Transimpedance Amplifier Gain Control for Linear Optical Receivers
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Solution Overview
Problem
Current optical communication systems, particularly optical receivers, face challenges in handling variations in received optical powers, leading to noisy and non-linear electric output signals due to fluctuations in voltage, temperature, and process variations, resulting in degraded performance.
Innovation Solution
An optical receiver circuit with a transimpedance amplifier circuit, automatic gain control, and DC restoration component that adjusts equivalent transimpedance based on input current levels, ensuring constant output voltage amplitude and high linearity across a wide dynamic range, incorporating multiple gain amplifier stages and programmable feedback resistors for stability and noise immunity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed transimpedance amplifier is used, then the circuit is simple, but the output signal becomes noisy and non-linear when received optical power varies over several orders of magnitude
Solution Approach 1:
The patent implements dynamic gain adjustment by switching between multiple feedback resistors (Rf1, Rf2, Rf3, Rf4) with different resistance values based on the input signal level. The automatic gain control circuit monitors the output voltage and selectively connects appropriate resistors to maintain optimal transimpedance gain across varying optical power levels, preventing saturation and maintaining linearity.
Solution Approach 2:
The transimpedance gain is changed by switching between different feedback resistor values. The automatic gain control circuit adjusts the equivalent transimpedance parameter dynamically by selecting from discrete resistor values (e.g., 10kΩ, 100kΩ, 1MΩ, 10MΩ) to match the input signal strength, thereby maintaining consistent output performance across wide dynamic ranges.
2Measurement precision
If high gain is used to amplify weak signals, then small photocurrents are detectable, but the amplifier saturates when large photocurrents occur
Solution Approach 1:
The feedback resistor network is dynamically reconfigured based on the input signal amplitude. The automatic gain control circuit detects the output voltage level and switches between feedback resistors to provide high gain for weak signals and low gain for strong signals, preventing saturation while maintaining sensitivity.
Solution Approach 2:
The automatic gain control circuit uses feedback from the transimpedance amplifier output to monitor the signal level and control the switching of feedback resistors. This feedback mechanism ensures the amplifier operates within its linear range by adjusting the gain according to the actual input signal conditions.
3Adaptability or versatility
If multiple feedback resistors are used for gain control, then the dynamic range is extended, but the circuit complexity increases
Solution Approach 1:
The feedback path is segmented into multiple parallel resistor branches (Rf1, Rf2, Rf3, Rf4), each providing a different gain level. This segmentation allows the circuit to handle different signal levels independently, extending the dynamic range while keeping each individual resistor value manageable and standard.
Solution Approach 2:
The feedback resistor network serves multiple functions: it provides gain control for different signal levels, acts as an attenuation network, and enables the single transimpedance amplifier to handle a wide dynamic range of optical powers. The same resistor network structure is used for both gain adjustment and signal conditioning.
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 improves the linearity and reliability of optical receivers by maintaining constant output amplitude and reducing distortion, accommodating high-speed communications with linear modulations and wide dynamic range, while enhancing noise rejection and adaptability to variations.
Implementation Method 1
at least one photo detector, e.g. a photo diode, configured to convert a received light signal to an input current signal, e.g. a photocurrent
Data Source
AI summary
This invention relates to a optical receiver circuit (200) comprising: at least one photo detector (207) configured to convert a received light signal to an input current signal, a transimpedance amplifier circuit (201) with an input to receive the input current signal from the at least one photo detector (207) and being configured to convert the received input current signal to an output voltage signal to generate an output signal of the transimpedance amplifier circuit (201), wherein the transimpedance amplifier circuit comprises a plurality of gain amplifier stages (209, 210, 211), a DC restoration component (205), wherein the DC restoration component (205) is configured to receive the output voltage signal of the transimpedance amplifier circuit (201) for restoring the DC component of the received current signal and configured for outputting a corresponding current signal, and an automatic gain control component (204) configured for controlling via at least one programmable feedback resistor (226, 227) the equivalent transimpedance of the transimpedance amplifier circuit based on the signal output by the DC restoration component (205) to provide a constant output voltage amplitude for different current ranges of the input current signal.