Differential Optical Receiver Biasing for EMI Rejection
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Solution Overview
Problem
Optical sensing devices are prone to electromagnetic interference (EMI), which contaminates weak optical signals and requires significant amplification, leading to interference amplification and signal distortion.
Innovation Solution
A fully differential signal path architecture with a photodetector reverse-biased by a common mode voltage, utilizing operational amplifiers and capacitors to filter out electromagnetic interference and prevent it from reaching the amplifier circuit, thereby reducing interference amplification and enhancing signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If amplification 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 adding common mode voltage offsets to the photodetector inputs before the optical signal is converted to electrical signal. This preliminary voltage conditioning establishes a stable operating point that prevents subsequent interference amplification in the amplification stages, while still allowing the weak optical signal to be properly amplified.
Solution Approach 2:
The patent introduces common mode voltage as an intermediary element that mediates between the photodetector and the amplification circuitry. This common mode voltage acts as a buffer that stabilizes the operating point and prevents interference from being amplified, while allowing the signal amplification to proceed independently.
2Reliability
If common mode voltage is added to the photodetector, then interference rejection is improved, but circuit complexity increases
Solution Approach 1:
The patent applies universality by using the same common mode voltage generation circuit to serve multiple functions: it provides the offset voltage to the photodetector, establishes the operating point for the amplification stages, and simultaneously rejects common mode interference. This multi-functionality reduces the need for separate circuits for each function.
Solution Approach 2:
The patent merges the common mode voltage generation with the existing biasing circuitry of the photodetector. Instead of adding a completely separate circuit, the common mode voltage is integrated into the existing voltage supply network, combining multiple functions into a unified circuit structure that minimizes additional complexity.
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 rejects common-mode interference, reduces electromagnetic interference and electrostatic discharge effects, and increases the dynamic range of the optical signal, minimizing non-linearity and amplification errors, resulting in a cleaner and amplified optical signal.
Implementation Method 1
a photodetector, wherein the photodetector is reverse-biased by a reverse-bias voltage (V RB )
Data Source
Figure 1
Figure 2
Figure 3A
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.