Photodetection Circuit Suppressing Oscillation and Limiting Current
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Solution Overview
Problem
Conventional photodetecting circuits experience oscillation issues with high modulation frequency light and generate excess current from intense light sources like direct sunlight, leading to operational troubles.
Innovation Solution
A photodetecting circuit design incorporating a transistor between the photodiode and integrating circuit, a resistive element, and an operational amplifier to control the bias voltage, suppressing oscillations and acting as a current limiter by using a resistive element to manage photoelectric current, and incorporating comparators and a reset signal generating mechanism to convert current into frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photodiode is driven to zero-bias to reduce dark current, then dark current is reduced, but output oscillation occurs when high modulation frequency light is incident
Solution Approach 1:
A transistor is introduced as an intermediary component between the photodiode and the integrating circuit. The transistor acts as a buffer that isolates the photodiode from the integrating circuit's influence, preventing oscillation while maintaining zero-bias operation. The transistor's gate/base is controlled by an operational amplifier that monitors the voltage across a series resistor, creating a feedback mechanism that stabilizes the photodiode's bias condition without requiring external bias voltage.
Solution Approach 2:
The invention changes the electrical parameters dynamically by using a transistor to adjust the coupling between the photodiode and integrating circuit. The transistor's operating state is modulated based on the light intensity and frequency, allowing the circuit to adapt to different operating conditions (dark state vs. illuminated state) and prevent oscillation across various modulation frequencies.
2Quantity of substance
If intense light such as direct sunlight is made incident on the photodiode, then photoelectric current increases, but excess current causes troubles in circuit operation
Solution Approach 1:
A transistor is introduced as an intermediary component between the photodiode and the integrating circuit. The transistor acts as a buffer that isolates the photodiode from the integrating circuit's influence, preventing oscillation while maintaining zero-bias operation. The transistor's gate/base is controlled by an operational amplifier that monitors the voltage across a series resistor, creating a feedback mechanism that stabilizes the photodiode's bias condition without requiring external bias voltage.
Solution Approach 2:
The invention changes the electrical parameters dynamically by using a transistor to adjust the coupling between the photodiode and integrating circuit. The transistor's operating state is modulated based on the light intensity and frequency, allowing the circuit to adapt to different operating conditions (dark state vs. illuminated state) and prevent oscillation across various modulation frequencies.
3Device complexity
If no resistive element is provided, then circuit is simpler, but output oscillation occurs at high modulation frequencies
Solution Approach 1:
A transistor is introduced as an intermediary component between the photodiode and the integrating circuit. The transistor acts as a buffer that isolates the photodiode from the integrating circuit's influence, preventing oscillation while maintaining zero-bias operation. The transistor's gate/base is controlled by an operational amplifier that monitors the voltage across a series resistor, creating a feedback mechanism that stabilizes the photodiode's bias condition without requiring external bias voltage.
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 circuit effectively suppresses output oscillations, operates as a zero-bias circuit for small photoelectric currents, and functions as a limiter for excess currents, preventing abnormal operations and reducing the impact of parasitic capacitance.
Implementation Method 1
a photodiode PD, a transistor TR1 provided between the photodiode and the integrating circuit
Data Source
Figure 1
Figure 2(a)~2(e)
Figure 3
AI summary
This photodetecting circuit 1 is capable of suppressing oscillation of an output, and operates as a zero bias circuit in a case of a small photoelectric current to an extent that a dark current is concerned about, and limits an output current in a case of a large photoelectric current to an extent that troubles are caused in the circuit operation. Because a resistive element TR2 is provided in the photodetecting circuit 1, even when a modulation frequency of light, in other words, a frequency of a photoelectric current I flowing in a photodiode PD is made higher, oscillation can be suppressed. Further, due to the resistive element TR2 being inserted, this functions as a limiter as well, and a bias voltage to be applied to the photodiode PD is made to be a positive bias voltage, which prevents an excess current from being generated to suppress abnormal operations of the circuit.