A Platform For What Ails You?

Despite having unique demands, medical applications also demonstrate a need for common features, such as a high-precision front end, powerful CPU, efficient battery management and convenient USB/Bluetooth connectivity. By focusing on these commonalities, OEMs are able to create optimised and flexible solutions for numerous medical and analytical applications.

An example from Infineon Technologies employs a high-performance ARM core to provide the compute power, while USB and Bluetooth interfaces deliver mobile communication. Possible areas of use range from electronic blood sugar and blood pressure meters, to electrochemical analyses through to state-of-the-art fitness and monitoring systems, which can transmit their readings automatically also by mobile communications technology to the computer systems at the doctor’s or hospital.

The device shown in Figure 1 is a highly integrated system-on-chip (SoC) capable of providing comprehensive data acquisition and signal processing functions for a diverse range of analysis and medical applications in networked environments.


Figure 1: The MD8710 from Infineon is an innovative platform solution for a diverse range of sophisticated medical technology and analysis devices

For this reason, the chip platform features a precision, multi-channel AFE (analogue front end) with 16-bit resolution. This makes it possible, for example, to carry out a diverse range of medical analyses such as measurements for electrochemical impedance spectroscopy or electro-optical measurements (pulse oximetry). The high-performance integrated CPU (ARM Cortex R4 processor) provides the necessary high level of computing power, whilst the large scale integration helps to keep the system costs down. For mobile applications, an efficient power management system permits a long battery life.

Diverse Range Of Options

While customer-specific analysis software can be implemented on the ARM Cortex R4 processor, Infineon also provides — as a member of the Continua Health Alliance with its software partner companies — support for data exchange protocols and standards, in addition to standard transmission technologies such as USB and Bluetooth.

Besides the ARM core, AFE, Bluetooth and USB interfaces, the SoC incorporates further integrated functions such as GPIO, PWM, a timer and multiple serial interfaces to allow it to cater to a whole range of different applications (Figure 2). A single module with customer-specific software/firmware can support a number of different products, with the aim of saving development time and costs, and providing economies of scale for production that simplifies the logistics required and the associated workflows.


Figure 2: Block diagram of the MD8710, showing a comprehensive range of functions for a variety of implementations

The analogue measuring module permits multiple stimuli with synchronous measurement, which facilitates its use in the most common measuring applications with photodiodes or other sensors (temperature, pressure, etc.).

The AFE features two high-resolution A/D and D/A channels plus four further current/voltage inputs multiplexed to an auxiliary ADC. What is more, flexible ‘on-the-fly’ programmable operation amplifiers are available along with pre- and post-filters.

The ARM Cortex R4 can run at up to 100MHz operating frequency and features 256k of RAM; 128k of which is ‘tightly coupled’, and a further 256k of ROM.

Comprehensive peripheral functions provides sufficient scope for a diverse range of the most sophisticated applications; a multi-layer AHB bus as part of the AMBA (advanced microcontroller bus architecture) links all the blocks and the I/O subsystem, while the DMA engine relieves the CPU of communication between the bus clients. By means of DMA, data can be transferred parallel to the CPU from interfaces or the AFE, without restricting the bandwidth.

The integrated PMU (power management unit) reduces the number of external components required, while the integrated Bluetooth I/F interface permits wireless communication without active external modules. Also, the highly configurable AFE minimises the components required for the system design.

AFE

The AFE of the MD8710 provides a multi-channel, precision measuring unit for a variety of medical analysis functions. For this reason it incorporates two independently programmable input channels (16-bit A/D converter) and two independent output channels (16-bit D/A converter). All the channels feature pre- and post-filters (integrated anti-aliasing filter with a -3dB bandwidth of 100kHz). Differential (+/-2.5V) or single-ended signals (+/-1.25V) can be processed at the input. In addition, four integrated, programmable operation amplifiers with flexible configurability are available. This allows the amplifiers to be connected, for example, either as transimpedance or differential instrument amplifiers.

Data is transferred between the main system and the ADC and DAC channels via FIFOs. Simple system integration is supported by means of a 12-bit auxiliary A/D converter with four multiplexed external inputs, an internal temperature sensor and a 2.5V reference output.

Communication Friendly

Convenient, wireless communication is ensured by the independent Bluetooth 2.1 subsystem with its own CPU. A typical external connection only requires three inductors (nH range) and a maximum of six capacitors (pF). The dual-mode-capable module supports Bluetooth 1.2, 2.0 and 2.1.

To permit simple connection with USB-enabled devices, the module features an interface in accordance with USB 2.0 (Hi-Speed), which can also be used for charging the battery. The interface supports USB-OTG Supplements Rev. 1.3 and is specified as a human interface device (HID).

The integrated display controller subsystem allows results to be graphically illustrated on the matrix displays (particularly LCD, OLED). The parallel bidirectional 8/9-bit interface supports MIPI DBI 2.0 and permits programmable signal timing. The high-speed synchronous serial interface (SSI) offers full duplex operation and supports various data formats (bits, shift order, clock polarity, timing). Graphics acceleration and a resolution of 240 x 320 pixels as in the starter kit offered combine to ensure that text and signal information is depicted in good quality.

A three-channel UART plus SPI, I2C and SWI interfaces facilitate diverse digital connectivity. The SWI (single wire interface) also allows the ORIGA chip from Infineon to be connected for authentication applications.

Further peripheral functions such as a real time clock, PWM output, audio output, timer and a GPIO block with 47 channels complete the range of functions.

An integrated battery management system supports the use of different batteries (e.g. li-ion, NiCd, NiMH) or disposable batteries. A battery charging circuit allows multiple algorithms to be used. DC up and down converters for the processor and I/O power supply ensure long device running times. The current consumption for the entire SoC when idle is extremely low (< 30µA, real-time clock, wakeup). The module comprises a corresponding watchdog for all voltage supplies.

Digital Weigh Scales

Weigh scales represent a typical application example; digital scales are not only capable of displaying the weight but also the time and outdoor/indoor temperature.

Generally, 4-point impedance spectroscopy is used for ascertaining the body fat. This also makes it possible to analyse individual body regions. Also for private use, body fat scales are now offered that have additional electrodes in handgrips. This allows the values to be ascertained far more accurately, since more measured and fewer extrapolated data go into the measurements. All the distances between the four measuring points are first measured individually and subsequently added up. The electronic design of such an efficient pair of scales requires features such as those offered by the MD8710: high-performance and flexible AFE with high measuring accuracy, USB or Bluetooth for the data transmission, efficient display control and a long battery life. Figure 3 shows the conceptual configuration for an impedance spectroscopy solution, as used in this modern pair of scales.


Figure 3: Conceptual configuration of the MD8710 for impedance spectroscopy

An important advantage of the design based on the MD8710 platform is the high degree of reusability of circuit components and software. This means that the software can also target, relatively easily, other applications using impedance spectroscopy. The Bluetooth interface can also simply be used for other wireless interfaces.

Effective Design Support

For the MD8710, a complete development environment is available from Hitex (with a limited 32k licence), which includes an evaluation board, comprehensive software and documentation. Thanks to the standard ARM architecture, the versatile ARM Ecosystem can be used. Peripherals and integrated functions are supported by an application programming interface (API).

The software suite is tested for use with the development environments from Hitex and IAR. The Hitex IDE also includes the free GNU Compiler Collection (GCC). The RTOS kernel (FreeRTOS) allows applications to run in real time and offers inter-task communication mechanisms. System libraries are available for all fields of application: graphics, AFE, memory and power management, keypad, display, UART, real time clock, audio output, error handling, Bluetooth, USB, performance-optimised mathematical functions, I2C and SWI.

Infineon also offers a complete tool chain for application development on the MD8710 — from idea to simulation and verification, through to prototyping. A GUI-based AFE simulation tool is available online, for the configuration and simulation of the AFE with a sensor circuit. Two options are available for circuit generation: with predefined application templates or by circuit diagram editor. The settings for the individual AFE blocks can be modified. Ultimately, source code is generated on the level of the application layer and the signals can be simulated for the AFE and the sensor circuit.

For verification, all the corresponding registers can be configured with a corresponding GUI-based AFE verification tool, or imported from the simulation tool. Alternatively, predefined example applications are available. The settings for the individual AFE blocks can be adapted and modified. The tool displays the blocks used and provides recommendations. The corresponding source code is then finally generated. The corresponding settings can then be transferred to the starter kit and executed there.

For further code development the starter kit evaluation board can be used (Figure 4) with the ARM Cortex R4 core. The code is loaded via an external SPI flash (conveniently via the flash loader from Infineon). The supplied USB stick comprises the corresponding software and tools. Also included are the Tantino debugger and the HiTOP development system as a 32k demo version. Further tools such as the Segger debugger are also supported or are in preparation.


Figure 4: Speedy, risk-free way to medical design: with the MD8710 starter kit