Abstract
This study aims to propose a capacitance-to-digital converter (CDC) based on a third-order cascade of integrators with a feed-forward (CIFF) incremental sigma-delta modulator for smart humidity sensor application. Disguised zoom-in technology was proposed to enlarge the measurable range of the CDC. The input range of the CDC was 0–388 pF. The proposed CDC was realized using 0.18 μm complementary metal-oxide-semiconductor technology. Results show that the CDC performs a 13-bit capacitance-to-digital conversion in 0.8 ms. The analog system consumes 169.7 μA from a 1.8 V supply, which corresponds to a figure of merit (FOM) of 3.0 nJ/step. The proposed CDC was combined with a HS1101 humidity sensor to demonstrate its incorporation in an overall system design. The resolution was 0.7% relative humidity (RH) over a range of 30%–90% RH.
Highlights
Relative humidity is an important factor in industrial processes, human health, and preservation of perishable food and cultural relics [1,2]
A capacitance-to-voltage front-end capacitance-to-digital converter (CDC) has been proposed [6] which relies on a successive approximation register analog-to-digital converter (ADC) such that the effective number of bits (ENOB) is only 8.35 bits
Aside from requiring a cumbersome working process, the signal-to-noise ratio (SNR) of this device is as low as 45.14 dB owing to error accumulation in the two conversion steps
Summary
Relative humidity is an important factor in industrial processes, human health, and preservation of perishable food and cultural relics [1,2]. Aside from requiring a cumbersome working process, the signal-to-noise ratio (SNR) of this device is as low as 45.14 dB owing to error accumulation in the two conversion steps Another proposed CDC [9] can operate in either fast or slow modes; it uses a charge amplifier that introduces a significant amount of additional error and consumes a large amount of power (as much as 1 W). A high-resolution CDC was recently developed [10], but its input capacitance range is only −4–4 pF, and it has a long measurement time of up to 62 ms These sensors did not meet the market’s requirements of low power consumption, large capacitance input range, and fast measurements.
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