Optical Receiver Amplifier Offset Compensation Without Linear Range Loss
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Solution Overview
Problem
Conventional amplifiers with offset compensation mechanisms narrow the linearly operable range due to the shift in operating point, making them inadequate for digital coherent applications where large discrepancies in optical hybrid and photodiode performance can lead to unacceptable offsets.
Innovation Solution
The amplifier incorporates a common base buffer with base-grounded transistors and an offset compensator that generates control signals to adjust the base of the transistors negatively, providing a low-pass filter to compensate for offsets without affecting the output levels, thus maintaining the linearly operable range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional offset compensation mechanisms are used in amplifiers, then offset between complementary signals is reduced, but the linearly operable range is narrowed due to operating point shift
Solution Approach 1:
The amplifier is divided into separate functional blocks: a differential amplifier for signal amplification and a dedicated offset compensator for offset correction. This segmentation allows each block to perform its function independently, preventing offset compensation from affecting the differential amplifier's operating point and linear range.
Solution Approach 2:
An offset compensator is introduced as an intermediary component between the differential amplifier and the output. This compensator generates correction signals that are added to the differential amplifier output, allowing offset compensation without directly interfering with the differential amplifier's bias conditions.
2Measurement precision
If offset compensator adjusts the operating point to compensate offset, then offset is reduced, but the bias level of differential amplifier shifts
Solution Approach 1:
The system separates offset compensation from bias control by using independent circuits for each function. The differential amplifier maintains stable bias levels while the offset compensator independently generates and applies correction signals, preventing bias level shifts.
Solution Approach 2:
The offset compensator uses feedback from the differential amplifier output to detect offset levels and generates appropriate correction signals. This feedback mechanism allows automatic offset compensation while maintaining stable bias conditions through proper circuit design.
Data Source
AI summary
An amplifier for an optical receiver is disclosed. The amplifier includes a common base buffer, a differential amplifier, and some buffer amplifiers, where circuit block from the common base buffer to the buffer amplifiers have the differential arrangement and are connected in series in this order. The amplifier further includes an offset compensator that receives the outputs of the buffer amplifier put in the rear end of the amplifier and outputs control signals, which are complementary to each other and filtered by a low-pass-filter, to the base of the transistors in the common base buffer to compensate the offset appeared in the output of the buffer amplifier.