Портативный анализатор крови

ADXL354 – это представитель нового семейства малопотребляющих трехосевых акселерометров МЭМС с низкой плотностью шума, малым дрейфом смещения нуля (0 g) и выбираемыми диапазонами измерений. ADXL354B поддерживает измерение в диапазонах ±2 g и ±4 g, а ADXL354C – в диапазонах ±2 g и ±8 g. ADXL354 обладает наилучшими в отрасли характеристиками шума, дрейфа смещения в температурном диапазоне и долговременной стабильности, что позволяет создавать на его основе прецизионные устройства с очень низкой потребляемой мощностью, требующие минимальной калибровки.

ADXL354 и ADXL355 (акселерометр с цифровым выходом. См. страницу продукта ADXL355) осуществляют измерение вибраций с высоким разрешением и очень низким шумом, делая возможным раннее детектирование структурных дефектов при помощи сетей беспроводных датчиков. Низкое энергопотребление новых акселерометров ADXL354 и ADXL355 продлевает срок службы батарей и, как следствие, время бесперебойного использования устройства. Низкий шум и малое энергопотребление ADXL354 и ADXL355 позволяют создавать на их основе недорогие устройства измерения слабых вибраций для применения в таких задачах как, например, мониторинг целостности конструкций. Кроме того, акселерометры обеспечивают превосходную стабильность измерения отклонения в диапазоне температур и во времени, что делает их идеальным выбором для систем ориентирования и навигации в беспилотных летательных аппаратах, основанных на инерциальных измерительных модулях и инклинометрах. Благодаря повторяемости измерений при любых условиях акселерометры ADXL354 и ADXL355 позволяют достичь минимальной погрешности показателей отклонения без детальной калибровки в самых жестких средах.

Акселерометры ADXL354 и ADXL355 обеспечивают температурную стабильность смещения нуля 0.15×10^-3 g/°C, макс. Столь высокая стабильность минимизирует ресурсы, затрачиваемые на калибровку и испытание, помогая увеличить объемы выпуска устройств на базе этих компонентов. Кроме того, герметичный корпус помогает гарантированно поддерживать характеристики стабильности и повторяемости в конечном продукте в течение долгого времени после его выхода из производства.

Благодаря комбинации диапазона полной шкалы измерений от ±2g до ±8g, выбираемой полосы цифровой фильтрации от 1 Гц до 1 кГц, низкой плотности шума (25мкВ/ÖГц) и малого потребляемого тока (150 мкА) акселерометр МЭМС ADXL354 обеспечивает уровень характеристик, сопоставимый с гораздо более дорогими продуктами, при меньшем энергопотреблении и меньшей общей стоимости решения.

Области применения

• Инерциальные измерительные модули (IMU)/курсовые системы (AHRS)
• Системы стабилизации платформ
• Мониторинг целостности конструкций
• Визуализация данных сейсмической активности
• Измерение отклонения
• Робототехника
• Мониторинг рабочих условий

ADXL355 – это представитель нового семейства малопотребляющих трехосевых акселерометров МЭМС с низкой плотностью шума, малым дрейфом смещения нуля (0 g) и выбираемыми диапазонами измерений. ADXL355 поддерживает измерение в диапазонах ±2.048 g, ±4.096 g и ±8.192 g. Он обладает наилучшими в отрасли характеристиками шума, дрейфа смещения в температурном диапазоне и долговременной стабильности, что позволяет создавать на его основе прецизионные устройства с очень низкой потребляемой мощностью, требующие минимальной калибровки.

ADXL355 и ADXL354 (акселерометр с аналоговым выходом. См. страницу продукта ADXL354) осуществляют измерение вибраций с высоким разрешением и очень низким шумом, делая возможным раннее детектирование структурных дефектов при помощи сетей беспроводных датчиков. Низкое энергопотребление новых акселерометров ADXL354 и ADXL355 продлевает срок службы батарей и, как следствие, время бесперебойного использования устройства. Низкий шум и малое энергопотребление ADXL354 и ADXL355 позволяют создавать на их основе недорогие устройства измерения слабых вибраций для применения в таких задачах как, например, мониторинг целостности конструкций. Кроме того, акселерометры обеспечивают превосходную стабильность измерения отклонения в диапазоне температур и во времени, что делает их идеальным выбором для систем ориентирования и навигации в беспилотных летательных аппаратах, основанных на инерциальных измерительных модулях и инклинометрах. Благодаря повторяемости измерений при любых условиях акселерометры ADXL354 и ADXL355 позволяют достичь минимальной погрешности показателей отклонения без детальной калибровки в самых жестких средах.

Акселерометры ADXL354 и ADXL355 обеспечивают температурную стабильность смещения нуля 0.15×10^-3 g/°C, макс. Столь высокая стабильность минимизирует ресурсы, затрачиваемые на калибровку и испытание, помогая увеличить объемы выпуска устройств на базе этих компонентов. Кроме того, герметичный корпус помогает гарантированно поддерживать характеристики стабильности и повторяемости в конечном продукте в течение долгого времени после его выхода из производства.

Благодаря комбинации диапазона полной шкалы измерений от ±2g до ±8g, выбираемой полосы цифровой фильтрации от 1 Гц до 1 кГц, низкой плотности шума (25мкВ/ÖГц) и малого потребляемого тока (менее 200 мкА) акселерометр МЭМС ADXL355 обеспечивает уровень характеристик, сопоставимый с гораздо более дорогими продуктами, при меньшем энергопотреблении и меньшей общей стоимости решения.

Области применения

• Инерциальные измерительные модули (IMU)/курсовые системы (AHRS)
• Системы стабилизации платформ
• Мониторинг целостности конструкций
• Визуализация данных сейсмической активности
• Измерение отклонения
• Робототехника
• Мониторинг рабочих условий

The ADuCM350 is a configurable Impedance Converter and Potentiostat with current and voltage measurement capability for both Electrochemical sensors and Biosensors. It is a complete, coin cell powered, high precision, MCU integrated solution for portable device applications such as point-of-care diagnostics and body-worn devices for monitoring vital signs.

The ADuCM350 analog front end (AFE) features a 16-bit, precision, 160 kSPS analog-to-digital converter (ADC); 0.17% precision voltage reference; 12-bit, no missing codes digital-to-analog converter (DAC); and a reconfigurable ultralow leakage switch matrix. It has 4 voltage measurement channels, up to 8 current measurement channels and an impedance measurement DFT engine. The ADuCM350 also includes an ARM Cortex-M3-based processor, memory, and all I/O connectivity to support portable meters with display, USB communication, and active sensors. The ADuCM350 is available in a 120-lead, 8 mm × 8 mm CSP_BGA and operates from −40°C to +85°C.

To support extremely low dynamic and hibernate power management, the ADuCM350 provides a collection of power modes and features, such as dynamic and software controlled clock gating and power gating. The AFE is connected to the ARM Cortex-M3 via an advanced high performance bus (AHPB) slave interface on the advanced microcontroller bus architecture (AMBA) matrix, as well as direct memory access (DMA) and interrupt connections.

Applications

• Point-of-care diagnostics
• Body-worn devices for monitoring vital signs
• Amperometric, voltametric, and impedometric measurements

The combination of parts shown in Figure 1 provides an ultralow power, 3-axis, motion activated power switch solution capable of controlling up to 1.1 A of load current. The circuit is ideal for applications where extended battery life is critical. When the switch is off, the battery current is less than 300 nA, and when the switch is on, it draws less than 3 μA. The circuit provides an industry leading, low power motion sensing solution suitable for wireless sensors, metering devices, home healthcare, and other portable applications.

The 3-axis accelerometer controls the high-side switch by monitoring the acceleration in three axes and closes or opens the switch depending on the presence or absence of motion.

The ADXL362 is an ultralow power, 3-axis accelerometer that consumes less than 100 nA in wake-up mode. Unlike accelerometers that use power duty cycling to achieve low power consumption, the ADXL362 does not alias input signals by under sampling; it samples continuously at all data rates. There is also an on-chip, 12-bit temperature sensor accurate to ±0.5°.

The ADXL362 provides 12-bit output resolution and has three operating ranges, ±2 g, ±4 g, and ±8 g. It is specified over a minimum temperature range of −40°C to +85°C. For applications where a noise level less than 480 μg/√Hz is desired, either of its two lower noise modes (down to 120 μg/√Hz) can be selected at a minimal increase in supply current.

The ADP195 is a high-side load switch designed for operation between 1.1 V and 3.6 V and is protected against reverse current flow from output to input. The device contains a low on-resistance, P-channel MOSFET that supports over 1.1 A of continuous load current and minimizes power losses.

Basic Operation of the ADXL362

The ADXL362 is a three-axis, ultralow power acceleration measurement system capable of measuring dynamic acceleration (resulting from motion or shock) as well as static acceleration (that is, gravity).

The moving component of the sensor is a polysilicon, surface micromachined structure, also referred to as a beam, built on top of a silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration forces.

Deflection of the structure is measured using differential capacitors. Each capacitor consists of independent fixed plates and plates attached to the moving mass. Any acceleration deflects the beam and unbalances the differential capacitor, resulting in a sensor output whose amplitude is proportional to acceleration. Phase-sensitive demodulation is used to determine the magnitude and polarity of the acceleration.

Modes of Operation

The three basic modes of operation for the ADXL362 are standby, measurement, and wake-up.

• Placing the ADXL362 in standby mode suspends measurement and reduces current consumption to 10 nA. Any pending data or interrupts are preserved; however, no new information is processed. The ADXL362 powers up in standby mode with all sensor functions turned off.

• Measurement mode is the normal operating mode of the ADXL362. In this mode, acceleration data is continuously read, and the accelerometer consumes less than 3 μA across its entire range of output data rates of up to 400 Hz using a 2.0 V supply. All described features are available while operating in this mode. The ability to continuously output data from the minimum 12.5 Hz to the maximum 400 Hz data rate while still delivering less than 3 μA of current consumption is what defines the ADXL362. as an ultralow power accelerometer. Under sampling and aliasing do not occur with the ADXL362. because it continuously samples the full bandwidth of its sensor at all data rates.

• Wake-up mode is ideal for simple detection of the presence or absence of motion at extremely low power consumption (270 nA at a 2.0 V supply voltage). Wake-up mode is useful particularly for implementation of a motion-activated on/off switch, allowing the rest of the system to be powered down until activity is detected. Wake-up mode reduces current consumption to a very low level by measuring acceleration only 6 times a second to determine whether motion is present. In wake-up mode, all accelerometer features are available with the exception of the activity timer. All registers are accessible, and real-time data is available from the part.

The CN0274 evaluation software uses the wake-up mode of the ADXL362. That is, the ADXL362 is asleep until it detects motion at which point it enters measurement mode.

Power/Noise Tradeoff

The ADXL362 offers a few options for decreasing noise at the expense of only a small increase in current consumption.

The noise performance of the ADXL362 in normal operation, typically 7 LSB rms at 100 Hz bandwidth, is adequate for most applications, depending upon bandwidth and the desired resolution. For cases where lower noise is needed, the ADXL362 provides two lower noise, operating modes that trade reduced noise for somewhat higher supply current.

Table 1 shows the supply current values and noise densities obtained for normal operation and the two lower noise modes, at a typical 3.3 V supply.

The CN0274 evaluation software uses the normal operation noise mode of the ADXL362.

Motion Detection

The ADXL362 has built-in logic that detects activity (acceleration above a certain threshold) and inactivity (lack of acceleration above a certain threshold).

Detection of an activity or inactivity event is indicated in the status register and can also be configured to generate an interrupt. In addition, the activity status of the device, that is, whether it is moving or stationary, is indicated by the AWAKE bit.

Activity and inactivity detection can be used when the accelerometer is in either measurement mode or wake-up mode.

Activity Detection

An activity event is detected when acceleration stays above a specified threshold for a user-specified time period. The two activity detection events are absolute and referenced.

• When using absolute activity detection, acceleration samples are compared to a user set threshold to determine whether motion is present. For example, if a threshold of 0.5 g is set, and the acceleration on any axis is 1 g for longer than the user defined activity time, the activity status is asserted. In many applications, it is advantageous for activity detection to be based not on an absolute threshold but on a deviation from a reference point or orientation. This is particularly useful because it removes the effect on activity detection of the static 1 g imposed by gravity. When an accelerometer is stationary, its output can reach 1 g, even when it is not moving. In absolute activity, if the threshold is set to less than 1 g, activity is immediately detected in this case.
• In the referenced activity detection, activity is detected when acceleration samples are at least a user set amount above an internally defined reference, for the user defined amount of time. The reference is calculated when activity detection is engaged, and the first sample obtained is used as a reference point. Activity is only detected when the acceleration has deviated sufficiently from this initial orientation. The referenced configuration results in a very sensitive activity detection that detects even the most subtle motion events.

The CN0274 evaluation software uses the referenced mode of operation when searching for activity.

Inactivity Detection

An inactivity event is detected when acceleration remains below a specified threshold for a specified time. The two inactivity detection events are absolute and referenced.

• In absolute inactivity detection, acceleration samples are compared to a user set threshold for the user set time to determine the absence of motion.
• In referenced inactivity detection, acceleration samples are compared to a user specified reference for a user defined amount of time. When the part first enters the awake state, the first sample is used as a reference point, and the threshold is applied around it. If the acceleration stays inside the threshold, the part enters the asleep state. If an acceleration value moves outside the threshold, this point is then used as a new reference, and the thresholds are reapplied to this new point.

The CN0274 evaluation software uses the referenced mode of operation when searching for inactivity.

Linking Activity and Inactivity Detection

The activity and inactivity detection functions can be used concurrently, and processed manually by a host processor, or they can be configured to interact in several ways:

• In default mode, activity and inactivity detection are both enabled, and all interrupts must be serviced by a host processor; that is, a processor must read each interrupt before it is cleared and can be used again.
• In linked mode, activity and inactivity detection are linked to each other such that only one of the functions is enabled at any given time. Once activity is detected, the device is assumed moving or awake and stops looking for activity: inactivity is expected as the next event so only inactivity detection operates. When inactivity is detected, the device is assumed stationary or asleep. Activity is now expected as the next event so that only activity detection operates. In this mode, a host processor must service each interrupt before the next is enabled.
• In loop mode, motion detection operates as previously described in linked mode; however, interrupts do not need to be serviced by a host processor. This configuration simplifies the implementation of commonly used motion detection and enhances power savings by reducing the amount of power used in bus communication.
• When enabling autosleep mode in linked mode or loop mode, it causes the device to autonomously enter wake-up mode when inactivity is detected, and reenter measurement mode when activity is detected.

The CN0274 evaluation software uses the autosleep and loop modes to demonstrate the functionality of the ADXL362.

The AWAKE Bit

The AWAKE bit is a status bit that indicates whether the ADXL362 is awake or asleep. The device is awake when it has seen an activity condition, and the device is asleep when it has seen an inactivity condition.

The awake signal can be mapped to the INT1 or INT2 pin and can thus be used as a status output to connect or disconnect power to downstream circuitry based on the awake status of the accelerometer. Used in conjunction with loop mode, this configuration implements a trivial, autonomous motion-activated switch.

If the turn-on time of the downstream circuitry can be tolerated, this motion switch configuration can save significant system-level power by eliminating the standby current consumption of the rest of the application. This standby current can often exceed the full operating current of the ADXL362.

Interrupts

Several of the built-in functions of the ADXL362 can trigger interrupts to alert the host processor of certain status conditions.

Interrupts may be mapped to either (or both) of two designated output pins, INT1 and INT2, by setting the appropriate bits in the INTMAP1 and INTMAP2 registers. All functions can be used simultaneously. If multiple interrupts are mapped to one pin, the OR combination of the interrupts determines the status of the pin.

If no functions are mapped to an interrupt pin, that pin is automatically configured to a high impedance (high-Z) state. The pins are placed in this state upon a reset as well.

When a certain status condition is detected, the pin that condition is mapped to is activated. The configuration of the pin is active high by default, so that when it is activated, the pin goes high. However, this configuration can be switched to active low by setting the INT_LOW pin in the appropriate INTMAP register.

The INT pins may be connected to the interrupt input of a host processor and interrupts responded to with an interrupt routine. Because multiple functions can be mapped to the same pin, the STATUS register can be used to determine which condition caused the interrupt to trigger.

The CN0274 evaluation software configures the ADXL362 such that when activity is detected, the INT1 pin is high, and when inactivity is detected, the INT1 pin is low.

Test Results

All testing was performed using the EVAL-CN0274-SDPZ and the EVAL-SDP-CS1Z. Functionality of the part is demonstrated by setting the activity threshold at 0.5 g, the inactivity threshold at 0.75 g, and the number of inactivity samples at 20. When looking for activity, only one acceleration sample on any axis is required to cross the threshold.

Starting with the circuit oriented so that the battery pack is flat against the table, the printed circuit board (PCB) can be slowly rotated 90° in any direction causing the acceleration to cross the threshold as it approaches perpendicular to the initial orientation.

Figure 2 shows a screen shot of the CN0274 evaluation software showing the ADXL362 first asleep, looking for activity. Then, when Sample 11 crosses the threshold, the ADXL362 enters the awake state and begins looking for inactivity. The thresholds adjust to show the device is now looking for inactivity.

For better visibility, the X-axis and Z-axis plots are disabled using the radio buttons above the chart.

The output of the ADP195, or the interrupt pin itself, was measured using a digital multimeter. When the ADXL362 is awake, the interrupt goes high and drives the EN pin of the ADP195, high, which in turn drives the gate of the MOSFET low, causing the switch to close, connecting any downstream circuitry to the power supply. Conversely, when the ADXL362 is asleep, the interrupt drives the EN pin of the ADP195 low, which in turn drives the gate of the MOSFET high, causing the switch to open.

PCB Layout Considerations

In any circuit where accuracy is crucial, it is important to consider the power supply and ground return layout on the board. The PCB should isolate the digital and analog sections as much as possible. The PCB for this system was constructed in a 4-layer stack up with large area ground plane layers and power plane polygons. See the MT-031 Tutorial for more discussion on layout and grounding, and the MT-101 Tutorial for information on decoupling techniques.

Decouple the power supply to the ADXL362 with 1 μF and 0.1 μF capacitors to properly suppress noise and reduce ripple. Place the capacitors as close to the device as possible. Ceramic capacitors are advised for all high frequency decoupling.

Power supply lines should have as large a trace width as possible to provide low impedance paths and reduce glitch effects on the supply line. Shield clocks and other fast switching digital signals from other parts of the board by digital ground. A photo of the PCB is shown in Figure 3.

A complete design support package for this circuit note can be found at www.analog.com/CN0274-DesignSupport.

The universal serial bus (USB) is rapidly becoming the standard interface for most PC peripherals. It is displacing RS-232 and the parallel printer port because of superior speed, flexibility, and support of device hot swap. There has been a strong desire on the part of industrial and medical equipment manufacturers to use this bus as well, but adoption has been slow because there has not been a good way to provide the isolation required for connections to machines that control dangerous voltages or low leakage defibrillation proof connections in medical applications.

The ADuM4160 provides an inexpensive and easy to implement isolation buffer for medical and industrial peripherals. The challenges that need to be met are:

1. Isolate directly in the USB D+ and D− lines allowing the use of existing USB infrastructure in microprocessors.
2. Implement an automatic scheme for data flow of control that does not require external control lines.
3. Provide medical grade isolation.
4. Allow a complete peripheral to meet the USB-IF certifi-cation standards.
5. Support full speed (12 Mbps) and low speed (1.5 Mbps) signaling rates.
6. Support flexible power configurations.

The circuit shown in Figure 1 isolates a peripheral device that already supports a USB interface. Because the peripheral is not explicitly defined in this circuit, power to run the secondary side of the isolator has been provided as part of the solution. If the circuit is built onto the PCB of a peripheral design, power could be sourced from the peripheral’s off line supply, a battery, or the USB cable bus power, depending on the needs of the application.

The application circuit shown is typical of many medical and industrial applications.