ADI公司的血壓計解決方案采用3軸±2 g/±4 g/±8 g/±16 g 數(shù)字加速度計ADXL345,
12位電容-數(shù)字轉(zhuǎn)換器AD7152/AD7153, 全速/低速USB數(shù)字絕緣器ADuM4160,單電極容性傳感器CapTouch可編程控制器AD7147,以及帶低部端口和數(shù)字輸出的iMEMS麥克風(fēng)ADMP421等器件.本文介紹了血壓計解決方案方框圖,以及所采用的主要元器件的主要特性,方框圖和應(yīng)用電路等.


圖1.電子血壓計方框圖

主要元器件介紹:

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應(yīng)用:

Handsets

Medical instrumentation

Gaming and pointing devices

Industrial instrumentation

Personal navigation devices

Hard disk drive (HDD) protection

Fitness equipment

圖2. ADXL345方框圖

http://www.analog.com/static/imported-files/data_sheets/ADXL345.pdf

12-Bit Capacitance-to-Digital Converter AD7152/AD7153

The AD7152/AD7153 are 12-bit sigma-delta (Σ-Δ) capacitance-to-digital converters (CDCs). The capacitance to be measured is connected directly to the device inputs. The architecture features inherent high resolution (12-bit no missing codes, up to 12-bit effective resolution) and high linearity (±0.05%). The AD7152/AD7153 have four capacitance input ranges per operation mode, ±0.25 pF to ±2 pF in differential mode and 0.5 pF to 4 pF in single-ended mode.

The AD7152/AD7153 can accept up to 5 pF common-mode capacitance (not changing), which can be balanced by a programmable on-chip, digital-to-capacitance converter (CAPDAC).

The AD7153 has one capacitance input channel, while the AD7152 has two channels. Each channel can be configured as single-ended or differential. The AD7152/AD7153 are designed for floating capacitive sensors.

The AD7152/AD7153 have a 2-wire, I2C®-compatible serial interface. Both parts can operate with a single power supply from 2.7 V to 3.6 V. They are specified over the temperature range of −40°C to +85°C and are available in a 10-lead MSOP package.

AD7152主要特性:

Capacitance-to-digital converters

Interfaces to floating sensors

Resolution down to 0.25 fF (that is, up to 12 ENOB)

Linearity: 0.05%

Common-mode (not changing) capacitance up to 5 pF

Four capacitance ranges selectable per operation mode

±0.25 pF to ±2 pF in differential mode

0.5 pF to 4 pF in single-ended mode

Tolerant of parasitic capacitance to ground up to 50 pF

Conversion time per channel: 5 ms, 20 ms, 50 ms, and 60 ms

Internal clock oscillator

2-wire serial interface (I2C-compatible)

Power

2.7 V to 3.6 V single-supply operation

100 μA current consumption     

Operating temperature: −40℃ to +85℃

10-lead MSOP package

AD7152應(yīng)用:

Automotive, industrial, and medical systems for

Pressure measurement

Position sensing

Level sensing

Flowmeters

Humidity sensing

圖3.AD7152和AD7153方框圖

圖4.AD7153差分容性傳感器基本應(yīng)用電路圖

http://www.analog.com/static/imported-files/data_sheets/AD7152_7153.pdf

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-p