Summary of TI chip combines body analysis in weighing scales
The AFE4300 is a low-cost analog front-end by Texas Instruments combining a weight-scale channel and a body-composition channel with a shared 16-bit, 860 SPS ADC. It supports up to four load cells with on-chip 1.7 V excitation, and up to three tetra-polar impedance measurements for segmental BIA and BIS (ECW/ICW). The BCM uses a 6-bit, 1-MSPS DAC to generate sinusoidal excitation; overall device current is under 1 mA, operates from 2 V to 3.6 V, is specified 0°C to +70°C, and comes in a 12 mm x 12 mm TQFP-80 package.
Parts used in the AFE4300 Project:
- AFE4300 analog front-end IC
- External resistor for INA gain setting
- External bridge/load cell (up to four supported)
- On-chip 6-bit DAC for offset correction
- Voltage-to-current converter (internal for BCM)
- 6-bit, 1-MSPS DAC for sine-wave generation (internal)
- Differential amplifier (internal)
- Rectifier and amplitude-extraction circuitry (internal)
- 16-bit, 860 SPS ADC (internal)
- Power supply (2 V to 3.6 V)
- TQFP-80 package (12 mm x 12 mm)
Description
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°C to +70°C, and is available in a TQFP-80 package.
Features
- 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
- Supports Up To Three Tetra-Polar Complex Impedance
- Analog-to_Digital Converter (ADC):
- 16 Bits, 860 SPS
- Supply current: 110 µA
Texas Instruments has introduced an analogue front end IC for use in weighing scales that incorporate also body composition meters.
The AFE4300 incorporates two separate signal chains, one targeting weight measurement and the other targeting body composition analysis, with a 16-bit, 860sample/s analogue-to-digital converter (ADC) multiplexed between them.
The device’s three BCM channels are designed to enable segmental body impedance analysis (BIA) for measurement across the body including hand to hand, foot to foot, or even hand to foot, which increases overall measurement accuracy.
The device also includes an option to accurately measure Extra Cellular Water (ECW) and Intra Cellular Water (ICW) using bio-impedance spectroscopy (BIS).
The AFE4300 consumes less than 1mA, operating from a 2V to 3.6V power supply.
It is available in a 12mm x 12mm TQFP-80 package.
For more read: TI chip combines body analysis in weighing scales
- What supply voltage range does the AFE4300 operate from?
The AFE4300 operates from 2 V to 3.6 V according to the article. - How many load cell inputs does the weight-scale front end support?
The weight-scale front end supports up to four load cell inputs. - What is the ADC resolution and sample rate in the AFE4300?
The ADC is 16 bits with an 860 samples per second rate. - How many body composition measurement channels does the AFE4300 provide?
The AFE4300 provides up to three tetra-polar complex impedance measurement channels. - What excitation voltage does the AFE4300 provide for ratiometric load cell measurement?
The AFE4300 provides an on-chip 1.7 V excitation voltage for ratiometric measurement. - Can the AFE4300 perform segmental body impedance analysis (BIA)?
Yes, the three BCM channels are designed to enable segmental BIA such as hand to hand, foot to foot, or hand to foot. - What is the dynamic range for the body composition measurement?
The dynamic range for BCM is 0 ohm to 2.8 kiloohm as stated in the article. - What is the typical supply current consumption of the AFE4300?
The article states the AFE4300 consumes less than 1 mA overall; the ADC supply current is listed as 110 µA. - Does the AFE4300 support bio-impedance spectroscopy for ECW and ICW measurement?
Yes, the device includes an option to measure ECW and ICW using bio-impedance spectroscopy.
