Lateral Electric Field Charge Modulator Research Articles

Resolving Multi-Path Interference in Compressive Time-of-Flight Depth Imaging with a Multi-Tap Macro-Pixel Computational CMOS Image Sensor.

Multi-path interference causes depth errors in indirect time-of-flight (ToF) cameras. In this paper, resolving multi-path interference caused by surface reflections using a multi-tap macro-pixel computational CMOS image sensor is demonstrated. The imaging area is implemented by an array of macro-pixels composed of four subpixels embodied by a four-tap lateral electric field charge modulator (LEFM). This sensor can simultaneously acquire 16 images for different temporal shutters. This method can reproduce more than 16 images based on compressive sensing with multi-frequency shutters and sub-clock shifting. In simulations, an object was placed 16 m away from the sensor, and the depth of an interference object was varied from 1 to 32 m in 1 m steps. The two reflections were separated in two stages: coarse estimation based on a compressive sensing solver and refinement by a nonlinear search to investigate the potential of our sensor. Relative standard deviation (precision) and relative mean error (accuracy) were evaluated under the influence of photon shot noise. The proposed method was verified using a prototype multi-tap macro-pixel computational CMOS image sensor in single-path and dual-path situations. In the experiment, an acrylic plate was placed 1 m or 2 m and a mirror 9.3 m from the sensor.

A Time-Resolved NIR Lock-In Pixel CMOS Image Sensor With Background Cancelling Capability for Remote Heart Rate Detection

This paper presents a time-resolved (TR) CMOS image sensor (CIS) using two-tap near-infrared (NIR) lock-in pixels with background light (BGL) cancelling capability for remote heart rate (HR) detection. Aimed to the application, the sensor features a 1024 (V) $\times $ 1280 (H) spatial resolution with 412 (V) $\times $ 1280 (H) region-of-interest-readout (ROI-readout) at 30 fps, a high sensitivity of 134.8 ke−/lux $\cdot $ s, and an ultra-low temporal random noise of 1.13 $\mathrm {e}_{\mathrm {rms}}^{\mathrm {-}}$ at analog gain of 64. A maximum charge modulation ratio of 90.1% is obtained for realizing lock-in operation by means of in-pixel lateral electric field charge modulator (LEFM). The remote HR detection is achieved by capturing the heart-beat-induced temporal variation of the oxy-hemoglobin (HbO2) concentration by the developed TR CIS with NIR lock-in technique, and larger than 98% detection accuracies are attained under both non-visible-light condition and fluctuant brightness ambient-light environments. This remarkable feature demonstrates the superiority of the proposed method for driver monitoring applications in particular.

Label-Free Biomedical Imaging Using High-Speed Lock-In Pixel Sensor for Stimulated Raman Scattering.

Raman imaging eliminates the need for staining procedures, providing label-free imaging to study biological samples. Recent developments in stimulated Raman scattering (SRS) have achieved fast acquisition speed and hyperspectral imaging. However, there has been a problem of lack of detectors suitable for MHz modulation rate parallel detection, detecting multiple small SRS signals while eliminating extremely strong offset due to direct laser light. In this paper, we present a complementary metal-oxide semiconductor (CMOS) image sensor using high-speed lock-in pixels for stimulated Raman scattering that is capable of obtaining the difference of Stokes-on and Stokes-off signal at modulation frequency of 20 MHz in the pixel before reading out. The generated small SRS signal is extracted and amplified in a pixel using a high-speed and large area lateral electric field charge modulator (LEFM) employing two-step ion implantation and an in-pixel pair of low-pass filter, a sample and hold circuit and a switched capacitor integrator using a fully differential amplifier. A prototype chip is fabricated using 0.11 μm CMOS image sensor technology process. SRS spectra and images of stearic acid and 3T3-L1 samples are successfully obtained. The outcomes suggest that hyperspectral and multi-focus SRS imaging at video rate is viable after slight modifications to the pixel architecture and the acquisition system.

A 7 ke-SD-FWC 1.2 e-RMS Temporal Random Noise 128×256 Time-Resolved CMOS Image Sensor With Two In-Pixel SDs for Biomedical Applications.

A large full well capacity (FWC) for wide signal detection range and low temporal random noise for high sensitivity lock-in pixel CMOS image sensor (CIS) embedded with two in-pixel storage diodes (SDs) has been developed and presented in this paper. For fast charge transfer from photodiode to SDs, a lateral electric field charge modulator (LEFM) is used for the developed lock-in pixel. As a result, the time-resolved CIS achieves a very large SD-FWC of approximately 7ke-, low temporal random noise of 1.2e-rms at 20fps with true correlated double sampling operation and fast intrinsic response less than 500 ps at 635nm. The proposed imager has an effective pixel array of and a pixel size of . The sensor chip is fabricated by Dongbu HiTek 1P4M 0.11 CIS process.

A Lateral Electric Field charge Modulator with Bipolar-gates for Time-resolved Imaging

This paper reports high time-resolved imaging technique using a lateral electric field charge modulator with bipolar-gates. The proposed pixel structure achieved high time-resolved signal detection by using negative bias effect by work function difference between the p-type gate and p-substrate. The test chip fabricated in 0.11 um CIS technology demonstrates the high-speed charge modulation, and the modulation contrast is measured to be 97%.