Light Receiver Bias Filter Using Series Capacitors for High Voltage
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Solution Overview
Problem
Integrated circuits with transimpedance amplifiers face challenges in applying low-pass filters to both photodiodes and avalanche photodiodes due to differing bias voltage requirements, as the internal capacitive elements' withstand voltage is limited to several volts, making them unsuitable for the higher voltage needs of avalanche photodiodes.
Innovation Solution
An integrated circuit design featuring a low-pass filter with multiple serially connected capacitive elements, where the capacitance value and withstand voltage can be adjusted by grounding select terminals, allowing the filter to handle both photodiode and avalanche photodiode bias voltages, utilizing a resistor and capacitor serial-connection configuration with one end connected to a power terminal and the other to a bias application electrode, and connecting each capacitive element's terminals to ground potential for reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an internal capacitive element is used in the low-pass filter, then the filter is easy to integrate into the circuit, but the withstand voltage is limited to several volts making it unsuitable for avalanche photodiodes
Solution Approach 1:
The patent divides a single large-capacitance capacitor into multiple smaller capacitive elements connected in series. Each capacitive element has a withstand voltage of several volts, and by connecting multiple elements in series, the total withstand voltage becomes the sum of individual voltages (e.g., 5 elements × several volts = 20-30 volts), enabling compatibility with avalanche photodiodes while maintaining integrability.
Solution Approach 2:
The patent changes the electrical parameters of the low-pass filter by adjusting the number of capacitive elements connected in series. This allows the filter to be configured for different voltage requirements: fewer elements for photodiodes (several volts) and more elements for avalanche photodiodes (20-30 volts), thus resolving the contradiction between integration ease and voltage tolerance.
2Reliability
If the low-pass filter is designed for high withstand voltage, then it can be used with avalanche photodiodes, but the capacitance value becomes insufficient for proper filtering
Solution Approach 1:
By segmenting the total capacitance into multiple series-connected elements, each with moderate capacitance value, the patent achieves both high withstand voltage (through series connection) and sufficient total capacitance (by having enough elements). The total capacitance is the reciprocal of the sum of reciprocals of individual capacitances, allowing proper filtering performance while maintaining high voltage tolerance.
3Reliability
If multiple capacitive elements are serially connected, then the withstand voltage increases to 20-30 volts, but the circuit complexity increases
Solution Approach 1:
The patent merges multiple capacitive elements into a unified low-pass filter structure that functions as a single filtering component. Although internally composed of multiple series-connected elements, the overall structure is integrated into the transimpedance amplifier circuit as one functional unit, minimizing external connections and reducing overall circuit complexity despite the internal segmentation.
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 configuration enables the low-pass filter to be applicable to both photodiode and avalanche photodiode bias voltages, effectively extending the usable voltage range from several volts to 20-30 volts, ensuring optimal performance for avalanche photodiodes while maintaining functionality for photodiodes.
Implementation Method 1
The low-pass filter has a resistor and a capacitor serial-connection in which a plurality of capacitive elements are serially connected
Implementation Method 2
With respect to a resistor in the low-pass filter, one end thereof is connected to a power terminal to which a bias voltage is inputted
Data Source
AI summary
An integrated circuit includes an amplifier for amplifying an electric current signal from an external light receiving element, and a low-pass filter. The low-pass filter has a resistor and a capacitor serial-connection in which multiple capacitive elements are serially connected. With respect to the resistor in the low-pass filter, one end thereof is connected to a power terminal to which the bias voltage is inputted, and the other end thereof is connected to an input terminal of the capacitor serial-connection and to a bias application electrode of the light receiving element through which the bias voltage is applied. With respect to the capacitor serial-connection in the low-pass filter, each connection terminal between two of the serially connected capacitive elements and an output terminal of the capacitor serial-connection, are connected to their respective capacitance terminals to which a ground potential as a reference for the bias voltage is connected selectively.