Delta-Sigma ADC Self-Dithering for Limit-Cycle Suppression
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Solution Overview
Problem
Delta-sigma modulators in analog-to-digital converters face issues with limit-cycle oscillations due to mechanical sensor lag, leading to reduced resolution and linearity, particularly in micromachined sensors, which existing solutions either require impractical adjustments or complex circuitry.
Innovation Solution
Implementing a proportional feedback mechanism around the comparator to modulate the reference voltage based on the digital output, using minimal circuitry such as a single transistor or resistor, which acts as a self-dithering mechanism independent of the analog input signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional delta-sigma modulation is used without additional circuitry, then device complexity is low, but limit-cycle oscillations occur reducing measurement precision
Solution Approach 1:
The patent implements self-dithering by using the quantizer's own output to modulate its reference voltage. The digital output signal is fed back through a modulator that adjusts the reference voltage dynamically, allowing the system to eliminate limit-cycle oscillations using its own output signal without requiring external dither sources or complex additional circuitry.
Solution Approach 2:
The patent applies feedback by taking the digital output from the quantizer and using it to modulate the reference voltage in real-time. This feedback mechanism creates a self-regulating system where the quantizer output directly influences its own operating conditions, effectively suppressing limit-cycle oscillations and improving measurement precision.
2Measurement precision
If dither is added to reduce limit-cycle oscillations, then measurement precision improves, but signal headroom is consumed
Solution Approach 1:
The system uses its own digital output signal to generate the dither effect through reference voltage modulation, eliminating the need for external dither signals that would consume additional signal headroom. The self-dithering mechanism derives the modulation source from the quantizer output itself.
Solution Approach 2:
The patent changes the reference voltage parameter dynamically based on the digital output signal. By modulating the reference voltage rather than adding a fixed dither signal to the analog input, the system achieves dithering effects without consuming additional signal headroom in the analog domain.
3Measurement precision
If existing solutions to reduce limit-cycle oscillations are implemented, then measurement precision improves, but device complexity increases
Solution Approach 1:
The quantizer serves dual functions by both generating the digital output and providing the modulation signal for reference voltage adjustment. This self-service approach eliminates the need for separate dither generation circuits, reducing overall device complexity while maintaining measurement precision.
Solution Approach 2:
The patent merges the dither generation function with the existing quantizer output. Instead of adding a separate dither circuit, the digital output from the quantizer is directly used to modulate the reference voltage, combining multiple functions into existing circuitry and minimizing additional complexity.
Data Source
AI summary
An analog-to-digital converter includes a delta circuit, a sigma circuit, and a quantizer circuit and further includes a feedback circuit that modulates a reference voltage provided to the quantizer circuit based on the quantizer circuit output. Modulation of the quantizer reference voltage dithers the quantizer circuit to effectively reduce or avoid lock bands. The analog-to-digital converter may be used in combination with a microelectromechanical (MEMS) device such as a gyroscope, an accelerometer, or a pressure sensor.