TIA Supply Regulation Using Output DC Feedback for Linearity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Trans-impedance amplifiers (TIAs) in high-speed fiber optic communication systems face challenges in maintaining linear and well-controlled gain, as well as stability of DC voltage outputs, which are affected by process, voltage, and temperature variations, leading to variations in the DC voltage at the output and potential non-linearity due to the current versus voltage characteristics of triode MOS transistors.
Innovation Solution
The implementation of a Low Drop-Out (LDO) circuit configured to adjust the supply voltage responsive to the DC voltage output of the TIA, using an operational amplifier to regulate the supply voltage towards a reference voltage, and an input DC current cancellation circuit to maintain a stable DC input voltage, thereby reducing variations and improving linearity by keeping the input and output DC biases at a common reference value.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the supply voltage to the TIA is regulated using a traditional LDO circuit, then the DC voltage stability is improved, but the linearity and gain control deteriorate due to voltage drops across feedback resistors
Solution Approach 1:
The patent implements a feedback mechanism where the LDO circuit monitors the DC voltage at the TIA output and adjusts the supply voltage accordingly. This closed-loop feedback compensates for voltage drops across feedback resistors, maintaining both DC stability and linearity by dynamically adjusting the supply voltage to counteract deviations caused by resistor voltage drops.
Solution Approach 2:
The patent changes the supply voltage parameter dynamically based on the measured DC output voltage. By adjusting the supply voltage in response to detected deviations, the system maintains optimal operating conditions for linearity while ensuring DC stability, resolving the contradiction between these two parameters.
2Stability of the object's composition
If the LDO circuit regulates a larger portion of the supply DC current, then the DC voltage control is improved, but the power overhead and complexity increase
Solution Approach 1:
The patent applies partial regulation by having the LDO circuit regulate only a portion of the total supply DC current rather than the entire current. This partial action approach provides sufficient DC voltage control to maintain stability while minimizing the power overhead and complexity associated with full-current regulation.
3Manufacturing precision
If the LDO circuit adjusts the supply voltage to compensate for PVT variations, then the gain control is improved, but the device complexity increases
Solution Approach 1:
The patent uses a feedback-based approach where the LDO circuit monitors the TIA output DC voltage and automatically adjusts the supply voltage to compensate for PVT variations. This feedback mechanism provides effective gain control without requiring complex compensation circuits, as the adjustment is performed automatically based on real-time measurements.
Solution Approach 2:
The LDO circuit performs self-adjustment by monitoring its own output effects on the TIA and automatically correcting supply voltage deviations. This self-service capability enables PVT compensation and gain control without requiring external complex control systems, thereby limiting the increase in overall device complexity.
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
An apparatus, such as a coherent optical receiver, includes a trans-impedance amplifier, TIA, (410) and a low dropout, LDO, voltage regulator circuit for providing a supply voltage (VCCREG) to the TIA (410). The LDO circuit is configured to adjust the supply voltage responsive to a DC voltage (VCMOUT) at an output of the TIA (410). In some implementations the LDO circuit may provide only a fraction of a supply current to the TIA (410), with another fraction provided by a partial current replica source.