Duobinary Optical Receiver Using Low-Resolution Soft Decisions
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Solution Overview
Problem
Existing passive optical network (PON) receivers face challenges with high power consumption, increased cost, and linearity requirements due to the use of analog-to-digital converters (ADCs) for deriving soft information, which are critical for error correction in high data rate transmissions.
Innovation Solution
Implementing electrical duobinary (EDB) receivers with two thresholds for demodulation and using low-resolution ADCs to derive soft information, coupled with clock-data recovery (CDR) and log-likelihood ratio (LLR) circuits to enhance decoder performance, thereby reducing power consumption and cost while maintaining high data rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-resolution ADCs are used to derive soft information, then decoder performance is improved, but power consumption increases
Solution Approach 1:
The patent changes the parameter of ADC resolution from high to low (2-3 bits) and compensates by modifying the signal format to duobinary modulation. This parameter change allows soft information to be derived with sufficient precision for decoder performance while dramatically reducing power consumption, as ADC power consumption approximately doubles with each additional bit of resolution.
Solution Approach 2:
The patent introduces duobinary modulation as an intermediary signal format between the optical signal and the ADC. This intermediary format spreads the signal energy over a wider voltage range, allowing low-resolution ADCs to capture sufficient information for soft decision decoding without requiring high precision conversions.
2Measurement precision
If high-resolution ADCs are used to derive soft information, then decoder performance is improved, but receiver cost increases
Solution Approach 1:
The patent changes the ADC resolution parameter to low (2-3 bits) and compensates by using duobinary modulation formatting. This reduces the cost of optical and analog electrical components, as higher receiver linearity and more expensive components are only required when using high-resolution ADCs for soft information derivation.
Solution Approach 2:
The patent replaces expensive high-resolution ADCs with cheap low-resolution ADCs. The duobinary modulation format compensates for the reduced resolution, allowing the system to achieve sufficient soft information quality without requiring costly high-precision conversion components.
3Measurement precision
If high-resolution ADCs are used to derive soft information, then decoder performance is improved, but linearity requirements increase
Solution Approach 1:
The patent changes the signal formatting parameter to duobinary modulation and reduces ADC resolution to low (2-3 bits). This combination reduces the linearity requirements of the receiver, as the duobinary format's wider voltage swing allows low-resolution ADCs to capture sufficient information without requiring the high linearity that would be needed for high-resolution ADCs.
Data Source
AI summary
A receiver circuit is disclosed and is configured to receive an optical signal. The receiver circuit includes a receiving circuit configured to receive the optical signal and convert the optical signal from a duobinary signal format into a binary signal based on a plurality of decision thresholds. The receiver circuit also includes a clock data recovery circuit configured to sample the binary signal per data period at a first time instant based on a predetermined clock data recovery technique, and sample the binary signal per data period at a second time instant offset from the first instant, as well as determine an intermediate sample based on an offset for decoding a transmitted bit sequence according to soft information based on the samples.