CMOS Phase Interpolator for SerDes Clock Phase Alignment
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Solution Overview
Problem
High-speed integrated circuits face challenges in producing clean, symmetric output waveforms due to noisy and inconsistent input signals, particularly at increased operating frequencies, which degrade the quality of differential signals and affect the fidelity of output clock signals.
Innovation Solution
A CMOS phase interpolator device that mixes two clock signals with a 90-degree phase relationship, using a digital-to-phase converter and a digital state machine in a feedback loop to adjust the output phase and maintain a correct clock phase alignment, ensuring a clock signal with a desirable phase for serializer/deserializer devices and other high-speed data applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If integrated circuits operate at increasingly higher frequencies, then processing speed and productivity improve, but signal quality and output waveform fidelity deteriorate due to noise and distortion
Solution Approach 1:
The patent introduces a phase interpolator as an intermediary device between the noisy input clock signal and the output driver. This interpolator mixes a primary clock signal with a quadrature clock signal to generate a phase-adjusted clock that serves as a clean intermediary reference, isolating the output driver from the noisy input signals while maintaining synchronization.
Solution Approach 2:
The patent combines multiple clock signals (primary clock and quadrature clock) to create a composite phase-interpolated clock signal. By merging these signals through the phase interpolator with specific weighting, the system generates a composite signal that maintains the frequency benefits of high-speed operation while achieving improved signal quality through constructive interference and phase optimization.
2Adaptability or versatility
If the input differential signal has substantial amplitude variation and common mode component, then the driver receives asymmetric low quality signal, but the output waveform quality deteriorates
Solution Approach 1:
The phase interpolator acts as a mediator that receives the noisy input clock and transforms it into a clean, phase-adjusted output clock. By using the interpolator to generate the clock signal that drives the output differential pair, the system isolates the output waveform generation from the amplitude variations and common mode components of the input signal, ensuring symmetric output regardless of input quality.
Solution Approach 2:
The patent implements a feedback mechanism where the phase interpolator continuously adjusts the phase of the output clock based on the quadrature clock signal. This feedback loop ensures that the output differential signal maintains proper symmetry and timing relationships, compensating for any asymmetry or distortion in the input signal and maintaining manufacturing precision in the output waveform.
3Ease of operation
If conventional analog phase locked loop is used for clock recovery, then the system can adjust clock phase, but the device complexity and circuit area increase
Solution Approach 1:
The patent replaces the conventional analog phase locked loop (which uses continuous analog circuitry including voltage-controlled oscillators and phase detectors) with a digital phase interpolator implementation. This substitution uses digital logic and signal mixing to achieve phase adjustment, significantly reducing the analog circuit area and complexity while maintaining the essential clock recovery and phase alignment functionality.
Solution Approach 2:
The patent changes the fundamental parameter of phase control from continuous analog voltage adjustment to discrete digital signal mixing. By representing phase adjustments as digital weights applied to the quadrature clock signal in the phase interpolator, the system achieves clock phase adjustment capability through parameter changes in the digital domain, reducing circuit complexity while maintaining operational ease.
Data Source
AI summary
A phase interpolator (PI) is provided to adjust the phase of a clock such that the phase is aligned to an incoming data pattern from a data stream. The data can be captured from a device such as a flip-flop or the like. The present technique uses a PI (digital to phase) and a digital state machine in a feedback loop to set the correct digital code to the PI inputs to achieve an appropriate clock phase. Of course, there can be variations.