Delta-Sigma Modulator Loop Design for Stable Resonance Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electromechanical delta sigma modulators face instability due to signal-dependent loop gain and bandwidth, leading to potential spurious resonance frequencies and nonlinearity, which affects the accuracy and reliability of micromechanical sensors in applications like motor vehicles.
Innovation Solution
The design incorporates a multibit analog-digital converter and digital-analog converter with a control loop that includes a low pass filter or bandpass filter and phase shifter, allowing for independent setting of gain and bandwidth, and utilizes a phase locked loop to control the midband frequency, ensuring stability and minimizing spurious resonances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-bit ADC is used in the delta sigma modulator, then the device complexity is reduced, but the loop gain becomes signal-dependent which causes instability and spurious resonance frequencies
Solution Approach 1:
The patent introduces a gain setting arrangement as an intermediary component between the ADC and the rest of the control loop. This arrangement includes a variable gain amplifier that receives the ADC output and provides a scaled version to the summing junction. The gain setting arrangement acts as a mediator that decouples the signal-dependent nature of the single-bit ADC from the loop gain, allowing independent control of loop gain through the gain setting arrangement while maintaining the simplicity of the single-bit ADC.
2Adaptability or versatility
If the bandwidth is set wide to capture all signal frequencies, then signal coverage is improved, but quantization noise increases across the entire bandwidth
Solution Approach 1:
The patent applies noise shaping that creates local quality differences in the quantization noise distribution. The noise shaping filter is designed to push quantization noise energy to higher frequencies outside the signal band, while maintaining low noise levels within the signal bandwidth. This results in non-uniform noise distribution where the signal band has low noise and out-of-band frequencies have high noise, allowing selective filtering of noise without losing signal information.
3Ease of manufacture
If electronic integrators are used instead of mechanical integrators, then the system becomes exclusively electronic which simplifies manufacturing, but the natural frequency tuning capability is lost
Solution Approach 1:
The patent implements dynamic tuning capability in the electronic integrators through variable capacitor arrays that can be electronically reconfigured. The integrator time constants are made adjustable via digital control of capacitor switching, allowing the natural frequency of the mechanical resonator to be tracked and compensated. This dynamic adjustment mechanism enables the electronic system to adapt to different operating conditions and maintain optimal performance across varying frequencies.
Data Source
AI summary
A delta sigma modulator includes an oscillatory system having a natural frequency and an electronics and a control loop which acts upon the electronics from the oscillatory system and again upon the oscillatory system from the electronics. The control loop provides that a gain in the control loop demonstrates a peaking in a frequency range around the natural frequency of the oscillatory system.