Clock Synthesizer INL Compensation for Low-Jitter DTC Interpolation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing digital-to-time converters (DTCs) in clock synthesizers suffer from non-linear effects that result in significant output clock jitter, which is not effectively compensated by pre-calibration methods due to temperature variations and non-linear interpolation points.
Innovation Solution
A method employing two paths with digital controlled oscillators (DCOs) and digital-to-time converters (DTCs), where a deliberate initial delay in one path is compensated by an analog delay in the other, allowing for adaptive adjustment of non-linear distortion by averaging measurements to derive discrete distortion values, effectively treating them as constants for circuit correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pre-calibration is used to eliminate non-linear distortion in DTC, then interpolation accuracy is improved, but the system must be constantly adjusted to compensate for temperature variations
Solution Approach 1:
The patent implements a feedback mechanism where the actual delay of the analog delay element is measured by comparing it with a digital delay, and the measured non-linear distortion values are used to adjust the DTC compensation values. This closed-loop feedback allows the system to adapt to temperature variations and other environmental changes, resolving the contradiction between initial calibration accuracy and ongoing adaptability.
Solution Approach 2:
The patent performs preliminary measurement of non-linear distortion by introducing deliberate initial delays and measuring the corresponding actual delays. These pre-measured distortion values are stored and used to pre-calculate compensation values that are applied to the DTC. This preliminary action reduces the impact of temperature variations during normal operation.
2Measurement precision
If analog delay elements are used to compensate for non-linear distortion, then measurement precision is improved, but non-linear distortion remains significant without proper compensation
Solution Approach 1:
The patent converts the harmful non-linear distortion effect into a useful measurement signal. By deliberately introducing known initial delays and measuring the actual delays produced by the non-linear analog delay element, the system characterizes the distortion and then uses this characterization to compensate for it. The harmful non-linearity becomes the basis for creating accurate compensation values.
Solution Approach 2:
The patent introduces a digital delay element as an intermediary reference to measure the actual delay of the analog delay element. This intermediary allows for precise measurement of the non-linear distortion without directly modifying the analog delay path, enabling accurate characterization and subsequent compensation of the distortion.
3Measurement precision
If multiple measurements are averaged to derive distortion values, then compensation accuracy is improved, but processing time increases
Solution Approach 1:
The patent performs the time-consuming multiple measurements and averaging process in advance, during an initialization or calibration phase. The measured non-linear distortion values and calculated compensation values are stored in memory. During normal operation, the pre-calculated compensation values are simply retrieved and applied, avoiding the time loss during critical timing operations.
Data Source
AI summary
A method of compensating for integral nonlinear interpolation (INL) distortion in a clock synthesizer driven by a system clock running at a frequency fsys, involves introducing a selected nominal analog delay I*dt with an actual delay of I*dt+δ at the output of the a first path with a digital controlled oscillator (DCO) and a digital-to-time converter (DTC) and a nominal digital delay I*D with an actual delay of I*D+Δ at the input of a second path with a DCO and a DTC that offsets the actual analog delay in the first path, adjusting the contents x(k) of a compensation module in the second path to align the output pulses of the first and second paths for different values of k, where k represents an interpolation point, iteratively repeating the two preceding steps for all N values of I, and averaging the contents x(k) of the compensation module to derive the compensation values to be applied to a one of the DTCs to correct for INL distortion.