PWM Image Integration for ToF Camera Peak Power Management
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Solution Overview
Problem
Time-of-flight (ToF) cameras face challenges in maintaining a desired signal-to-noise ratio (SNR) in high ambient light conditions, leading to peak power draw issues that can exceed battery bandwidth, particularly in portable devices, and the addition of auxiliary voltage regulators and capacitors increases weight, size, and cost.
Innovation Solution
Implementing a pulse width modulated (PWM) image integration plan that divides integration cycles into illumination and non-illumination cycles, directing photocharge away from in-pixel memory during non-illumination periods to manage power within device limitations without additional storage capacitors or special voltage regulators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the illumination source operates at higher power to maintain SNR in high ambient light conditions, then signal-to-noise ratio is improved, but peak power draw exceeds battery bandwidth
Solution Approach 1:
The patent applies periodic action by implementing PWM illumination cycles that alternate between illumination phases and non-illumination phases. During illumination phases, the illumination source emits light at high power to maintain SNR, while during non-illumination phases, the illumination is turned off to reduce peak power draw. This periodic modulation allows the system to achieve adequate signal detection while staying within battery power bandwidth constraints.
Solution Approach 2:
The patent applies dynamics by making the illumination source power level dynamic rather than static. The illumination power is modulated over time with varying duty cycles, allowing the system to adapt between high-power illumination periods for signal acquisition and low-power periods for battery conservation. This dynamic power management resolves the contradiction between maintaining SNR and limiting peak power draw.
2Power
If auxiliary voltage regulators and capacitors are added to manage peak power draw, then power management is improved, but weight, size, and cost increase
Solution Approach 1:
The patent applies self-service by using the existing in-pixel memory structures to temporarily store photocharge during illumination phases and then transfer it during non-illumination phases. The system utilizes its own existing components (in-pixel memory, transfer gates) to manage power demands without requiring external auxiliary voltage regulators or large capacitors. This self-service approach to power management avoids adding weight, size, and cost.
Solution Approach 2:
The patent applies universality by making the in-pixel memory serve multiple functions: it acts as both the integration storage for depth information and as a temporary buffer for managing photocharge during PWM illumination cycles. This multi-functionality eliminates the need for separate power management components, thereby avoiding increased weight, size, and cost.
3Reliability
If photocharge is continuously integrated during illumination cycles, then signal accumulation is improved, but power consumption increases beyond device limitations
Solution Approach 1:
The patent applies periodic action by implementing alternating illumination and non-illumination cycles. During illumination cycles, photocharge is accumulated from the reflected light signal. During non-illumination cycles, the illumination source is turned off, reducing power consumption, while the system can transfer stored photocharge from the in-pixel memory to readout circuits. This periodic operation enables signal accumulation while managing power consumption within device limitations.
Solution Approach 2:
The patent applies preliminary action by accumulating photocharge in the in-pixel memory during illumination phases before the actual readout occurs. This preliminary accumulation allows the system to gather sufficient signal during high-power illumination periods, then perform the energy-intensive readout operation during lower-power non-illumination periods, thereby balancing signal accumulation with power consumption management.
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 approach maintains SNR performance while reducing peak power draw, avoiding the need for external storage capacitors and special voltage regulators, making ToF cameras more suitable for portable devices by managing power within existing bandwidths.
Implementation Method 1
a ToF camera may emit a temporally-modulated light signal to illuminate the scene, and the image sensor captures reflected, phase-shifted signals at each pixel
Implementation Method 2
directing photocharge to the in-pixel memory for each pixel that is performing image integration
Data Source
AI summary
One example provides a method of operating a time-of-flight camera system comprising an illumination source and an image sensor. The method comprises operating the illumination source and the image sensor to control a plurality of integration cycles and a plurality of readout cycles. In each integration cycle, the method comprises performing a plurality of pulse width modulated (PWM) illumination cycles where each PWM illumination cycle is separated from one or more adjacent PWM illumination cycles by a non-illumination cycle. For each PWM illumination cycle, the method comprises directing photocharge to in-pixel memory for each pixel that is performing image integration and for each non-illumination cycle conducting photocharge away from the in-pixel memory for each pixel that is performing image integration. The readout cycle comprises, for each pixel that performed image integration, reading a charge stored in the in-pixel memory after the integration cycle.