Digital VCO Phase Control for Resonant Gyroscope Tracking
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Solution Overview
Problem
Vibrating structure gyroscopes face challenges in maintaining precise resonance at natural frequency due to narrow bandwidth, leading to errors like quadrature bias, which existing digital reference oscillators struggle to accurately control, especially with increased Q values of resonators.
Innovation Solution
A digitally controlled reference oscillator that directly controls phase rather than frequency, using a digitally controlled voltage-controlled oscillator with an Nbit digital-to-analogue converter and integrator to provide high-resolution phase control, allowing adaptation to resonant frequency changes and reducing timing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a digitally controlled reference oscillator with finite word length is used, then the system achieves repeatable manufacture and digital control, but the frequency adjustment resolution is limited and cannot meet the stringent requirements for high Q resonators
Solution Approach 1:
The patent changes the controlled parameter from frequency to phase. By controlling phase rather than frequency directly, the system achieves much finer resolution. The phase control uses a 32-bit accumulator that accumulates frequency adjustment commands, allowing resolution far beyond what direct frequency control with finite word length can provide. This resolves the contradiction by maintaining digital manufacturability while achieving the required precision through parameter transformation.
Solution Approach 2:
The patent introduces a phase accumulator as an intermediary between the digital control input and the voltage-controlled oscillator. This accumulator integrates frequency adjustment commands over time to produce precise phase control. The intermediary translates coarse digital inputs into fine phase adjustments, enabling high-resolution control without requiring high-resolution digital-to-analog conversion, thus resolving the precision limitation while maintaining digital control benefits.
2Measurement precision
If the resonator Q value is increased to improve gyro bias performance, then the measurement precision improves, but the bandwidth becomes narrower and requires even higher accuracy and resolution from the reference oscillator
Solution Approach 1:
The patent transforms the control parameter from frequency to phase, which allows the reference oscillator to achieve the extremely high resolution required for high Q resonators. The phase accumulator provides 32-bit resolution, enabling accuracy levels (e.g., 0.005 degree or 1 ns timing error) that are necessary when Q values are increased tenfold or more. This parameter change enables the system to meet the stringent requirements imposed by high Q resonators.
Solution Approach 2:
The patent implements dynamic phase tracking where the phase accumulator continuously integrates frequency adjustment commands to track resonant frequency changes in real-time. This dynamic approach allows the system to adapt to frequency drift while maintaining high resolution, ensuring that the reference oscillator remains accurate even as operating conditions change, thus meeting the reliability requirements for high Q resonators.
3Measurement precision
If a high frequency reference oscillator (1000 MHz or higher) is used to achieve 1 ns timing accuracy, then the measurement precision improves, but the device complexity and cost increase significantly
Solution Approach 1:
The patent introduces a phase accumulator as an intermediary that allows a lower frequency clock to achieve the timing accuracy that would otherwise require a 1000 MHz or higher clock. The accumulator integrates phase information over multiple clock cycles, effectively synthesizing high-resolution timing from a lower frequency source. This reduces device complexity and cost while maintaining the required 1 ns timing accuracy through cumulative phase measurement rather than requiring ultra-high frequency operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution significantly improves the accuracy and resolution of the system, enabling precise tracking of resonant frequency and reducing quadrature bias errors, thus enhancing the performance of vibrating structure gyroscopes.
Implementation Method 1
voltage controlled oscillator configured to provide an in-phase frequency output and a quadrature phase frequency signal output
Implementation Method 2
having an output provided via an integrator to a voltage controlled oscillator
Implementation Method 3
comprising an Nbit digital to analogue convertor arranged to receive a frequency change demand signal as a digital Nbit word
Implementation Method 4
maintain a resonance carrier mode oscillation at a natural, resonant frequency determined by the mechanical vibratory structure
Implementation Method 5
Vibrating structure gyroscopes function as a result of Coriolis forces which are developed when a particle undergoes linear motion in a rotating frame of reference
Data Source
AI summary
A digitally controlled voltage controlled oscillator comprising an Nbit digital to analogue convertor arranged to receive a frequency change demand signal as a digital Nbit word, and having an output provided via an integrator to a voltage controlled oscillator configured to provide a frequency output.