Abstract
This paper presents a low-power CMOS analog front-end (AFE) IC designed with a selectable on-chip dual AC/DC- coupled paths for bio-sensor applications. The DC-coupled path can be selected to sense a biosignal with useful DC information, and the AC-coupled path can be selected for sensing the AC content of the biosignal by attenuating the unwanted DC component. The AFE IC includes a DC-coupled instrumentation amplifier (INA), two variable-gain 1st-order low pass filters (LPF) with tunable cut-off frequencies, a fixed gain 2nd-order Sallen-Key high-pass filter (HPF) with tunable cut-off frequencies, a buffer and an 8-bit differential successive approximation register (SAR) ADC. The entire AFE channel is designed and fabricated in a proprietary 0.35-μm CMOS technology. Excluding an external buffer needed to properly drive the ADC, the measured AFE IC consumes only 2.37 μA/channel with an input referred noise of ~40 μVrms in [1 Hz, 1 kHz], and successfully displays proper ECG (electrocardiogram) and electrogram (EGM) waveforms for QRS peaks detection. We expect that the low-power dual-path design of this AFE IC can enable it to periodically record both the AC and the DC signals for proper sensing and calibration for various bio-sensing applications.
Highlights
Wearable sensors are widely used to monitor patients’ medical/health conditions, and can provide quantitative data for clinical use
The entire analog front-end (AFE) IC is designed and fabricated in a Texas Instruments (TI) proprietary 0.35 μm Bipolar-CMOSDMOS process, while only the standard 0.35-μm 3 V CMOS devices and the on-chip passive components were used for this design
Compared with the size of die, if we had chosen the AFE IC architecture shown in Figure 1, the size of the AFF IC with external resistors and capacitors would have been much larger
Summary
Wearable sensors are widely used to monitor patients’ medical/health conditions, and can provide quantitative data for clinical use. A typical analog frontend (AFE) circuit for a bio-sensor can have an instrumentation amplifier (INA), a filter, a variable gain amplifier (VGA) and an analog-to-digital converter (ADC) [1,2,3,4,5]. In order to effectively digitize both the signal’s DC and AC components for applications such as continuous ECG/EEG monitoring and/or with additional temperature sensing, we introduce in Figure 2 a design option for the AFE circuits with dual AC-coupled and DC-coupled paths.
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