3D Image Sensor Pixel Circuit With Buffered Time-Gated Sampling
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Solution Overview
Problem
Existing image sensing devices in active imaging systems face limitations in resolving small signals due to capacitive load interference, leading to reduced photosensitivity and limited depth resolution, especially in terrestrial applications where fast switching is required.
Innovation Solution
An image sensing device with pixel circuits that include a buffer amplifier to isolate the photo detector circuit from capacitive loads, using a source follower transistor and current source load, and a timing controller to operate switches in sequence, capturing samples at different times during the gate period, with a bias controller to manage transistor current, allowing for high gain and reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple storage circuits are connected directly to the photo detector circuit, then the device can capture samples at different times during the gate period, but the capacitive load from multiple storage circuits reduces photosensitivity and resolves small signals
Solution Approach 1:
A buffer amplifier is introduced as an intermediary component between the photo detector circuit and multiple storage circuits. The buffer amplifier has high input impedance and low output impedance, allowing it to isolate the photo detector from the capacitive load of multiple storage circuits while maintaining signal integrity. This enables the photo detector to maintain high photosensitivity even when multiple storage circuits are connected for simultaneous sampling.
2Measurement precision
If fast switching is implemented to capture 3D image data, then depth resolution is improved, but power consumption increases due to frequent switching operations
Solution Approach 1:
The switching operation is performed periodically at specific timing points during the gate period rather than continuously. The buffer amplifier maintains signal levels between switching events, allowing switches to operate only when needed for capturing depth information at different ranges. This periodic switching approach achieves fast depth resolution while minimizing power consumption by avoiding continuous switching operations.
3Length of stationary object
If the gate period is extended to capture reflected light from distant objects, then detection range is improved, but depth resolution deteriorates due to increased gate time
Solution Approach 1:
The gate period is segmented into multiple time intervals, with each storage circuit capturing signals from specific time windows. By dividing the extended gate period into discrete segments and assigning them to different storage circuits, the system maintains deep detection range while preserving depth resolution through temporal segmentation of the captured signals.
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
The solution maintains photosensitivity and enables high-resolution 3D image data capture by isolating the photo detector from capacitive loads, achieving fast switching times and efficient power usage, suitable for terrestrial applications.
Implementation Method 1
a photo detector circuit comprising a photo detector element arranged to output a time varying photo signal during a gate period
Implementation Method 2
each pixel circuit comprises a buffer amplifier connected between the photo detector circuit and the storage circuits to substantially isolate the photo detector circuit from changes in the capacitive load of the multiple storage circuits
Data Source
AI summary
An active imaging system including a laser to illuminate a scene and an imaging device to receive returns reflected from the scene. The imaging device including an array of pixel circuits, each pixel circuit including a photodiode connected to multiple track and hold circuits and a timing circuit configured to operate the track and hold circuits in quick succession such that each track and hold circuit captures an information signal indicative of returns arriving during different successive time periods during a gate period and thus provides 3D image data based on the arrival times of returns from the scene during the gate period.