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Outlook 2014: Embedding digital processing in analogue and mixed signal designs

The market for analogue and mixed signal semiconductors is set for some significant evolution over the next few years. The Internet of Things – in which billions of objects (smart or otherwise) will become IP enabled and connected – offers an abundance of opportunities for devices and systems that sense, control, actuate and communicate with the physical and most decidedly analogue world in which we live.

Embedding digital processing in analogue and mixed signal designs is becoming an attractive proposition.

The market for analogue and mixed signal semiconductors is set for some significant evolution over the next few years. The Internet of Things – in which billions of objects (smart or otherwise) will become IP enabled and connected – offers an abundance of opportunities for devices and systems that sense, control, actuate and communicate with the physical and most decidedly analogue world in which we live.

Another important trend that is uppermost in the collective mind of the entire electronics industry is delivering solutions that provide reduced power consumption and increased energy efficiency at the system level. Could the encroachment of digital processing technology into the esoteric field of analogue chip design provide an answer for each of these strategic trends?

Analogue design is, of course, the proverbial black art and combining it with digital is a highly complex process in advanced mixed signal designs. Arguably, though, it has become much easier in recent times. One important factor that has eased and sped up the development process is the growing sophistication of the mixed signal design flow with EDA tools that now allow engineers to design and simulate both the analogue and digital in mixed-signal designs, while running C code simultaneously.

Previously, there have always been varying degrees of separation between the design and simulation of analogue and digital circuitry; and when it comes together in a single chip layout, the design might not always work first time. But, increasingly, thanks to these new advanced design tools, the process is now almost instantaneous, rather than taking many extra weeks in development. And when the increasing commercial availability of analogue IP along with digital libraries is added into the mix, this makes it significantly easier and quicker for any analogue or mixed signal chip vendor to come up with fast and efficient designs in a way that that just was not possible a few years ago – and certainly for those without huge experience in this field.

Embedding processing capability
These advanced capabilities in the design flow make it increasingly easy to embed a digital processor into an analogue or mixed signal design. There is no real penalty, for example, with the inclusion of a 32bit Cortex-M0 processor core in a design. The core can be implemented using only 12,000 logic gates and so it is virtually negligible in size compared to the surrounding analogue circuitry, which is larger perhaps by a factor of 10:1. Any additional cost for increased die area is therefore correspondingly low.

Meanwhile, the addition of a digital subsystem brings a significantly improved ability to test the device – a huge benefit that has not been fully recognised to date. A digital processor becomes a flexible engine that can be used to do all manner of on chip tests and calibration in mixed signal system on chip devices (SoCs), enabling much easier validation of the analogue electronics. Another advantage is increased system integration and therefore lower overall cost with the end system. The chances are a that standalone microcontroller is already used in a customer design alongside an analogue or mixed signal chip. An analogue chip vendor is now in a much better position to offer a greater level of integration.

Of course, this may or may not happen: some vendors may wish to use the digital processor for on chip testability, for example, and not necessarily open it up to customers for further feature development. But overall, this is a very clear value proposition for an analogue chip vendor. And, on the other side of the equation, leading digital vendors are seeking to augment their digital processing portfolio with analogue components.

Improving energy efficiency
While this new and emerging generation of mixed signal devices has the capability to fulfil the requirements of the Internet of Things, the big point to make is that embedding a digital processor will improve the efficiency significantly and the performance of the system overall, representing huge savings in power consumption.

So what can digital do to enhance the capabilities of analogue components to improve system power consumption? One specific and very important example is in motor control, where power electronics and the analogue are very clearly crucial. A digital processor can enable significantly better motor management of speed and/or rotation, delivering a potential saving in power consumption of around 40%. And the motors in this example are large devices in industrial applications, not necessarily those in low cost consumable products, such as toys. The digital element does not replace or take anything away from the analogue side – it simply enables digital control to improve the quality of the overall system.

So, with these advanced capabilities, in conjunction with the increased integration possibilities and higher levels of on chip functionality, the return on investment can be very fast with the inclusion of a small and powerful digital processor core.

The corroboration of all this is that analogue and mixed signal devices that embed digital processing capabilities are now coming on to the market. One example is a mixed signal processor from Analog Devices. The ADSP-CMX40X includes a Cortex-M4 processor and enables motor drive developers to add more features into the silicon.

The device targets energy efficient applications in industrial markets specifically and is designed to deliver more precise motor control in motor drives, photovoltaic inverters and closed loop servo control. A second instance is Infineon's XMC4000 family, which also embeds a Cortex-M4 processor. This range is also aimed at improving energy efficiency in industrial applications. And a third is the recent licensing by Dialog Semiconductor of the Cortex-M0 processor, which the company plans to use as the controller in a range of power management devices for power control and battery management functions in smart phones or tablets.

The future
In a few year's time, or even sooner, it could be that the vast majority or at least a high percentage of analogue and mixed signal chip designs will integrate a high performance digital processing subsystem to control and manage it. This would also enable developers to add their own software code on top.

The key applications are likely to be in motor control and power electronics and, today, the vast majority of these applications are essentially 'dumb'. Endowing them with digital intelligence, in the case of motors, could potentially save enormous amounts of energy. One estimate posited recently is that electric motors consume 40% of the world's electrical energy and much of that is in industrial motor drives. So, a little digital treatment of analogue could slash this footprint enabling significant environmental and cost benefits.

In the coming years, as the Internet of Things becomes a larger reality and the demand for reduced power consumption heightens, the model for the next generation of sophisticated analogue and mixed signal circuits, is likely to combine 'analogue on the edge' – to sense and actuate – with 'digital at the heart' – to control, make decisions and communicate.

A highly integrated and digitally controlled analogue SoC that has the potential to save 40% of the energy consumption of an industrial motor, whether it comes from an analogue or a digital semiconductor vendor, is an extremely compelling technology that has every reason to be in much demand in the very near future.

ARM
ARM designs the technology that is at the heart of advanced digital products, ranging from wireless, networking and consumer entertainment solutions to imaging, automotive, security and storage devices.

ARM's comprehensive product offering includes RISC microprocessors, graphics processors, video engines, enabling software, cell libraries, embedded memories, high speed connectivity products, peripherals and development tools. Combined with comprehensive design services, training, support and maintenance, and the company's broad partner community, they provide a total system solution that offers a fast, reliable path to market for leading electronics companies.

Richard York is director of embedded processor products for ARM.

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Richard York

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