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Sensors 2016, 16(3), 325; doi:10.3390/s16030325

A Low-Noise CMOS THz Imager Based on Source Modulation and an In-Pixel High-Q Passive Switched-Capacitor N-Path Filter

1
Univ. Grenoble Alpes, CEA, LETI, MINATEC Campus, Grenoble F-38054, France
2
ICLAB, EPFL, Rue de la Maladière 71, Neuchâtel 2000, Switzerland
*
Author to whom correspondence should be addressed.
Academic Editors: Vincenzo Spagnolo and Dragan Indjin
Received: 31 December 2015 / Revised: 8 February 2016 / Accepted: 26 February 2016 / Published: 3 March 2016
(This article belongs to the Special Issue Infrared and THz Sensing and Imaging)
View Full-Text   |   Download PDF [2574 KB, uploaded 11 March 2016]   |  

Abstract

This paper presents the first low noise complementary metal oxide semiconductor (CMOS) terahertz (THz) imager based on source modulation and in-pixel high-Q filtering. The 31 × 31 focal plane array has been fully integrated in a 0 . 13 μ m standard CMOS process. The sensitivity has been improved significantly by modulating the active THz source that lights the scene and performing on-chip high-Q filtering. Each pixel encompass a broadband bow tie antenna coupled to an N-type metal-oxide-semiconductor (NMOS) detector that shifts the THz radiation, a low noise adjustable gain amplifier and a high-Q filter centered at the modulation frequency. The filter is based on a passive switched-capacitor (SC) N-path filter combined with a continuous-time broad-band Gm-C filter. A simplified analysis that helps in designing and tuning the passive SC N-path filter is provided. The characterization of the readout chain shows that a Q factor of 100 has been achieved for the filter with a good matching between the analytical calculation and the measurement results. An input-referred noise of 0 . 2 μ V RMS has been measured. Characterization of the chip with different THz wavelengths confirms the broadband feature of the antenna and shows that this THz imager reaches a total noise equivalent power of 0 . 6 nW at 270 GHz and 0 . 8 nW at 600 GHz. View Full-Text
Keywords: CMOS; terahertz direct detection; terahertz imaging; sub-millimeter wave detectors; sub-millimeter wave imaging; N-path; bandpass filter; high-Q; inductorless filter; Gm-C; tunable; low noise CMOS; terahertz direct detection; terahertz imaging; sub-millimeter wave detectors; sub-millimeter wave imaging; N-path; bandpass filter; high-Q; inductorless filter; Gm-C; tunable; low noise
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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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MDPI and ACS Style

Boukhayma, A.; Dupret, A.; Rostaing, J.-P.; Enz, C. A Low-Noise CMOS THz Imager Based on Source Modulation and an In-Pixel High-Q Passive Switched-Capacitor N-Path Filter. Sensors 2016, 16, 325.

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