On-chip Gain Research Articles

TU-F-CAMPUS-I-05: Investigation of An EMCCD Detector with Variable Gain in a Micro-CT System

Purpose: To investigate the performance of a newly built Electron Multiplying Charged Coupled Device (EMCCD) based Micro-CT system, with variable detector gain, using a phantom containing contrast agent of different concentrations. Methods: We built a micro- CT system with an EMCCD having 8 microns pixels and on-chip variable gain. We tested the system using a phantom containing five tubes filled with different iodine contrast solutions (30% to 70%). First, we scanned the phantom using various x-ray exposures values at 40 kVp and constant detector gain. Next, for the same tube currents, the detector gain was increased to maintain the air value of the projection image constant. A standard FDK algorithm was used to reconstruct the data. Performance was analyzed by comparing the signal-to-noise ratio (SNR) measurements for increased gain with those for the low constant gain at each exposure. Results: The high detector gain reconstructed data SNR was always greater than the low gain data SNR for all x-ray settings and for all iodine features. The largest increases were observed for low contrast features, 30% iodine concentration, where the SNR improvement approached 2. Conclusion: One of the first implementations of an EMCCD based micro- CT system was presented and used to image a phantom with various iodine solution concentrations. The analysis of the reconstructed volumes showed a significant improvement of the SNR especially for low contrast features. The unique on-chip gain feature is a substantial benefit allowing the use of the system at very low x-ray exposures per frame.Partial support: NIH grant R01EB002873 and Toshiba Medical Systems Corp. Partial support: NIH grant R01EB002873 and Toshiba Medical Systems Corp.

A Noise-Cancelling Receiver Resilient to Large Harmonic Blockers

By employing two passive-mixer-based downconversion paths, a recently proposed noise cancelling receiver achieves a low-noise figure and tolerates most out-of-band blockers up to 0 dBm with little performance degradation. However, like most wideband passive-mixer-based designs, the architecture is far less tolerant of harmonic blockers, that is blockers located at or around precise integer multiples of the LO frequency. These blockers are problematic because they are downconverted inside the bandwidth of the baseband TIAs and, so, experience significant on-chip voltage gain. This work presents an enhanced noise-cancelling architecture that prevents harmonic blockers experiencing large on-chip gain, thereby boosting the receiver's resilience to such blockers. It will be shown that separate techniques are required for the voltage-driven main path and the current-driven auxiliary path. To validated these ideas, single-ended and fully-differential prototypes were fabricated in 28 nm silicon.

A SiGe 8–18-GHz Receiver With Built-In-Testing Capability for Self-Healing Applications

A wideband (8-18 GHz) built-in test receiver in silicon-germanium technology is presented. The receiver chain consists of a low-noise amplifier (LNA), an image-reject mixer, on-chip automatic gain control ring oscillator sources that are used to provide test signals of a predefined amplitude, and control circuitry in the form of digital-to-analog converters and data registers. Both the LNA and the mixer circuit blocks incorporate tuning knobs to enable tuning of RF metrics to ensure consistent performance and mitigate the negative effects of process, voltage, and temperature variations, aging, and damage from extreme environments such as ionizing radiation. A maximum post-healed gain greater than 30 dB, an image rejection ratio exceeding 30 dB, output third-order intercept point greater than 8 dBm, and noise figure less than 9 dB are obtained in measurement. An automated healing algorithm was developed and shown to be effective at improving the overall performance of the receiver. The receiver was fabricated in an 0.18- μm SiGe BiCMOS process with a peak fT of 150 GHz, and consumes 240-260 mA from a 4-V supply.

Chip-scale parametric amplifier with 11 dB gain at 1550 nm based on a slow-light GaInP photonic crystal waveguide

We report on a chip scale parametric amplifier based on a GaInP photonic crystal waveguide. The amplifier operates with both pump and signal in the 1550nm wavelength range and offers an on-chip gain of 11dB (5dB including the 6dB coupling losses) when pumped at only 800mW. It enables us, therefore, to incorporate the many advantages of parametric amplification within photonic chips for optical communication applications.

The Noise Performance of Electron-Multiplying Charge-Coupled Devices at X-ray Energies

Electron-multiplying charge-coupled devices (EM-CCDs) are used in low-light-level (L3) applications for detecting optical, ultraviolet, and near-infrared photons (10-1100 nm). The on-chip gain process is able to increase the detectability of any signal collected by the device through the multiplication of the signal before the output node. Thus, the effective readout noise can be reduced to subelectron levels, allowing the detection of single photons. However, this gain process introduces an additional noise component due to the stochastic nature of the multiplication. In optical applications, this additional noise has been characterized. The broadening of the detected peak is described by the excess noise factor. This factor tends to a value of √{2} at high gain (>; 100x). In X-ray applications, the situation is improved by the effect that Fano factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> has on the shot noise associated with X-ray photon detection ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> ≈ 0.12 at X-ray energies). In this paper, the effect of the detection of X-ray photons in silicon is assessed both analytically and through a Monte Carlo model of the gain amplification process. The excess noise on the signal is predicted (termed the modified Fano factor) for photon detection in an EM-CCD at X-ray energies. A hypothesis is made that the modified Fano factor should tend to 1.115 at high levels of gain (>; 10x). In order to validate the predictions made, measurements were taken using an <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">55</sup> Fe source with Mn k-alpha X-ray energy of 5898 eV. These measurements allowed the hypothesis to be verified.

Influence du profil tabagique sur le sevrage

Thanks to the electron multiplying function that can effectively convert the weak incident photon signal to amplified electron output, electron multiplying charged-coupled devices (EMCCDs) are becoming useful and popular detectors in photon counting regimes necessitating also spatial resolution. A multi-imaging strategy has been already proposed and experimentally tested to improve the accuracy of photon counting with an EMCCD, by taking into account the random nature of its on-chip gain and the possibility of multiple photodetection events on 1 pixel. In this paper, referring to the thresholding procedure developed for photon counting, we present a clear graphical method for the threshold and the optimal light level estimations. Thanks to the graphical visualization of the probabilities involved in the detection errors on 1 pixel, we are able to derive in a straightforward way and for any EMCCD, the threshold level and thus the best mean level of illumination to be used in order to minimize the false detection probabilities that might ruin the image statistics, especially in cases where quantum spatial effects might be observed.

50 dB parametric on-chip gain in silicon photonic wires

A pulsed mid-infrared pump at λ=2173 nm is used to demonstrate wideband optical parametric gain in a low-loss 2 cm long silicon photonic wire. Using dispersion engineering to obtain negative second-order (β2) and positive fourth-order (β4) dispersion, we generate broadband modulation instability and parametric fluorescence extending from 1911 nm-2486 nm. Using a cw probe signal to interrogate the modulation instability spectrum, we demonstrate parametric amplification >40 dB with an on-chip gain bandwidth wider than 580 nm, as well as narrowband Raman-assisted peak gain >50 dB.

Graphical thresholding procedure and optimal light level estimation for spatially resolved photon counting with EMCCDs

Thanks to the electron multiplying function that can effectively convert the weak incident photon signal to amplified electron output, electron multiplying charged-coupled devices (EMCCDs) are becoming useful and popular detectors in photon counting regimes necessitating also spatial resolution. A multi-imaging strategy has been already proposed and experimentally tested to improve the accuracy of photon counting with an EMCCD, by taking into account the random nature of its on-chip gain and the possibility of multiple photodetection events on 1 pixel. In this paper, referring to the thresholding procedure developed for photon counting, we present a clear graphical method for the threshold and the optimal light level estimations. Thanks to the graphical visualization of the probabilities involved in the detection errors on 1 pixel, we are able to derive in a straightforward way and for any EMCCD, the threshold level and thus the best mean level of illumination to be used in order to minimize the false detection probabilities that might ruin the image statistics, especially in cases where quantum spatial effects might be observed.

A Fully Differential Rail-to-Rail CMOS Capacitance Sensor With Floating-Gate Trimming for Mismatch Compensation

This paper presents a fully differential capacitance sensor employing the CBCM technique to map differential input capacitances into rail-to-rail differential output voltages. The circuit has been designed for measuring capacitances in the plusmn25-fF range, appropriate for sensing live cells using on-chip microelectrodes. An array architecture based on a shielded current routing bus has been developed for incorporating the capacitance measurement circuit into sensor arrays, with each pixel comprising four minimum-size digital transistors, enabling high-density integration. In addition to improving spatial resolution, the shielded current bus also eliminates the need for individual pixel calibration, conserves sensor evaluation speed, and provides protection from junction leakage. The sensor employs a 3-phase clocking scheme that enables on-chip gain tuning. The paper also presents a modified version of the sensor circuit incorporating floating-gate transistors for mismatch compensation and output offset cancellation, performed using a combination of impact-ionized channel hot electron injection and Fowler-Nordheim tunneling mechanisms. Chips comprising both versions of the sensor circuits in test arrays employing the shielded current routing bus were fabricated in a commercially available 2-poly, 3-metal, 0.5-mum CMOS process. The sensor operation was demonstrated by measuring on-chip test capacitances comprising single and interdigitated metal electrodes, configured using different capacitance compensation schemes. The differential sensor in combination with the shielded current bus exhibits a maximum sensitivity of 200 mV/fF, a resolution of 15 aF, and an output dynamic range of 65 dB.

Er–Yb Waveguide Amplifiers in Novel Silicate Glasses

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A set of novel silicate glasses containing ZnO and co-doped with <formula formulatype="inline"><tex>${\hbox {Er}}^{3+}$</tex></formula> and <formula formulatype="inline"><tex>${\hbox {Yb}}^{3+}$</tex></formula> was designed as substrates for optical waveguide amplifiers. Characterized by exceptionally low up-conversion, minimum Er concentration quenching and high mechanical as well as chemical stability, the reported glasses can compete with phosphate-based materials typically used in the state-of-art active devices. Straight channel waveguides with propagation losses as low as 0.18 dB/cm were fabricated in these substrates using <formula formulatype="inline"><tex>${\hbox {Ag}}^{+} \Leftrightarrow {\hbox {Na}}^{+}$</tex></formula> and <formula formulatype="inline"> <tex>${\hbox {K}} ^{+} \Leftrightarrow {\hbox {Na}}^{+}$</tex></formula> thermal ion exchange. Net on-chip gain values of 6.7 dB at 1537 nm were measured and a net fiber to-fiber gain of 5 dB was achieved when pumped at 976 nm. A six-level spatially resolved numerical model of an Er–Yb co-doped active waveguide was developed to analyze and optimize the amplifier performance. Modification of the rare-earth dopant concentration and the channel waveguide geometry was proposed to increase the gain figure and improve the overall amplifier efficiency. </para>

A Build-in Self-Test Technique for RF Low-Noise Amplifiers

A built-in self-test (BIST) technique suitable for RF low-noise amplifiers (LNAs) is presented in this paper. With fully integrated amplitude detectors and logarithmic amplifiers, the BIST module can be employed as a generic platform for gain extraction of the device-under-test (DUT) without expensive testing instruments, while maintaining a reasonable hardware overhead and minimum loading effects to the DUT. Using a 0.18-mum CMOS process, a 5-GHz variable-gain LNA with the proposed BIST module is implemented. Based on the experimental results, on-chip gain extraction of the LNA has been demonstrated with an error less than 1 dB for various gain modes. The additional chip area required for the BIST functionality measures 0.042 mm2, which is considerably small compared with the physical size of the RF amplifiers.

Multi-imaging and Bayesian estimation for photon counting with EMCCDs

A multi-imaging strategy is proposed and experimentally tested to improve the accuracy of photon counting with an electron multiplying CCD (EMCCD), by taking into account the random nature of its on-chip gain and the possibility of multiple photodetection events on one pixel. This strategy is based on Bayesian estimation on each image, with a priori information given by the sum of the images. The method works even for images with large dynamic range, with more improvement in the low light level areas. In these areas, two thirds of the variance added by the EMCCD in a conventional imaging mode are removed, making the physical photon noise predominant in the detected image.

EMCCD Camera Technology Advances

Several years ago, Photometrics' introduction of the first electron-multiplying CCD (EMCCD) cameras designed for microscopy enabled life science researchers to detect ultra-low-light signals via on-chip multiplication gain. Since the advent of EMCCDs, camera manufacturers have focused their R&D efforts on areas that offer the most room for improvement of such devices, including bias and EM gain stability as well as sensor aging. Here we highlight the development of a new imaging platform that provides a greater capacity to control EMCCDs, thus allowing biological researchers to quantitatively measure low-light signals with extremely high fidelity. Advantages in high-speed measurement of a calcium ratiometric time-course application are demonstrated.

A CCD-based detector for SPECT

We are investigating the use of a CCD for high-resolution radionuclide imaging. The use of a CCD has the potential to provide very high spatial resolution on the order of 200 to 400 /spl mu/m, while significantly simplifying the readout electronics. The detector is based on a special CCD with on-chip multiplication gain that allows high-speed operation while maintaining the read noise at a very low level of <1 electron. To achieve high detection efficiency and excellent spatial resolution for incident gamma flux, a specially fabricated thick microcolumnar CsI(Tl) scintillator was optically coupled to the CCD. A prototype SPECT imaging system was assembled by incorporating pinhole/parallel hole collimators in the design. The use of this system for radionuclide imaging has been demonstrated through tomographic imaging of a test phantom filled with /sup 99m/Tc.

Performance comparison of GaInNAs vertical-cavity semiconductor optical amplifiers

This paper reports on theoretical and experimental investigations of the influence of the number of GaInNAs quantum wells (QWs) on performance of 1.3-/spl mu/m vertical-cavity semiconductor optical amplifiers (VCSOAs). Full characterization is carried out for two optically pumped VCSOAs with 6 and 15 QWs in the active layer. The 15-QW amplifier is found to be more efficient for amplification purposes but the highest gain to date was obtained for a 6-QW GaInNAs VCSOA, 19-dB on-chip gain in single-mode operation, having a top mirror reflectivity of 97.7%. At high-gain and for low enough reflectivity, the intrinsic noise figure is smaller than 5 dB.

1.3-μm GaInNAs surface-normal devices

The compatibility of GaInNAs/GaAs active regions with AlGaAs Bragg mirror technology opens up a range of surface-normal device formats for the spectral region around 1.3 μm. The authors report recent progress on the development of diode-pumped vertical external-cavity surface emitting lasers (VECSELs) and vertical cavity semiconductor optical amplifiers (VCSOAs) based on this technology. Pertinent performance characteristics are reported for GaInNAs 1.3-μm VECSELs capillary-bonded to diamond heatspreader platelets. In a conventional three-mirror air-spaced laser cavity up to 0.6 W of TEM00 output power was obtained. With the outer surface of the diamond platelet coated to form a dielectric output coupler mirror, it was possible to obtain the first monolithic microchip operation of a GaInNAs VECSEL, where a Gaussian beam with output power up to 120 mW was obtained. The influence of temperature on the performance of a six-quantum-well VCSOA with on-chip gain values of up to 16 dB was also reported. It reveals that on-chip gain of 9 dB can be achieved over a range of 85°C, allowing the amplifier characteristics to be tuned over more than 9.5 nm. Further investigations of the influence of optical feedback on the performance of these vertical amplifiers demonstrate that a three-mirror analysis explains the observed phenomena.

Long-wavelength monolithic GaInNAs vertical-cavity optical amplifiers

We report on the continuous-wave amplification characteristics of an optically pumped 1.3-/spl mu/m multiple-quantum-well GaInNAs-GaAs vertical-cavity semiconductor optical amplifier (VCSOA). The VCSOA structure was monolithically grown by molecular beam epitaxy and operated in reflection mode in a fiber-coupled system. The maximum on-chip gain attained, limited by the onset of laser action, was 15.6 dB at 196 mW of 980-nm pump power. For a chip gain of 10.4 dB, the optical bandwidth was 10.8 GHz and the saturation output power was -9 dBm. By varying the pump laser power, a maximum extinction ratio of 22.3 dB was obtained. Temperature-controlled tuneable operation of the device is also presented and demonstration of 9 dB of chip gain obtained over 9.5 nm with an optical bandwidth of 12 GHz is reported.

Photon counting strategies with low-light-level CCDs

Low light level charge coupled devices (L3CCDs) have recently been developed, incorporating on-chip gain. They may be operated to give an effective readout noise much less than one electron by implementing an on-chip gain process allowing the detection of individual photons. However, the gain mechanism is stochastic and so introduces significant extra noise into the system. In this paper we examine how best to process the output signal from an L3CCD so as to minimize the contribution of stochastic noise, while still maintaining photometric accuracy. We achieve this by optimising a transfer function which translates the digitised output signal levels from the L3CCD into a value approximating the photon input as closely as possible by applying thresholding techniques. We identify several thresholding strategies and quantify their impact on photon counting accuracy and effective signal-to-noise. We find that it is possible to eliminate the noise introduced by the gain process at the lowest light levels. Reduced improvements are achieved as the light level increases up to about twenty photons per pixel and above this there is negligible improvement. Operating L3CCDs at very high speeds will keep the photon flux low, giving the best improvements in signal-to-noise ratio.

Low light level CCDs and visibility parameter estimation

Recently, low light level charge-coupled devices (L3CCDs) capable of on-chip gain have been developed, leading to subelectron effective readout noise, allowing for the detection of single photon events. Optical interferometry usually requires the detection of faint signals at high speed and so L3CCDs are an obvious choice for these applications. Here we analyse the effect that using an L3CCD has on visibility parameter estimation (amplitude and triple product phase), including situations where the L3CCD raw output is processed in an attempt to reduce the effect of stochastic multiplication noise introduced by the on-chip gain process. We establish that under most conditions, fringe parameters are estimated accurately, whilst at low light levels, a bias correction which we determine here may need to be applied to the estimate of fringe visibility amplitude. These results show that L3CCDs are potentially excellent detectors for astronomical interferometry at optical wavelengths.

A WDM receiver photonic integrated circuit with net on-chip gain

We demonstrate a photonic circuit with an optical preamplifier, a WDM filter and a fast photodetector integrated on the same chip. The passive integrated filter is formed by an aspheric waveguide lens and a planar Bragg grating. This arrangements yields narrow filter response (8 /spl Aring/ width at -3 dB is demonstrated) and high rejection ratio of 24 dB. The optical preamplifier consisting of strained multi-quantum well layers provides sufficient amplification to overcome the passive losses. Response curves demonstrate net on-chip gain with low ripple.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>