Dynamic Photodiode Time-of-Flight Sensing With Digital Noise Reduction
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Solution Overview
Problem
Existing time of flight measurement systems face challenges such as incompatibility with CMOS sensors, high voltage issues, decreased sensitivity to background light, and noise introduction due to analog processing, particularly when using output current for distance measurements.
Innovation Solution
A time of flight measurement system utilizing dynamic photodiodes (DPDs) that perform time domain measurements through time to digital conversion (TDC) without analog amplification, minimizing noise and interference, and enabling distance calculations using the triggering time of DPDs in an all-digital environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If output current is used for distance measurements, then distance measurement capability is achieved, but noise is introduced and measurement sensitivity to background light decreases
Solution Approach 1:
The patent replaces the electrical current-based measurement system with an optical photon-counting system. Instead of measuring output current from photodiodes, the system directly detects individual photons using single-photon avalanche diodes (SPADs) in photon-counting mode. This substitution of measurement mechanism eliminates the need for analog-to-digital conversion and associated noise, while significantly improving sensitivity to background light through single-photon detection capability.
Solution Approach 2:
The patent changes the operating parameter of the photodetector from continuous current mode to discrete photon-counting mode. By operating SPADs in Geiger mode with voltage above breakdown threshold, the system transforms the detection mechanism to count individual photon events rather than measuring continuous current. This parameter change enables digital time-of-flight measurements with superior noise immunity and background light rejection.
2Ease of operation
If analog processing is used, then signal processing capability is achieved, but noise is introduced into the system
Solution Approach 1:
The patent replaces analog signal processing circuits with digital signal processing. The time-to-digital converter (TDC) directly converts time-of-flight measurements into digital values without requiring analog amplification, filtering, or integration stages. This digital approach eliminates noise introduced by analog components while maintaining full signal processing capability through digital algorithms.
3Measurement precision
If dynamic photodiodes with driving voltage are used, then photon detection capability is improved, but device complexity increases
Solution Approach 1:
The patent merges the photodetection function and time measurement function into a single integrated module. The SPAD array is directly coupled with time-to-digital converters (TDCs) in each pixel, eliminating the need for separate analog amplification stages and external processing circuits. This integration reduces overall device complexity while maintaining high photon detection capability through the combined structure.
Solution Approach 2:
The patent implements self-service functionality where each pixel element (SPAD + TDC) autonomously performs photon detection and time-to-digital conversion without requiring external analog processing circuits. The driving voltage control and photon counting are handled within each pixel, reducing the need for complex external circuitry and simplifying the overall system architecture.
4Object-affected harmful factors
If all-digital environment is used, then noise is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent designs a universal pixel structure where the SPAD and TDC can be fabricated using standard CMOS processes. The same basic cell design serves multiple functions: photon detection, time measurement, and digital output generation. This multi-functionality in a single manufacturable structure reduces overall manufacturing complexity compared to separate analog and digital components.
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 system provides accurate distance measurements with reduced noise and complexity, allowing for smaller circuit footprints and power consumption, while maintaining high sensitivity and precision.
Implementation Method 1
a dynamic photodiode (DPD) ... output current I indicating an amount of reflected light from one or more objects sensed by the DPD
Data Source
Figure 1A(a)~1A(d)
Figure 1B
Figure 1C(i)~1C(ii)
AI summary
In some embodiments, a measurement system may include a time to digital converter (TDC) configured to determine a first digitized time at which it receives a command signal and a second digitized time at which it receives an alert signal. The first digitized time and the second digitized time may be determined for N number of iterations. The command signal may be delayed by a delay time, and the delay time may be varied for each of the N number of iterations. The measurement system may include a first dynamic photodiode (DPD) configured to switch from a reverse bias mode to an active mode based on the command signal. The TDC may calculate a difference between the first digitized time and the second digitized time for each of the N number of iterations, and the difference may vary as the delay time is varied.