This paper introduces a new series of time-of-flight (TOF) range image sensors that can be used for outdoor middle-range (10m to 100m) applications by employing a small duty-cycle modulated light pulse with a relatively high optical peak power. This set of TOF sensors is referred to here as a hybrid TOF (hTOF) image sensor. The hTOF image sensor is based on the indirect TOF measurement principle but simultaneously uses the direct TOF concept for coarse measurements. Compared to conventional indirect TOF image sensors for outdoor middle-range applications, the hTOF image sensor has a distinct advantage due to the reduction of capturing ambient light charge. To show the potential of the hTOF image sensor for outdoor middle-range operation, a model of estimating distance precision of hTOF image sensors is built and applied it by using possible sensor specifications to estimate the distance precision of the hTOF range camera in 10m, 20m and 40m measurements under the ambient-light condition of 100klux and its feasibility is discussed. In outdoor 10m-range measurements, the advantage of hTOF image sensors compared to the conventional indirect TOF image sensors is discussed by considering the amount of captured ambient-light charge in pixels.

A complementary metal-oxide semiconductor (CMOS) lock-in pixel to observe stimulated Raman scattering (SRS) using a high speed lateral electric field modulator (LEFM) for photo-generated charges and in-pixel readout circuits is presented. An effective SRS signal generated after the SRS process is very small and needs to be extracted from an extremely large offset due to a probing laser signal. In order to suppress the offset components while amplifying high-frequency modulated small SRS signal components, the lock-in pixel uses a high-speed LEFM for demodulating the SRS signal, resistor-capacitor low-pass filter (RC-LPF) and switched-capacitor (SC) integrator with a fully CMOS differential amplifier. AC (modulated) components remained in the RC-LPF outputs are eliminated by the phase-adjusted sampling with the SC integrator and the demodulated DC (unmodulated) components due to the SRS signal are integrated over many samples in the SC integrator. In order to suppress further the residual offset and the low frequency noise (1/f noise) components, a double modulation technique is introduced in the SRS signal measurements, where the phase of high-frequency modulated laser beam before irradiation of a specimen is modulated at an intermediate frequency and the demodulation is done at the lock-in pixel output. A prototype chip for characterizing the SRS lock-in pixel is implemented and a successful operation is demonstrated. The reduction effects of residual offset and 1/f noise components are confirmed by the measurements. A ratio of the detected small SRS to offset a signal of less than 10⁻⁵ is experimentally demonstrated, and the SRS spectrum of a Benzonitrile sample is successfully observed.

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.

This paper presents a time-of-flight image sensor based on 8-Tap P-N junction demodulator (PND) pixels, which is designed for hybrid-type short-pulse (SP)-based ToF measurements under strong ambient light. The 8-tap demodulator implemented with multiple p-n junctions used for modulating the electric potential to transfer photoelectrons to eight charge-sensing nodes and charge drains has an advantage of high-speed demodulation in large photosensitive areas. The ToF image sensor implemented using 0.11 µm CIS technology, consisting of an 120 (H) × 60 (V) image array of the 8-tap PND pixels, successfully works with eight consecutive time-gating windows with the gating width of 10 ns and demonstrates for the first time that long-range (>10 m) ToF measurements under high ambient light are realized using single-frame signals only, which is essential for motion-artifact-free ToF measurements. This paper also presents an improved depth-adaptive time-gating-number assignment (DATA) technique for extending the depth range while having ambient-light canceling capability and a nonlinearity error correction technique. By applying these techniques to the implemented image sensor chip, hybrid-type single-frame ToF measurements with depth precision of maximally 16.4 cm (1.4% of the maximum range) and the maximum non-linearity error of 0.6% for the full-scale depth range of 1.0–11.5 m and operations under direct-sunlight-level ambient light (80 klux) have been realized. The depth linearity achieved in this work is 2.5 times better than that of the state-of-the-art 4-tap hybrid-type ToF image sensor.

Multitap CMOS image sensors offer the capability of programmable exposure patterns. This paper proposes a method to extend the dynamic range by changing the duty cycle of the exposure for each tap. Unlike the overflow method, the proposed approach does not require any large in-pixel capacity. It also allows for dynamic range adjustment during operation, similar to the multi-exposure method, while significantly reducing motion artifacts and LED flicker. The maximum dynamic range of the proposed method is determined by factors such as reset noise, read noise, and shutter efficiency of the sensor. In this work, we demonstrated the extension of the dynamic range up to 110.1 dB with a four-tap ToF CMOS image sensor.

This article proposes a CMOS lock-in pixel image sensor aiming for time-resolved near-infrared spectroscopy (TR-NIRS). The pixel employs lateral electric field charge modulation (LEFM) with an eight-tap multisimultaneous gate structure and negative substrate bias. The optimization of pixel structure creates a high potential slope with no barrier to facilitate the high-speed photo-generated charge transfer required in the time-resolved application. The sensor employs a two-stage charge transfer architecture with pinned storage diodes (SDs). The effectiveness of the sensor is demonstrated through simulations and experimental measurements. A prototype sensor with 70 (V) $\times110$ (H) effective pixels to characterize the multisimultaneous gate lock-in pixel is implemented in a 0.11- $\mu \text{m}$ 1-poly-4-metal CMOS image sensor (CIS) technology. A fast intrinsic response of 240 ps is achieved using an 80-ps pulsewidth 780-nm laser diode by the characterization using two simultaneous gates and a single time window of the lock-in pixel. Performance evaluation using silicon phantoms and further measurement with a rat demonstrates the feasibility of the proposed sensor and setup for TR-NIRS applications.