CAMERA TEMPORAL DARK NOISE PC

The system noise characteristics for a typical iDus вЂ“ BRDD CCD camera are shown in figure 1. The various sources of noise may be added in quadrature to give the overall system or camera noise which may be expressed as: Usually a high performance camera is operated at certain temperatures and clocking speeds such that the detection limit is determined by the readout noise.

CAMERA TEMPORAL DARK NOISE PC

Readout Noise (NRN) вЂ“ this arises in the readout electronics before the digitized signal is sent to the PC and may be reduced by using lower readout rates and clean clocking pulses.Clock Induced Charge Noise (NCIC) вЂ“ spurious noise generated during the clocking of the pixels when moving the charge out of the sensor this is minimised by implementation of fine tuned and well controlled clocking voltages, in particular fine control over clocking edges down to nanosecond resolutions.Dark noise (NDN) вЂ“ associated with the thermally generated dark current NDN =v(DC.t) вЂ“ where вЂtвЂ™ corresponds to the exposure time: dark current (DC) is reduced by cooling of sensor.Signal Shot Noise (NSN) вЂ“ fundamentally intrinsic to any signal NSN = vS = v(QE.P).The sources of noise and the means of dealing with them are summarized below: Next to consider is the system or camera noise which has three main contributors, the dark current (DC) of the sensor, spurious charge such as clock induced charge (CIC), and the readout noise from the output electronics (pre-amp and A/D node). If the number of photons in the incident signal is denoted by P and the quantum efficiency by QE, the photoelectron signal generated will be given by S = (QE.P). Shot noise within the photon generated (electronic) signal (S) is an intrinsic contribution to the overall noise and is related to fundamental quantum physics it will always be part of any signal. The next key challenge is reducing the overall noise to its minimum (the latter is often referred to as the noise floor). Micro-lenses вЂ“ more relevant to imaging sensors than Spectroscopy вЂ“ allows more light to be collected into the sensitive area of the sensor leading to an increase in the fill-factor.Lumogen coatings вЂ“ to enhance the sensitivity in the UV region by the absorption and conversion of UV photons to visible photons which are more readily detected by the CCD.Deep-depletion вЂ“ where the active layer is increased in extent to increase probability of absorption of photons in the nearinfrared (NIR) part of the spectrum.Anti-reflection coatings вЂ“ optimised for the particular wavelength region of interest.Back Illumination вЂ“ where the sensor is back-thinned and the light is delivered through the back making it easier for the incident photons to reach and be absorbed in the active layer of the sensor.Various means have been employed to improve the quantum efficiency of CCD sensors. QE is a wavelength or photon energy dependent function, and a sensor is generally chosen which has the highest QE in the wavelength region of interest. QE is usually expressed as a probability вЂ“ typically given in percentage format вЂ“ where for example a QE of 0.6 or 60% indicates a 60% chance that a photoelectron will be released for each incident photon. Clearly the greater the number of photoelectrons produced for a given photon signal the higher the QE. Quantum Efficiency (QE) is related to the ability of the sensor to respond to the incoming photon signal and the conversion of it to a measurable electron signal. The approach to ensure the best possible SNR ratio is to a) develop a sensor with the highest possible quantum efficiency and b) reduce the various sources of noise to a minimum. This encapsulates the capacity to have the signal stand out from the surrounding noise.ДЇigure 1: The detection limit as a function of exposure time for single pixel (imaging mode) which are read out at 33 kHz with readout noise of 4.6 electrons. When assessing the sensitivity of any CCD sensor it is the achievable Signal-to-Noise Ratio (SNR) which is of key importance. Sensitivity is a key performance feature of any detection system. Assessing CCD Sensitivity Camera Sensitivity

Camera temporal dark noise