DLL Offset Calibration for High-Frequency Phase Alignment
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Solution Overview
Problem
Delay locked loops (DLLs) face challenges due to offset errors caused by mismatches in circuit components, such as phase detectors and charge pumps, leading to non-zero phase errors even when the output and input signals are perfectly in-phase, which restricts their operation to lower frequencies.
Innovation Solution
A DLL design that includes a phase detector, amplifier, measurement block, and correction block, where an identical signal is applied to both reference and feedback inputs during calibration to identify and correct offset errors by changing electrical characteristics until a desired comparison result is achieved, eliminating the need for charge pumps and reducing systematic and random offset errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offset correction calibration is implemented, then phase alignment precision is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by implementing an offset correction calibration phase before normal DLL operation. During this calibration phase, the DLL characterizes and stores offset values from the phase detector and charge pump, which are then used to compensate for systematic errors during actual operation. This preliminary characterization eliminates the need for complex real-time correction mechanisms while maintaining high phase alignment precision.
2Measurement precision
If charge pump is used in DLL, then phase detection capability is improved, but offset errors increase
Solution Approach 1:
The patent applies feedback by measuring the offset errors generated by the charge pump during a calibration phase and then using these measured values to compensate for the errors during normal operation. The DLL controller adjusts the phase detector output based on the stored offset characteristics, creating a feedback loop that eliminates the harmful offset effects while maintaining the charge pump's phase detection capability.
Solution Approach 2:
The patent converts the harmful offset errors generated by the charge pump into beneficial calibration data. By deliberately measuring and characterizing the offset values during calibration, the system transforms what would be persistent errors into useful compensation parameters that improve overall phase detection accuracy during normal operation.
3Speed
If offset correction is implemented, then DLL operation frequency range is improved, but power consumption increases
Solution Approach 1:
The patent applies periodic action by implementing offset correction calibration only once during DLL initialization or when needed, rather than continuously during operation. The calibration phase is performed periodically or event-driven, after which the stored offset values are used for an extended period without additional power consumption for correction operations, thus enabling wider frequency range operation with minimal incremental power cost.
Data Source
AI summary
A delay locked loop (DLL) is calibrated to obtain a measure of offset error in the DLL. The offset error is compensated for in normal operation. In an embodiment, a current corresponding to the measure of offset is forced into one of a pair of paths carrying error signals representing a phase-mismatch between a reference signal and a feedback signal. In another embodiment, additional delay corresponding to the measure of offset is introduced on one of the pair of paths. Offset error is thus largely removed in normal operation of the DLL. The DLL employs an amplifier in place of a charge pump to remove systematic offset errors due to a charge pump. A phase detector in the DLL is designed such that an overlap interval of error outputs of the phase detector is at least half the period of the reference signal, thereby lending to high-frequency operation.