PLL Ring-Oscillator Integrator for Smaller Loop Filter Capacitors
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Solution Overview
Problem
Existing phase-locked loops (PLLs) face challenges in achieving a reduced area and high performance simultaneously, particularly due to the need for large loop filter capacitors and strict current matching requirements.
Innovation Solution
The integration of an analog part and an integral part with a voltage-controlled oscillator (VCO) that includes a current generator and a ring oscillator with interconnected integrator cells, allowing for a digital-analog conversion and reduced VCO gain, enabling smaller loop filter capacitors and stable current supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a classical analog PLL is used, then high performance is achieved, but the area is large due to large loop filter capacitors
Solution Approach 1:
The PLL is divided into two distinct parts: an analog part (phase detector and loop filter) and a digital integral part (integrator cells forming a ring oscillator). This segmentation allows each part to be optimized independently, with the digital integrator replacing the traditional large analog integrator, thereby reducing the required loop filter capacitor size while maintaining performance.
Solution Approach 2:
The patent replaces the traditional analog integration mechanism with a digital integration mechanism implemented through integrator cells configured as a ring oscillator. This substitution of digital logic for analog circuitry enables area reduction while preserving the essential PLL functionality and performance characteristics.
2Area of stationary object
If the loop filter capacitor size is reduced, then area is reduced, but current matching requirements become stricter
Solution Approach 1:
By replacing the analog integrator with a digital integrator implemented through integrator cells, the patent eliminates the need for precise current matching in the loop filter. The digital logic-based integration mechanism is inherently more robust to process variations and does not suffer from the same current matching sensitivity as analog circuits, thereby relaxing the manufacturing precision requirements.
Solution Approach 2:
The patent changes the operating parameters and mechanism of integration from analog current-based integration to digital logic-based integration. This parameter change fundamentally alters the sensitivity characteristics, making the system less dependent on precise current matching and more tolerant of process, voltage, and temperature variations.
3Area of stationary object
If digital integrator cells are used, then area is reduced, but the complexity of digital-analog conversion is increased
Solution Approach 1:
The patent merges the digital integrator output with the analog phase detector output through a unified current summation node. The digital integrator cells generate current signals that are directly added to the analog part's current signal, eliminating the need for complex digital-to-analog conversion circuits and simplifying the overall architecture.
Solution Approach 2:
The integrator cells are designed to directly output current signals that are compatible with the analog part's current inputs. This self-service design allows the digital integrator to interface directly with the analog circuitry without requiring external conversion mechanisms, thereby reducing overall system complexity.
Data Source
AI summary
A phase-locked loop circuit comprises an analog part, an integral part, and a voltage controlled oscillator configured to receive a first current signal from the analog part and a second current signal from the integral part, and to output an output clock. The integral part is configured to receive a first and a second update signal each having at least one state based on a phase difference between an input clock and the output clock. The integral part comprises three integrator cells interconnected to form a ring oscillator.