Demodulation Pixel With Drift Field Charge Transport
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Solution Overview
Problem
Current demodulation pixels face limitations in achieving high sampling frequencies and a large number of samples due to slow charge transport through semiconductor materials, leading to reduced precision in 3D imaging and other applications.
Innovation Solution
A pixel architecture featuring a photosensitive region with a static drift field and a daisy chain of storage sites, allowing for high-speed charge transport and simultaneous sampling across multiple storage sites, reducing mismatch and enabling high-speed, high-precision phase measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If photocharges are transferred through the photo-sensitive detection region to storage areas using conventional methods, then the pixel can accumulate photo-generated charges during different time intervals, but the charge transport speed is slow due to thermal diffusion dominating instead of lateral electric drift fields
Solution Approach 1:
The patent applies dynamic control of potential distribution through demodulation gates that are dynamically switched based on the modulation signal. This creates time-varying lateral electric drift fields that actively guide photocharges at different phases, transforming the static thermal diffusion process into a dynamic drift-dominated transport mechanism, thereby achieving both high speed and high precision demodulation.
2Speed
If drift field pixel concepts are used to speed up charge transport, then in-pixel lateral charge transport is accelerated, but large capacitances need to be switched and electronic current is used to generate drift fields resulting in significant in-pixel power consumption
Solution Approach 1:
The patent utilizes the photo-generated charge carriers themselves to generate the drift fields through their movement and accumulation in the potential wells created by the demodulation gates. The system essentially uses the signal charges to drive their own transport, eliminating the need for separate high-power electronic current sources, thus achieving fast transport with minimal additional power consumption.
3Quantity of substance
If the number of storage sites is increased to take more samples, then the number of samples is increased, but the sampling frequency must be reduced due to slow charge transport
Solution Approach 1:
By implementing dynamic potential distribution control through multiple demodulation gates that can be independently switched, the patent enables parallel charge routing to multiple storage sites. The dynamic gate switching creates time-multiplexed charge transport paths, allowing multiple samples to be captured simultaneously at high frequency without being limited by sequential transfer speeds.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This architecture enables high sampling frequencies with an arbitrary number of samples, improving precision in applications like submillimeter pseudo noise 3D-imaging and reducing power consumption, while maintaining efficient charge transport and minimizing the impact of inclined optical incidence.
Implementation Method 1
a photosensitive region in which incoming light is converted into photocharges
Implementation Method 2
a lateral drift field in the photosensitive region transporting the photocharges to a pickup point
Data Source
AI summary
A demodulation pixel architecture allows for demodulating an incoming modulated electromagnetic wave, normally visible or infrared light. It is based on a charge coupled device (CCD) line connected to a drift field structure. The drift field is exposed to the incoming light. It collects the generated charge and forces it to move to the pick-up point. At this pick-up point, the CCD element samples the charge for a given time and then shifts the charge packets further on in the daisy chain. After a certain amount of shifts, the multiple charge packets are stored in so-called integration gates, in a preferred embodiment. The number of integration gates gives the number of simultaneously available taps. When the cycle is repeated several times, the charge is accumulated in the integration gates and thus the signal-to-noise ratio increases. The architecture is flexible in the number of taps. A dump node can be attached to the CCD line for dumping charge with the same speed as the samples are taken. Different implementations are described herein, which allow for smaller design or faster speed. The pixel structure can be exploited for e.g. 3D time-of-flight imaging. Both heterodyne and homodyne measurements are possible. Due to the highly-efficient charge transport enabled by static drift fields in the photo-sensitive region and small-sized gates in the CCD chain, high frequency bandwidth from just a few Hertz (Hz) up to greater GHz is supported. Thus, the pixel allows for highly-accurate optical distance measurements. Another possible application of this pixel architecture is fluorescence lifetime imaging microscopy (FLIM), where short laser pulses for triggering the fluorescence have to be suppressed.