The circuit shown in Figure 1 is an optimum 12-bit data acquisition front end circuit to measure skin impedance for wearable fitness bands. The circuit design and selection of driving amplifier is optimized for minimum power and maximum input dynamic range.
Figure 1: Low Power Data Acquisition Block for Skin Impedance Measurement
The measurement is accomplished by using a known ac excitation source, “VIN” with a mid-scale reference voltage to create a current waveform that is proportional to the complex impedance of the body. The current waveform is then converted back into a voltage using the “I-V Converter with Gain” block, after which it get sampled by the data acquisition circuit.
To see details on how to design the low power data acquisition front end circuit, click on the following link:
http://www.ti.com/tool/tipd168
To order samples of the ADS7042 or other low power ADCs designed for wearable and portable applications, click on the following product links: