Photodiode Receiver Capacitive Attenuation for Wide Dynamic Range
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Solution Overview
Problem
Conventional photodiode receivers face challenges in achieving a high dynamic range with noise optimization, particularly in handling weak and strong light signals while maintaining a consistent frequency response, as existing solutions either degrade noise or compromise on admissibility and pulse shape.
Innovation Solution
The implementation of a reactive series-parallel circuit with a capacitive current divider and an aperiodic attenuation pad, which includes a resistor and capacitor in parallel, upstream of the transimpedance amplifier, allows for signal attenuation without degrading noise and maintains low-frequency response, and can be switched for different gain settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gain of the TIA amplifier is increased by increasing the feedback resistor Rf, then the sensitivity for weak signals is improved, but the admissibility for strong signals deteriorates and the voltage swing at the output is limited
Solution Approach 1:
The receiver is divided into multiple TIA amplifier stages with different gain levels. Each stage has its own feedback resistor (Rf1, Rf2, etc.) with progressively lower values, allowing the system to segment the dynamic range into multiple manageable ranges rather than using a single high-gain amplifier
Solution Approach 2:
The system dynamically switches between different TIA amplifier stages based on the input signal level. A detector monitors the output voltage swing and activates appropriate stages to maintain optimal operation, making the gain adaptive rather than fixed
2Adaptability or versatility
If the feedback resistor Rf is reduced to improve admissibility for strong signals, then the dynamic range is extended, but the noise performance deteriorates and the conversion gain decreases
Solution Approach 1:
Multiple TIA stages with different feedback resistor values segment the signal range. Low-signal stages use high Rf values for low noise, while high-signal stages use lower Rf values for high admissibility, with each stage optimized for its specific range
Solution Approach 2:
Switching elements act as intermediaries to connect the photodiode to different TIA stages based on signal level. These switches route the input signal to the appropriate amplifier stage, enabling the system to achieve both low noise and high admissibility at different times
3Adaptability or versatility
If a switched resistive attenuator is placed between the photodiode and TIA amplifier to reduce gain for strong signals, then the admissibility is improved, but the noise is degraded due to resistor noise and parasitic capacitances affect the transfer function
Solution Approach 1:
The patent replaces resistive attenuation with capacitive attenuation using a current divider formed by capacitors. This substitution eliminates the thermal noise generated by resistors while achieving the same gain reduction effect, and the capacitive elements have negligible parasitic effects compared to resistors
4Adaptability or versatility
If the feedback resistor Rf is changed to modify the gain, then the conversion gain is adjusted, but the transfer function and frequency response are modified due to changes in proper pulsation and damping
Solution Approach 1:
The patent changes the capacitive parameters (adding parallel capacitance Cp and adjusting Cf) to compensate for the effects of different Rf values. By adjusting these capacitive parameters, the system maintains a constant transfer function and frequency response across different gain settings, decoupling gain control from transfer function modification
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 solution enables a receiver with higher admissibility, gain-independent frequency response, optimized noise performance, and consideration of parasitic capacitances, without compromising sensitivity or power handling, while maintaining the same transfer function with and without attenuation.
Implementation Method 1
a photodiode (1) capable of generating an electric current (Id) in response to this light signal
Implementation Method 2
a reactive series-parallel circuit, consisting of a capacitor (Cp) which, combined with the capacitor (Cd) of the diode, produces a current divider, called an attenuation pad
Data Source
Figure 1a~2
Figure 3a
Figure 3b
AI summary
The invention relates to a receiver of a pulsed light signal which comprises: - a photodiode (1) able to generate an electric current (ID) in response to this light signal, having as characteristic a capacitance Cd, - an electric earth, - a transimpedance amplifier (2) linked at the input of the photodiode by a linking capacitor Clink. It comprises an attenuation pad (30) situated between the photodiode and the transimpedance amplifier, consisting of a capacitor Cp with Cp=Cd/(α-1 ), a being a predetermined attenuation with a >1.