采用AFE4900可穿戴无线多参数病人监护器参考设计TID-01580详解

电子工程师 2018-07-22 12876

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描述

TI公司的AFE4900是超低功耗集成模拟前端（AFE），用于同步化心电图（ECG）和光电血管容积图（PPG）信号收集，也可用于光生物检测应用如心率监测（HRM）和外周血氧饱和度（SpO2）。同步PPG和ECG信号采集数据速率高达1kHz，PPG接收器动态范围高达100 dB.本文介绍了AFE4900主要特性和框图，以及采用AFE4900的可穿戴无线多参数病人监护器参考设计TIDA-01580主要特性，框图，电路图，材料清单和PCB设计图。

The AFE4900 device is an analog front-end （AFE） forsynchronized electrocardiogram （ECG），photoplethysmogram （PPG） signal acquisition. Thedevice can also be used for optical bio-sensingapplications， such as heart-rate monitoring （HRM）and saturation of peripheral capillary oxygen （SpO2）。

The PPG signal chain supports up to four switchinglight-emitting diodes （LEDs） and up to threephotodiodes （PDs）。 The LEDs can be switched onusing a fully integrated LED driver. The current fromthe photodiode is converted into voltage by thetransimpedance amplifier （TIA） and digitized using ananalog-to-digital converter （ADC）。 The ECG signal chain has an instrumentation amplifier （INA） with aprogrammable gain that interfaces to the same ADC.

A right-leg drive （RLD） amplifier set can be used tothe bias for the ECG input pins. AC and dc lead-offdetect schemes are supported. The ADC codes fromthe PPG and ECG phases can be stored in a 128-sample first in， first out （FIFO） block and read outusing either an I2C or a serial programming interface（SPI） interface.

AFE4900主要特性：

• Synchronized PPG， ECG Signal Acquisition atData Rates Up to 1 kHz

• ECG Signal Chain：

– Standalone ECG Acquisition Up to 4 kHz

– Input Bias： 1-Lead ECG With RLD Bias

– Programmable INA Gain： 2 to 12

– Input Noise （1 Hz to 150 Hz）： 2.5 μVrms at1 kHz， 1.25 μVrms at 4-kHz Data Rate

– AC， DC Lead-Off Detect： 12.5-nA to 100-nA

• PPG Receiver：

– Supports Three Time-Multiplexed PD Inputs

– 24-Bit Representation of Current From PD

– DC Offset Subtraction DAC （Up to ±126-μA） atTIA Input for Each LED， Ambient

– Digital Ambient Subtraction at ADC Output

– Noise Filtering With Programmable Bandwidth

– Transimpedance Gain： 10 kΩto 2 MΩ

– Dynamic Range Up to 100 dB

– Receiver Operates in PPG-Only mode atApproximately 1-μA/Hz Sampling Rate

– Power-Down Mode： Approximately 0 μA

• PPG Transmitter：

– Four LEDs in Common Anode Configuration

– 8-Bit LED Current Up to 200 mA

– Mode to Fire Two LEDs in Parallel

– Programmable LED On-Time

– Simultaneous Support of Three LEDs forSpO2， or Multiwavelength HRM

– Average Current of 30 μA Adequate for aTypical Heart-Rate Monitoring Scenario：

– 20-mA Setting， 60-μs Pulse Duration，25-Hz Sampling Rate

• Clocking Using an External or Internal Clock

• FIFO With 128-Sample Depth for ECG and PPG

• I2C， SPI™ Interfaces： Selectable by Pin

• Operating Temperature Range： –20℃ to +70℃

• 2.6-mm × 2.1-mm， 0.4-mm Pitch DSBGA Package

• Supplies：

– Rx： 1.8 V to 1.9 V （LDO Bypass），

2.0 V to 3.6 V （LDO Enabled）

– Tx： 3 V to 5.25 V

– IO： 1.7 V to Rx_SUP

AFE4900应用：

• Synchronized PPG， ECG for Blood PressureEstimation

• HRM for Wearables， Hearables

• Heart-Rate Variability （HRV）

• Pulse Oximetry （SpO2） Measurements

图1.AFE4900简化框图

可穿戴无线多参数病人监护器参考设计TIDA-01580

TIDA-01580 Wearable， Wireless， Multi-Parameter Patient Monitor Reference Design This reference design is a simple， wearable， multiparameter，patient monitor that uses a single-chip，biosensing front end， the AFE4900 device， forsynchronized electrocardiography （ECG） andphotoplethysmography （PPG） measurements. Themeasured data is transferred to a remote locationusing the CC2640R2F device （supporting BLE 4.2 and5）。 The reference design is operated using a singleCR3032 battery and provides a battery life of 30 days.

The raw data is available for the user to calculateheart rate， oxygen concentration in blood （SpO2），pulse-transit time （PTT）， and ECG. Two onboard lightemittingdiodes （LEDs） indicate low-battery detectionand ECG lead-off detection for users.

病人监护器参考设计TIDA-01580主要特性：

• Simple， Wearable， Multi-Parameter， Patient Monitorfor PPG and ECG

• Provides Raw Data to Calculate Heart Rate， SpO2，and PTT

• Uses Single-Chip， Biosensing Front-End AFE4900Device for Synchronized ECG and PPGMeasurements

– PPG （Optical Heart-Rate Monitoring and SpO2）Supports Four LEDs and Three Photodiodes（PDs）， With Digital Ambient Subtraction toImprove Signal-to-Noise Ratio （SNR）

– ECG （LEAD I） Signals

• Integrated Arm® Cortex®-M3 and 2.4-GHz RFTransceiver （CC2640R2F） Supports Wireless DataTransfer – BLE 4.2 and 5.0

• Operated By CR3032 （3-V， 500-mA Coin-CellBattery）， With Battery Life of 30 Days Using HighlyEfficient DC/DC Converters

• Small Form Factor Helps With Easy Adaptation toWearable Applications

病人监护器参考设计TIDA-01580应用：

• Wireless Patient Monitor

• ECG

• Pulse Oximeter

• Wearable Fitness and Activity Monitor

图2.病人监护器参考设计TIDA-01580外形图

图3.病人监护器参考设计TIDA-01580 PCB顶视图（无电池夹头）

图4.病人监护器参考设计TIDA-01580 PCB底视图