TI公司的AFE4300是低成本的衡器和人體成份(BCM)測量模擬前端(AFE),集成了兩個單獨的信號鏈:一個用來重量測量,一個采用16位860SPS ADC進行人體成份分析.器件中的三個BCM通路允許對身體手和足間的部分身體阻抗進行分析(BIA),從而得出人體成份的全圖.器件的工作電壓2 V- 3.6 V,主要用于衡器和人體成份測量.本文介紹了AFE4300主要特性,方框圖,衡器前端框圖和BCM前端框圖以及評估板AFE4300EVM-PDK框圖,電路圖,材料清單和PCB元件布局圖,并介紹了典型的人體成份分析圖.
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應用:
• Weight Scales with Body Composition Measurements
圖1.AFE4300功能框圖
圖2.AFE4300方框圖
圖3.AFE4300衡器前端框圖
圖4.AFE4300 AC整流器模式的人體成分測量儀(BCM)前端框圖
評估板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.
評估板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
圖5.評估板AFE4300EVM-PDK外形圖
圖6.評估板AFE4300EVM-PDK框圖
圖7.評估板AFE4300EVM-PDK電路圖(1)
圖8.評估板AFE4300EVM-PDK電路圖(2)
圖9.評估板AFE4300EVM-PDK電路圖(3)
圖10.評估板AFE4300EVM-PDK電路圖(4)
圖11.評估板AFE4300EVM-PDK電路圖(5)
圖12.評估板AFE4300EVM-PDK電路圖(6)
評估板AFE4300EVM-PDK材料清單(BOM):
圖13.評估板AFE4300EVM-PDK元件布局圖(頂層)
圖14.評估板AFE4300EVM-PDK元件布局圖(底層)
詳情請見:
http://www.ti.com/lit/ds/sbas586a/sbas586a.pdf
和
http://www.ti.com/lit/ug/sbau201/sbau201.pdf
