Loop Filter Frequency Adaptation by Differential Noise Evaluation
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Solution Overview
Problem
Existing methods for automated frequency adjustment of filters in closed control loops, particularly in angular rate sensors, face challenges such as high energy and surface requirements, limited accuracy, and potential disruption by angular rate signals, especially in non-linear filters like Gm-C filters, and require additional components that increase complexity and cost.
Innovation Solution
A system with a first component for rough initial alignment of frequencies using the primary control loop's oscillator control signal and a second component for background frequency adjustment based on differential noise evaluation around the primary resonance frequency, allowing for accurate and efficient adjustment without interrupting the readout circuit or relying on additional filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If automated frequency adjustment methods are implemented in closed control loops, then frequency alignment accuracy is improved, but device complexity and energy consumption increase
Solution Approach 1:
The system uses the existing primary oscillator and readout circuit to automatically adjust the filter frequency without external intervention. The oscillator's control signal is directly utilized for frequency alignment, and the readout circuit performs background noise evaluation to drive the adjustment process, making the system self-adjusting and eliminating the need for additional complex control mechanisms
Solution Approach 2:
The primary oscillator serves dual functions: generating the primary oscillation for Coriolis force detection and providing the control signal for filter frequency adjustment. The readout circuit also performs multiple functions including signal detection and background noise evaluation for frequency alignment, reducing the need for separate dedicated components
2Measurement precision
If additional components are added for frequency adjustment, then frequency alignment accuracy is improved, but surface area and manufacturing cost increase
Solution Approach 1:
The frequency adjustment functionality is merged into the existing primary oscillator and readout circuit. The oscillator's control signal is repurposed for frequency alignment, and the readout circuit integrates background noise evaluation and adjustment control, eliminating the need for separate frequency adjustment components and reducing overall surface area
Solution Approach 2:
The system uses a simplified approach by evaluating background noise characteristics rather than implementing complex frequency sweep or test signal injection methods. This allows frequency alignment to be achieved through software-based processing of existing circuit behavior, reducing hardware requirements
3Measurement precision
If traditional frequency adjustment methods are used, then frequency alignment can be achieved, but the readout circuit must be interrupted causing loss of measurement time
Solution Approach 1:
The frequency adjustment is performed periodically in the background using noise evaluation, allowing the readout circuit to continue normal operation. The system continuously monitors background noise characteristics and makes incremental adjustments without requiring complete interruption of the measurement process
Solution Approach 2:
The system performs preliminary frequency alignment using the oscillator control signal before detailed measurement begins. This preliminary adjustment establishes the correct frequency range, allowing subsequent measurements to proceed without interruption while maintaining accurate frequency alignment
4Use of energy by moving object
If non-linear filters like Gm-C filters are used, then energy efficiency is improved, but frequency adjustment becomes unreliable due to non-linearity
Solution Approach 1:
The system uses feedback from background noise evaluation to continuously monitor and adjust the filter frequency. By measuring the noise spectrum and identifying the peak frequency, the system provides feedback to the oscillator control to maintain accurate frequency alignment, compensating for non-linear effects through continuous adaptation
Solution Approach 2:
The system dynamically changes the oscillator control parameter based on background noise characteristics. By adjusting the control voltage or frequency parameter in response to measured noise spectrum changes, the system adapts to non-linear filter behavior and maintains reliable frequency alignment despite the non-linear nature of Gm-C filters
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
Enables reliable, high-resolution detection of angular rate signals with minimal energy and space usage, achieving accurate frequency alignment within the bandwidth of the angular rate signal, and is applicable to non-linear filters like Gm-C filters, reducing surface requirements and operational complexity.
Implementation Method 1
The primary oscillator performs an oscillation in the primary direction and is coupled with the secondary oscillator in a way that the primary oscillation is transferred to the secondary oscillator
Implementation Method 2
Hence and due to an angular rate, a Coriolis force that impacts on the primary oscillator does not lead to the primary oscillator being deflected in the secondary direction as this degree of movement space does not exist for the primary oscillator due to its suspension
Implementation Method 3
The secondary oscillator is suspended in a way that it can move both in the primary direction as well as in the secondary direction. The secondary movement leads to a movement of the secondary oscillator in the secondary direction, wherein this secondary movement can be detected by the secondary detection device
Implementation Method 4
ΔΣM are based inter alia on noise shaping. In this process, quantization noise nq that is formed at the output is suppressed through filters, which are provided within the modulator, in the signal band and shifted towards other frequencies
Implementation Method 5
a first component for rough initial alignment of frequencies ff with fd, in particular by using the control signal of an oscillator of the phase-locked loop (PLL)
Data Source
AI summary
A method for adjusting the resonance frequency of a loop filter in a delta-sigma modulator includes input of a filter input signal of a loop filter into a frequency adjustment circuit and determination of a noise spectrum of the filter input signal in a first frequency band and a second frequency band. The first frequency band and the second frequency band are arranged symmetrically around the predetermined frequency. The method includes comparison of the noise spectra and creation of an adjustment signal that leads to a frequency adjustment when the noise spectra deviate from one another. The method also includes feedback of the adjustment signal of the frequency adjustment circuit to a control input of the loop filter for setting the filter frequency in response to the comparative result.