Optical Receiver DC and AC Shunting for Overload Distortion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Fiber optic receivers using higher order modulation schemes face signal distortion due to gain requirements for low input signals, which become unacceptable at high input signal strengths, necessitating a method to remove DC and AC current components without altering the receiver's operational integrity.
Innovation Solution
A circuit with amplifier and overload circuitry is used to convert current signals to voltage, detect threshold exceedance, and shunt DC and AC currents through separate paths, maintaining signal integrity by scaling AC components linearly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gain is increased to improve sensitivity for low input signals, then signal detection capability is improved, but signal distortion increases at high input signal strength
Solution Approach 1:
The amplifier gain is made dynamically adjustable through automatic gain control circuitry that responds to signal strength levels. The system automatically switches between high gain mode (for low input signals) and low gain mode (for high input signals), preventing distortion while maintaining sensitivity. This dynamic adaptation resolves the contradiction by allowing the gain to change based on operating conditions rather than being fixed.
Solution Approach 2:
The system changes the amplifier gain parameter based on detected signal strength. When the input signal exceeds a threshold level, the automatic gain control reduces the gain to prevent distortion. This parameter change allows the system to maintain optimal performance across varying signal conditions, resolving the trade-off between sensitivity and distortion.
2Object-affected harmful factors
If DC component is removed from the current signal, then distortion at high input levels is reduced, but signal processing complexity increases
Solution Approach 1:
The signal processing is segmented into distinct functional blocks: a transimpedance amplifier stage, an automatic gain control stage, and a detection stage. The DC removal function is specifically implemented in the automatic gain control stage through separate DC and AC signal paths. This segmentation allows DC removal to be implemented in a controlled manner without unnecessarily complicating the entire signal processing chain.
Solution Approach 2:
An automatic gain control circuit acts as an intermediary between the amplifier and the detector. This intermediary circuit selectively removes DC components while preserving AC signal components, and it also provides gain control to prevent distortion. By placing this intermediary stage, the system achieves distortion reduction without requiring complex processing throughout the entire signal chain.
Data Source
AI summary
A circuit may include amplifier circuitry configured to receive a current signal at an amplifier input node, convert the current signal to a voltage signal, and output the voltage signal at an amplifier output node. The circuit may also include overload circuitry configured to receive a replica DC input voltage and a replica DC output voltage. The overload circuitry may be further configured to detect that the current signal exceeds a threshold level based on the replica DC input voltage and the replica DC output voltage. In addition, the overload circuitry may be configured to, in response to and based on detecting that the current signal exceeds the threshold level, direct DC current of the current signal through a DC shunt path and direct AC current of the current signal through an AC shunt path. The AC shunt path may be different from the DC shunt path.