Single SPAD Array Ranging System with Electrical Delay Compensation
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Solution Overview
Problem
Conventional time of flight (ToF) sensors require both a return and reference single-photon avalanche diode (SPAD) array, which increases silicon area usage and power consumption due to the need for separate routing and power supply for each array, introducing propagation delays that can affect ranging accuracy.
Innovation Solution
The use of a single SPAD array with a driving signal from a VCSEL driver replacing the reference SPAD array, where the driving signal is directly fed into the circuitry to compensate for common propagation delays, reducing the need for a reference array and minimizing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference SPAD array is used to compensate for propagation delays, then measurement precision is improved, but device complexity and power consumption increase
Solution Approach 1:
The patent creates an electrical copy of the driving signal that experiences the same propagation delays as the optical path. This electrical reference signal is generated by tapping the driving signal at the VCSEL driver and routing it through matched circuitry to the readout circuit, eliminating the need for a separate reference SPAD array while preserving delay compensation functionality
Solution Approach 2:
The VCSEL driver serves multiple functions: it drives the light-emitting device to generate optical pulses and simultaneously provides the reference signal for delay compensation. By making the driver multi-functional, the patent eliminates the need for a separate reference sensor array, reducing device complexity while maintaining ranging accuracy
2Measurement precision
If a reference SPAD array is used to compensate for propagation delays, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The patent extracts the reference signal functionality from the optical detection path and implements it purely in the electrical domain. By taking out the reference SPAD array and replacing it with an electrical signal copy, the system eliminates the power consumption associated with operating a second sensor array while maintaining the ability to compensate for propagation delays
3Measurement precision
If separate routing for reference and return arrays is used, then measurement precision is improved, but silicon area usage increases
Solution Approach 1:
The patent merges the reference signal path with the return signal path at the readout circuit level. Both the electrical reference signal (from the VCSEL driver) and the optical return signal (from the single SPAD array) are routed to the same readout circuit, which processes them together to determine time of flight. This merging eliminates the need for separate reference array routing and reduces silicon area
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 reduces silicon area usage and power consumption while maintaining sufficient accuracy for applications that do not require absolute range precision, such as gesture recognition and user detection, by inherently compensating for voltage and temperature-dependent delays.
Implementation Method 1
The VCSEL emits light based on the received pulse
Implementation Method 2
The return and reference arrays generate respective electrical signals indicative of the received radiation
Data Source
AI summary
In one embodiment, an imaging device includes a light-emitting device, a driving circuit, a return single-photon avalanche diode (SPAD) array and readout circuitry. The driving circuit generates a driving signal, and the light-emitting device generates an optical pulse based on the driving signal. The return SPAD array is configured to receive a first portion of the optical pulse that is reflected by an object in an image scene. The readout circuitry receives a signal indicative of the received first portion of the optical pulse, and a signal indicative of the driving signal, and determines a distance between the imaging device and the object based on a difference between a time of receiving the signal indicative of the received first portion of the optical pulse and a time of receiving the signal indicative of the driving signal.