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
