1. Цифровая обработка сигналов (цос)

Integrated multi-parameter portable patient monitoring with OMAP from Texas Instruments

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ntegrated multi-parameter portable patient monitoring with OMAP from Texas Instruments

Block Diagram

Design Considerations

Over time, multitudes of portable, single parameter monitors/meters emerged for measuring such things as blood pressure, glucose levels, pulse, tidal carbon dioxide, and various other biometric values. Today, patient monitors are portable, flexible devices capable of being adapted to a variety of clinical applications, supporting various wired and wireless interfaces. Whether the monitor is a single or multi-parameter device; targeted capability, power consumption and system versatility are often key requirements. Nowadays, a monitor can move with the patient from the operating room to an intensive care unit, to the hospital room, and even into their home. This is paramount in today’s world of health care.

The most important features in today’s patient monitors are mobility, ease of use, and effortless patient data transfer. Mobility includes portability as well as the ability to interface with other medical devices such as anesthesia machines or defibrillators. Ease of use can be achieved with touch screen displays and multilevel menu driven profiles that can be configured for the environment as well as the patient’s vital statistics. Data transfer across everything from wireless to RS232 needs to be possible. Hospitals may support a specific infrastructure throughout all areas; however, ambulance, home and other environments may need support for different protocols. The ever-increasing need to minimize healthcare costs is driving the healthcare providers to move the patient treatment and monitoring outside the hospital. Providing healthcare in highly populated rural and remote areas in emerging economies is driving the need for remote patient monitoring and telemedicine.

The challenges in implementing such patient treatment and monitoring equipments are strikingly similar to cellular phone systems. TI’s OMAP™ technology with embedded ARM and DSP processor cores directly addresses these challenges. TI has extensive analog front end solutions for essential signal conditioning. The OMAP 3 processor performs further digital signal processing, measurements and analytics to monitor patient condition. Powerful ARM processor runs a high-level OS (HLOS) which makes adding multi-modal monitoring easy and provides extensive user interface and system control. Detecting abnormal conditions and communicating to a central server is essential in providing timely and on-demand healthcare. OMAP 3 has extensive peripheral set to support various connectivity options such as Bluetooth, WiFi, Zigbee and other emerging standards.

2.12. Pulse Oximeter (Пульсоксиметр)

Medical Solutions from Texas Instruments

Block Diagram

Design Considerations


TI's TMS320C5515 DSP Evaluation Module together with TI's pulse oximeter analog front-end module make up the new C5505 PO or SpO2 Medical Development Kit (MDK) which provides developers access to a development tool set that offers a complete signal chain solution along with software to save months of development time and for portable patient monitoring applications that demand battery efficiency.

Pulse oximeters measure arterial blood oxygen saturation by sensing absorption properties of deoxygenated and oxygenated hemoglobin using various wavelengths of light. A basic meter is comprised of a sensing probe attached to a patient's earlobe, toe, finger, or other body locations, and data acquisition system for the calculation and display of oxygen saturation level, heart rate, and blood flow.

Low-End Portable Pulse Oximeter

For low-end designs, TI's family of highly integrated MSP430 Ultra-Low-Power microcontrollers (MCUs) reduces the number of external components needed in the design. Since elements of the signal chain, power management and display driver are integrated into the MCU.

Signal Acquisition Challenges: An inverting resistor-feedback configuration is commonly used with the gain amplifier in the signal chain. However, large feedback resistor values may drive extreme output swings with small changes in light intensity due to the sensitivity level of the circuit. Some designs may benefit from driving the output swing down to or below ground. Dual supply Auto-zero trans-impedance amplifiers allow the output swing to ground and single supply devices swing very close to ground. A pull-down resistor tied to -5V allows the output to swing slightly below ground, minimize errors as the output gets very close to 0V. TI offers a family of transimpedance amplifiers that provide extremely high precision, excellent long-term stability, and very low 1/f noise.

Mid-Range and High-End Portable Pulse Oximeters

For mid and high-end implementations, higher performance processors and higher precision analog components with low supply current could be required. TI's low power DSP technology can eliminate signal distortion caused by other light sources or motion occurring while readings are taken, extracting only the signal of interest. DSP technology allows accurate readings of very low level signals through sophisticated algorithms. This additional processing capability is very useful in pulse oximeters measuring the absorption of additional wavelengths to detect the saturation of other species of hemoglobin.

Signal Acquisition Challenges: TI's precision switched integrator transimpedance amplifiers do not have the thermal noise of feedback resistors and do not suffer from stability problems commonly found in transimpedance amps using large feedback resistor. Using one photodiode with two integrator transimpedance amplifiers eliminates dark current and ambient light errors, since errors common to both can be subtracted. Additionally, these amplifiers allow for synchronized sampling at an integer multiple of the AC line frequency, providing extremely high noise rejection. Transimpedance gain can be easily changed by manipulating on-chip settings. Also, TI's high precision ADCs offer small packaging, excellent AC/DC performance, and single-chip solution for measuring photodiodes.

In general, Pulse Oximeters require ultra-low power consumption, and low noise power rails; in order to support extended battery life and precision measurements. TI's buck-boost converters provide support for Li-ion battery technologies, and 96% efficiency. For additional low noise power rails, high PSRR LDOs are also available. Requirements for wall-plug and USB-port charging can be addressed with the TI's linear lithium low single-cell charger family. Innovative next-generation gas gauge solutions are offered with "Impedance Track" to automatically learn/detect battery characteristics, extending both battery life and system run time.

2.13. Stethoscope: Digital (Стетоскоп: Цифровой)

Digital Stethoscope Solutions from Texas Instruments

Block Diagram

Design Considerations

TI's TMS320C5515 DSP Evaluation Module together with TI's digital stethoscope analog front-end module make up the new C5505 DS Medical Development Kit (MDK) provides developers access to a development tool set that offers a complete signal chain solution along with software to save months of development time and for portable patient monitoring applications that demand battery efficiency.

The main elements of a Digital Stethoscope are the sensor unit that captures the heart and lung sounds (also known as auscultations), digitization, and digital processing of the auscultations for noise reduction, filtering and amplification. Algorithms for heart rate detection and heart defect detection may also be included.

Power and Battery Management are key in this ultra-portable diagnostic tool, where key design considerations are ultra-low power consumption and high efficiency driven by the need for extended battery life, and high precision with a fast response time allowing quick determination of the patient's health status. Additional requirements may drive the need for recording the auscultations, cabled or wireless interfaces for transmission of the auscultations. Also, to enable ease of use, features like touch screen control and display backlighting are key to usability of the device. Adding all these features without significantly increasing power consumption is a huge challenge.  Texas Instruments portfolio of Processors, Instrumentation and Buffer Amplifiers, Power and Battery Management, Audio Codecs, and both wired and wireless interface devices provides the ideal tool box for Digital Stethoscope applications.

The common core subsystems of a Digital Stethoscope are:

  • Analog Front-End/Sensor Interface and Codec

Auscultations signal input is amplified and then digitized by the Audio Codec. Auscultations signal after being digitized and subjected to signal processing, is converted to analog and sent to the stethoscope earpiece.

  • Low Power Processor

Processors capable of executing all of the digital stethoscopes signal processing including key functions such as noise reduction, algorithms for heart rate detection, and heart defect detection while maintaining a very low constant current draw from the battery are good fit. The ability to control interfacing with memory and peripheral devices is also helpful. Given the nature of the device, processors that can manage the digital display and keyed functions allowing auscultation waveforms to be displayed and manipulated without additional components are ideal.

  • Data Storage and Transmission

The auscultations can be recorded on MMC/SD card, or on a USB device. It can also be transmitted via wireless capability such as Bluetooth.

2.14. X-ray: Medical/Dental (X-Ray: Медицина / Стоматология)

X-ray: Medical/Dental Solutions from Texas Instruments

lock Diagram

Design Considerations

What's New

Integrate and save power with the AFE0064, 64 channel analog front end for flat panel digital X-Ray systems. This device includes 64 integrators, a PGA for full scale charge level selection, correlated double sample, 64 as-to-2 multiplexer, two differential output drivers and a power saving nap feature.

Digital x-ray imaging is revolutionizing diagnostic radiology. With conventional x-ray systems, the signal degradation from each component consumes more than 60% of the original x-ray signal. At each system stage, the x-ray signal is degraded to some extent, even if the individual components are optimized for the application. As a result, typically less than 40% of the original image information is available to produce an image. By adding a digital detector to digital x-ray imaging, it’s possible to capture more than 80% of the original image information and use a wide-range of post-processing tools to further improve the image. Other digital x-ray technology advantages include: reduced patient dosage, reduced diagnosis time by elimination of photographic processing, reduced costs by eliminating photographic processing chemicals, processing image data to highlight regions of interest and suppress irrelevant information; combining image data with other pertinent patient RIS/HIS systems information available; quickly transmitting the information anywhere over network connections; and archiving all desired information in a minimal space. There are two different approaches to digital x-ray technology, direct and indirect.

Direct Conversion

In direct conversion, flat-panel selenium detectors absorb x-rays directly and convert them into individual pixel electrical charges. In indirect conversion, x-ray signals first are converted to light, then converted to electric charges. Both tiled CCD (charge-coupled device) arrays and computed tomography use indirect conversion technology. Tiled CCD transitional technology employs multiple CCDs coupled to a scintillator plate via fiber optics. Computed tomography involves trapping electrons on photo-stimulated plates and then exposing them to generate image data. In both approaches, charges proportional to x-ray intensity seen by the pixel is stored in the Thin Film Transistor (TFT) storage cap. A number of such pixels form the Flat Detector Panel (FDP). The charges are deciphered by read-out electronics from the FDP and transformed into digital data.

The following block diagram shows the readout electronics required for direct imaging to convert the charge in the FDP to digital data. It has two chains: the acquisition and the biasing ones. At the beginning of the acquisition chain, an analog front-end is capable of multiplexing the charges on different FDP (channels) storage caps and converting these charges into voltage. The biasing chain generates bias voltages for the TFT array through intermediate bias-and-gate control circuitry. Digital control and data conditioning is controlled by an FPGA, which also manages high-speed serial communications with the external image processing unit through a high-speed interface (serialized, LVDS, optical). Temperature sensors, DACs, amplifiers and high-input voltage capable switching regulators are other key system blocks. Each block must have an enable pin and synchronize frequencies to avoid crosstalk with other blocks in the acquisition chain. The number of FDP pixels will determine the number of ADC channels vs. the ADC speed. Static or dynamic acquisition also determines the ADC speed. While static acquisition means a single image in less than 1s, dynamic means an image is refreshed at 30Hz, for more specific cardiovascular, fluoroscopic or related applications that require much faster data conversion with the same number of channels. An ADC in the range of 2MSPS and more with excellent DC performance will work well.

Indirect Conversion

For indirect conversion, the  CCD output requires correlated double sampling (CDS). The signal level’s reset voltages and image signal level are converted to digital data by an Analog Front End (AFE).. The sampling speed of the AFE is determined by the number of pixels in the CCD array and the frame rate. In addition, the AFE corrects sensor errors such as dark current correction, offset voltages and defective pixels. Depending on the signal level, the presence of Programmable Gain Amplifiers (PGAs), the linearity of the PGAs and the range of gains available may also be important. During digitization, the number of bits will determine the contrast of the image. Typically, one wants to digitize the initial data with two to four bits more precision than is desired in the final image. Thus, if 8-bits of final image data are required, then initially digitize to 10-bits to allow for rounding errors during image processing.

The main metric for image quality is “Detection Quantum Efficiency” (DQE), a combination of contrast and SNR expressed in percentage. The higher the contrast and lower the noise, the higher is the DQE. Contrast is the number of shades of gray, determined by the ADC’s output resolution Generally, 14-bits or 16-bits will be suitable for the application. SNR indicates not only SNR from the ADC, but system SNR impact from x-ray dose, pixel size and all electronic components. SNR can be improved by increasing x-ray dose, increasing photodiode spacing and decreasing electronics noise. Increasing the x-ray dose is not suitable for patients or operators. Increasing photodiode spacing may also not be suitable, because this decreases spatial resolution. Decreasing the noise from the system’s electronics is the main challenge. The total noise in the system is: root-square-sum of all noise contributions over the signal chain assuming all are uncorrelated. This means that all parts have to be ultra-low noise or heavily filtered when applicable including ADCs, op amps and references. Stability over temperature is another important challenge. Internal temperature increases due to power dissipation may off-set gray levels and distort an image especially during dynamic acquisitions. Hence, temperature stability of ADCs, op amps and references should be high.

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