Sub-electron Read Noise Research Articles

Noise Reduction Effect of Multiple-Sampling-Based Signal-Readout Circuits for Ultra-Low Noise CMOS Image Sensors.

This paper discusses the noise reduction effect of multiple-sampling-based signal readout circuits for implementing ultra-low-noise image sensors. The correlated multiple sampling (CMS) technique has recently become an important technology for high-gain column readout circuits in low-noise CMOS image sensors (CISs). This paper reveals how the column CMS circuits, together with a pixel having a high-conversion-gain charge detector and low-noise transistor, realizes deep sub-electron read noise levels based on the analysis of noise components in the signal readout chain from a pixel to the column analog-to-digital converter (ADC). The noise measurement results of experimental CISs are compared with the noise analysis and the effect of noise reduction to the sampling number is discussed at the deep sub-electron level. Images taken with three CMS gains of two, 16, and 128 show distinct advantage of image contrast for the gain of 128 (noise(median): 0.29 e−rms) when compared with the CMS gain of two (2.4 e−rms), or 16 (1.1 e−rms).

Single Photon Counting Performance and Noise Analysis of CMOS SPAD-Based Image Sensors.

SPAD-based solid state CMOS image sensors utilising analogue integrators have attained deep sub-electron read noise (DSERN) permitting single photon counting (SPC) imaging. A new method is proposed to determine the read noise in DSERN image sensors by evaluating the peak separation and width (PSW) of single photon peaks in a photon counting histogram (PCH). The technique is used to identify and analyse cumulative noise in analogue integrating SPC SPAD-based pixels. The DSERN of our SPAD image sensor is exploited to confirm recent multi-photon threshold quanta image sensor (QIS) theory. Finally, various single and multiple photon spatio-temporal oversampling techniques are reviewed.

Determining Conversion Gain and Read Noise Using a Photon-Counting Histogram Method for Deep Sub-Electron Read Noise Image Sensors

A new method for characterizing deep sub-electron read noise image sensors is reported. This method, based on the photon-counting histogram, can provide easy, independent and simultaneous measurements of the quanta exposure, conversion gain, and read noise. This new method provides a more accurate measure of conversion gain and read noise over conventional characterization techniques for image sensors with read noise from 0.15–0.40e- rms.

Photon Counting Error Rates in Single-Bit and Multi-Bit Quanta Image Sensors

Photon or photoelectron counting error (bit error) rates are determined for single-bit and multi-bit quanta image sensors (QISs). The results are also applicable to CMOS image sensors with deep sub-electron read noise. The effects of read noise, gain variation, and quanta exposure level on the counting errors (bit errors) in a QIS device are investigated. The interaction of these factors yields complex behavior of the counting error rate. Still, photon-counting is predicted to be remarkably accurate for quanta exposures greater than unity despite read noise and conversion-gain variation, and accurate at very low-light levels if the read noise is less than 0.15e- r.m.s.

Characterization of Quanta Image Sensor Pump-Gate Jots With Deep Sub-Electron Read Noise

Characterization of quanta image sensor pixels with deep sub-electron read noise is reported. Pixels with conversion gain of $423\mu \text{V}$ /e- and read noise as low as 0.22e- r.m.s. were measured. Dark current is 0.1e-/s at room temperature, and lag less than 0.1e-. This is one of the first works reporting detailed characterization of image sensor pixels with mean signals from sub-electron (0.25e-) to a few electrons level. Such pixels in a nearly-conventional CMOS image sensor process will allow realization of photon-counting image sensors for a variety of applications.

Simulations of charge transfer in Electron Multiplying Charge Coupled Devices

Electron Multiplying Charge Coupled Devices (EMCCDs) are a variant of traditional CCD technology well suited to applications that demand high speed operation in low light conditions. On-chip signal amplification allows the sensor to effectively suppress the noise introduced by readout electronics, permitting sub-electron read noise at MHz pixel rates. The devices have been the subject of many detailed studies concerning their operation, however there has not been a study into the transfer and multiplication process within the EMCCD gain register. Such an investigation has the potential to explain certain observed performance characteristics, as well as inform further optimisations to their operation. In this study, the results from simulation of charge transfer within an EMCCD gain register element are discussed with a specific focus on the implications for serial charge transfer efficiency (CTE). The effects of operating voltage and readout speed are explored in context with typical operating conditions. It is shown that during transfer, a small portion of signal charge may become trapped at the semiconductor-insulator interface that could act to degrade the serial CTE in certain operating conditions.

Electron multiplication CCDs for astronomical applications

Electron multiplication CCDs have been commercially available for a few years but have yet to make a wider impact in the astronomical community. They have specifically been designed to use an avalanche gain process during the serial charge transfer process to give large signal gain. In all other respects they are identical to the very latest generation of low-noise CCDs. They have been used with great success in “lucky” imaging, for adaptive optics systems and also in high-speed faint object spectroscopy science programs. Their sub-electron read noise makes them an obvious choice for any observation, which is normally detector read noise limited. I present a detailed summary of the typical performance and characteristics of these devices and compare and contrast them against standard low-noise astronomical CCDs. I also present modeled and real data for these detectors with particular regard to some of their lesser known issues such as clock-induced charge. Finally, I present results from real-world astronomical testing, which shows the superior performance of these devices.

Soft X-ray spectroscopy with sub-electron readnoise charge-coupled devices

We demonstrate use of a charge-coupled device (CCD) with sub-electron readnoise performance as a non-dispersive X-ray spectrometer. The exceptionally low readnoise (0.9 electrons rms) was achieved by applying a floating gate output amplifier with 16 readouts per pixel. The soft X-ray quantum efficiency was enhanced over other front-side illuminated devices by using a novel thin-poly gate structure. The combination of sub-electron noise and good soft X-ray quantum efficiency have enabled us to detect photons in the EUV energy range ( E < 100 eV) in photon counting mode with this detector. These low energy events are well separated from the readnoise floor. The measured energy resolution is 16.3 eV (FWHM) at Al L ( E = 72 eV), 33.8 eV at C K α ( E = 277 eV) and 120 eV at Mn K α ( E = 5.9 keV).