Differential Optical Receiver Circuit for RF Interference Rejection
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Solution Overview
Problem
Optical sensing devices face interference from electromagnetic interference (EMI), particularly radio frequency (RF) interference, which contaminates optical signals and is amplified along with the desired signal, making it challenging to accurately detect and process weak optical signals.
Innovation Solution
A fully differential architecture is implemented in the circuit for detecting optical signals, which includes capacitors coupled in parallel to filter common-mode interference and noise, and a controller manages switches to alter the circuit mode between reset and scan periods, reducing input-referred current detection errors and effectively rejecting common-mode interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If amplifier circuits are used to amplify weak optical signals, then the signal strength is improved, but electromagnetic interference is also amplified along with the signal
Solution Approach 1:
The patent applies preliminary action by performing interference filtering before the amplification stage. The circuit processes and filters the optical signal to remove electromagnetic interference components before they enter the amplifier circuits, preventing the interference from being amplified along with the desired signal.
Solution Approach 2:
The patent segments the signal processing into distinct functional stages: an interference filtering stage that processes the optical signal first, followed by a separate amplification stage. This segmentation allows independent optimization of each stage - the filtering stage removes interference while the amplification stage boosts the cleaned signal without amplifying interference.
2Object-generated harmful factors
If interference filtering is performed before amplification, then interference signals are reduced, but the circuit complexity increases
Solution Approach 1:
The patent merges the interference filtering function with the existing optical detection circuitry by implementing the filtering within the detector circuit itself rather than as a separate external component. This integration approach reduces overall system complexity while still achieving effective interference reduction before amplification.
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 fully differential architecture significantly reduces noise power and RF electromagnetic interference, enhancing the accuracy of optical signal detection by canceling common-mode interference and reducing errors, thereby improving the signal-to-noise ratio.
Implementation Method 1
capacitors coupled in parallel to filter common-mode interference and noise
Implementation Method 2
effectively rejecting common-mode interference
Data Source
AI summary
An apparatus for detecting optical signals includes a photodetector. The photodetector is reverse-biased by a first voltage and a second voltage is added to the first voltage to provide an offset equal to the second voltage for the photodetector. A first circuit is coupled to the first circuit to provide the second voltage for the photodetector and a second circuit is coupled to the first circuit to provide the first voltage to the photodetector to reverse-bias the photodetector. The second circuit provides an output voltage proportional to a current of the photodetector at an output of the second circuit.