Optical Receiver Calibration via Decaying Symbol Sequence
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Solution Overview
Problem
Existing optical receivers face challenges in calibrating the bias point and reference voltage due to variations in the average DC level of optical signals, leading to instability and increased complexity, cost, and power consumption, particularly in tracking changes and preventing loading of the current-to-voltage converter output.
Innovation Solution
A method for calibrating an optical receiver using a sequence with alternating groups of symbol types, where durations progressively decrease, allowing the feedback circuit to reach steady state and store a calibration value, which is used to adjust the bias point and reference voltage, enabling efficient operation without additional components or complex feedback loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an RC filter is used to obtain Vref from the output voltage, then the reference voltage can be obtained, but the optical signal must be DC balanced and the filter bandwidth must be carefully controlled to track DC level changes while providing stable Vref
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the optical receiver using a sequence with alternating groups of symbol types before normal operation. The calibration process determines optimal bias and reference voltage settings in advance, eliminating the need for complex continuous DC balancing during data transmission. This preliminary calibration stores the necessary correction values that compensate for DC level variations without requiring ongoing complex signal processing.
2Reliability
If periodic calibration is performed with Vref stored on a capacitor, then calibration can be maintained, but leakage current from the capacitor and inability to scale on-chip capacitor increase difficulty of implementation
Solution Approach 1:
The patent extracts the calibration information from the capacitor storage approach and implements it digitally through calibration values stored in standard memory elements or registers. By taking out the reliance on physical capacitor storage and its associated leakage current problems, the solution replaces it with digital representation of calibration parameters that can be easily stored, updated, and scaled on-chip without manufacturing difficulties.
Solution Approach 2:
The patent substitutes the mechanical/electrical capacitor-based storage system with a digital storage and processing system. Instead of relying on physical capacitor characteristics that suffer from leakage and scaling issues, the calibration information is represented as digital values that can be stored in standard semiconductor memory structures, eliminating the manufacturing and reliability problems associated with analog capacitor storage.
3Stability of the object's composition
If additional switches and capacitors are added to prevent loading of the current-to-voltage converter output and store bias voltage, then the feedback loop can be stabilized, but the cost, power consumption and complexity of the optical receivers increase
Solution Approach 1:
The patent applies self-service by using the existing output signal from the current-to-voltage converter to generate the feedback control voltage through digital processing. The calibration sequence causes the output to dither around the decision threshold, and this self-generated signal is processed digitally to produce the appropriate bias adjustments. This eliminates the need for additional dedicated components like switches and storage capacitors, reducing power consumption and complexity while maintaining feedback loop stability.
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 approach stabilizes the bias point and reference voltage, reducing the complexity, cost, and power consumption of optical receivers while allowing for efficient tracking of changes in optical signal levels without the need for DC-free encoding, thereby improving the accuracy and reliability of optical signal reception.
Implementation Method 1
an optical signal is received by a photodiode, which generates current
Data Source
AI summary
A technique for calibrating an optical receiver is described. During this technique, a front-end circuit in the optical receiver receives an optical signal that corresponds to a sequence with alternating groups of symbol types that correspond to binary values, where durations of the groups of a given symbol type, which can correspond to a first binary value or a second binary value, progressively decrease during the sequence. Then, the output of the feedback circuit is adjusted based at least on the sequence. When the durations of groups corresponding to the first binary value and the second binary value reach their minimum values in the sequence, a calibration value corresponding to the output of the feedback circuit is stored for use during a normal operating mode of the optical receiver.