Portable medical monitoring system design challenges faced by (1)

Today's Government and medical institutions are striving to improve its health care system to better services for patients.

In order to allow more time to recuperate at home, you don't have to go to the hospital or doctor's Office, the medical industry and give full play to the portable, long-distance connections advantages of medical monitoring system. These devices range from blood glucose meter to portable electrocardiogram (ECG) system.

Portable medical electronic devices, the challenge is on long-distance connection portability requirements, while also maintaining the acquisition data quality and responsiveness.

"Portable" means that the device is equipped with wheels, in the door. But now that this definition be changed. Today many medical devices is completely removable and even can be "wearable". This course presents a design challenge, not just the device volume, but also the internal electronic components.

If the laptop from medical monitoring equipment, can be found in the anatomy of which there are five basic parts:

◆ Display and display interface

◆ Battery and power management

◆ Bio-sensor interface

◆ Data interface

¡Ô system micro-controller or digital signal processor (DSP)

Clearly, different systems each module specific performance would not be the same.

Monitor

Whether the patients tell their temperature or electrocardiogram (ECG) as a result, the monitor's display will be an important performance characteristics, the effect is to some extent depends on appropriate backlighting solution.

Whether it's induction or simple charge pump topology, because portable system battery, there is a wide input voltage range of backlight solutions can reduce the additional adjustment system requirements. Select the step-up or step-down/boost bi-directional converter can easily be multiple battery to work, greater design flexibility. Of course, the device size and power efficiency are key issues, using a highly integrated and advanced packaging of the device is more efficient and economic way.

Touch screen controller (TSC) is to simplify the use of portable electronic equipment and one of the key factors, eliminates the traditional keyboard, you can further narrow the device volume.

TSC-use menu driven functions select, input and output data display to fine tune, to enlarge the "press" and easier to use. Implementation of TSC, an important factor to consider is the selected programme of electrostatic discharge (ESD). If the TSC circuit cannot have divergent electrostatic energy, this energy through Central micro-controller and causing damage/DSP. Implementation of the TSC to consider other factors have resolution, screen size, the conversion type and speed, as well as the overall power consumption.

Sensor interfaces and signal chain

Regardless of the temperature, pulse, blood glucose reading or other biological sensors, implementation of appropriate signal chain are the most important issue.

The signal chain of first-order is the instrument amplifier (Figure 2), if there is a low input offset voltage, low drift and Exchange performance of large DC precision micropower amplifiers INA326. Most of the implementation is in the noise of millivolt tries to find a microvolt signal. Because the target signal have AC characteristics, needs to have a high pass filtering programmes combining good amplifier. The use of automatic reset to zero or automatic calculation function to further simplify the system of compensation requirements.

Typically, the second order is a low-power operational amplifier, such as OPA376, it has a wide bandwidth, rail-to-rail input and output (RRIO), and with excellent precision.

Zero crossover category of properties available in the entire input common-mode range produce linear offset signal. This indicates that the micro-controller does not need additional algorithms for computing correction offset.

Signal chain next order is good delta-sigma or successive approximation analog-to-digital converter (ADC).

Single-cycle filter settings and an on demand transformation features simplified ADC design requirements, but also improves conversion speed, and provides a large source impedance. In a multi-channel system, global synchronization feature provides continuous signal acquisition capabilities that allow the same clock cycle-to-multipoint signals resources.