Dark current is strongly influenced by temperature (Figure 1), doubling every 8 to 10 degrees Centigrade. The dynamic range of a particular CCD is dependent upon several variables. To fully utilize the potential of this CCD, a 17-bit A/D converter having 131,072 grayscale levels should be employed (although a 16-bit A/D converter having 65,536 grayscale levels would also suffice). Coupled with a readout noise root-mean-square ( rms) level of three electrons at 20 kilohertz (when cooled), the CCD39-01 is capable of yielding a dynamic range of approximately 100,000 :1.
#Analog to digital converter dynamic range full#
The full well capacity of this device can reach a level 300,000 electrons. As an example, the Marconi Applied Technologies CCD39-01 sensor is a back-illuminated, frame-transfer CCD having a square pixel size of 24 microns with a split output register allowing the utilization of quad output amplifiers. Higher performance cooled CCD sensors designed with low noise output amplifiers and suitable for use in slow-scan imaging of photomicrographs often have lower read noise and an extended dynamic range. Controlling the size of the read and dark noise is a critical factor in maintaining a high dynamic range in these devices. In order to utilize the full range of grayscale levels available with this dynamic range, the camera should have a 12-bit analog-to-digital ( A/D) converter capable of resolving 4096 gray levels. At a typical readout rate of 1 MHz, the read noise for this CCD is about 10 electrons/pixel, which yields a dynamic range of 44,900/10 or 4,490. Thus, a CCD with 6.7 x 6.7 micron photodiodes should have a maximum charge storage capacity (a full-well capacity) of about 44,900 electrons (or holes). In a high-performance cooled CCD camera, the well capacity is proportional to the size of the individual photodiode, such that the maximum number of electrons stored is about 1000 times the cross sectional area of each photodiode. Where N(sat) is the linear full well capacity stated as the number of electrons and N(noise) is the total value of the read and dark noise, also expressed as the number of electrons.
The dynamic range is expressed in decibel units according to the following equation : Read noise is usually specified in the performance data sheets that accompany a CCD sensor, with typical values ranging from 10-20 electrons/pixel in high quality chips operated at room temperature, and dropping to 2-5 electrons/pixel in Peltier-cooled CCDs for scientific imaging applications. This includes noise from input clocking and fixed pattern, along with reset transistor noise and amplifier output noise. Read noise is a combination of all noise generated during readout of the device. Typical diode sizes in modern CCDs utilized in photomicrography range from 4.5 to 24 microns with corresponding well capacities of 20,000 to 600,000 electrons. Photodiode size determines, in part, the size of the depletion wells-larger diodes having greater full-well capacity compared to camera noise. The interscene dynamic range represents the spectrum of intensities that can be accommodated when detector gain, integration time, lens aperture, and other variables are adjusted for differing fields of view. As the dynamic range of a device is increased, the ability to quantitatively measure the dimmest intensities in an image (intrascene performance) is improved. The dynamic range of a charge-coupled device ( CCD) or complementary metal oxide semiconductor ( CMOS) image sensor is typically specified as the maximum achievable signal divided by the camera noise, where the signal strength is determined by the full-well capacity, and noise is the sum of dark and read noises. The ADS5422 is available in an LQFP-64 package.Concepts in Digital Imaging Technology Dynamic Range.A lower input voltage can also be selected using the internal references, further optimizing SFDR. The differential operation gives the lowest even-order harmonic components. 2 inputs) for optimum Spurious-Free Dynamic Range (SFDR).