CMOS

Complementary Metal Oxide Semiconductor

CCD

Charge-Coupled Device

1. Imaging Process

The principle of photoelectric conversion CMOS VS CCD image sensors is the same. The main difference between them is that the readout process of the signal is different.

The CCD has only one (or a few) output nodes to read out uniformly, the consistency of its signal output is very good. In the CMOS chip, each pixel has its own signal amplifier, which performs charge-voltage conversion, and the consistency of its signal output is poor. However, in order to read out the entire image signal. the CCD requires a wide signal bandwidth of the output amplifier. In a CMOS chip, the bandwidth requirement of the amplifier in each pixel is low, which greatly reduces the power consumption of the chip. This is the main reason CMOS has lower power consumption than CCD. Despite the reduced power consumption, the inconsistency of the multi-million amplifiers results in higher stationary noise, again an inherent disadvantage of CMOS over CCD.

2. Integration

From the point of view of the manufacturing process, the circuits and devices in CCD are integrated with semiconductor single-crystal material manufacturers, and the process is more complicated. Only a few manufacturers in the world can produce CCD wafers, such as DALSA, SONY, Panasonic, and so on. The CCD can only output analog electrical signals, which requires subsequent processing by address decoders, analog converters, and image signal processors. It also needs to provide three groups of power synchronous clock control circuits with different voltages, so the integration level is very low.

CMOS is integrated into a single material called metal oxide. This process is the same as the process of producing tens of thousands of semiconductor integrated circuits such as computer chips and storage devices. Therefore, the cost of producing CMOS is much lower than that of CCD. At the same time, the CMOS chip can integrate the image signal amplifier, signal reading circuit, A/D conversion circuit, image signal processor, and controller into one chip. Only one chip can realize all the basic functions of the camera, and the integration is very high. The high, chip-scale camera concept was born from this.

With the continuous development of CMOS imaging technology, more and more companies can provide high-quality CMOS imaging chips, including Micron, CMOSIS, Cypress, etc.

3. Speed

CCD adopts photosensitive output one by one, and can only output according to the specified program, and the speed is relatively slow.

CMOS cameras have the potential for higher frame rates, as the process of reading out each pixel can be done more quickly than with the charge transfer in a CCD sensor’s shift register. For digital cameras, exposures can be made from tens of seconds to minutes, although the longest exposures are only possible with CCD cameras, which have lower dark currents and noise compared to CMOS. The noise intrinsic to CMOS imagers restricts their useful exposure to only seconds.

4. Noise

CCD technology has developed earlier and is relatively mature. It uses a PN junction or silicon dioxide (SiO2) isolation layer to isolate noise, and the imaging quality has certain advantages over CMOS photoelectric sensors.

Due to the high integration of CMOS image sensors, the distance between components and circuits is very close, so there are have some interference, and the noise has a great impact on the image quality. In recent years, with the continuous development of CMOS circuit noise reduction technology, good conditions are provided for the production of high-density and high-quality CMOS image sensors.

With the advancement of CMOS image sensor technology, it has the advantages of fast imaging speed, low power consumption, and low cost. Therefore, most of the industrial cameras on the market now use CMOS image sensors.

5. Applications

There are very many applications where both types of technology are important. In general, a need for CCD technology can be seen in life science, as well as in high-end inspection applications – that is, applications where high image quality is required, such as in microscopy – but also in applications where longer exposure times play a major role. Here, CCDs can exploit their advantage of a lower dark current.

A wide range of applications is opening up for global shutter CMOS technology: From traditional automation inspection of a production line to traffic applications. We are also seeing a lot of interest in many 3D scanner applications. There, CMOS technology is preferred due to lower power consumption and often lower cost. While not impossible, it is more difficult to work with a rolling shutter for 3D scanning. Therefore, a global shutter CMOS sensor is especially worthwhile for any kind of 3D scanning application.

Different applications demand different requirements. Anyway, all that matter is to choose the right chip to assemble your product perfectly according to your own needs.