Publication date: 10 February 2010
With a rapidly aging population, the home health care equipment is set to become a high growth market. Climbing costs in health care will further add to the increased demand for home health care in ways to monitor health in the home where total spending on health care will rise significantly over the next 10 years! Increases in age and health spending is expected to help push spending on semiconductors used in the portable health care market to grow from $171 million in 2005 to $250 million by year 2013. Such products will be needed to monitor health in the home, such as tracking blood pressure, blood oxygen levels, and blood glucose levels for self-diagnostics and treatment.
While consumer products are generally very price sensitive, the consumer portable health market adds other stringent requirements in order to be successful in the market. First and foremost, they must be very reliable and accurate to prevent health problems. These requirements are regulated by government entities, such as the Food and Drug Administration (FDA) in the United States.
Additionally, portable medical devices should have the following features:• Ease of use• Highly reliable and safe (government regulated)• Easy, secure connectivity• Low power (i.e., long battery life)• Support a wide range of voltages (lower voltages)• High measurement accuracy• Small form factor• Low cost
In order to deliver such features to the consumer within budget, engineers will not be able to continue to design such products with discrete component designs. Semiconductor suppliers will be tasked with supplying integrated solutions to the portable healthcare market to allow increased performance and reliability within strict power and cost budgets. The workhorse will be highly integrated mixed-signal microcontrollers that can deliver high-performance at the lowest supply currents.
Ease of use is more than just a selling point: it reduces errors in measurement due to operator error. Such devices should require minimal user interaction for proper operation, simple user input (for example, few buttons and simple software menus) and large, easy to see displays (e.g., large LCD displays with backlighting). To support this, MCUs will need field programmable NV memory storage (typically in-system programmable Flash) will be useful with flexible I/O configurations to make the best use of limited pins.
While many devices today will display results and leave the interpretation and logging to the end-user, newer devices will feature simple connectivity to log and transmit results automatically. Typically, this will be a personal computer or mobile health appliances with software that can track results, or securely send information to medical professionals, caretakers, or web-based applications. Technology companies have even adopted a new USB device standard, the Personal Health Care Device (PHCD) Class to better utilize the popular USB interface allowing standardized transmission of data and messages, regardless of manufacturer. Moving forward, wireless transmission of data will make connectivity even easier with simple, short range wireless connections for even greater convenience. MCUs will need to provide a variety of integrated connectivity interface methods, such as integrated USB controllers with precision oscillators. Short range wireless ICs in combination with MCUs can provide wireless connectivity, and is also offered as integrated solutions as well. Whatever the method, communication protocol stacks will require more code space in the MCU and so more memory in smaller footprints will be in increasing demand.
Fig 1: USB personal healthcare device class supports connectivity
While choices in high speed CPUs and communications options will be important, all medical devices will measure some physical parameter in order to quantify some aspect of a person’s health (e.g., blood pressure or oxygen levels). This requires measurement of light sensors (blood oxygen), conductivity (blood glucose), pressures (blood pressure) and temperatures – and these measurements must be highly accurate and consistent. In this market, errors in measurement can affect someone's health!
Mixed-signal MCUs must give superior analog voltage measurement results in the presence of noisy digital processor and communications signals in small spaces. This is one of the most challenging engineering problems faced by semiconductor suppliers and such specifications will be scrutinized by the product engineers, especially when faced with low battery voltages for the IC. Measurements must be low in noise and distortion (good signal to noise and distortion ratios) and highly linear. ADC operation must be allowed even when the CPU is in operation as the customer will expect to observe function during measurement, and likely the CPU will interpret results in real-time. Further, all chip features should be permitted even at the lowest battery voltages – what good is the MCU if you cannot make a measurement over the full battery life? In short, MCU suppliers in this market must integrate accurate analog measurements without compromise.
The next challenge to the MCU supplier is the demand for long battery life in the end product. “Portable” means the device in likely battery powered. Typically, added features require more power consumption, but product engineers cannot sell a product in which the customer will have to use large batteries or change them frequently. MCUs must support three parts of a low-power strategy: Low active power (MCU is in full operation), low power while off (or “standby”), and reduced time in its active state. The product and so MCU will be in an off, or lower power state most of the time, though will often maintain some sort of function like clock/calendar or alarm when not in use. While active power consumption is important, minimizing time awake is the key to extending battery life. MCU designers must continue to find ways to wake the CPU clock, and analog circuits for fast measurements to then allow the MCU to go back to a low power state. For example, making a voltage measurement with an analog-to-digital converter (ADC) requires a voltage reference. Such voltage references typically require 10’s of milliseconds to turn on and stabilize before a measurement can be made. During this time, the MCU is on and draining the battery. The Silicon Labs C8051F920 will wake in microseconds like many low-power MCUs, but the on-chip voltage reference is designed to also wake within 2 microseconds allowing accurate ADC measurements to begin quickly. The ADC is also designed to rapidly accumulate many measurements without CPU intervention for improved results while further minimizing time awake. The less time awake, the less current is drawn on the battery while giving good results.
Fig 2: Fast wake times and short operation intervals will extend battery life
Another important trend is in supporting new battery use configurations and technologies. Rechargeable batteries are popular and typically need higher voltage support, and integrated on-chip voltage regulators are mandatory. A newer trend is using only one alkaline battery in order to reduce product size or to save cost when the end customer expects the supplier to ship an installed battery. Until recently, this required the cost and space of a DC-DC switching regulator design to boost the alkaline battery voltage for proper MCU operation (alkaline batteries have a useful life to 0.9V). Not only do these switching regulators create a large amount of noise in voltage measurements, they must remain on at all times to allow the MCU to wake from sleep mode costing power and battery life. Newer MCUs like will offer an integrated DC-DC regulator that solves these problems for the engineer. The result is lower noise, less cost, reduced footprint, and better control allowing the DC-DC regulator to be off while the MCU is in its low-power state extending battery life. Even though this regulator is integrated, it should still output the boosted voltage supply externally to the rest of the system for a true low-power, single battery solution.
Continued integration and features like these to help reduce battery drain and supporting new battery technologies are essential to support portable medical equipment designs.
Fig 3: MCU’s should support a wide range of voltages supplied by batteries
While MCU suppliers continue to innovate and integrate the above features, this would not be so helpful if the MCU cost and footprints were to grow. The end-goal is to allow the engineer to deliver a lower cost, smaller solution. Such solutions must reduce the bill of materials and size. The best MCUs will deliver plenty of CPU speed, integrated connectivity, memory, and superior analog peripherals in the smallest form factors. In other words, semiconductor suppliers must provide increased functional density without compromise. Note the example below – 64kB of Flash code storage, 4kB of data RAM, an ADC, and two voltage regulators (LDO and boost regulator) in only 16mm2. This allows a complete measurement and interface system on chip without sacrificing performance or battery life. Product designers will be careful to choose MCUs like this with just the right set of peripherals to obtain the greatest cost/performance benefit (i.e., memory, I/O, communications peripherals).
Engineers and product managers are under a great deal of pressure, and must push the envelope of cost, size, and performance. The answer is highly integrated mixed-signal ICs to deliver solutions to a market that demands the very best in performance in the smallest form factors. Functionally dense MCUs will be the workhorse of the portable medical equipment market, and those who deliver will enjoy the benefits of this fast growing market segment.
