ToF Illumination Circuit Reverse Bias for Fast Turn-Off
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Solution Overview
Problem
Existing time-of-flight (ToF) camera driving circuits face challenges in achieving fast turn-on and turn-off times for light emitting elements, which limits distance resolution, and require bulky blocking capacitors that hinder scalability, while also increasing complexity due to synchronization issues with multiple modulation switches.
Innovation Solution
A driving circuit using a constant current DC-DC converter coupled with an RC circuit element and a second modulation switch to apply a reverse bias, allowing for fast turn-off times and eliminating the need for blocking capacitors by using a single modulation switch, thereby enhancing distance resolution and scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If blocking capacitors are used in the driving circuit, then the circuit can provide stable voltage during switching, but the circuit size increases and scalability is hindered
Solution Approach 1:
The patent removes the blocking capacitor from the driving circuit by using a current-mode DC-DC converter that inherently provides stable current output during switching operations. This extraction of the bulky blocking capacitor component directly reduces circuit size while maintaining voltage stability through the converter's control mechanism.
2Speed
If multiple modulation switches are used, then fast turn-on and turn-off times can be achieved, but circuit complexity increases due to synchronization issues
Solution Approach 1:
The patent combines the functions of multiple modulation switches into a single integrated switching mechanism controlled by the DC-DC converter. This merging approach achieves fast turn-on and turn-off times while eliminating the synchronization complexity that would arise from coordinating multiple independent switches.
Solution Approach 2:
The patent changes the control parameter from voltage-based switching to current-based switching through the DC-DC converter. This parameter change enables precise control of the light emitting element's current, achieving fast response times without the synchronization issues of multiple voltage-controlled switches.
3Measurement precision
If high frequency modulation is used, then distance resolution is improved, but the light emitting element requires extremely fast turn-on and turn-off times
Solution Approach 1:
The patent changes from voltage control to current control of the light emitting element through the DC-DC converter. This parameter change enables extremely fast current modulation that can keep pace with high frequency modulation signals, thereby achieving the required turn-on and turn-off times for improved distance resolution.
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 achieves improved turn-on and turn-off times for light emitting elements, increasing distance resolution and reducing circuit complexity and size, while maintaining independent optical power from temperature variations.
Implementation Method 1
an RC circuit element coupled to an output electrode of the light emitting element and configured to apply a reverse bias to decrease turn-off time of the light emitting element
Data Source
AI summary
Some aspects of the present disclosure provide system and method of operation of a driving circuit for a light emitting element in a Time-of-Flight (ToF) camera. A DC-DC converter is configured to emit a constant current, and is coupled in parallel to a first modulation switch configured to connect the driving circuit to ground. The first modulation switch is further configured to alternate connections between the current source and ground at a frequency in a desired range of operation to produce an AC current. In some embodiments, an RC circuit element is coupled to an output electrode of the light emitting element and configured to apply a reverse bias to decrease turn-off time of the light emitting element. In some embodiments, a second modulation switch is coupled to the output electrode and configured to apply the reverse bias across the light emitting element. Other systems and methods are also disclosed.