Pixel pitch is a straightforward concept. It refers to the distance from the center of one pixel to the center of an adjacent pixel, typically measured in micrometers (µm). As pixel pitch decreases, crosstalk between pixels becomes more likely.
In electronics, crosstalk is any phenomenon where a signal transmitted in one circuit or channel creates unwanted interference in another. It is usually caused by unintended capacitive, inductive, or conductive coupling between circuits. Crosstalk is a critical issue in structured cabling, audio electronics, integrated circuit design, wireless communication, and other communication systems.
In image sensors, crosstalk occurs when pixel pitch becomes smaller and electrons generated by the photoelectric effect spill over into neighboring photodiodes, introducing noise. For example, due to the arrangement of the pixel array, electrons generated by light passing through a green filter may leak into adjacent red pixels. As a result, the image signal processor receives incorrect data, leading to color noise.
Another cause is stray light entering neighboring pixels when pixel spacing is too tight, unintentionally activating adjacent pixels.
Other Sources of Noise
Noise is not caused by crosstalk alone. High ISO settings and sensor overheating can also introduce noise.
Increasing ISO effectively raises the amplifier gain, boosting both signal and noise.
Long exposures can generate thermal noise due to heat buildup in CMOS sensors. While in-camera noise reduction can mitigate this, thermal noise becomes more noticeable beyond certain exposure durations.
Common types of noise include:
Fixed pattern noise (long exposure, low ISO)
Banding noise (readout issues)
Random noise (short exposure, high ISO)
Improving Image Quality
One way to improve image quality is by increasing the number of pixels, which effectively raises resolution.
To reduce noise caused by small pixel pitch, there are generally two approaches:
Use a larger CMOS sensor to maintain a wider pixel pitch
Improve fabrication processes to isolate pixels more effectively, preventing photon and electron leakage between them
For example, introducing physical barriers or air gaps between pixels can help block stray light and electron diffusion.
Practical Constraints in Mobile Devices
In smartphones, compact size is a critical constraint. It is not feasible to use large sensors like full-frame or APS-C. Therefore, manufacturers typically adopt the second approach-enhancing pixel isolation technologies while reducing pixel pitch and increasing sensor area within limited space.
Technologies such as deep trench isolation are used to achieve this.
Advances in Sensor Technology
In recent years, improvements in CMOS noise reduction and fabrication technologies have enabled the development of high-density image sensors.
For example, Samsung's ISOCELL HP3 sensor has achieved:
0.56 µm pixel pitch
200 megapixels resolution
14-bit RAW output with high dynamic range (HDR)
Tetra²pixel (16-in-1 pixel binning technology)
These advancements support the growing demand for high-resolution, small-pixel sensors in multi-camera mobile devices.
Trade-offs of High Pixel Density
Higher pixel density allows for greater resolution, which improves detail retention during zooming and cropping.
However, there are trade-offs:
Smaller individual pixels capture less light, leading to poorer low-light performance
Increasing pixel count beyond a certain point provides diminishing returns
Another limitation comes from the lens. Once sensor resolution reaches the diffraction limit of the optical system, increasing pixel count further does not improve image quality.
