The drive for full-screen smartphones has accelerated the adoption of under-display sensor technology. As screen sizes continue to increase and screen-to-body ratios improve, the demand for higher precision and sensitivity in optical sensors has boosted. Full-screen designs, particularly those offering vibrant color clarity and features of intelligent mode, require sensors capable of maintaining accurate performance under various lighting conditions.

The self-emissive property of OLEDs, which do not require a backlight layer, provides an ultra-low optical transmittance, making the implementation of under-display sensor technology possible. In recent years, leading smartphone brands have increasingly adopted under-display optical sensor technology to meet these new demands.

Under-display sensor technology seamlessly integrates sensors with the screen, enhancing the smartphone's perception and interaction capabilities without modifying its appearance or user operation. This technology is widely applied in areas such as under-display ambient light, color temperature, and proximity detections, providing users with a more intelligent and secure smartphone experience. However, as display technology rapidly advances, the demands of under-display optical sensing technology continue to grow. The key challenge is to maintain precise sensor performance while optimizing screen transparency and reducing power consumption. 

Maxic has introduced MT3321, an ultra-sensitive color temperature and proximity sensor designed specifically for OLED under-display applications. This chip fits seamlessly under the screen and incorporates three functions—ambient light, color temperature, and proximity detection—into one. MT3321 is available in compact OLGA package with dimensions of 3.32mm x 1.7mm x 0.6mm, which can meet the requirements of full screen applications and perfect for smartphones, smartwatches, fitness trackers, and other smart devices. It also has a low-power mode to extend battery life and advanced ambient light subtraction and multi-channel independent parallel triggering and sampling logic techniques to ensure accurate light, color temperature and proximity detection.

Features

• Advanced coating technology, including CRGBW five ambient light detection channels and a dedicated IR detection channel

• Excellent SNR and sensitivity, with ambient light sensitivity less than 0.00001 lux/lsb, compatible with OLED displays with a transmittance <0.5%

• Capable of driving up to 4 independently controllable VCSEL power sources

• Supports 1.8V/1.2V I/O voltage for enhanced compatibility

• Supports synchronous refresh and sampling with the screen 

MT3321 Block Diagram

Technical Highlights

MT3321 integrates infrared sensing technology to accurately detect distance by controlling an external near-infrared VCSEL, which emits and detects reflected infrared energy. This enables recognition of user movements, such as the movement of smartphone. During calls, it automatically controls screen off function, reducing accidental touches and saving power, thus extending battery life.

Equipped with a high-precision photodiode array, MT3321 processes optical signals through a dedicated ADC, enabling precise, real-time measurement of ambient light intensity and color temperature. After getting the processed information, application system adjusts screen brightness and color temperature for best visual experience.

Based on dedicated process, MT3321 integrates advanced photodiodes, specialized coatings, low-noise high-gain sensitive amplifiers and sophisticated signal process algorithms, providing optical solutions with ultra-high sensitivity and SNR to the customers.