DEM-Driven DCO Calibration for Linear Millimeter-Wave PLLs
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Solution Overview
Problem
High-frequency digital phase-locked loops (PLLs) face challenges in achieving improved linearity and phase noise performance, particularly in millimeter-wave applications, due to non-linearity in digitally controlled oscillators (DCOs) which affect radar systems' accuracy and sensitivity.
Innovation Solution
A method involving dynamic element matching (DEM) driven DCOs, where the PLL is calibrated in open-loop mode by measuring output frequencies with test control words, generating correction data to compensate for non-linearity, and using this data in closed-loop operation to maintain improved linearity, independent of input sequences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional DCOs are used in high-frequency PLLs, then the system can operate at millimeter-wave frequencies, but the linearity and phase noise performance deteriorate due to non-linearity in the DCO
Solution Approach 1:
The patent applies preliminary action by performing calibration in open-loop mode before closed-loop operation. The calibration process measures the actual output frequencies of the DCO and generates correction coefficients that compensate for non-linearity. This preliminary characterization of the DCO's frequency response allows the system to pre-correct for non-linearities, improving linearity and phase noise performance before the PLL enters normal operation.
Solution Approach 2:
The patent changes parameters by introducing correction coefficients that modify the control words supplied to the DCO. Based on the measured frequency output, the system adjusts the control parameters to compensate for non-linearities. This parameter adjustment allows the DCO to operate with improved linearity across its frequency range, directly addressing the performance degradation at millimeter-wave frequencies.
2Measurement precision
If calibration is performed with multiple input sequences to account for non-linearity, then measurement precision improves, but calibration time increases
Solution Approach 1:
The patent performs the time-consuming frequency measurements and correction coefficient generation in open-loop mode as a preliminary step. By completing the calibration before closed-loop operation, the system captures the DCO's non-linear characteristics once, and then reuses the correction coefficients during normal operation. This approach avoids repeated lengthy calibration procedures while maintaining measurement precision.
Solution Approach 2:
The system uses its own DCO output frequency measurements to generate self-correction coefficients. The calibration process is self-contained, using the DCO's actual performance characteristics to create its own correction data. This self-service approach eliminates the need for external calibration equipment or multiple input sequence tests, reducing calibration time while maintaining accuracy.
3Measurement precision
If dynamic element matching is used to correct non-linearity, then linearity improves, but device complexity increases due to additional circuitry
Solution Approach 1:
The patent introduces an intermediary element - the correction coefficient - that mediates between the control word and the DCO output. Rather than modifying the DCO hardware structure, the system uses digital correction coefficients to adjust the control signals. This software-based intermediary approach improves linearity without requiring complex hardware modifications to the DCO itself.
Solution Approach 2:
The patent replaces potential hardware-based dynamic element matching circuitry with a digital correction approach. Instead of physically switching or reconfiguring DCO elements based on input patterns, the system uses digital correction coefficients applied to the control words. This substitution of mechanical/hardware complexity with digital processing simplifies the overall device structure while maintaining linearity correction effectiveness.
Data Source
AI summary
A method of operating a phase-locked loop (PLL) having a dynamic element matching (DEM)-driven digitally controlled oscillator (DCO) includes calibrating the PLL, where calibrating the PLL includes opening a loop of the PLL and performing linearity measurements of the DEM-driven DCO when the loop of the PLL is open and when dynamic matching of the DEM-driven DCO is activated, where performing the linearity measurements includes: applying test control words to the DEM-driven DCO to obtain frequencies in a first range of frequencies; and measuring output frequencies of the DEM-driven DCO corresponding to the test control words. Calibrating the PLL further includes calculating calibration information based on the test control words and the measured output frequencies.