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Mixed-signal FPGAs heed medical calling

Posted: 15 Oct 2008 ?? ?Print Version ?Bookmark and Share

Keywords:FPGA? mixed signal? medical?

Increasing health care costs, the prevalence of chronic diseases, aging populations and large emerging markets!such as China, India and Brazil!are creating tremendous demand for affordable, robust and reliable medical devices to improve the treatment and care of millions of patients worldwide, and cure an increasing range of diseases. In turn, medical device designers are exploring new technologies from various industries to improve the diagnostic, monitoring and therapeutic capabilities of next-generation devices.

Two trends have emerged to make medical devices more affordable and more accessible for patients!miniaturization and portability. Today, medical manufacturers are moving entire systems into a portable unit the size of a hand, or even smaller. As an example, clinical medical devices, such as EKG, hemodialysis machines and patient monitors, are essential tools in hospitals and clinics, but they too are shrinking. What was once huge equipment tethered to a wall has become available in mobile clinics, ambulances, and even in a doctor's bag for house calls.

One implication of the trends toward miniaturization and portability is that these complex instruments must be reliable enough to withstand a wider range of operating conditions. It used to be enough for a machine to work in a spotless operating room, clinic or laboratory. However, modern medical devices must deliver improved accuracy and reliability in the more dynamic environment of a mobile clinic or ambulance. With medical devices, there is often no room for error.

Many clinical medical devices are microprocessor-based, electromechanical instruments that use a common set of building blocks: power control and temperature management; a user interface that includes a keypad, LCD monitor and audio control; flash or EEPROM for data logging; and device interfaces for connections to other machines. Though there are many similarities, individual medical applications are highly use-specific and often very complex.

So, in addition to their "core" building block elements, clinical medical devices also include unique diagnostic or functional blocks to complete their particular tasks. Ultrasound machines, for example, include a transducer probe and transducer pulse controls, while hemodialysis machines use a dialyzer. Changing features and complex functionality in a small footprint, with requirements for low power, high accuracy and reliable operation make clinical medical devices an excellent market for reprogrammable nonvolatile semiconductor technologies. In particular, flash-based, mixed-signal FPGAs are uniquely suited to these applications due to their high levels of integration, intelligent power- and system-management capabilities, small footprint and high reliability.

Flourishing market
Market analyst firm Gartner Dataquest named medical applications one of the fastest growing segments for semiconductors. In September, Gartner estimated the medical electronics market for semiconductors at approximately $3.42 billion in 2008 and growing to $4.48 billion by 2012, with FPGAs making up approximately $323 million of that total.

A hemodialysis machine is designed to filter blood, continuously control and monitor venous and arterial blood pressures, and administer anticoagulants during treatment. A typical hemodialysis session lasts three to five hours and is performed approximately three times per week.

In a typical session, blood is pumped from the body into the hemodialysis machine. There, the machine's dialyzer (filter) purges the blood of metabolic wastes, restores the proper electrolyte balance, and eliminates extra fluid. Then, the clean blood is pumped back into the body.

To fulfill the critical functions of the machine, a typical hemodialysis device leverages several microcontrollers to monitor and control the flow of blood and other fluids, sound alarms, and shut down the machine when necessary.

Within a typical hemodialysis machine are specific design building blocks. The power control block performs temperature sensing to enable the fan driver and performs watchdog and battery backup functions. The user block inputs patient information via a keyboard or touchpad for customization of the treatment parameters. It also enables the health provider to monitor patient status and treatment during dialysis.

The data-log/communication interface manages the use of flash/EEPROM and the communication port. The audio/alarm output function is accessible via several blocks and controllers to sound the status alerts.

The signal conditioning/sensor control block is tightly integrated with the mechanical components of the system!the dialyzer and tubes. Together, these control the release of various anticoagulants, control and sense temperature using comparators, general-purpose and precision Op Amps, and ADCs, control the mix and flow of the dialysate, and other critical functions.

The pump/motor control and driver circuitry manage the many pumps, valves, motors, and heaters in the machine while the arterial and venous control monitors the level and pressure sensors. It is interesting to note that though the pump motor control and arterial and venous control monitors are unique to the hemodialysis machine, many other controllers are common to most clinical medical devices.

Today's single-chip, flash-based mixed-signal FPGAs offer integrated analog capabilities, flash memory, FPGA fabric and, often, an embedded industry-standard microprocessor. As a result, they can perform the system, power and thermal management and control functions of clinical medical devices!from system power-down/up functions and data logging to temperature and voltage sensing.

Trimming down costs
The mixed-signal FPGA enables several components to automatically be removed from the system board due to redundancy. These include the flash memory, PWM, discrete analog ICs, clock sources, and real-time clocks. Because flash-based FPGAs store their configuration information in on-chip flash cells, no external configuration data needs to be loaded at system power-up!unlike SRAM-based FPGAs. Therefore, these flash-based, mixed-signal FPGAs do not require separate system configuration components, such as EEPROMs or microcontrollers, to load device configuration data at every system power-up. This reduces system costs, board space requirements, as well as increasing security and system reliability.

Further, these highly integrated devices allow designers to absorb the functions typically served by several discrete components into a single, highly reliable, mixed-signal FPGA.

For example, the Power Control block, which may consist of the watchdog elements, fan drivers and temperature sensors, can be replaced by a single mixed-signal FPGA device. A mixed-signal FPGA can also provide the functionality that the entire motor/pump driver block originally offered, including the microprocessor and ADCs.

The user interfaces in a dialysis machine commonly include the keypad, touch screen or LCD display, and the speakers. A well-designed interface enables the healthcare provider to monitor the patient status and administer treatment effectively. These functions could be combined into one mixed-signal FPGA chip. The device's embedded microprocessor and flash memory can enable data logging, while other intellectual property solutions can help to manage data inputs, alarms and other tasks.

In hemodialysis machines, the power and thermal management units perform critical tasks, such as temperature sensing in the blood and system power-down/up functions. Accurately measuring the temperature and controlling power of the system using separate blocks can increase cost but also can increase the reliability of the machine, thereby increasing the life of the product and of the patient. The analog circuitry of today's mixed-signal FPGAs, however, allows these critical features to be easily integrated and implemented.

The elimination of discrete devices and the integration of diverse functions, such as processing functions, analog inputs and outputs, real-time clocks and flash memory, into a single, mixed-signal FPGA increases reliability, reduces cost, reduces power consumption, and minimizes board space.

- Shabnam Zarrinkhameh
EE Times

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