Photodiode Receiver Attenuation Pad for Wide Dynamic Range
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Solution Overview
Problem
Conventional photodiode receivers face challenges in maintaining optimal sensitivity and noise performance across a wide dynamic range, as increasing gain degrades noise and reducing gain increases bandwidth, making it difficult to achieve a pulse shape independent of gain while maintaining frequency response.
Innovation Solution
A receiver design incorporating a series-parallel reactive circuit with a capacitor forming a current divider upstream of the transimpedance amplifier, along with an aperiodic attenuation pad that compensates for parasitic capacitance, allowing for adjustable gain without degrading noise, and using switchable components to maintain low-frequency response and bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gain of the TIA is increased to improve sensitivity for weak signals, then the noise performance degrades and the admittance decreases
Solution Approach 1:
The patent implements a switchable attenuation pad that can be dynamically activated or deactivated based on the signal strength. This dynamic adjustment allows the system to optimize between sensitivity and noise performance by switching configurations rather than using a fixed gain setting.
Solution Approach 2:
The attenuation pad acts as an intermediary element between the photodiode and the TIA. It provides controlled signal attenuation when needed, allowing the TIA to operate at optimal gain settings while preventing noise degradation through the use of low-noise resistive components.
2Speed
If the feedback resistor Rf is reduced to improve admittance, then the bandwidth increases but the noise performance worsens
Solution Approach 1:
The patent segments the gain control function into two independent parts: the TIA feedback resistor Rf that determines noise performance and bandwidth, and the switchable attenuation pad that provides gain adjustment. This segmentation allows Rf to be optimized for low noise while the attenuation pad handles bandwidth and gain requirements.
3Adaptability or versatility
If a switched resistive attenuator is placed between the photodiode and TIA to reduce gain for strong signals, then the admittance improves but the noise degrades and parasitic capacitance affects the transfer function
Solution Approach 1:
The patent applies local quality by using specific low-noise resistive components in the attenuation pad with carefully selected resistance values and noise figures. The attenuator is designed with local optimizations including matched impedance and minimized parasitic effects in critical signal paths.
4Adaptability or versatility
If the gain is changed to accommodate different signal levels, then the dynamic range improves but the transfer function and frequency response are modified
Solution Approach 1:
The switchable attenuation pad provides dynamic gain adjustment while the TIA maintains a fixed transfer function. The attenuation occurs before the TIA input, allowing gain variation without affecting the amplifier's frequency response characteristics or stability.
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 solution enables a receiver with improved admittance, noise-optimized performance, and frequency response independent of gain, allowing for effective detection of both weak and strong light signals without compromising sensitivity or power behavior.
Implementation Method 1
a photodiode adapted to generate an electric current Id in response to the light signal
Implementation Method 2
a series-parallel reactive circuit, consisting of a capacitor Cp which, combined with the diode capacitance Cd, forms a current divider, called an attenuation pad
Data Source
AI summary
A receiver of a pulsed light signal comprises a photodiode adapted to generate an electric current in response to this light signal, having a parasitic capacitance Cd as its characteristic; an electrical ground; and a transimpedance amplifier connected to the input of the photodiode by a linking capacitor Cliaison. It includes an attenuation pad located between the photodiode and the transimpedance amplifier, consisting of a capacitor Cp where Cp=Cd/(α−1), α being a predetermined attenuation, where α>1.