1. Field of the Invention
This invention relates generally to charge coupled devices (CCDs), MOS, and other pixel sensor arrays, cameras, controllers, imaging systems, and methods of controlling and operating the same. The invention is directed to a controller and camera system having a modularized architecture making it extensible to all known types of CCDs and other pixel sensor arrays. The present invention is particularly well suited for use in scientific imaging applications such as adaptive optics, wavefront sensing, interferometry, fringe tracking, and neuroscience research. The small form factor with remote head of the present invention also makes the system ideally suited to microscopy applications, applications with limited space near the optical path, and applications sensitive to thermal disturbance.
2. Description of the Related Art
CCDs (Charge Coupled Devices) are semiconductor imaging devices that are essentially an array of photo-sensitive capacitors controlled by a grid of wires. Bias voltages are used to power the device and clock voltages are used to move the charge through the device. Frame transfer CCDs have an image array and one or more serial registers. The image accumulates as photo-electrons are generated by light incident on the device. A shutter is generally employed to prevent streaking while the image is transferred to the serial register(s) through which the pixels are shifted out to an output driver one pixel at a time. Frame storage CCDs also have an image (frame) store, lessening the requirement for a shutter. Interline CCDs are similar, but have a storage pixel for each image pixel within the image array. The storage pixels, however, take up space within the image and they therefore result in the disadvantage of the image pixels not being contiguous.
A CCD camera is generally comprised of a CCD and a CCD controller. They are frequently housed in the same enclosure, especially in consumer applications, but are also commonly housed separately in high performance and specialty applications. The CCD controller provides the bias voltages, the clock voltages, output driver(s), and must clock the CCD in a manner that achieves image integration and readout. In the case of digital cameras, the analog voltage(s) from the output(s) must also be digitized.
There are many parameters that must be considered when evaluating the performance of a CCD or a CCD camera. These include CCD well depth (the number of electrons that can be stored in each pixel); the readnoise (a fundamental property of the CCD output amplifier which is frequency dependent); the dark current noise (a fundamental property of the bulk silicon, which is temperature dependent); the pixel rate (the frequency at which the pixels are output); the frame rate and the frame size.
There are many CCD camera designs extant in the consumer and scientific domains. Consumer CCD camera design choices are generally influenced by consumer-driven ideals of attractive appearance and acceptable performance, and scientific CCD cameras are generally designed with a specific application in mind and support a limited number of CCDs in a single form factor. Consumer grade CCDs and CCD cameras typically strive to deliver the highest resolution image at an acceptable visual quality. Scientific CCD cameras are typically designed to minimize readnoise at a desired readout rate while maximizing dynamic range.
Many of the technologies used in prior art cameras are becoming obsolete. One of the major disadvantages of the prior art is the difficulty in achieving the very highest performance in terms of small form factor, high frame rate and low readnoise with a variety of different CCDs due to the diversity of CCD input and output requirements.