TI公司的AFE4300是低成本的衡器和人体成份(BCM)测量模拟前端(AFE),集成了两个单独的信号链:一个用来重量测量,一个采用16位860SPS ADC进行人体成份分析.器件中的三个BCM通路允许对身体手和足间的部分身体阻抗进行分析(BIA),从而得出人体成份的全图.器件的工作电压2 V- 3.6 V,主要用于衡器和人体成份测量.本文介绍了AFE4300主要特性,方框图,衡器前端框图和BCM前端框图以及评估板AFE4300EVM-PDK框图,电路图,材料清单和PCB元件布局图,并介绍了典型的人体成份分析图.

TI introduces the industry’s first fully integrated analog front end for both weight and body composition measurement (BCM). The AFE4300 is an easy-to-use, precision, low-power front end solution, which allows engineers designing weigh scales that incorporate body composition meters, body impedance analyzers, and impedance measurement equipment to get their products to market faster than by implementing existing, more complex multi-chip solutions.

The AFE4300 incorporates two separate signal chains, one targeting weight measurement and the other targeting body composition analysis, with a 16-bit, 860-sps analog-to-digital converter (ADC) multiplexed between them. The device’s three BCM channels enable segmental body impedance analysis (BIA) between body extremities, which allows for a full picture of the subject’s body composition.

The AFE4300 is a low-cost analog front-end incorporating two separate signal chains: one chain for weight-scale (WS) measurement and the other for  body composition measurement (BCM) analysis. A 16-bit, 860-SPS analog-to-digital converter (ADC) is  multiplexed between both chains. The weight  measurement chain includes an instrumentation amplifier (INA) with the gain set by an external  resistor, followed by a 6-bit digital-to-analog converter (DAC) for offset correction, and a circuit to drive the  external bridge/load cell with a fixed 1.7 V for ratiometric measurements.

The AFE4300 can also measure body composition by applying a sinusoidal current into the body. The sinusoidal current is generated with an internal pattern generator and a 6-bit, 1-MSPS DAC. A voltage-to-current converter applies this sinusoidal  current into the body, between two terminals. The  voltage created across these two terminals as a result of the impedance of the body is measured back  with a differential amplifier, rectified, and its amplitude is extracted and measured by the 16-bit ADC.

The AFE4300 operates from 2 V to 3.6 V, is specified from 0℃ to +70℃, and is available in a TQFP-80 package.

AFE4300主要特性:

• Weight-Scale Front-End:

– Supports up to Four Load Cell Inputs

– On-Chip Load Cell 1.7-V Excitation Voltage for Ratiometric Measurement

– 68-nVrms Input-Referred Noise (0.1 Hz to 2 Hz)

– Best-Fit Linearity: 0.01% of Full-Scale

– Weight-Scale Measurement : 540 μA

• Body Composition Front-End:.

– Supports Up To Three Tetra-Polar Complex Impedance Measurements

– 6-Bit, 1-MSPS Sine-Wave Generation Digital-to-Analog Converter (DAC)

– 375-μArms, ±20% Excitation Source

– Dynamic Range : 0 Ω to 2.8 kΩ

– 0.1-Ω Measurement RMS Noise in 2-Hz BW

– Body Composition measurement : 970 μA

• Analog-to_Digital Converter (ADC):

– 16 Bits, 860 SPS

– Supply current: 110 μA

AFE4300应用:

• Weight Scales with Body Composition Measurements

图1.AFE4300功能框图


图2.AFE4300方框图

图3.AFE4300衡器前端框图

图4.AFE4300 AC整流器模式的人体成分测量仪(BCM)前端框图

评估板AFE4300EVM-PDK

AFE4300EVM-PDK is a platform for evaluating the AFE4300 device. AFE4300 is a low cost Analog-Front-End incorporating two separate signal chains, one targeting weight measurement and the other targeting body composition analysis. The EVM provides access for load cell terminals to support up to four load cell inputs for weigh scale measurements, BCM terminals to support up to three tetra-polar complex impedance measurements. Users can also feed any type of single ended or differential signals directly to the AFE4300 through the auxiliary (AUX1 and AUX2) inputs. External support circuits such as anti-aliasing network for load cell terminals, trim-pot for setting the gain of the Instrumentation Amplifier at the Weigh Scale Front-end, Instrumentation amplifiers for the BCM differential terminals, load cell simulation block, impedance simulation block, clocks and external references are provided for testing purposes.

The evaluation module comes with a LabVIEW-based graphical user interface that allows the user to easily configure the device to capture data and perform analysis on the data. Note that the AFE4300EVM-PDK is intended for prototyping and evaluation purposes only and is not intended to be used with real subjects or patients.

评估板AFE4300EVM-PDK主要特性:

Support for up to four load cell inputs

Support for three tetra-polar impedance measurements

On-board load cell simulation block

Acquire data at up to 860 samples/second in data capture mode

USB based power and PC application connectivity

图5.评估板AFE4300EVM-PDK外形图

图6.评估板AFE4300EVM-PDK框图

图7.评估板AFE4300EVM-PDK电路图(1)

图8.评估板AFE4300EVM-PDK电路图(2)

图9.评估板AFE4300EVM-PDK电路图(3)

图10.评估板AFE4300EVM-PDK电路图(4)

图11.评估板AFE4300EVM-PDK电路图(5)

图12.评估板AFE4300EVM-PDK电路图(6)

评估板AFE4300EVM-PDK材料清单(BOM):




图13.评估板AFE4300EVM-PDK元件布局图(顶层)

图14.评估板AFE4300EVM-PDK元件布局图(底层)

详情请见:
http://www.ti.com/lit/ds/sbas586a/sbas586a.pdf
和
http://www.ti.com/lit/ug/sbau201/sbau201.pdf