Key Takeaways & Executive Findings
- •• A 20-channel AFE for bio-potential recording achieves 1.25 μW per channel, significantly reducing power consumption. • A charge-sharing multiplexer eliminates active buffers, extending sampling time and lowering system power. • The AFE achieves an input-referred noise of 1.8 μVrms and a noise efficiency factor of 4.1, suitable for high-quality bio-signal acquisition. • Real-world ECG recording demonstrates the AFE's practical applicability in medical devices.
Abstract
This paper presents the design of a low-power multi-channel analog front-end (AFE) for bio-potential recording. By using time division multiplexing (TDM), a successive approximation register analog-to-digital converter (SAR ADC) is shared among all 20 channels. A charge-sharing multiplexer (MUX) is proposed to transmit the output signals from the respective channels to the ADC. By separately pre-sampling the output of each channel, the sampling time of each channel is greatly extended and additional active buffers are avoided. The AFE is fabricated in a 65-nm CMOS process, and the whole system consumes 28.2 μW under 1 V supply. Each analog acquisition channel consumes 1.25 μW and occupies a chip area of 0.14 mm2. Measurement results show that the AFE achieves an input referred noise of 1.8 μV∙rms in a 350 Hz bandwidth and a noise efficiency factor (NEF) of 4.1. The 12-bit SAR ADC achieves an ENOB of 9.8 bit operating at 25 kS/s. The AFE is experimented on real-world applications by measuring human ECG and a clear ECG waveform is captured.
1. Introduction
Neural sensors have been widely used in medical devices in recent years to detect common bio-potential signals, such as electrocardiograms (ECG), electroencephalograms (EEG), electromyograms (EMG) and so forth. In many modern medical applications, multiple electrodes are usually necessary to record the electric field activity in different areas of human tissue, thus requiring multi-channel analog front-end (AFE) to amplify and quantify bioelectrical signals. However, multi-channel neural sensors call for a significant increase in chip area and power consumption, which is a major challenge in implantable or wearable medical applications.
In a single-channel AFE for bio-potential recording illustrated in Fig. 1(a), the power consumption of the system is mainly contributed by the instrumentation amplifier (IA) and the ADC. But in a multi-channel AFE, the driving buffers are usually the main power consumers. In multi-channel systems, time division multiplexing (TDM) is commonly used to share an ADC among multiple channels, as is shown in Fig. 1(b). The ADC sampling time shortens with the increase of channels, requiring buffers with large driving capability to drive the sampling capacitors. As reported in Ref. [1] with a TDM structure, the preamplifier only consumes 2 μA while each buffer draws a large current of 20.3 μA. Therefore, in multi-channel acquisition systems, the high power of the buffers is a major problem to be solved for system power reduction. Some techniques have been adopted to minimize the power of the driving circuits. In Ref. [2], a sampling strategy is implemented using a dual sample-and-hold circuit, which doubles the time of a single sampling and thus reduces the power of each buffer to a level...
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Yifan Huang, Jing Wang, Lin Cheng (2024). A 1.25 μW/ch TDM-based analog front-end using a charge-sharing multiplexer for bio-potential recording. SinoTechIntel Verified Research. https://doi.org/10.1088/1674-4926/24120034
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Frequently Asked Questions
What is the power consumption per channel of the proposed AFE?
The proposed AFE consumes only 1.25 μW per channel, making it highly suitable for power-constrained implantable and wearable medical devices.
How does the charge-sharing multiplexer reduce power consumption?
The charge-sharing multiplexer eliminates the need for active buffers by pre-sampling each channel's output, thereby extending sampling time and reducing overall system power.
What are the key performance metrics of the AFE?
The AFE achieves an input-referred noise of 1.8 μVrms in a 350 Hz bandwidth, a noise efficiency factor of 4.1, and the 12-bit SAR ADC achieves an ENOB of 9.8 bit at 25 kS/s.
In which CMOS process is the AFE fabricated?
The AFE is fabricated in a 65-nm CMOS process, operating under a 1 V supply.
Has the AFE been validated in real-world applications?
Yes, the AFE was used to measure human ECG signals, and a clear ECG waveform was successfully captured, demonstrating its practical applicability.
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