Optical Coupler Comparator Circuit for Noise-Resistant Small Chips
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Solution Overview
Problem
Optical coupling devices with trans-impedance amplifiers are prone to power source noise, and the inclusion of dummy photodiodes increases the semiconductor chip area, making it difficult to reduce the chip size while maintaining noise-resistant characteristics.
Innovation Solution
The optical coupling device employs a configuration with two photodiodes and two inverting amplifiers, where the product of the junction capacitance of one photodiode and its feedback resistor is matched with the product of the junction capacitance of a dummy photodiode and its feedback resistor, allowing for a reduction in chip size by reducing the area of the dummy photodiode and increasing the area of its feedback resistor, and optionally replacing the dummy photodiode with a MOS capacitor to further minimize chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dummy photodiode is provided to suppress power source noise influence, then noise-resistant characteristics are improved, but the occupation area of the semiconductor chip increases
Solution Approach 1:
The patent changes the physical form of the dummy photodiode from an actual photodiode structure to a MOS capacitor structure. This parameter change maintains the electrical characteristics (capacitance value) needed for noise suppression while dramatically reducing the occupation area on the semiconductor chip. The MOS capacitor replicates the capacitive effect of the photodiode without requiring the same physical space.
Solution Approach 2:
The patent creates a simplified copy of the photodiode's electrical function using a MOS capacitor. Instead of replicating the entire photodiode structure, it copies only the essential capacitive characteristic needed for noise filtering. This allows the dummy element to maintain its noise-suppression function while occupying minimal chip area.
2Area of stationary object
If the area of dummy photodiode is reduced, then chip area is reduced, but the product of junction capacitance and feedback resistor changes affecting noise resistance
Solution Approach 1:
The patent adjusts the capacitance parameter of the MOS capacitor to match the electrical characteristics of the original dummy photodiode. By carefully selecting the capacitance value of the MOS capacitor to equal the product of junction capacitance and feedback resistor of the original photodiode configuration, the noise-resistant characteristics are preserved despite the area reduction.
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 configuration effectively reduces the semiconductor chip area by up to 63% while maintaining noise-resistant characteristics, as the response to power source noise remains unchanged, and can be further reduced by using a MOS capacitor, which decreases the chip area by up to 90.3%.
Implementation Method 1
The first photodiode receives an optical signal generated by the light emitting element and converts the optical signal into a first electrical signal
Implementation Method 2
The second photodiode converts an optical signal generated by the light emitting element into a second electrical signal
Data Source
AI summary
According to one embodiment, an optical coupling device is provided.A first photodiode receives an optical signal generated by a light emitting element and converts the optical signal into a first electrical signal. A first inverting amplifier is provided with a first feedback resistor and a first operating amplifier connected in parallel with each other. The input end is connected to a cathode of the first photodiode. A first signal which is obtained by inverting the first electrical signal is output from the output end. A second inverting amplifier is provided with a second feedback resistor and a second operating amplifier connected in parallel with each other. The input end of the second inverting amplifier is connected to a cathode of a second photodiode. The second inverting amplifier outputs a second signal from the output end. A comparator receives the first and second signals and outputs a comparison amplified signal.