A Time-of-Flight Range Sensor Using Four-Tap Lock-In Pixels with High near Infrared Sensitivity for LiDAR Applications

Abstract

In this paper, a back-illuminated (BSI) time-of-flight (TOF) sensor using 0.2 µm silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) technology is developed for long-range laser imaging detection and ranging (LiDAR) application. A 200 µm-thick bulk silicon in the SOI substrate is fully depleted by applying high negative voltage at the backside for higher quantum efficiency (QE) in a near-infrared (NIR) region. The proposed SOI-based four-tap charge modulator achieves a high-speed charge modulation and high modulation contrast of 71% in a NIR region. In addition, in-pixel drain function is used for short-pulse TOF measurements. A distance measurement up to 27 m is carried out with +1.8~−3.0% linearity error and range resolution of 4.5 cm in outdoor conditions. The measured QE of 55% is attained at 940 nm which is suitable for outdoor use due to the reduced spectral components of solar radiation.

An 8-Tap CMOS Lock-In Pixel Image Sensor for Short-Pulse Time-of-Flight Measurements

“…In order to expand the application areas of TOF imagers, improvements for depth resolution under aggressive conditions, such as longer distance and stronger ambient light, are necessary. Indirect TOF image sensors are classified into two types: a continuous-wave (CW) TOF method [1][2][3][4][5][6][7][8][9] and a short-pulse (SP) TOF method [10][11][12][13][14][15]. In CW-TOF imagers, the high depth resolution and longer distance measurements are simultaneously realized by using higher and multiple (2 or 3) modulation frequencies [5,8].…”

“…In CW-TOF imagers, the high depth resolution and longer distance measurements are simultaneously realized by using higher and multiple (2 or 3) modulation frequencies [5,8]. On the other hand, in the SP-TOF method, the depth resolution is improved by making the gating-time width shorter, and the distance is extended by increasing the number of signal taps of the pixel and by using range-shifting techniques [14][15][16]. For the outdoor use of TOF sensors, the SP-TOF method is more advantageous because a lower amount of ambient light charge is accumulated by using a small-duty, energy-concentrated light pulse and the short gating-time window of the pixel.…”

“…In addition to this, the pulse-based method has a flexibility regarding the gating clock patterns to be programmed for having advanced functions and performances. Though the reported SP-TOF pixels have maximally four taps for signal outputs [14,15], a SP-TOF pixel with a further number of signal taps will create opportunities of indirect TOF imagers to be used for a variety of applications under aggressive operating conditions. This paper presents an 8-tap lock-in pixel image sensor [17,18] for SP-TOF measurements.…”

Temporal and Spatial Focusing in SPAD-Based Solid-State Pulsed Time-of-Flight Laser Range Imaging

“…This kind of scanning LIDAR can achieve high performance but at a relatively high price, partly due to the device’s complicated construction. On the other hand, many of the new applications would favor a 3-D range imager with solid-state realization, i.e., without any mechanically moving parts, since it is this which would pave the way for reduced costs and miniaturization [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 ].…”

“…One quite successful approach to solid-state 3-D range imaging is based on phase comparison techniques, in which the transmitter sends a continuous wave (CW) modulated laser beam and the per-pixel distances to the target are deduced from the phase of the received signal with a CMOS active pixel sensor (APS) [ 19 , 20 , 21 , 22 , 23 ]. This technology gives a high image pixel resolution (x-y), but unfortunately, the measurement range (z) is currently limited to only a few meters.…”