Optical Receiver Circuit with Dynamic Variable Resistors
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Solution Overview
Problem
Optical receiver modules face challenges in achieving linear amplification and flat frequency characteristics across a wide dynamic range, especially at high modulation speeds like 64 Gbaud, due to variations in optical signal intensity and frequency response degradation.
Innovation Solution
The optical receiver circuit incorporates an inductor and variable resistors connected to a trans-impedance amplifier, with control signals adjusting resistance values to stabilize peaking effects and maintain flat frequency characteristics, thereby improving output quality across varying signal intensities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an inductor is provided between the photosensor and the preamplifier circuit to raise high-frequency gain, then the frequency band of -3 dB is improved, but the flatness of frequency characteristics deteriorates when optical signal intensity is high
Solution Approach 1:
The patent applies dynamics by making the resistance values changeable according to optical signal intensity. Two variable resistors are used: a first variable resistor connected to the input terminal whose resistance varies with optical signal intensity, and a second variable resistor connected to the inductor whose resistance also varies with optical signal intensity. This dynamic adjustment allows the circuit to adapt its frequency characteristics based on operating conditions, resolving the contradiction between maintaining wide frequency band and flat frequency response.
Solution Approach 2:
The patent changes the resistance parameters of the variable resistors based on optical signal intensity. When optical signal intensity is high, the resistance values are adjusted to reduce the peaking effect caused by the inductor, thereby flattening the frequency characteristics. When optical signal intensity is low, the resistance values are adjusted to maintain the frequency band extension provided by the inductor. This parameter change strategy resolves the technical contradiction.
2Adaptability or versatility
If a gain variable circuit is used to achieve linear amplification within a wide dynamic range, then the adaptability to different optical signal intensities is improved, but the device complexity increases
Solution Approach 1:
The patent achieves multi-functionality by having the variable resistors serve dual purposes: they control the gain of the preamplifier circuit to handle wide dynamic range of optical signal intensities, and simultaneously control the frequency characteristics by adjusting the interaction between the inductor and resistive elements. This universal approach allows one circuit configuration to address both gain control and frequency response optimization, reducing overall device complexity while maintaining adaptability.
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 enhances the frequency band of the trans-impedance amplifier, reducing distortion and maintaining optimal output characteristics across the dynamic range of optical signal intensities, even at high modulation speeds.
Implementation Method 1
an inductor having one end electrically connected to the input terminal and another end electrically connected to the input of the trans-impedance amplifier
Implementation Method 2
a photosensor PD (photo-detector), for example, an avalanche photodiode (APD) converting an optical signal subjected to intensity modulation into a current signal (photo-current)
Data Source
AI summary
An optical receiver circuit includes an input terminal receiving current signal from photodetector; a trans-impedance amplifier converting the current signal into voltage signal; an inductor having one end connected to the input terminal and another end connected to the input of the trans-impedance amplifier; a first variable resistor having a first end connected to the other end of the inductor, a second end receiving bias voltage, and a third end receiving a control signal, where the first variable resistor varies a resistance between the first end and the second end in accordance with the control signal; and a second variable resistor having a first end connected to the one end of the inductor, a second end receiving bias voltage, and a third end receiving a control signal, where the second variable resistor varies a resistance between the first end and the second end in accordance with the control signal.