Heterodyne Depth Sensor SPAD Digital Counters
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Solution Overview
Problem
Existing heterodyne depth sensors face challenges in achieving acceptable resolution, precision, power consumption, and area for effective FMCM imaging.
Innovation Solution
A heterodyne sensor comprising optical mixers to combine reference and return light beams, generating beat signals, and an array of pixels with single-photon avalanche diodes and digital counters, operated in a rolling shutter mode with a sequencer, and optionally including optical elements for directing return light beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional imaging pixels are used to detect the amplitude of the return signal in FMCW systems, then depth imaging can be achieved, but the sensor suffers from high power consumption and large area requirements
Solution Approach 1:
The patent replaces traditional analog imaging pixels with a digital counting system based on single-photon avalanche diodes (SPADs). Each pixel uses a digital counter to count the number of detected photons directly, substituting complex analog signal processing with simple digital counting. This substitution dramatically reduces power consumption while maintaining depth imaging capability, as the digital counters can operate at very low sampling frequencies (e.g., 100 Hz or lower) compared to traditional high-speed analog pixels.
2Measurement precision
If traditional imaging pixels are used to detect the amplitude of the return signal in FMCW systems, then depth imaging can be achieved, but the sensor requires large area
Solution Approach 1:
The patent replaces traditional analog imaging pixels with a digital counting system based on single-photon avalanche diodes (SPADs). Each pixel uses a digital counter to count the number of detected photons directly, substituting complex analog signal processing with simple digital counting. This substitution dramatically reduces power consumption while maintaining depth imaging capability, as the digital counters can operate at very low sampling frequencies (e.g., 100 Hz or lower) compared to traditional high-speed analog pixels.
Solution Approach 2:
The patent changes the operating parameters of the imaging system by using very low sampling frequencies (e.g., 100 Hz or lower) for the digital counters. This parameter change allows the use of simpler, smaller circuitry with lower power consumption, thereby reducing the overall sensor area required while maintaining adequate depth imaging performance for many applications.
3Measurement precision
If high sampling frequencies are used in the pixel array, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent introduces dynamic adaptability by allowing the sampling frequency of each digital counter to be independently adjusted based on the specific application requirements. The system can operate at very low sampling frequencies (e.g., 100 Hz or lower) when high precision is not critical, dramatically reducing power consumption. When higher precision is needed, the sampling frequency can be increased for specific pixels or regions, optimizing the trade-off between precision and power consumption on a per-pixel or per-region basis rather than requiring the entire array to operate at high frequencies.
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 proposed solution enables the capture of high-resolution depth images with low sampling frequencies, reducing power consumption and area requirements while maintaining high signal-to-noise ratio.
Implementation Method 1
a single-photon avalanche diode configured to receive a corresponding one of the one or more beat signals and to generate an output signal as a function of the light intensity of the received beat signal
Implementation Method 2
The reference beam and the transmission beam interfere with each other at the optical mixer of the image sensor, resulting in a beat signal
Data Source
AI summary
An example heterodyne sensor of the present disclosure includes one or more optical mixers and an array of pixels. The optical mixers are configured to combine a reference light beam with one or more return light beams in order to generate one or more beat signals. Each pixel of the array of pixels includes a single-photon avalanche diode configured to receive a corresponding one of the one or more beat signals and to generate an output signal as a function of a light intensity of a received beat signal, and a digital counter configured to generate a count value based on the output signal of the single-photon avalanche diode.