TOF Receiver Circuit With Coupling Capacitor for Ambient Light Rejection
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Solution Overview
Problem
Time-of-flight (TOF) systems face challenges in achieving high dynamic range due to ambient light interference, which saturates the receiver and leads to errors in estimating target distance, especially when the signal strength of reflected light pulses is significantly lower than interference signals.
Innovation Solution
A receiver design incorporating a photodiode, a sigma delta analog-to-digital converter (ADC), a digital mixer, and an ambient cancellation circuit, which generates a modulation signal and cancels direct current signals from ambient light, allowing for high dynamic range operation without saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional receiver processes reflected light pulses directly, then the system structure is simple, but ambient light causes DC signal saturation and reduces dynamic range
Solution Approach 1:
A coupling capacitor is introduced as an intermediary component between the photodiode and the processing circuit. This capacitor blocks the DC component generated by ambient light while allowing the AC component containing the reflected light pulse information to pass through, thereby preventing saturation and improving dynamic range without significantly increasing overall system complexity
Solution Approach 2:
The harmful DC component is extracted and removed from the signal path using the coupling capacitor's blocking property. By separating the AC signal of interest from the DC offset caused by ambient light, the receiver can process weak reflected pulses without being saturated by the strong DC background
2Loss of information
If the receiver processes both DC and AC signals simultaneously, then all signal components are captured, but the DC signal saturates the receiver and masks weak AC signals
Solution Approach 1:
The coupling capacitor acts as a frequency-selective intermediary that automatically separates DC and AC components in the time domain, allowing the AC signal to be processed with high precision while the DC component is blocked, thus improving measurement precision without losing the reflected light pulse information
Solution Approach 2:
The reflected light pulse is a periodic or transient AC signal superimposed on a DC background. By using the coupling capacitor to pass only the periodic AC component, the system achieves precise measurement of the pulse characteristics necessary for distance estimation while ignoring the steady DC offset
3Measurement precision
If high gain is used to amplify weak reflected light signals, then signal detection sensitivity is improved, but the receiver becomes more susceptible to saturation from ambient light interference
Solution Approach 1:
The coupling capacitor is positioned before the high-gain amplification stage to block the DC component that would otherwise be amplified along with the weak AC signal. This prevents the amplifier from saturating due to the DC offset while still providing high gain to the reflected light pulse signal, thereby improving signal detection sensitivity without increasing saturation susceptibility
Solution Approach 2:
The DC blocking action is performed preliminarily before the signal enters the high-gain amplification stage. By removing the harmful DC component in advance, the subsequent amplification process can operate at high gain without risk of saturation from ambient light, thus enabling sensitive detection of weak reflected 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 effectively cancels ambient light interference, enabling the receiver to detect weak alternating current signals from reflected light pulses while avoiding saturation, thus achieving high dynamic range and accurate distance estimation in TOF systems.
Implementation Method 1
a photodiode that generates a current signal
Implementation Method 2
A coupling capacitor is coupled to the photodiode, and generates a modulation signal in response to the current signal received from the photodiode
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.