIC design team and the system designers, so it is crucial to build this relationship early in a project. With mature development processes and excellent relationships with the fabrication plants, with 100% in-house wafer probe and ATE test and over 350 successful projects, SWINDON has all the experience and expertise to guide you through the many choices you have. 

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