Application of PSoC in Electronic Medical Devices
Medical devices are getting smaller and more sophisticated. To achieve portability, high functionality and low cost, a programmable system on chip can be configured to serve a number of different functions to create a medical device on chip.
SAMMY LEE, CYPRESS SEMICONDUCTOR
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In order to respond to the increase of medical expenses and the rise of health insurance costs, home health examinations that reduce the number of hospital visits and cut down the squandering of medical resources have become the latest trend in the medical health community. The often large and cumbersome measurement devices such as the infrared electronic thermometer, blood pressure monitor, blood glucose meter, pulse oximeter and ECG monitor have become smaller in terms of dimensions, remain durable for a longer period of time, and are less expensive as the electronic technology evolves to maturity. Portable electronic medical devices, in general, have a number of working components in common.
For example, all the devices shown in Figure 1 require some form of vital sign biosensor or transducer to provide the signals. These signals must then be amplified with the appropriate circuitry and/or converted between digital and analog signals. A microcontroller is required for signal analysis and processing as well as for logic judgment. Battery power is required for portability as are power control components to optimize power usage. Human interface components such as the screen, keyboard, button and switch are also needed in all such devices. Then, depending on the particular system requirements, other components can be included such as those for data access and storage; wired or wireless communication, and sometimes feedback components using vibration or voice are included.
Examples of portable electronic medical devices.
As they are portable electronic devices, the engineer also needs to consider the design scope of consumer electronics during the product development. For example, performance: The measurement result shall be sufficiently accurate, so the proper, yet not excessive range of performance must be selected. Low power consumption is also a vital consideration. As a rule of thumb, the product should function normally without changing the battery for more than 6 months. The product shall be as small as possible, easy to carry and more energy-saving. Quick evolution is as important as it is in the consumer market. You need to be the first to release new products to claim or secure the market. And of course, low cost is paramount. The product has to be affordable.
After understanding the needs of portable electronic medical devices, we now turn to how PSoC helps the engineers to develop more advanced products. PSoC combines the programmable digital and analog components, indicating that it is able to provide the signal amplifier, analog-to-digital converter/digital-to-analog converter, filter and PWMs required for the portable electronic medical devices. PSoC includes the 8-bit (8051) or 32-bit (Arm Cortex M3) microprocessor, meaning that it is able to support various unifunctional medical devices, or integrates three to four functions to become the control chip of the physiological monitor (infrared electronic thermometer, blood pressure, blood oxygen analysis and heart beat). The USB, UART, I2C and SPI transmission managements inherent to PSoC allow free-flowing communication among ICs.
Medical Devices on Chip?
Let us take as an example the application of a programmable system on chip (PSoC) in the blood pressure monitor. The PSoC integrates an ARM Cortex M3/8051 processor on the same silicon die as an array of programmable I/O logic. It takes advantage of the oscillometric method, which is the most widely used method in portable electronic blood pressure monitors. Referring to Figure 2, the PSoC uses the built-in pulse width modulation (PWM) to drive the air motor for pressurizing the cuff on the arm. During the gas release, the pulse of the internal artery, through the cuff and air pressure sensor, is converted to the signal that is transmitted to PSoC. As the signal is only a few mV, it is amplified (InAmp + PGA) and the noise of the blood in the blood vessel is filtered (band pass filter). Finally, the signal passes through the analog-to-digital converter to become the digital signal for PSoC to measure the subject’s systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP). All of these components can be configured in the digital and analog subsystems of the PSoC. These signals are displayed on the LCD screen to complete blood pressure measurement.
Blood Pressure Monitor Diagram.
What’s worth mentioning is that all electronic components other than the external components such as the LCD screen, motor, air pressure sensor and motor driver are replaced by one single PSoC. This is able to save much space and accomplish the product development swiftly. PSoC can thus be regarded as a BPM on chip!
Next, consider the application of PSoC in the pulse oximeter. The oxygen saturation SaO2/SpO2 is the ratio of oxyhemoglobin (HbO2) to total hemoglobin (oxyhemoglobin + reduced hemoglobin) in the blood. Usually, the higher the ratio the healthier a person is. Most oximeters are fixed on top of the finger. There is an infrared LED above the finger and an infrared sensor below the finger. According to the difference in the infrared absorption between the oxyhemoglobin and reduced oxyhemoglobin, one can calculate the blood oxygen concentration based on the infrared signal intensity. As it varies with the heartbeat, one can then figure out the heartbeat rate based on the cycle alteration and measure the heart rate and the blood oxygen content simultaneously.
As indicated in the PSoC pulse oximeter of Figure 3, one can see that, except the current source (LED driver) and infrared sensor, all other components are replaced by PSoC. All the calculations are completed inside PSoC to save the development cost and time.
Pulse Oximeter Diagram.
After the examples of the applications of PSoC in the blood pressure monitor and pulse oximeter, we hope readers may have a more advanced understanding about PSoC. You are welcome to download the PSoC work environment PSoC Designer and PSoC Creator on the Cypress website and consult the application notes of the blood pressure monitor [http://www.cypress.com/?docID=20249] and pulse oximeter [http://www.cypress.com/?id=1001&rtID=5&rID=40117] for the practical operations. We believe that the powerful functions of PSoC will present more surprises and benefits to you.
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