Backside-illumination 14µm-pixel QVGA time-of-flight CMOS imager

Abstract

This paper presents a BSI(backside-illumination) 14μm-pixel QVGA CMOS image sensor SOC(System On a Chip) measuring TOF(Time-Of-Flight) by 20MHz-intensity modulation of 850nm-wavelength light. The 34% of overall QE(Quantum Efficiency) at 850nm-wavelength is acquired by BSI structure and optimized micro-lens. The DE(Depth Error) less than 1.5% within 6m is achieved with imaging lens of f/1.2 and LED array of which the optical intensity is 0.6W/m 2 at 1m-distance. Additionally, the depth linearity is measured as that the coefficient of determination is equal to 0.9999. In order to operate under background light illumination on a scene, dual CG(Conversion Gain) scheme is implemented in each pixel.

Four-transistor pinned photodiodes in standard CMOS technologies for time-of-flight sensors

“…Also, C FD varies with X FD , so this parameter was also varied. These simulations show great agreement with the results obtained using (13), showing a difference less than 10% between them. The results from (13) are shown in table 3.…”

“…These simulations show great agreement with the results obtained using (13), showing a difference less than 10% between them. The results from (13) are shown in table 3. Using ΔV thermal calculated in the last section, this table also includes the distance error generated when only ΔV syst,clk as a source of systematic voltage reduction is taken into account.…”

“…Distance measurements on ToF sensors can be classified according to the type of light signal used as modulated or pulsed ToF. In the first case the light is modulated by a continuous-wave function and the phase difference between the emitted and received signal is detected [4,8,12,13]. In the pulsed ToF the light signal is a pulse and the time between the emission and reception of the pulse is measured [11,[14][15][16].…”

Distance Measurement Error in Time-of-Flight Sensors Due to Shot Noise

“…The principal problem of using photogates as sensing elements in ToF sensors is the fact that the polysilicon of the gate partially blocks the light reaching the device, hence reducing the light power of the signal more. One solution proposed for this is presented in [ 8 ], where backside-illumination is used, so that the polysilicon gate is removed from the light path.…”