A 2.5nJ duty-cycled bridge-to-digital converter integrated in a 13mm3 pressure-sensing system
A 2.5nJ duty-cycled bridge-to-digital converter integrated in a 13mm3 pressure-sensing system
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集成在 13mm3 压力传感系统中的 2.5nJ 占空比桥数字转换器
DOI：
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发表时间：
2018
期刊：
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通讯作者：
D. Blaauw
中科院分区：
文献类型：
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作者：
Sechang Oh;Yao Shi;Gyouho Kim;Yejoong Kim;Taewook Kang;Seokhyeon Jeong;D. Sylvester;D. Blaauw
小尺寸压阻式MEMS传感器通常配置在惠斯通电桥中，广泛用于测量物理信号，如压力[1-3]、温度[4]、力[1]和气体浓度。实现电桥数字输出的常用方法包括用直流电压源对电桥进行偏置，然后使用低噪声放大器和ADC。虽然电桥测量可以实现高分辨率和线性度，但它非常耗电，因为电桥电阻很低（通常为1-10kΩ）。高功率和高瞬时电流使其不适合作为电池容量<10μAh和内阻为~ 15kΩ的小型化微系统的传感接口。在[1]中提出了占空比励磁，以降低中等动态范围（DR）应用中的功率，与静态偏置相比，将电桥励磁能量降低高达125倍。然而，激发能量消耗（~ 250nJ）仍然远远大于接口电路转换能量，因此限制了传感器的整体能量效率。为了解决这一挑战，我们提出了一种高效节能的高占空比激励电桥传感器读出电路，用于小型电池供电系统。由于电池电阻高，激励电压（VEX）来自片上去耦电容，在激励期间下降~ 100mV，然后从电池缓慢充电。为了避免这种电压波动导致的精度下降，设计不仅对输入（VIN+/−）进行采样，还对VEX进行采样，从而产生DAC参考电压（VDAC）。我们还提出了一种偏移校准和输入范围匹配方法。我们演示了与完整且功能齐全的压力传感系统集成的桥数字转换器（BDC）的操作，该系统包括处理器、电池、电源管理单元、射频发射器和光接收器。
Small form-factor piezoresistive MEMS sensors, often configured in a Wheatstone bridge, are widely used to measure physical signals such as pressure [1-3], temperature [4], force [1], and gas concentration. A common method to realize a digital output from the bridge involves biasing the bridge with a DC voltage source and using a low-noise amplifier followed by an ADC. While a bridge measurement can achieve high resolution and linearity, it is very power hungry [3] because the bridge resistance is low (typically 1–10kΩ). Both the high power and high instantaneous current make it unsuitable as a sensing interface in miniaturized microsystems with battery capacities of <10μAh and ∼15kΩ internal resistance [5]. Duty cycled excitation was proposed in [1] to reduce power in moderate dynamic range (DR) applications, lowering bridge excitation energy by up to 125x compared to static biasing. However, the excitation energy consumption (∼250nJ) is still much larger than the interface circuit conversion energy, and therefore limits overall sensor energy efficiency. To address this challenge, we propose an energy-efficient highly duty-cycled excitation bridge-sensor readout circuit for small battery-operated systems. Due to high battery resistances, the excitation voltage (VEX) is sourced from an on-chip decoupling capacitance that drops ∼100mV during excitation and then slowly recharges from the battery. To avoid accuracy degradation from this voltage fluctuation, the design samples not only the inputs (VIN+/−) but also VEX, from which it generates a DAC reference voltage (VDAC). We also propose an offset calibration and input-range matching method. We demonstrate operation of the bridge-to-digital converter (BDC) integrated with a complete and fully functional pressure-sensing system, including a processor, battery, power management unit, RF transmitter, and optical receiver.