Questions on Sensors

Why do we choose CMOS in 3D camera instead of CCD?

Advantages of CMOS over CCD:

  1. Strong integration
    The CMOS chip can integrate the image signal amplifier, signal reading circuit, A/D conversion circuit, image signal processor and controller into one chip, and only one chip can realize all the basic functions of the camera, with a high degree of integration . The CCD manufacturing process is complicated, and only a few manufacturers can produce CCD wafers. CCD can only output analog electrical signals, which requires subsequent address decoders, analog converters, image signal processors, and three sets of different Voltage power supply synchronous clock control circuit with very low integration.
  2. Fast operation speed
    The CCD charge coupler needs to output information bit by bit under the control of the synchronous clock, and the speed is relatively slow; while the CMOS photoelectric sensor can take out the electrical signal while collecting the optical signal, and can also process the images of each unit at the same time Information, the speed is much faster than the CCD charge coupler.
  3. Easy to read information
    The charge information stored by the CCD charge coupler needs to be read after the transfer is carried out bit by bit under the control of the synchronous signal. The charge information transfer and read output need to be coordinated with a clock control circuit and three different power supplies. The whole circuit is relatively complex. The CMOS photoelectric sensor directly generates a current (or voltage) signal after photoelectric conversion, and the signal reading is very simple.
  4. Lower production cost
    The CMOS structure is relatively simple, which is the same as the existing large-scale integrated circuit production process, so that the production cost can be reduced. Although the CMOS process is not yet very mature, advanced CMOS is no worse than CCD.
  5. Low static power consumption
    The main advantage of CMOS for CCD is that it is very power-saving. Unlike CCD composed of diodes, CMOS circuits have almost no static power consumption, and only power consumption occurs when the circuit is turned on. This makes the power consumption of CMOS only about 1/3 of that of ordinary CCD.

Disadvantages of CMOS compared to CCD:

  1. The image quality is poor and the noise influence is great
    CCD charge coupler manufacturing technology started early and is mature. It uses PN junction or silicon dioxide (SiO2) isolation layer to isolate noise. Compared with CMOS photoelectric sensor, the imaging quality has certain advantages. 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. However, in recent years, with the continuous development of CMOS circuit noise elimination technology, good conditions have been provided for the production of high-density and high-quality CMOS image sensors.

Summary: For NIR imaging applications or other applications that require extremely high image quality, choose a CCD sensor; otherwise, a CMOS sensor with similar performance and cheaper cost may make the most sense.