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Analogue SoCs set to bring designers a signal chain in a package

It's hard to disagree with Microchip's contention that analogue design is difficult and takes time. Analogue design is an area which requires experience and often a degree of creativity. It's also an area where there is a decline in specialists. Yet modern designs are still as reliant as they have ever been on analogue circuitry – and some would say even more so.

Looking to address these and other issues, Microchip launched last year its Intelligent Analog approach, creating what it calls analogue SoCs. Not only do these parts feature much of the analogue signal chain required for a particular application, they also come with a PIC microcontroller built in.

Jason Tollefson, Microchip's senior product marketing manager for the MCU16 range, said: "Microchip has been integrating analogue components for some time. Before, we were integrating more general purpose devices; items you'd find on any board, such as a 10bit A/D converter.

"But as this approach started to gain traction in the medical sector, we realised that there was a need for the integration on more higher end analogue components."

Microchip's main focus was to integrate the type of analogue functionality needed by designers for these various apps. Tollefson continued: "We talked to customers to assess their requirements and came away with a better understanding of their specific needs, particularly those designing medical instrumentation.

"We know that you can't implement a medical device, for example, without including an MCU or some other kind of processor. Neither can you build such a device without an analogue signal chain, so both have important roles to play. While there will be designers who wish to create their own signal chain, we're looking to eliminate this need."

One of the first members of Microchip's Intelligent Analog approach is the impressively named PIC24FJ128GC010, or GC (see fig 1). Based around the PIC24F, a 16bit flash MCU, the GC family features a 16bit Sigma-Delta A/D converter, a 12bit pipeline A/D converter sampling at up to 10Msample/s and two 10bit D/A converters running at 1Msample/s. Other analogue components in the device include two op amps, three comparators, three voltage references and a charge time measurement unit.



Tollefson noted: "If someone is, for example, designing a blood pressure meter, they will need a 12bit A/D converter to take a lot of measurement, but they'll also need a 16bit converter for precision."

To what extent is Microchip preselecting the components to be integrated? "Typically, we're not building application specific products," Tollefson explained. "We're looking to create something that has more horizontal application; we're adding features to make the device more widely applicable. In this way, users get a complete analogue signal chain and a microcontroller in one package."

Microchip says the combination of analogue integration and low power consumption not only reduces system cost and noise, but also improves signal throughput in applications such as portable medical monitoring devices and industrial applications, such as portable monitoring devices.

"These apps tend to be battery powered," Tollefson noted, "so there is an integrated LCD controller which can drive up to 472 segment displays." Integrated USB connectivity supports the uploading of data and can act as a service/data port for industrial equipment. Meanwhile, capacitive touch sensing is also supported.

Microchip says the integration of a 16bit A/D converter, USB and LCD into one package with an MCU allows the development of small form factor, battery powered applications.
Tollefson said the biggest benefit of this integrated approach is in cost. "If you do the maths on the cost of a GC device against the cost of a discrete solution, it works out to be about 40% less expensive. But there are other benefits, including reduced warehousing and inventory costs.

"But another big benefit is in terms of analogue throughput. Typically, in a discrete design with an off chip A/D converter, data has to be communicated over some kind of serial port and that takes time. By having the converter on chip, it all happens more quickly and design is easier, because everything is on chip."

A further area where the integrated approach brings benefits is at the board level, Tollefson contended. "If you have discretes, you typically have to use some form of shielding and the board becomes larger and more complex. It opens the design up to potential revisions and may increase cost. With the GC family, we've done the work."

Whilst the GC family is aimed mainly at those developing portable medical and industrial products with some form of display, Microchip also has similar devices aimed at digital power and automotive lighting. "These parts have a choice of 8 and 16bit MCUs, allowing them to serve a range of needs," Tollefson continued. "In some devices, there is a PIC16 MCU optimised for low cost motor control. But if you want to increase the performance, you might want to choose a part with a dsPIC that offers a higher throughput A/D converter. And the same is true with devices aimed at digital power. When you're doing control, it's all about analogue throughput, rather than resolution.

"To support this, we've included things like multiple inputs to the A/D converter so data can be applied simultaneously."

Microchip has looked at the market and segmented it to identify the applications that can be targeted, integrating as many relevant components as possible. "Our challenge is to integrate something like a 16bit sigma-delta A/D converter on to the same die as an MCU," Tollefson noted. "It has pushed our design teams to new levels because we haven't done it before."

The integration has been achieved through a modification to its process technology that allows for higher levels of isolation. "Devices in the GC family have an isolation area where the sigma-delta can be positioned, allowing it to offer the best resolution."

Selecting the correct manufacturing process was also an issue. "The Intelligent Analog portfolio features devices suited to high volume foundry, as well as proprietary technology," said Tollefson. "Each has its own attributes. For example, the GC family needed very low power consumption, but also high density memory and that's a combination you can't always get. But we have a 'grab bag' of processes and can match these to the product needs."

Microchip is continuing to evolve the Intelligent Analog range. "Recently, we've launched a device with a PIC16 MCU," Tollefson noted, "and we have a new dsPIC in the works, which will have a higher resolution A/D converter, faster throughput and the addition of op amps. Applications that require a dsPIC based solution will always be about analogue throughput and we're pushing that envelope."

To help designers get to grips with devices such as the GC family, there are dedicated starter kits available. "These have an analogue header so the user can bring the signals out to an accessible location. The boards also have a range of sensors and feature a capacitive touchscreen. Someone who needs to do a design can interface their sensors to the board and quickly get an idea of what their application might look like," Tollefson concluded.

Author
Graham Pitcher

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