Dual-Slope Optical Sensor Eliminates Reset Delay
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Solution Overview
Problem
Conventional optical sensors experience unstable current and significant error in counting due to long pull-down delay times when dealing with large photocurrents, leading to inaccurate value counting.
Innovation Solution
A dual-slope optical sensor design that replaces the NMOS or PMOS transistor with a charging switch circuit and discharging switch circuit, allowing the capacitor to be charged or discharged by photocurrent, with an initial voltage higher than zero, preventing unstable current and eliminating the need for a reset delay time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transistor is used to reset the comparator input voltage by pulling it down to zero, then the comparator can be reset for continuous comparison, but the current becomes unstable and significant error occurs in counting when dealing with large photocurrents
Solution Approach 1:
The patent changes the reset mechanism from pulling voltage to zero (conventional method) to charging the capacitor to a predetermined initial voltage (e.g., 2.5V). This parameter change in the reset strategy eliminates the need for long pull-down delay times and prevents unstable current conditions, thereby improving both current stability and counting accuracy when handling large photocurrents
Solution Approach 2:
The patent applies preliminary action by pre-charging the capacitor to a predetermined initial voltage before the comparison process begins. This preliminary charging action ensures that the capacitor starts at a known stable voltage level, eliminating the instability that occurs with conventional zero-pull-down methods and preventing counting errors from the outset
2Reliability
If a long pull-down delay time is used to reset the comparator input voltage multiple times, then the voltage can be reset for large photocurrents, but the value counted by the counter exhibits significant error
Solution Approach 1:
The patent changes the voltage reset parameter from zero (conventional pull-down method) to a predetermined initial voltage (e.g., 2.5V). This parameter change allows the capacitor to be quickly charged to the required voltage level without needing long delay times, thereby eliminating the time loss while ensuring complete voltage reset for large photocurrents
Solution Approach 2:
The patent replaces the mechanical pull-down delay mechanism with an electronic pre-charging mechanism. Instead of waiting for the voltage to be pulled down to zero and then recovering, the system electronically charges the capacitor to the predetermined initial voltage, substituting a time-consuming mechanical process with a faster electronic control approach
3Ease of operation
If the capacitor voltage is pulled down to zero during pull-down delay time, then the comparator input can be reset, but unstable current occurs in the conventional optical sensor
Solution Approach 1:
The patent changes the comparator reset parameter from pulling voltage to zero to charging to a predetermined initial voltage. This parameter change maintains the comparator reset capability while eliminating the unstable current condition that occurs when the voltage is pulled down to zero, as the capacitor is now charged to a stable predetermined voltage level
Solution Approach 2:
The patent applies preliminary action by pre-charging the capacitor to the predetermined initial voltage before comparison operations begin. This preliminary charging action ensures the comparator is properly reset with a stable voltage foundation, eliminating current instability while maintaining full reset capability
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 dual-slope optical sensor achieves improved sensing efficiency and curve linearity, resulting in more accurate value sensing compared to conventional sensors.
Implementation Method 1
an optoelectronic component of the conventional optical sensor converts energy of the light into a photocurrent
Data Source
AI summary
A dual-slope optical sensor is provided. Two terminals of a first charging switch are respectively connected to an optoelectronic component and a first terminal of a capacitor. Two terminals of a second charging switch are respectively connected to a second terminal of the capacitor and grounded. First terminals of third charging and discharging switches are respectively connected to the first and second terminals of the capacitor. First terminals of fourth charging and discharging switches are respectively coupled to first and second reference voltages. Two terminals of a first discharging switch are respectively connected to the optoelectronic component and the second terminal of the capacitor. A first input terminal of a comparator is connected to second terminals of the third charging switch and the fourth discharging switch. A second input terminal of the comparator is connected to second terminals of the fourth charging switch and the third discharging switch.