ADI采用3轴数字加速度计的ADXL345血压计解决方案

中心议题：

*  ADI ADXL345血压计解决方案

ADI公司的血压计解决方案采用3轴±2 g/±4 g/±8 g/±16 g 数字加速度计ADXL345,12位电容-数字转换器AD7152/AD7153, 全速/低速USB数字绝缘器ADuM4160,单电极容性传感器CapTouch可编程控制器AD7147,以及带低部端口和数字输出的iMEMS麦克风ADMP421等器件.本文介绍了血压计解决方案方框图,以及所采用的主要元器件的主要特性,方框图和应用电路等.

图1.电子血压计方框图

主要元器件介绍:

ADXL345: 3-Axis, ±2 g/±4 g/±8 g/±16 g Digital Accelerometer

The ADXL345 is a small, thin, low power, 3-axis accelerometer with high resolution (13-bit) measurement at up to ±16 g. Digital output data is formatted as 16-bit twos complement and is acces-sible through either a SPI (3- or 4-wire) or I2C digital interface.

The ADXL345 is well suited for mobile device applications. It measures the static acceleration of gravity in tilt-sensing appli-cations, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4 mg/LSB) enables measurement of inclination changes less than 1.0°.

Several special sensing functions are provided. Activity and inactivity sensing detect the presence or lack of motion and if the acceleration on any axis exceeds a user-set level. Tap sensing detects single and double taps. Free-fall sensing detects if the device is falling. These functions can be mapped to one of two interrupt output pins. An integrated, patent pending 32-level first in, first out (FIFO) buffer can be used to store data to minimize host processor intervention.

Low power modes enable intelligent motion-based power management with threshold sensing and active acceleration measurement at extremely low power dissipation.

The ADXL345 is supplied in a small, thin, 3 mm × 5 mm × 1 mm, 14-lead, plastic package.

ADXL345主要特性:

Ultralow power: as low as 40 μA in measurement mode and 0.1 μA in standby mode at VS = 2.5 V (typical)

Power consumption scales automatically with bandwidth

User-selectable resolution

Fixed 10-bit resolution

Full resolution, where resolution increases with g range, up to 13-bit resolution at ±16 g (maintaining 4 mg/LSB scale factor in all g ranges)

Embedded, patent pending FIFO technology minimizes host processor load

Tap/double tap detection

Activity/inactivity monitoring

Free-fall detection

Supply voltage range: 2.0 V to 3.6 V

I/O voltage range: 1.7 V to VS

SPI (3- and 4-wire) and I2C digital interfaces

Flexible interrupt modes mappable to either interrupt pin

Measurement ranges selectable via serial command

Bandwidth selectable via serial command

Wide temperature range (?40℃ to +85℃)

10,000 g shock survival

Pb free/RoHS compliant

Small and thin: 3 mm × 5 mm × 1 mm LGA package

ADXL345应用:

Handsets

Medical instrumentation

Gaming and pointing devices

Industrial instrumentation

Personal navigation devices

Hard disk drive (HDD) protection

Fitness equipment

图2. ADXL345方框图

图3.AD7152和AD7153方框图

图4.AD7153差分容性传感器基本应用电路图

Full/Low Speed USB Digital Isolator ADuM4160

The ADuM4160 is a USB port isolator, based on Analog Devices, Inc., iCoupler? technology. Combining high speed CMOS and monolithic air core transformer technology, these isolation components provide outstanding performance characteristics and are easily integrated with low and full speed USB-compatible peripheral devices.

Many microcontrollers implement USB so that it presents only the D+ and D? lines to external pins. This is desirable in many cases because it minimizes external components and simplifies the design; however, this presents particular challenges when isolation is required. USB lines must automatically switch between actively driving D+/D?, receiving data, and allowing external resistors to set the idle state of the bus. The ADuM4160 provides mechanisms for detecting the direction of data flow and control over the state of the output buffers. Data direction is determined on a packet-by-packet basis.

The ADuM4160 uses the edge detection based iCoupler tech-nology in conjunction with internal logic to implement a transparent, easily configured, upstream facing port isolator. Isolating an upstream facing port provides several advantages in simplicity, power management, and robust operation.

The isolator has propagation delay comparable to that of a standard hub and cable. It operates with the supply voltage on either side ranging from 3.1 V to 5.5 V, allowing connection directly to VBUS by internally regulating the voltage to the signaling level. The ADuM4160 provides isolated control of the pull-up resistor to allow the peripheral to control connection timing. The device has a low idle current; a suspend mode is required.

ADuM4160主要特性:

USB 2.0 compatible

Low and full speed data rate: 1.5 Mbps and 12 Mbps

Bidirectional communication

Short-circuit protection for xD+ and xD? lines

3.3 V and 5 V (dual mode power configuration) operation

7 mA maximum upstream supply current @ 1.5 Mbps

8 mA maximum upstream supply current @ 12 Mbps

2.3mA maximum upstream idle current

Class 3A contact ESD performance per ANSI/ESD STM5.1-2007

High temperature operation: 105℃

High common-mode transient immunity: >25 kV/μs

16-lead SOIC wide-body package

RoHS compliant

Safety and regulatory approvals

UL recognition: 5000 V rms for 1 minute per UL 1577 (pending)

CSA Component Acceptance Notice #5A

IEC 60601-1: 125 V rms (reinforced)

IEC 60950-1: 380 V rms (reinforced)

VDE certificate of conformity (pending)

DIN V VDE V 0884-10 (VDE V 0884-10):2006-12

VIORM = 846 V peak

ADuM4160应用:

USB peripheral isolation

Isolated USB hub

图5.ADuM4160方框图

图6.ADuM4160典型应用

CapTouch Programmable Controller for Single-Electrode Capacitance Sensors AD7147

The AD7147 CapTouch? controller is designed for use with capacitance sensors implementing functions such as buttons, scroll bars, and wheels. The sensors need only one PCB layer, enabling ultrathin applications.

The AD7147 is an integrated CDC with on-chip environmental calibration. The CDC has 13 inputs channeled through a switch matrix to a 16-bit, 250 kHz sigma-delta (Σ-Δ) converter. The CDC is capable of sensing changes in the capacitance of the external sensors and uses this information to register a sensor activation. By programming the registers, the user has full control over the CDC setup.

High resolution sensors require minor software to run on the host processor.

The AD7147 is designed for single electrode capacitance sensors (grounded sensors). There is an active shield output to minimize noise pickup in the sensor.

The AD7147 has on-chip calibration logic to compensate for changes in the ambient environment. The calibration sequence is performed automatically and at continuous intervals as long as the sensors are not touched. This ensures that there are no false or nonregistering touches on the external sensors due to a changing environment.

The AD7147 has an SPI-compatible serial interface, and the AD7147-1 has an I2C?-compatible serial interface. Both parts have an interrupt output, as well as a GPIO. There is a VDRIVE pin to set the voltage level for the serial interface independent of VCC.

The AD7147 is available in a 24-lead, 4 mm × 4 mm LFCSP and operates from a 2.6 V to 3.6 V supply. The operating current con-sumption in low power mode is typically 26 μA for 13 sensors.

AD7147主要特性:

Programmable capacitance-to-digital converter (CDC)

Femtofarad resolution

13 capacitance sensor inputs

9 ms update rate, all 13 sensor inputs

No external RC components required

Automatic conversion sequencer

On-chip automatic calibration logic

Automatic compensation for environmental changes

Automatic adaptive threshold and sensitivity levels

Register map is compatible with the AD7142

On-chip RAM to store calibration data

SPI-compatible (serial-peripheral-interface-compatible) serial interface (AD7147)

I2C-compatible serial interface (AD7147-1)

Separate VDRIVE level for serial interface

Interrupt output and general-purpose input/output (GPIO)

24-lead, 4 mm × 4 mm LFCSP

2.6 V to 3.3 V supply voltage

Low operating current

Full power mode: 1 mA

Low power mode: 21.5 μA

AD7147应用:

Cell phones

Personal music and multimedia players

Smart handheld devices

Television, A/V, and remote controls

Gaming consoles

Digital still cameras

图7. AD7147方框图

图8.AD7147 SPI接口应用电路

图9.AD7147 I2C接口应用电路

ADMP421: iMEMS? Microphone Omni Directional Microphone with Bottom Port and Digital Output

The ADMP421 is a low cost, low power, digital output bottom ported omni-directional MEMs microphone. The ADM421 consists of a MEMs microphone element, an output amplifier and a 4th order sigma delta modulator. The digital interface allows for the PDM (Pulse Density Modulated) output of two microphones to be time multiplexed on a single data line using a single clock.

The ADMP421 has a high SNR of 60.5 dBA, and a high sensitivity, of -26 dBFS. The high SNR and sensitivity make the ADMP421 excellent for far field applications. The ADMP421 has a flat frequency response from 100 Hz through 15 kHz. Low current consumption enables long battery life for portable applications. A built in particle filter provides for high reliability.

The ADMP421 will be available in a very thin 3 mm × 4 mm × 1 mm surface mount package. It is reflow solder compatible with no sensitivity degradation.

AD7147主要特性:

Small and thin 3 mm × 4 mm × 1 mm surface mount package

High SNR 60.5 dBA

High Sensitivity -26 dBFS

Flat Frequency Response from 100 to >12 kHz

Low Current Consumption < 650 μAmps

High PSRR of 80 dBFS

4th Order Sigma Delta Modulator

Digital PDM output

Compatible with Sn/Pb and Pb-free solder processes

RoHS Compliant

AD7147应用:

Cell Phones

PC Audio

Digital Cameras

图10.AD7147功能方框图

更多医疗电子信息请关注：21ic医疗电子频道