Current-assisted Photonic Demodulator Research Articles

Physical Model of Current-Assisted Photonic Demodulator (CAPD) for Time-of-Flight CMOS Image Sensor

This article presents a physical model of the current-assisted photonic demodulator (CAPD) for the time-of-flight (TOF) CMOS image sensor. An analytical expression relating the optical photogenerated current to the input bias and incident light intensity is derived by solving the continuity and drift-diffusion equations along the optical window of the CAPD. The model has been extensively verified with numerical simulations, as well as with published experimental data. Based on the developed model, the CAPD efficiency with respect to peak modulation voltage is discussed.

$320 \times 240$ Back-Illuminated 10- $\mu \text{m}$ CAPD Pixels for High-Speed Modulation Time-of-Flight CMOS Image Sensor

A $320\times 240$ back-illuminated (BI) time-of-flight CMOS image sensor with 10- $\mu \text{m}$ current-assisted photonic demodulator (CAPD) pixels has been developed. The BI pixel structure maximizes fill factor, allows for flexible transistor positioning, and makes the light path independent of the metal layers. The BI-CAPD pixel, which has relatively thinner substrate than that of front-illuminated CAPD, makes it possible to generate steeper electric-potential gradient in the vertical direction of the substrate, and results in 80% modulation contrast at 100-MHz modulation frequency. A higher modulation contrast contributes to suppress system power consumption as the sensor integration time for reaching specific signal-to-noise ratio is reduced. Alternatively, it contributes to improve depth accuracy when integration time is fixed.

Design and Characterization of Current-Assisted Photonic Demodulators in 0.18- $\mu\hbox{m}$ CMOS Technology

We report on the design of a current-assisted photonic demodulator (CAPD) using standard 0.18-μm complementary metal-oxide-semiconductor technology and its electrooptical characterization. The device can perform both light detection and demodulation in the charge domain, owing to a drift field generated in the silicon substrate by a majority carrier flow. Minimum-sized 10 × 10 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> CAPDs exhibit a direct-current charge-transfer efficiency larger than 80% (corresponding to demodulation contrast larger than 40% under sine-wave modulation) at the modest power consumption of 10 μW and a 3-dB bandwidth of >; 45 MHz. An excellent linearity value with an error lower than 0.11% is obtained in phase measurements. CAPDs with optimized modulation electrode geometries are finally designed, aiming at an improved contrast-versus-power tradeoff.

A 1 &amp;times; 64 Complementary Metal Oxide Semiconductor ranging sensor based on Current-Assisted Photonic Demodulators

A new Complementary Metal Oxide Semiconductor (CMOS) active pixel-ranging sensor is presented, realised as a 1 x 64 array of 30 μm x 30 μm lock-in pixels. The sensor is based on the Current-Assisted Photonic Demodulator (CAPD), implemented in a Standard CMOS 0.35 μm technology. The ranging pixel achieves 75% Fill-Factor, 0.22 A W-1 total QE and a demodulation bandwidth up to 70 MHz, both at 860 nm light. Range-finding is achieved through Modulated Wave Time-Of-Flight (TOF) measurements with a modulation frequency of 20 MHz. Distance measurements are presented. This sensor represents the first step towards integrating CAPD-based lock-in pixels in large TOF CMOS ranging systems.

Lock-in Pixel Using a Current-Assisted Photonic Demodulator Implemented in 0.6 µm Standard Complemetary Metal–Oxide–Semiconductor

A complemetary metal–oxide–semiconductor (CMOS) lock-in pixel sensor based on a current-assisted photonic demodulation (CAPD) detector is described. The CAPD detector provides high demodulation contrast and yields excellent photo-response. The prototype followed standard active pixel sensor (APS) architecture and was fabricated using a 0.6 µm CMOS process from AMS. We obtained a near infrared (NIR) light responsivity of 0.26 A/W at 860 nm. The pixel exhibits demodulation contrast of nearly 100% at low frequencies and above 90% even up to 2 MHz. The phase response is linear up to 2 MHz, and even up to 10 MHz with the appropriate phase extraction equations.

Photonic Demodulator With Sensitivity Control

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A current assisted photonic demodulator for use as a pixel in a 3-D time-of-flight imager shows nearly 100% static demodulator contrast and is operable beyond 30 MHz. An integrated tunable sensitivity control is also presented for increasing the distance measurement range and avoiding unwanted saturation during integration periods. This is achieved by application of a voltage on a dedicated drain tap showing a quenching of sensor sensitivity to below 1%. </para>