TOF Receiver Digital Mixing for Ambient Light Saturation
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Solution Overview
Problem
Time-of-flight (TOF) systems face challenges in achieving high dynamic range due to saturation from ambient light, which affects the accuracy of distance estimation in receivers.
Innovation Solution
A receiver design incorporating a photodiode, a sigma delta analog-to-digital converter, and an ambient cancellation circuit that cancels direct current signals from ambient light, allowing for digital mixing and processing without the need for a trans-impedance amplifier, thereby maintaining high dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If ambient light is present in the TOF system, then the receiver receives strong DC signals from ambient light, but this causes receiver saturation and reduces the dynamic range
Solution Approach 1:
The patent extracts and removes the harmful DC component from the ambient light signal using a high-pass filter or AC coupling capacitor in the receiver circuit. This separates the useful modulated signal from the harmful DC offset, allowing the receiver to maintain high dynamic range even in bright ambient light conditions.
Solution Approach 2:
The patent introduces an intermediary high-pass filter or AC coupling stage between the photodetector and the subsequent signal processing stages. This intermediary component blocks the DC component from ambient light while allowing the AC modulated signal to pass through, thereby protecting the receiver from saturation.
2Power
If a trans-impedance amplifier is used to amplify the photodiode signal, then the signal strength is increased, but the receiver becomes more susceptible to saturation from ambient light
Solution Approach 1:
The patent applies preliminary action by placing the high-pass filter or AC coupling capacitor before the trans-impedance amplifier. This preprocessing step removes the DC component of ambient light before amplification, so that the TIA only amplifies the modulated signal without being saturated by large DC currents from ambient light.
3Quantity of substance
If the receiver processes both reflected light pulses and ambient light simultaneously, then all incoming light is captured, but the distance estimation accuracy deteriorates due to signal saturation
Solution Approach 1:
The patent applies local quality by making different parts of the signal processing chain have different frequency response characteristics. The high-pass filter or AC coupling capacitor creates a frequency-selective path that passes the modulated signal frequency while blocking DC, allowing selective processing of different signal components with different qualities.
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 effectively cancels ambient light-induced direct current signals, preventing receiver saturation and enabling accurate distance estimation even under high ambient light conditions, thus achieving a high dynamic range in TOF systems.
Implementation Method 1
A receiver includes a photodiode that generates a current signal
Data Source
AI summary
The disclosure provides a receiver with high dynamic range. The receiver includes a photodiode that generates a current signal. A coupling capacitor is coupled to the photodiode, and generates a modulation signal in response to the current signal received from the photodiode. A sigma delta analog to digital converter (ADC) is coupled to the coupling capacitor, and generates a digital data in response to the modulation signal. A digital mixer is coupled to the sigma delta ADC, and generates an in-phase component and a quadrature component corresponding to the digital data. A processor is coupled to the digital mixer, and processes the in-phase component and the quadrature component corresponding to the digital data.