Photoreceiver Circuit Bootstrapping Parasitic Capacitance
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Solution Overview
Problem
Conventional photo receiver circuits face limitations in signal bandwidth and noise due to parasitic capacitances, which compromise their performance in fiber optic and lidar systems, requiring higher bandwidth and lower noise to achieve effective signal processing.
Innovation Solution
The proposed solution involves a photo receiver circuit design that includes a photo diode, a first amplifier for voltage level shifting, and a feedback resistor, which effectively bootsrap parasitic capacitance and reduces noise by using a level shifting amplifier to maintain a constant voltage difference, thereby increasing signal bandwidth and reducing noise gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional transimpedance amplifier with feedback resistor is used, then the photo current is converted to voltage signal, but the signal bandwidth is limited and noise is increased due to parasitic capacitances
Solution Approach 1:
The circuit is divided into two separate amplifier stages: a first amplifier (transimpedance amplifier) that converts photo current to voltage, and a second amplifier (voltage buffer) that provides impedance transformation and level shifting. This segmentation allows each stage to be optimized independently, with the first stage focusing on low-noise current-to-voltage conversion and the second stage providing bandwidth extension through impedance transformation.
Solution Approach 2:
The second amplifier acts as an intermediary between the first amplifier and the load. It transforms the high-impedance output of the first amplifier to a low-impedance output, effectively isolating the noise-sensitive transimpedance conversion stage from the bandwidth-demanding load, thereby extending overall signal bandwidth without compromising noise performance.
2Object-affected harmful factors
If the feedback resistor is increased to reduce noise, then the noise gain is reduced, but the signal bandwidth is further limited by parasitic capacitances
Solution Approach 1:
The second voltage buffer amplifier serves as an intermediary that decouples the feedback network from the load. By providing a low-impedance drive to the load, it reduces the effective capacitive loading on the first amplifier, allowing the use of larger feedback resistors for noise reduction without proportionally sacrificing bandwidth.
Solution Approach 2:
The circuit transforms the impedance parameters between stages: the first amplifier operates with high output impedance optimized for noise performance, while the second amplifier provides low output impedance optimized for bandwidth. This parameter transformation allows the system to achieve both low noise and high bandwidth simultaneously.
3Speed
If a level shifting amplifier is added to the circuit, then the signal bandwidth is increased and noise is reduced, but the circuit complexity increases
Solution Approach 1:
The second amplifier is designed to perform multiple functions simultaneously: voltage buffering, impedance transformation, and level shifting. By consolidating these functions into a single amplifier stage, the circuit achieves bandwidth extension and noise reduction without adding excessive complexity, as the same components serve multiple purposes.
Solution Approach 2:
The voltage buffer and level shifter functions are merged into a single second amplifier stage. This consolidation avoids the need for separate buffer and level-shifting circuits, reducing the overall component count and circuit complexity while still achieving the desired bandwidth and noise performance improvements.
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 design achieves a significantly higher signal bandwidth and lower noise compared to conventional circuits, with the signal bandwidth increased by five times and noise reduced by a factor of the square of the ratio of feedback capacitor to parasitic capacitance, while maintaining a simpler circuit design and lower power consumption.
Implementation Method 1
The photo diode receives a light signal producing a photo current
Data Source
AI summary
Photo receiver circuits comprising photo diode, a first amplifier, a second amplifier, and a feedback resistor are disclosed. The photo diode receives a light signal producing a photo current and the circuit produces an output voltage proportional to the photo current. In one example, the second amplifier coupled across the photo diode provides a voltage level shift between the input terminal and the output terminal, bootstrapping the parasitic capacitance out.