Low-Power Operational Amplifier with Self-Calibration

The emergence of advanced personal medical devices at reasonable prices is changing the entire healthcare industry, allowing consumers to monitor their vital signs and other key indicators at home or on the go without having to go to the hospital for a visit. According to Gartner, portable consumer medical devices such as blood glucose monitors, blood pressure monitors, insulin pumps and heart rate monitors are the fastest growing segment in the medical device market. A recent medical semiconductor report by Databeans also pointed out that the home medical device market will grow by 9% (compound annual growth rate, CAGR) in the next five years.

       The rapid growth of the personal medical device market is due to a variety of factors: the need for regular health checks for the elderly, the high cost of traditional medical services, consumers' growing awareness of the benefits of health care devices, the convenience of purchasing personal medical devices online or in retail stores, and the continuous advancement of semiconductor technology, which makes these consumer health care devices increasingly mature, easy to use, and affordable.
    Consumer products are generally susceptible to price factors, and consumer portable medical devices need to meet more stringent requirements to succeed in the market. Most importantly, these products must be very reliable and accurate to prevent health problems. These requirements are regulated by government agencies, such as the U.S. Food and Drug Administration (FDA).

To succeed in the increasingly competitive home healthcare market, portable medical devices should have the following features:

      Ease of use; high reliability and safety (government regulation); simple and secure connections; low power operation (i.e., long battery life); support for a wider voltage range (especially lower voltages); high measurement accuracy; small form factor; and reasonable price.
      To achieve these product features and provide them to consumers at an affordable price, medical device developers must reduce system costs and limit the number of discrete components used in the design. Semiconductor suppliers are also responsible for developing highly integrated embedded control solutions that have high performance and reliability under strict power and cost control conditions. At the core of portable device design is a highly integrated mixed-signal microcontroller (MCU) that can provide excellent processing performance at the lowest supply current.
     Ease of use is a basic requirement for all portable medical devices because it can reduce measurement errors caused by incorrect operation. Such devices should require minimal interaction, simple user input (e.g., fewer buttons and simpler software menus), and a large and easy-to-view display (e.g., a large LCD with backlight). To support these features, the MCU must provide field-programmable nonvolatile memory (usually in-system programmable flash) and flexible I/O configurations that can make full use of the limited number of pins.
    While many portable medical devices today only display health test results, leaving interpretation and documentation to the end user and their physician, newer devices also feature easy connectivity and automatic recording and transmission of test results. Typically, these more advanced portable medical devices are connected to a PC or mobile medical device with software that tracks the results, or securely transmit information wirelessly to medical staff, caregivers, or web-based applications, a practice known as telemedicine.
   As shown in Figure 1, the medical device market has adopted an optimized USB device standard, the Personal Healthcare Device Class (PHDC), and the ubiquitous USB interface has standardized data and information transmission, eliminating the need to care about which manufacturer the device comes from. In the future, simple and reliable wireless connections will make data transmission even easier. Therefore, MCUs need to provide multiple ways to integrate connection interfaces, such as USB controllers with integrated precision oscillators.

   RF transmitters and transceivers work together with MCUs to provide wireless connectivity for remote medical applications. In addition, wireless MCUs (highly integrated devices that combine a low-power MCU core with a high-performance RF transceiver in the same package) are also widely used. For example, Silicon Labs' Si10xx wireless MCU series meets the ultra-low power requirements of battery-powered portable medical devices. At the same time, the integrated Sub-GHz band transceiver can provide a wider operating range and excellent RF sensitivity.

    Regardless of the connection method or system architecture, the communication protocol stack requires more code space on the MCU. Therefore, the demand for storage space in small-size devices will gradually increase.