Publications
Time delay integration and in-pixel spatiotemporal filtering using a nanoscale digital CMOS focal plane readout
November 1, 2009
Journal Article
Published in:
IEEE Trans. on Electron Devices, Vol. 56, No. 11, November 2009, pp. 2516-2533.
Summary
A digital focal plane array (DFPA) architecture has been developed that incorporates per-pixel full-dynamic-range analog-to-digital conversion and orthogonal-transfer-based realtime digital signal processing capability. Several long-wave infrared-optimized pixel processing focal plane readout integrated circuit (ROIC) designs have been implemented, each accommodating a 256 x 256 30-um-pitch detector array. Demonstrated in this paper is the application of this DFPA ROIC architecture to problems of background pedestal mitigation, wide-field imaging, image stabilization, edge detection, and velocimetry. The DFPA architecture is reviewed, and pixel performance metrics are discussed in the context of the application examples. The measured data reported here are for DFPA ROICs implemented in 90-nm CMOS technology and hybridized to HgxCd1-xTe (MCT) detector arrays with cutoff wavelengths ranging from 7 to 14.5 m and a specified operating temperature of 60 K-80 K.
Summary
A digital focal plane array (DFPA) architecture has been developed that incorporates per-pixel full-dynamic-range analog-to-digital conversion and orthogonal-transfer-based realtime digital signal processing capability. Several long-wave infrared-optimized pixel processing focal plane readout integrated circuit (ROIC) designs have been implemented, each accommodating a 256 x 256 30-um-pitch detector array. Demonstrated in this...
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Design approaches for digitally dominated active pixel sensors: leveraging Moore's law scaling in focal plane readout design
January 20, 2008
Conference Paper
Published in:
SPIE Vol. 6900, Quantum Sensing and Nanophotonic Devices V, 20-23 January 2008, 69000W.
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R&D area:
Summary
Although CMOS technology scaling has provided tremendous power and circuit density benefits for innumerable applications, focal plane array (FPA) readouts have largely been left behind due to dynamic range and signal-to-noise considerations. However, if an appropriate pixel front end can be constructed to interface with a mostly digital pixel, it is possible to develop sensor architectures for which performance scales favorably with advancing technology nodes. Although the front-end design must be optimized to interface with a particular detector, the dominant back end architecture provides considerable potential for design reuse. In this work, digitally dominated long wave infrared (LWIR) active pixel sensors with cutoff wavelengths between 9 and 14.5 um are demonstrated. Two ROIC designs are discussed, each fabricated in a 90-nm digital CMOS process and implementing a 256 x 256 pixel array on a 30-um pitch. In one of the implemented designs, the feasibility of implementing a 15-um pixel pitch FPA with a 500 million electron effective well depth, less than 0.5% non-linearity in the target range and a measured NEdT of less than 50 mK at f/4 and 60 K is demonstrated. Simple on-FPA signal processing allows for a much reduced readout bandwidth requirement with these architectures. To demonstrate the potential for commonality that is offered by a digitally dominated architecture, this LWIR sensor design is compared and contrasted with other digital focal plane architectures. Opportunities and challenges for application of this approach to various detector technologies, optical wavelength ranges and systems are discussed.
Summary
Although CMOS technology scaling has provided tremendous power and circuit density benefits for innumerable applications, focal plane array (FPA) readouts have largely been left behind due to dynamic range and signal-to-noise considerations. However, if an appropriate pixel front end can be constructed to interface with a mostly digital pixel, it...
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Advanced trigger development
November 1, 2007
Journal Article
Published in:
Lincoln Laboratory Journal, Vol. 17, No. 1, November 2007, pp. 29-62.
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R&D area:
Summary
The deadliest form of a biological attack is aerosolized agents dispersed into the atmosphere. Early detection of aerosolized biological agents is important for defense against these agents. Because of the wide range of possible attack scenarios and attack responses, there is also a wide range of detector requirements. This article focuses on real-time, single-particle, optically based bio-agent trigger detectors--the first responder to an aerosol attack--and how to engineer these detectors to achieve optimal detection performance.
Summary
The deadliest form of a biological attack is aerosolized agents dispersed into the atmosphere. Early detection of aerosolized biological agents is important for defense against these agents. Because of the wide range of possible attack scenarios and attack responses, there is also a wide range of detector requirements. This article...
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The digital focal plane array (DFPA) architecture for data processing "on-chip"
February 5, 2007
Conference Paper
Published in:
2007 Meeting of the Military Sensing Symposia (MSS) Specialty Group on Camouflage, Concealment & Deception; Passive Sensors; Detectors; and Materials, 5-9 February 2007.
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Summary
The digital focal plane array (DFPA) project seeks to develop readout integrated circuits (ROICs) utilizing aggressively scaled and commercially available CMOS. Along with focal plane scaling and readout robustness benefits, the DFPA architecture provides a very simple way to implement processing algorithms directly on image data, in real-time, and prior to read-out of the data to an external digitizer or computer. In principle, almost any linear image processing filter kernel can be convolved with the scene image prior to readout. The useful size of the filter kernel is only limited by the size of the DFPA. Time domain filters can also be implemented on the ROIC to accomplish digital time domain integration (TDI) or change detection algorithms. The unique architecture can achieve the processing capability without the use of traditional digital adders or multipliers, like those used in most signal processors. Instead, a DFPA manipulates sequential digital counters under every pixel in a unique way to achieve the desired functionality. A non-addressable readout scheme is used for data transfer in four possible directions across the array. Although we are currently targeting longwave infrared (LWIR) applications, the approach can be potentially applied to any imaging application in any band.
Summary
The digital focal plane array (DFPA) project seeks to develop readout integrated circuits (ROICs) utilizing aggressively scaled and commercially available CMOS. Along with focal plane scaling and readout robustness benefits, the DFPA architecture provides a very simple way to implement processing algorithms directly on image data, in real-time, and prior...
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Laser-induced fluorescence-cued, laser induced- breakdown spectroscopy biological-agent detection
December 1, 2006
Journal Article
Published in:
Appl. Opt., Vol. 45, No. 34, 1 December 2006, pp. 8806-8814.
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Summary
Methods for accurately characterizing aerosols are required for detecting biological warfare agents. Currently, fluorescence-based biological agent sensors provide adequate detection sensitivity but suffer from high false-alarm rates. Combining single-particle fluorescence analysis with laser-induced breakdown spectroscopy (LIBS) provides additional discrimination and potentially reduces false-alarm rates. A transportable UV laser-induced fluorescence-cued LIBS test bed has been developed and used to evaluate the utility of LIBS for biological-agent detection. Analysis of these data indicates that LIBS adds discrimination capability to fluorescence-based biological-agent detectors. However, the data also show that LIBS signatures of biological agent simulants are affected by washing. This may limit the specificity of LIBS and narrow the scope of its applicability in biological-agent detection.
Summary
Methods for accurately characterizing aerosols are required for detecting biological warfare agents. Currently, fluorescence-based biological agent sensors provide adequate detection sensitivity but suffer from high false-alarm rates. Combining single-particle fluorescence analysis with laser-induced breakdown spectroscopy (LIBS) provides additional discrimination and potentially reduces false-alarm rates. A transportable UV laser-induced fluorescence-cued LIBS...
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An end-to-end demonstration of a receiver array based free-space photon counting communications link
August 13, 2006
Conference Paper
Published in:
SPIE Vol. 6304, Free-Space Laser Communications VI, 13-17 August 2006, pp. 63040H-1 - 63040H-13.
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Summary
NASA anticipates a significant demand for long-haul communications service from deep-space to Earth in the near future. To address this need, a substantial effort has been invested in developing a free-space laser communications system that can be operated at data rates that are 10-1000 times higher than current RF systems. We have built an endto- end free-space photon counting testbed to demonstrate many of the key technologies required for a deep space optical receiver. The testbed consists of two independent receivers, each using a Geiger-mode avalanche photodiode detector array. A hardware aggregator combines the photon arrivals from the two receivers and the aggregated photon stream is decoded in real time with a hardware turbo decoder. We have demonstrated signal acquisition, clock synchronization, and error free communications at data rates up to 14 million bits per second while operating within 1 dB of the channel capacity with an efficiency of greater than 1 bit per incident photon.
Summary
NASA anticipates a significant demand for long-haul communications service from deep-space to Earth in the near future. To address this need, a substantial effort has been invested in developing a free-space laser communications system that can be operated at data rates that are 10-1000 times higher than current RF systems...
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Design and testing of an all-digital readout integrated circuit for infrared focal plane arrays
August 3, 2005
Conference Paper
Published in:
SPIE Vol. 5902. Focal Plane Arrays for Space Telescopes II, 3-4 August 2005, pp. 1-11.
Summary
The digital focal plane array (DFPA) project demonstrates the enabling technologies necessary to build readout integrated circuits for very large infrared focal plane arrays (IR FPAs). Large and fast FPAs are needed for a new class of spectrally diverse sensors. Because of the requirement for high-resolution (low noise) sampling, and because of the sample rate needed for rapid acquisition of high-resolution spectra, it is highly desirable to perform analog-to-digital (A/D) conversion right at the pixel level. A dedicated A/D converter located under every pixel in a one-million-plus element array, and all-digital readout integrated circuits will enable multi- and hyper-spectral imaging systems with unprecedented spatial and spectral resolution and wide area coverage. DFPAs provide similar benefits to standard IR imaging systems as well. We have addressed the key enabling technologies for realizing the DFPA architecture in this work. Our effort concentrated on demonstrating a 60-micron footprint, 14-bit A/D converter and 2.5 Gbps, 16:1 digital multiplexer, the most basic components of the sensor. The silicon test chip was fabricated in a 0.18- micron CMOS process, and was designed to operate with HgxCd1-xTe detectors at cryogenic temperatures. Two A/D designs, one using static logic and one using dynamic logic, were built and tested for performance and power dissipation. Structures for evaluating the bit-error-rate of the multiplexer on-chip and through a differential output driver were implemented for a complete performance assessment. A unique IC probe card with fixtures to mount into an evacuated, closed-cycle helium dewar were also designed for testing up to 2.5 Gbps at temperatures as low as 50 K.
Summary
The digital focal plane array (DFPA) project demonstrates the enabling technologies necessary to build readout integrated circuits for very large infrared focal plane arrays (IR FPAs). Large and fast FPAs are needed for a new class of spectrally diverse sensors. Because of the requirement for high-resolution (low noise) sampling, and...
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A method for correcting Fourier transform spectrometer (FTS) dynamic alignment errors
April 12, 2004
Conference Paper
Published in:
SPIE Vol. 5425, Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery X, 12-15 April 2004, pp. 443-455.
Summary
The Cross-track Infrared Sounder (CrIS), like most Fourier Transform spectrometers, can be sensitive to mechanical disturbances during the time spectral data is collected. The Michelson interferometer within the spectrometer modulates input radiation at a frequency equal to the product of the wavenumber of the radiation and the constant optical path difference (OPD) velocity associated with the moving mirror. The modulation efficiency depends on the angular alignment of the two wavefronts exiting the spectrometer. Mechanical disturbances can cause errors in the alignment of the wavefronts which manifest as noise in the spectrum. To mitigate these affects CrIS will employ a laser to monitor alignment and dynamically correct the errors. Additionally, a vibration isolation system will damp disturbances imparted to the sensor from the spacecraft. Despite these efforts, residual noise may remain under certain conditions. Through simulation of CrIS data, we demonstrated an algorithmic technique to correct residual dynamic alignment errors. The technique requires only the time-dependent wavefront angle, sampled coincidentally with the interferogram, and the second derivative of the erroneous interferogram as inputs to compute the correction. The technique can function with raw interferograms on board the spacecraft, or with decimated interferograms on the ground. We were able to reduce the dynamic alignment noise by approximately a factor of ten in both cases. Performing the correction on the ground would require an increase in data rate of 1-2% over what is currently planned, in the form of 8-bit digitized angle data.
Summary
The Cross-track Infrared Sounder (CrIS), like most Fourier Transform spectrometers, can be sensitive to mechanical disturbances during the time spectral data is collected. The Michelson interferometer within the spectrometer modulates input radiation at a frequency equal to the product of the wavenumber of the radiation and the constant optical path...
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Hyperspectral environmental suite for the Geostationary Operational Environmental Satellite (GOES)
April 12, 2004
Conference Paper
Published in:
SPIE Vol. 5425, Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery X, 12-15 April 2004, pp. 329-340.
Summary
The GOES satellites will fly a Hyperspectral Environmental Suite (HES) on GOES-R in the 2012 timeframe. The approximately 1500 spectral channels (technically ultraspectral), leading to improved vertical resolution, and approximately five times faster coverage rate planned for the sounder in this suite will greatly exceed the capabilities of the current GOES series instrument with its 18 spectral channels. In the GOES-R timeframe, frequent measurements afforded by geostationary orbits will be critical for numerical weather prediction models. Since the current GOES soundings are assimilated into numerical weather prediction models to improve the validity of model outputs, particularly in areas with little radiosonde coverage, this hyperspectral capability in the thermal infrared will significantly improve sounding performance for weather prediction in the western hemisphere, while providing and enhancing other products. Finer spatial resolution is planned for mesoscale observation of water vapor variations. The improvements over the previous GOES sounders and a primary difference from other planned instruments stem from two-dimensional focal plane array availability. These carry an additional set of challenges in terms of instrument specifications, which will be discussed. As a suite, HES is planned with new capabilities for coastal ocean coverage with the goal of including open ocean coverage. These new planned imaging applications, which will be either multispectral or hyperspectral, will also be discussed.
Summary
The GOES satellites will fly a Hyperspectral Environmental Suite (HES) on GOES-R in the 2012 timeframe. The approximately 1500 spectral channels (technically ultraspectral), leading to improved vertical resolution, and approximately five times faster coverage rate planned for the sounder in this suite will greatly exceed the capabilities of the current...
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Proton irradiations of large area Hg(1-x)Cd(x)Te photovoltaic detectors for the cross-track infrared sounder
July 7, 2002
Conference Paper
Published in:
SPIE Vol. 4820, Pt. 1, Infrared Technology and Applications XXVIII, 7-11 July 2002, pp. 479-490.
Summary
The effect of radiation on Hg(1-x)Cd(x)Te photodiodes is an important parameter to understand when determining the long-term performance limitations for the Cross-track Infrared Sounder (CrIS), a Fourier Transform interferometric sensor that will fly as part of the National Polar-orbiting Operational Enviornmental Satellite System (NPOESS). The CrIS sensor uses relatively large area photovoltaic detectors, 1mm in diameter. Each p-on-n Hg(1-x)Cd(x)Te photodiode consists of MBE grown, n-type material on lattice matched CdZnTe, with arsenic implantation used to form the junction. A 1mm diameter detector is achieved by using a lateral collection. Solar, and trapped protons are a significant source of radiation in the NPOESS 833 km orbits. We irradiated 22 LWIR detectors with protons at the Harvard Cyclotron Laboratory (HCL) and monitored the I-V performance and dynamic impedance of each detector. Three groups of detectors were irradiated with either 44, 99, 153-MeV protons, each between 1x10(10) - 4x10(12) p+/cm(2) (total range ~ 0.7 - 690 krad(Si)). Several I-V data sets were collected within that fluence range at all three energies. All the detectors were warmed to room temperature for approximately 96 hours following the largest proton dose, recooled, and then re-characterized in terms of I-V performance and dynamic impedance. The total noise increase predicted for CrIS after 7-years in orbit is less than 1%.
Summary
The effect of radiation on Hg(1-x)Cd(x)Te photodiodes is an important parameter to understand when determining the long-term performance limitations for the Cross-track Infrared Sounder (CrIS), a Fourier Transform interferometric sensor that will fly as part of the National Polar-orbiting Operational Enviornmental Satellite System (NPOESS). The CrIS sensor uses relatively large...
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