Digitally Calibrated Ring Oscillator for PVT-Stable Clocking
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Solution Overview
Problem
Existing ultra-low power clock reference circuits face challenges in achieving stability across process, voltage, and temperature variations, with conventional solutions either having high power consumption, large component counts, or being sensitive to PVT variations.
Innovation Solution
A multi-stage ring oscillator with digitally controlled leakage current sources and a calibration circuit that adjusts the frequency of the output clock signal to match a reference clock signal, using a proportional-integral control mechanism to lock the frequency ratio, thereby addressing sensitivity to PVT variations and power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a quartz oscillator (XTAL) is used for stable frequency, then frequency stability is improved, but area overhead increases and integration capability deteriorates
Solution Approach 1:
The patent uses a ring oscillator to generate the clock signal, copying the frequency stability characteristics of quartz oscillators through digital calibration rather than physically integrating a quartz crystal. The calibration circuit adjusts the ring oscillator's frequency to match a reference, achieving quartz-like stability without the area overhead of actual XTAL components.
Solution Approach 2:
The patent changes the operating parameters of the ring oscillator by adjusting the leakage current magnitude through digital calibration. By varying the leakage current parameter, the oscillator frequency is tuned to achieve the target frequency ratio, thereby achieving frequency stability without requiring physical quartz components.
2Use of energy by stationary object
If leakage current-based oscillators are used for ultra-low power, then power consumption is reduced, but frequency accuracy deteriorates due to poor timer accuracy across fabrication process
Solution Approach 1:
The patent implements a feedback mechanism where the calibration circuit continuously monitors the frequency of the ring oscillator and adjusts the leakage current magnitude accordingly. The calibration circuit compares the output clock signal frequency with a reference frequency and modifies the leakage current to achieve the target frequency ratio, thereby maintaining frequency accuracy despite process variations.
Solution Approach 2:
The patent performs preliminary calibration of the ring oscillator frequency before normal operation. The calibration circuit adjusts the leakage current magnitude in advance to set the correct frequency ratio, ensuring that the oscillator operates at the desired frequency from the start, thereby compensating for fabrication process variations.
3Ease of manufacture
If ring oscillators are used for integration, then full integration capability is improved, but sensitivity to PVT variation worsens
Solution Approach 1:
The patent uses a feedback-based calibration approach where the calibration circuit monitors the ring oscillator output frequency and adjusts the leakage current magnitude to compensate for PVT variations. This feedback mechanism enables the fully integrated ring oscillator to maintain frequency stability despite process, voltage, and temperature changes.
Solution Approach 2:
The patent makes the leakage current magnitude dynamically adjustable through digital calibration. By allowing the current magnitude to change in response to PVT conditions, the ring oscillator maintains its frequency characteristics across varying operating conditions, thereby achieving adaptability to PVT variations.
4Adaptability or versatility
If digitally controlled leakage current sources are used for frequency control, then frequency adjustability is improved, but circuit complexity increases
Solution Approach 1:
The patent divides the leakage current control into multiple discrete levels that can be independently controlled. The calibration circuit selects from a set of predefined leakage current magnitudes, allowing frequency adjustment in discrete steps. This segmentation simplifies the control mechanism compared to continuous analog adjustment.
Solution Approach 2:
The calibration circuit serves multiple functions: it measures the ring oscillator frequency, compares it with the reference frequency, calculates the required adjustment, and controls the leakage current magnitude. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby managing complexity.
Data Source
AI summary
A multi-stage ring oscillator generates an output clock signal having a frequency which is dependent on a digitally leakage current that is applied to each stage of the multi-stage ring oscillator. A magnitude of a leakage current sourced by each digitally controlled leakage current source is set by a control circuit in response to a selection signal. A calibration circuit processes a reference clock signal and the output clock signal generated by the multi-stage ring oscillator to make adjustment to the selection signal which drives a locking of a frequency of the output clock signal to a desired frequency.