Single-Pin Crystal Oscillator BIST for Capacitor Matching
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Solution Overview
Problem
Modern clocking circuits in integrated circuits face challenges in calibrating and testing single-pin crystal oscillators due to the need for precise matching of capacitors in feedback paths, which is complicated by limited pin availability and stringent frequency stability requirements, especially in complex systems and low-supply-voltage environments.
Innovation Solution
A built-in self-test (BIST) methodology and apparatus that uses dedicated test circuitry with digitally-controlled switches to selectively connect oscillator components to test circuitry, allowing for calibration and testing of both active and passive blocks, including programmable capacitor banks, while accounting for parasitic capacitance, and employing a reconfigurable capacitor connection matrix and DC test matrix to evaluate bias voltages and ensure correct operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two capacitors are used in feedback paths for high-performance oscillator operation, then frequency stability is improved, but testing and calibration complexity increases due to the need for precise capacitance matching
Solution Approach 1:
The patent applies preliminary action by performing capacitance matching calibration before the oscillator enters normal operation. The system automatically adjusts the capacitance values of C1 and C2 to achieve precise matching during a calibration phase, ensuring frequency stability is achieved without requiring complex manual testing and calibration procedures later.
2Measurement precision
If reference capacitance is made smaller than load capacitance to ensure operation at desired resonant frequency, then frequency accuracy is improved, but oscillator start-up time increases
Solution Approach 1:
The patent applies dynamics by making the capacitance values of C1 and C2 programmable and adjustable. The system can dynamically change the capacitance ratios during different operational phases - using a capacitance ratio that ensures accurate resonant frequency operation while minimizing start-up time, and adjusting these values based on operational requirements rather than using fixed values.
3Difficulty of detecting and measuring
If dedicated test circuitry is added for oscillator calibration and testing, then testing capability is improved, but device complexity and pin usage increase
Solution Approach 1:
The patent applies merging by integrating the test circuitry directly into the oscillator structure. The same capacitors C1 and C2 that are used for oscillator operation are also utilized for testing and calibration purposes. The programmable capacitor blocks serve dual functions as both oscillator components and test elements, eliminating the need for separate dedicated test circuitry and reducing pin usage.
Solution Approach 2:
The patent applies universality by designing the capacitor blocks to serve multiple functions. The programmable capacitor blocks can operate as normal oscillator capacitors during operation mode and as test elements during calibration mode. This multi-functionality allows the system to perform self-testing and calibration without requiring additional external test equipment or pins.
4Stability of the object's composition
If capacitor values are precisely matched for good oscillator performance, then oscillation stability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by making the capacitance values programmable rather than fixed. The system can adjust the capacitance values of C1 and C2 through digital control to achieve precise matching. This allows for post-manufacturing calibration to compensate for manufacturing variations, ensuring oscillation stability without requiring extremely tight manufacturing tolerances on the physical capacitors.
Data Source
AI summary
A built-in self-test (BIST) methodology and apparatus provide for testing and calibration of an integrated circuit oscillator circuit topology that uses a one-pin (a single-pin) external resonator. The method employs dedicated test circuitry, also referred to herein as BIST apparatus, for the pass/fail verification of both the active and passive building blocks of the oscillator. At the same time, the methodology ensures accurate calibration and matching of the capacitors using dedicated digital circuitry and algorithms.