The Difference between CCD and CMOS

CCD: (Charge Coupled Device), charge coupled device image sensor

The charge is transferred between pixels in sequence, and finally concentrated in the series register, converted into a voltage signal, then amplified, and converted into a digital signal after analog-to-digital conversion.

CMOS: (Complementary Metal-Oxide Semiconductor) Complementary Metal-Oxide Semiconductor

Each pixel has an independent node, which is converted into a voltage signal, then amplified, and converted into a digital signal after analog-to-digital conversion.

1.Different imaging process

Since CCD has only one (or a few) output nodes for unified readout, the consistency of its signal output is very good; in CMOS chips, each pixel has its own signal amplifier, each pixel has its own charge-voltage conversion, and the consistency of signal output is poor.

2.Different integration

CCD can only output analog electrical signals, which require subsequent address decoders, analog converters, and image signal processors for processing. It also needs to provide three sets of power synchronization clock control circuits with different voltages, and the integration is very low. CMOS chips can integrate image signal amplifiers, signal reading circuits, A/D conversion circuits, image signal processors, and controllers into the chip. Only one chip is needed to realize all the basic functions of the camera, and the integration is very high.

3.Different speeds

CCD uses photosensitive output and can only output according to the specified program, which is slow; CMOS is controlled by multiple charge-voltage converters and row and column switches, and the readout speed is much faster. Most of the above-mentioned high-speed cameras with 500fps are CMOS cameras.

4.Different noise

CCD technology developed earlier and is relatively mature. It uses PN junction or silicon dioxide (SiO2) isolation layer to isolate noise. The imaging quality has certain advantages compared with CMOS photoelectric sensors. Due to the high integration of CMOS image sensors, the distance between components and circuits is very close, the interference is serious, and the noise has a great impact on image quality.

5.Power consumption

CCD requires three power supplies to meet the needs of special clocks, and the power consumption is relatively high.

CMOS only needs one power supply, and the power consumption is only 1/10 of that of CCD.