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Sensors 2018, 18(6), 1867; https://doi.org/10.3390/s18061867

A Low-Noise Direct Incremental A/D Converter for FET-Based THz Imaging Detectors

Center for Materials and Microsystems, Integrated Radiation and Image Sensors Group, Fondazione Bruno Kessler, Trento 38122, Italy
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Received: 20 March 2018 / Revised: 9 May 2018 / Accepted: 5 June 2018 / Published: 7 June 2018
(This article belongs to the Special Issue Image Sensors)
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Abstract

This paper presents the design, implementation and characterization results of a pixel-level readout chain integrated with a FET-based terahertz (THz) detector for imaging applications. The readout chain is fabricated in a standard 150-nm CMOS technology and contains a cascade of a preamplification and noise reduction stage based on a parametric chopper amplifier and a direct analog-to-digital conversion by means of an incremental ΣΔ converter, performing a lock-in operation with modulated sources. The FET detector is integrated with an on-chip antenna operating in the frequency range of 325–375 GHz and compliant with all process design rules. The cascade of the FET THz detector and readout chain is evaluated in terms of responsivity and Noise Equivalent Power (NEP) measurements. The measured readout input-referred noise of 1.6 μ V r m s allows preserving the FET detector sensitivity by achieving a minimum NEP of 376 pW/ Hz in the optimum bias condition, while directly providing a digital output. The integrated readout chain features 65-dB peak-SNR and 80-μ W power consumption from a 1.8-V supply. The area of the antenna-coupled FET detector and the readout chain fits a pixel pitch of 455 μm, which is suitable for pixel array implementation. The proposed THz pixel has been successfully applied for imaging of concealed objects in a paper envelope under continuous-wave illumination. View Full-Text
Keywords: readout circuit; field-effect transistor (FET); terahertz imaging; direct detectors; incremental ADC; flicker noise; lock-in; chopper; parametric amplifier readout circuit; field-effect transistor (FET); terahertz imaging; direct detectors; incremental ADC; flicker noise; lock-in; chopper; parametric amplifier
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Khatib, M.; Perenzoni, M. A Low-Noise Direct Incremental A/D Converter for FET-Based THz Imaging Detectors. Sensors 2018, 18, 1867.

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