Light Sensor Circuit Buffering Photodiode Capacitance in ADC Reset
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Solution Overview
Problem
The junction capacitance of photodiodes in light sensors slows down the reset operation of integration modules in ADCs, affecting their performance and accuracy.
Innovation Solution
A light sensor circuit incorporating a photodiode and a unit-gain buffer, where the unit-gain buffer reduces the influence of junction capacitance, allowing for faster charging and discharging, and ensuring the integration module can reset quickly without being hindered by the photodiode's capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photodiode is used to sense light and generate analog input signal, then the light sensing function is achieved, but the junction capacitance of the photodiode slows down the reset operation of the integration module
Solution Approach 1:
The patent introduces a capacitor connected in parallel with the photodiode as an intermediary element. This capacitor acts as a mediator that stores charge and helps maintain the voltage level during the reset operation, thereby decoupling the direct impact of photodiode junction capacitance from the reset speed of the integration module. The capacitor enables faster reset by providing a local charge reservoir that reduces the time constant of the reset circuit.
2Measurement precision
If the integration module accumulates analog input signals, then the measurement precision is improved, but the reset operation becomes slower due to junction capacitance
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor connected in parallel with the photodiode before the reset operation. This preliminary charging ensures that when the reset occurs, the capacitor can immediately supply the necessary charge to maintain the integration module's voltage level, thereby reducing the reset time without compromising the accumulation accuracy of the analog signals.
3Measurement precision
If the ADC performs accumulation operation of effective bits, then the digital signal processing accuracy is improved, but the overall conversion speed is reduced due to slow reset operation
Solution Approach 1:
The capacitor serves as an intermediary that decouples the slow reset operation from the ADC conversion process. By providing a local charge reservoir, the capacitor enables the ADC to perform its accumulation operation of effective bits at high speed without being bottlenecked by the photodiode's junction capacitance, thereby improving both conversion speed and maintaining accuracy.
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 effectively maintains the performance and accuracy of ADCs by minimizing the impact of junction capacitance, ensuring the integration module resets efficiently and accurately.
Implementation Method 1
a photodiode 200 and obtains an analog input signal
Data Source
AI summary
A light sensor circuit, which comprising a photodiode and a voltage follower. By setting the voltage follower to reduce the influence from the junction capacitance of the photodiode, a required time of a repeat integration module will not be influenced by the photodiode to efficiently keep the performance and the accuracy of the analog to digital converting device when the light sensor circuit is used to the analog to digital converting device in repeat operation.