Optical Receiver Adjustable Pulse-Width Feedback ISI Cancellation
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Solution Overview
Problem
High-speed optical receivers face inter-symbol interference (ISI) due to communication channel degradation, leading to incomplete cancelation of post-cursors and reduced sensitivity, especially at higher data rates, where the delay in the optical receiver causes imperfect feedback correction.
Innovation Solution
An optical receiver design with a front-end circuit that applies a feedback signal corresponding to at least one previous bit, with a pulse width less than the bit time, to cancel post-cursors before conversion, utilizing a digital slicer and a feedback circuit that implements a one-tap decision-feedback equalizer, allowing for adjustable pulse width to compensate for delays and improve equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If decision feedback equalization is applied to correct ISI, then post-cursor interference is reduced, but the optical receiver becomes more sensitive to delay variations at higher data rates
Solution Approach 1:
The patent applies dynamics by making the feedback signal pulse width adjustable rather than fixed. The pulse width can be dynamically adapted to compensate for variations in optical receiver delay, allowing the system to maintain effective ISI correction across different operating conditions and data rates without becoming overly sensitive to delay variations.
Solution Approach 2:
The patent changes the parameter of feedback signal pulse width to optimize performance. By adjusting this parameter, the system can compensate for delay variations and maintain effective post-cursor cancellation across different data rates, resolving the contradiction between ISI correction capability and delay tolerance.
2Reliability
If feedback correction is applied at the output of the photo-detector, then multiple post-cursors can be canceled, but the number of previous bits that must be tracked increases prohibitively
Solution Approach 1:
The patent applies preliminary action by implementing the feedback correction at the input of the photo-detector rather than at the output. This提前 intervention allows the feedback signal to counteract the channel impulse response before it fully develops, enabling effective post-cursor cancellation with significantly reduced complexity in tracking previous bits.
Solution Approach 2:
The patent uses the feedback signal as an intermediary that mediates between the transmitted signal and the received signal. This feedback mechanism, when applied at the photo-detector input, acts as a mediator that pre-compensates for channel effects, reducing the burden on subsequent processing stages to track and correct ISI.
3Measurement precision
If TIA gain is increased to improve signal recovery, then noise performance deteriorates, but reducing gain leaves signal recovery insufficient
Solution Approach 1:
The patent applies feedback by using a feedback signal that is generated based on the received signal and fed back to the photo-detector input. This feedback mechanism compensates for channel effects and enhances signal recovery accuracy without requiring excessive TIA gain, thereby improving both measurement precision and noise performance simultaneously.
Solution Approach 2:
The feedback signal performs preliminary compensation for channel effects before the signal reaches the TIA. By pre-correcting the signal in this manner, the TIA operates more effectively with moderate gain settings, avoiding the noise performance deterioration that would occur with excessive gain while still achieving accurate signal recovery.
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 design effectively cancels multiple post-cursors, relaxes tradeoffs between gain and noise performance, reduces sensitivity to optical receiver delay, and improves error rates by ensuring complete impulse response correction, thereby increasing data rate capabilities.
Implementation Method 1
an optical signal (i.e., light) is usually converted into an analog electrical current by a photo-detector
Data Source
AI summary
An optical receiver includes a feedback circuit that applies a feedback signal to a front-end circuit prior to the front-end circuit converting an optical signal into an analog electrical signal. In particular, the optical receiver includes a digital slicer that determines a digital electrical signal from the analog electrical signal based on a reference voltage that specifies a decision threshold and a clock that specifies sampling times. The feedback circuit determines the feedback signal at least one previous bit preceding a current bit in the analog electrical signal that is provided by the digital slicer and an impulse response of a communication channel. Moreover, the feedback signal has a pulse width that is less than a bit time of the clock. In this way, the optical receiver can cancel post-cursors of the current bit, even when the communication channel includes a low-pass filter.