Embedded Processing Trends, Part 2: Hyper-integrated MCUs

For example, currently a typical MCU device (Figure 1, below) may contain the following components: 120kB Flash, 8kB RAM, (4) 16-bit timers, supply voltage supervisor, Brownout Reset, programmable low-dropout regulator, I2C, SPI, UART, IrDA, Direct Memory Access controller, hardware multiplier (32x32), Analog Comparator, 12 channel 12-bit SAR analog-to-digital converter, 12-bit digital-to-analog converter,3 op amps, and 48 general purpose input/output pins " all on a 100 pin device!

Figure 1. Mixed Signal MCU block diagram

Anyone in the semiconductor industry knows that the rate of integration of new components is accelerating, and not just for MCUs. There are almost an infinite number of permutations of new cores, memory densities, power management and protection systems, communication peripherals, display controllers and data converters.

The industry has been increasing the integration of new technologies and modules in order to reach new markets and reduce costs on existing applications. In the past two years, features such as multi-core, floating point cores, ubiquitous USB (Host, Device, and the adaptable On-The-Go variety), wireless radios, op amps, high performance A/Ds, DACs and advanced display controllers (VGA, QVGA) have all been squeezed onto a single MCU. Within the next two years, we will see even more unique, powerful and innovative components added.

The future may look a bit foggy due to the sheer number of new paths for this integration to take; however, clear skies are ahead with a few technologies that will emerge as game-changers in the market.

These include advanced wireless (such as Zigbee, Bluetooth and WiFi), integrated power management modules (multiple power levels on and off chip), modules that allow chips to harvest some of their own power from the environment (energy harvesting) in addition to application specific modules like medical sensors and analog front ends.

Furthermore, MCUs will start to close the gap with the latest wired communication interfaces like high speed USB 2.0, Ethernet and IEEE 1394 at data rates that were only available on the highest end processors just a few years ago.

Wired and Wireless Communications
Adding wireless communication (RF usually) seems to be the most obvious area for integration, but it's also perhaps the most difficult to implement. Radio Frequency (RF) components are tough to add onto a PCB, and doing this at the chip scale is orders of magnitude more difficult.

There is a reason why only 8051 core-based MCUs have been added to the latest low power RF System-on-Chips (SOCs). The mating of these two completely different systems is complex and difficult because of problems like noisy ground planes, antenna and balun interfacing, data transfer, and accounting for the plethora of different wireless protocols and modulation schemes.

There are some huge technical challenges, but in many cases each successive monolithic RF + MCU chip makes the next one easier to design. This will result in a rapid acceleration of the number of integrated RF solutions as well as increased differentiation in this genre.

Today, MCU vendors have taken the first step by creating multi-chip modules and one or two with integrated RF on CPUs other than the 8051. But, this is just the ramp-up phase for a set of devices which have the potential to enable dozens of new applications that have not even been thought of yet.

In addition, innovations in die stacking and packaging have made it easier to put more diverse silicon on the same chip. Companies like ZeroG Wireless have started created low power WiFi modules and are taking advantage of the intersection of the increased demand for extremely low power consumption in MCUs and the emerging smart grid to gain a lot of support from the big SOC vendors. It is only a matter of time before this technology merges with existing MCUs.

Wired communications interfaces are already very common (Figure2 below). Several different MCU vendors have already integrated CAN, Ethernet 10/100, and USB full-speed onto a single chip. There are even small 100 MHz MCU that have integrated high speed USB 2.0(480Mbps) onto a microcontroller!

Figure 2. CC430 Integrated MSP430 + Chipcon Radio

Not only will these peripherals improve through added hardware acceleration such as PHY layers, MAC layers, integrated isolation and power management, but there will be further integration of other protocols such as IEEE 1394, DALI for lighting, or LIN/FlexRay for vehicles.