The image sensor is a device that converts optical signals into electrical signals, and it is widely used in the digital television and the visual communication market. In the late 1960s, Bell Laboratory in the US discovered the phenomenon of charge transfer through semiconductor potential wells and proposed a new concept of solid-state imaging and a one-dimensional CCD (Charge-Coupled Device) model device. By the early 1990s, CCD technology has been relatively perfect and has been widely used.
However, the shortcomings of CCD are gradually exposed with the expansion of the application range. Firstly, the chip technology process of CCD is complicated and cannot be compatible with the standard process. Secondly, the CCD technology chip is expensive and inconvenient to use because it requires high voltage and power consumption.
At present, the most eye-catching and promising technique is to use the standard CMOS(Complementary Metal Oxide Semiconductor) technology to produce image sensors, which is the CMOS image sensor. The CMOS image sensor chip adopts the CMOS technology so that it can integrate the image acquisition unit and the signal processing unit on the same chip.Based on the characteristics mentioned above, it is suitable for mass production and application that require small size and low prices without high cameras quality requirements, such as small security cameras, miniature cameras, mobile phones, computer network video conferencing systems, wireless handheld video conference system, barcode scanners, fax machines, toys, biological microscope counting, car camera systems and a large number of commercial fields.
The image sensor CMOS is a typical solid imaging sensor, and it has a common history with CCD. In general, CMOS image sensors are composed of the image sensitive unit array, row driver, column driver, timing control logic, AD converter, data bus output interface, control interface, etc., and these parts are usually integrated on the same silicon chip. The working process usually can be divided into reset, photoelectric conversion, integration, and readout.
The CMOS image sensor chip can also be integrated with other digital signal processing circuits, such as AD converter, automatic exposure control, non-uniform compensation, white balance processing, black level control, gamma correction, etc. Even DSP devices with programmable functions can be integrated with CMOS devices in order to have fast calculation, so as to form a single-chip digital camera and image processing system.