Differential Optical Receiver Circuit for EMI-Resistant Sensing
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Solution Overview
Problem
Optical sensing devices face interference from electromagnetic interference (EMI), particularly radio frequency (RF) interference, which is amplified along with the optical signal, contaminating the detected signals and requiring effective rejection mechanisms to maintain signal integrity.
Innovation Solution
The implementation of fully differential signal paths and reverse-biasing of photodetectors, combined with common mode voltage adjustment and ESD protection, effectively cancels common-mode interference and reduces non-linearity, thereby minimizing the impact of EMI and electrostatic discharge (ESD) on the detected signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If amplifier circuits are used to amplify weak optical signals, then signal detection capability is improved, but electromagnetic interference is also amplified along with the signal
Solution Approach 1:
The patent divides the signal path into differential pairs (positive and negative paths) that process signals separately but in a coordinated manner. By segmenting the signal processing into parallel differential paths, the system can amplify the optical signal while the differential structure inherently rejects common-mode electromagnetic interference that affects both paths equally.
Solution Approach 2:
The patent converts the harmful effect of electromagnetic interference into a beneficial filtering mechanism. By using fully differential architectures where both positive and negative paths are equally affected by EMI, the common-mode interference is transformed into a rejectable artifact that can be eliminated through differential subtraction, turning the universal coupling of EMI into a feature that enables common-mode rejection.
2Object-affected harmful factors
If fully differential architectures are used to reject common-mode interference, then EMI rejection is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple functions into the fully differential architecture: signal amplification, common-mode rejection, and ESD protection are all achieved through the integrated differential structure. By combining these functions into a unified architecture rather than adding separate components, the patent reduces overall system complexity while maintaining EMI rejection capabilities.
Solution Approach 2:
The fully differential architecture serves multiple purposes simultaneously: it amplifies weak optical signals, rejects common-mode electromagnetic interference, provides ESD protection through symmetric clamping diodes, and maintains signal integrity. This multi-functional design eliminates the need for separate dedicated components for each function, thereby reducing device complexity.
3Measurement precision
If reverse-bias voltage is applied to photodetectors, then detection linearity is improved, but susceptibility to electrostatic discharge increases
Solution Approach 1:
The patent applies ESD protection diodes in parallel with the reverse-biased photodetector before ESD events can occur. These protective elements are pre-positioned to clamp voltage spikes and protect the reverse-biased photodetector from electrostatic discharge damage, allowing the photodetector to operate at optimal reverse bias without compromising reliability.
Solution Approach 2:
The ESD protection diodes act as intermediary elements between the reverse-biased photodetector and external electrostatic threats. These diodes provide a safe discharge path for ESD events while leaving the photodetector's reverse bias intact, mediating between the need for high linearity operation and protection from electrostatic damage.
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 approach significantly reduces EMI and ESD-induced errors, enhancing the dynamic range and linearity of the optical signal detection, with EMI rejection improved by more than two orders of magnitude compared to non-differential architectures.
Implementation Method 1
A current of a photodetector is received... The current of the photodetector is amplified...
Data Source
AI summary
An apparatus includes a first circuit that has a photodetector. The photodetector is reverse-biased by a reverse-bias voltage. A common mode voltage is added to the reverse-bias voltage to provide an offset to the photodetector voltage. A second circuit is coupled to the first circuit to provide the common mode voltage for the first circuit. A third circuit is coupled to the second circuit that includes a first voltage source and a second voltage source having opposite voltages equal to half of the reverse-bias voltage. Each one of the first voltage source and the second voltage source are coupled between separate input and output nodes of input and output ports of the third circuit. The first voltage source and the second voltage source provide the reverse-bias voltage to the first circuit to reverse-bias the photodetector. The third circuit provides a photodetector current at an output of the third circuit.