Optical Coupling Circuit With Noise-Current Cancellation
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Solution Overview
Problem
Optical coupling circuits face issues with noise propagation due to capacitive coupling between light-emitting and light-receiving units, leading to incomplete noise elimination and limitations in comparator power supply and dynamic range.
Innovation Solution
Incorporating a current duplication circuit and current-voltage conversion circuit to cancel noise currents, with a comparator comparing the converted voltage signal to a threshold voltage, ensuring noise-free output signals regardless of noise properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a comparator is used to cancel noise signals in an optical coupling circuit, then noise immunity is improved, but the noise elimination is limited by the comparator's directionality and power supply capabilities
Solution Approach 1:
The light-receiving unit is segmented into two separate photo diodes: one for receiving optical signals and another for detecting noise. This segmentation allows each component to specialize in its function, with the signal photo diode focusing on optical signal conversion and the noise photo diode dedicated to noise detection, thereby overcoming the comparator's limited directionality
Solution Approach 2:
A current duplication circuit is introduced as an intermediary to duplicate the noise current detected by the noise photo diode and inject it into the signal processing path. This intermediary mechanism enables precise noise cancellation by matching the noise current characteristics without being constrained by comparator power supply limitations
2Measurement precision
If transimpedance amplifiers are used to convert current signals to voltage signals, then signal processing capability is improved, but the dynamic range limitation prevents complete noise elimination
Solution Approach 1:
The noise current is detected and duplicated before being subtracted from the signal current. This preliminary action of noise detection and duplication occurs prior to the final comparison stage, allowing the system to prepare the exact noise current magnitude and direction needed for cancellation, thereby overcoming dynamic range limitations
Solution Approach 2:
The noise current, which is normally a harmful factor, is converted into a beneficial element by duplicating it and using it for active cancellation. The noise photo diode converts noise into a measurable current signal, and this same noise current is then used to counteract the harmful noise in the output, transforming the harmful factor into a useful tool for noise elimination
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
Effectively eliminates noise from output signals without relying on comparator directionality or dynamic range limitations, ensuring accurate signal transmission.
Implementation Method 1
a light-emitting device 11 that emits light L in accordance with an input electric signal
Implementation Method 2
a photo diode 21 that converts the optical signal L1 into an optical current
Data Source
AI summary
A light-emitting unit outputs an optical signal corresponding to an input electric signal. A light-receiving unit is electrically insulated from the light-emitting unit and outputs an electric signal according to the received optical signal as an output signal. In the light-receiving unit, a first light-receiving device outputs an optical current according to the optical signal. A second light-receiving device is provided not to receive the optical signal. A current duplication circuit duplicates a current flowing through the second light-receiving device. A current-voltage conversion circuit converts a current, which is generated by subtracting the current duplicated by the current duplication circuit from a current flowing through the first light-receiving device, into a voltage signal. A comparator output a result of a comparison between the voltage signal converted by the current-voltage conversion circuit and a threshold voltage as the output signal.