Receiver Front-End Offset Cancellation for Coupled Clock Interference
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Solution Overview
Problem
High-speed serial links face challenges in effectively canceling coupled clock signals, which reduce signal-to-interference ratio and increase bit-error rates due to the difficulty in measuring and de-coupling the clock effect from the transmit signal.
Innovation Solution
A receiver system with an analog input and correction circuits that iteratively update parameter vectors using a constant step size, sign functions, and error values to calculate offset corrections, incorporating decision feedback equalizer (DFE) signals for adaptive cyclic offset cancellation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If DC offset cancellation circuits are used to cancel the coupled clock signal, then the receiver front end sensitivity is improved, but it is difficult to effectively decouple and measure the coupled clock signal for correction
Solution Approach 1:
The patent segments the offset cancellation process into distinct phases: a training phase where the coupled clock signal is measured and characterized, and a normal operation phase where the pre-calculated correction is applied. This segmentation allows the system to measure the coupled clock signal when it is stable and predictable (during training) rather than attempting to measure it continuously during normal operation, thereby reducing the difficulty of detection and measurement.
Solution Approach 2:
The patent performs preliminary measurement and characterization of the coupled clock signal during a training phase before normal data transmission begins. The system pre-calculates the correction values that will be needed during normal operation, storing them for later use. This preliminary action eliminates the need to continuously measure and adjust during data transmission, solving the measurement difficulty while maintaining high receiver sensitivity.
2Object-affected harmful factors
If the coupled clock signal is canceled during signal transmission, then the signal to interference ratio is improved, but the system complexity increases due to the need for continuous measurement and adjustment
Solution Approach 1:
The patent implements periodic offset cancellation by performing measurements and corrections during designated training intervals rather than continuously during normal operation. The system periodically updates the correction values at specific intervals (e.g., after certain numbers of bits are received or at predefined training sequences), reducing computational complexity while maintaining effective interference cancellation. This periodic approach balances signal quality improvement with system simplicity.
Solution Approach 2:
The system pre-calculates and stores correction values during a training phase before normal operation begins. During normal data transmission, the pre-calculated corrections are applied without continuous measurement or adjustment. This preliminary action eliminates the need for complex real-time measurement and adjustment systems, reducing device complexity while maintaining high signal-to-interference ratio through the pre-established correction values.
3Ease of operation
If the P and N inputs of the differential input are shorted to cancel DC offset, then the offset correction is simplified, but the transmit signal cannot be simultaneously transmitted for measurement
Solution Approach 1:
The patent divides the system operation into distinct segments: a training phase where offset measurement and correction are performed (with inputs shorted), and a normal operation phase where data transmission occurs (with inputs connected to the transmit signal). This temporal segmentation allows the system to perform simplified offset correction measurements without the complexity of simultaneously handling data transmission, while the transition between phases is managed efficiently to minimize time loss.
Solution Approach 2:
The system periodically switches between training mode (inputs shorted for offset measurement) and normal operation mode (inputs connected for data transmission). The periodic training intervals are scheduled at appropriate moments, allowing the system to perform simplified offset corrections without continuous interruption of data transmission. This periodic switching minimizes the time loss associated with mode transitions while maintaining the operational simplicity of separate measurement and transmission phases.
Data Source
AI summary
A receiver for a serial link. The receiver has an analog input configured to receive a received signal and includes a first front end comprising a first sampler configured to sample a signal at an input of the first front end, and a first correction circuit configured to add a first correction to the signal at the input of the first front end, the first correction including a first offset correction. The offset correction is updated by a modified sign-sign least mean squares method.