Opto-Electric Amplifier Feedback Circuit for DC Current Cancellation
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Solution Overview
Problem
Existing opto-electric amplifier circuits with photodiodes face challenges in reducing noise levels and dynamic signal range due to large DC or low-frequency components, particularly under low supply voltages, where typical solutions like transimpedance amplifiers with resistors and capacitors result in high noise and large component sizes.
Innovation Solution
An amplifier circuit with a detection path and feedback path incorporating an integrator, level-shifter circuit, and bypass transistor, which uses negative feedback to filter out high-frequency components and suppress DC and low-frequency signals, allowing for low-noise operation and reduced dynamic range requirements, suitable for integrated circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transimpedance amplifier with a resistor for DC current path and a capacitor for separating target signal is used, then the DC or low frequency components can be reduced, but the noise levels increase and the capacitor size becomes large
Solution Approach 1:
The patent implements an active feedback loop using an operational amplifier to sense the output voltage and generate a compensating current that cancels the DC component at the photodiode. This feedback mechanism eliminates the need for large passive components while maintaining low noise performance, as the feedback amplifier actively suppresses DC rather than relying on passive filtering
Solution Approach 2:
The patent changes the operating parameters by using an operational amplifier with high gain to dynamically adjust the feedback current based on the output voltage. This allows the system to maintain low noise while achieving DC suppression, as the active feedback can adapt to varying signal conditions unlike fixed passive components
2Adaptability or versatility
If the resistor value is reduced to handle large DC current range, then the dynamic signal range is reduced, but the noise levels increase
Solution Approach 1:
The active feedback loop dynamically adjusts the DC operating point by sensing the output voltage and generating a compensating current. This allows the circuit to handle large DC current ranges without being constrained by fixed resistor values, as the feedback mechanism actively maintains the desired operating conditions across varying current levels
Solution Approach 2:
The patent transitions from static passive components to dynamic active feedback that continuously adapts to changing DC current conditions. The operational amplifier actively regulates the feedback current to maintain optimal operating conditions, providing adaptability across large DC current ranges without the noise penalties of fixed resistor-based approaches
3Area of stationary object
If smaller capacitor size is used, then the chip area is reduced, but the noise performance deteriorates
Solution Approach 1:
The active feedback loop replaces the need for large passive filtering capacitors by using an operational amplifier to actively suppress DC and low-frequency components. This feedback mechanism achieves the same signal separation function with much smaller or eliminated capacitors, reducing chip area while maintaining low noise performance through active rather than passive filtering
4Adaptability or versatility
If active feedback loops are used to overcome resistor limitations, then the DC current range handling is improved, but the sensitivity to noise increases
Solution Approach 1:
The patent implements a carefully designed active feedback loop that achieves DC current range adaptability while controlling noise sensitivity. The feedback architecture uses the operational amplifier to generate a compensating current that cancels DC components without amplifying noise, and the feedback path is designed to be less sensitive to noise than previous active feedback approaches
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 proposed circuit achieves improved noise performance and reduced dynamic range, enabling effective DC current cancellation with a lower cut-off frequency and smaller chip area, maximizing DC suppression without linearizing transconductance, thus addressing the limitations of existing solutions.
Implementation Method 1
The integrator is connected to the amplifier output via an integrator input and comprises a level-shifter circuit in a negative feedback
Implementation Method 2
the DC transconductance of the feedback path varies the DC current due to the DC current dependency of the transconductance of bypass transistor
Implementation Method 3
The measurement current is a photocurrent if the connected detector is a photo detector, like a photodiode
Data Source
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AI summary
An amplifier circuit for an opto-electric device comprises a detection path comprising a main amplifier (1) for providing an output voltage (Vout) as a function of a measurement current (Ipd) having a first and second amplifier input (11, 12) and an amplifier output (13). A feedback path comprises an integrator (2) and a bypass transistor (3). The integrator (2) is connected to the amplifier output (13) via an integrator input (25) and comprises a level-shifter circuit (23) in a negative feedback path for controlling a level-shifted voltage (VR2). The bypass transistor (3) is connected to the level-shifter circuit (23) via its control side (31) to receive a control voltage (VM2) depending on the level-shifted voltage (VR2), and provides a feedback current (Ifb) at the first amplifier input (11) being proportional to the level-shifted voltage (VR2).