PLL Digital-to-Time Converter Monitoring via Ring Oscillator BIST
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Solution Overview
Problem
Monitoring the performance of digital-to-time converters in complex phase-locked loops is difficult due to the challenges of direct measurement with high precision, especially in system-on-a-chip applications with fine quantization steps and potential aliasing effects.
Innovation Solution
Incorporating a ring oscillator with a predefined oscillation frequency and an evaluation unit to measure the actual frequency of the digital-to-time converter, allowing for a reliable self-test through frequency comparison and calibration to account for manufacturing variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct measurement of the digital-to-time converter is performed with high precision requirements, then measurement accuracy is improved, but measurement difficulty and device complexity increase significantly
Solution Approach 1:
The patent introduces a ring oscillator as an intermediary measurement system. Instead of directly measuring the digital-to-time converter's output with complex high-precision equipment, the converter's output controls the ring oscillator's oscillation frequency. The ring oscillator translates the difficult-to-measure time domain signal into an easier-to-measure frequency domain signal, serving as a mediator between the digital-to-time converter and the measurement system.
Solution Approach 2:
The patent replaces direct time domain measurement with frequency domain measurement. By measuring the oscillation frequency of the ring oscillator instead of directly measuring the time interval output by the digital-to-time converter, the system substitutes a mechanically simpler measurement approach for a complex time domain measurement task.
2Ease of operation
If the digital-to-time converter is integrated into a ring oscillator for monitoring, then ease of measurement is improved, but potential interference with normal PLL operation may occur
Solution Approach 1:
The patent segments the measurement function from the normal PLL operation by using a separate ring oscillator dedicated to monitoring purposes. The ring oscillator uses the digital-to-time converter in a test configuration independent from the main PLL feedback path, allowing measurement operations to be performed without interfering with normal phase-locked loop functionality.
Solution Approach 2:
The ring oscillator provides periodic oscillation that can be measured without continuously interfering with the PLL operation. The periodic nature of the oscillation allows for sampling and measurement at appropriate intervals, minimizing disruption to the normal operation of the phase-locked loop while still providing continuous monitoring capability.
Data Source
AI summary
A phase-locked loop. The phase-locked loop including a time-to-digital converter for acquiring a phase of a reference signal. A feedback signal formed from an output signal of the phase-locked loop is fed to the time-to-digital converter. The phase-locked loop including a digital-to-time converter which is configured to apply dithering to the feedback signal or to the reference signal. The digital-to-time converter is part of a ring oscillator with a predefined oscillation frequency. The phase-locked loop includes an evaluation unit for acquiring an actual frequency of the ring oscillator.