Delta-Sigma ADC Reference Switching for Lower Thermal Noise
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Solution Overview
Problem
Delta-sigma analog-to-digital converters (ADCs) face significant thermal noise issues due to switched-capacitor sampling, which results in increased reference noise and error levels, directly proportional to the switching rate of the reference voltage.
Innovation Solution
The ADC selectively couples reference capacitors to the integrator's summing node based on the output of the quantizer and feedback digital-to-analog converter (DAC), allowing for reduced thermal noise by decoupling capacitors when not necessary, and switching between different reference polarity applications to minimize thermal noise sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If switched-capacitor sampling is used to apply reference charge, then the ADC can be implemented with simple architecture and linear behavior, but thermal noise is sampled from the reference voltage and reference error is captured by the sampling switching network
Solution Approach 1:
The reference capacitor is segmented into multiple capacitors, each independently controllable. This allows selective coupling of individual capacitors to the summing node based on quantizer output, enabling the system to maintain simplicity while reducing noise by avoiding unnecessary switching operations.
Solution Approach 2:
The reference capacitor coupling is made dynamic and adaptive - capacitors are selectively coupled or decoupled from the summing node based on real-time quantizer output. This dynamic control reduces the switching rate and minimizes thermal noise sampling while preserving the simple switched-capacitor architecture.
2Measurement precision
If the reference voltage is switched at high rate, then the feedback charge can be accurately applied, but the overall reference noise and error level increases directly proportional to the switching rate
Solution Approach 1:
The harmful switching operation is extracted and minimized - the patent removes unnecessary switching events by selectively coupling reference capacitors only when needed. This reduces the reference switching rate and consequently lowers the reference noise level while maintaining adequate feedback charge application.
Solution Approach 2:
The switching rate parameter is dynamically adjusted by changing the coupling state of reference capacitors. By transitioning between coupled and decoupled states based on quantizer output, the effective switching rate is reduced, lowering reference noise while preserving feedback accuracy through selective charging.
3Duration of action of stationary object
If reference capacitors are continuously coupled to the summing node, then the reference charge is continuously applied, but thermal noise is continuously sampled and injected into the loop filter
Solution Approach 1:
Instead of continuous coupling, the reference capacitors are periodically coupled and decoupled based on quantizer output requirements. This periodic action maintains necessary feedback charge application while creating intervals where no switching occurs, thereby reducing continuous thermal noise sampling and injection.
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 approach effectively reduces the overall reference noise and error by minimizing the sampling of thermal noise, improving the accuracy and reliability of the ADC output.
Implementation Method 1
the instantaneous thermal noise (and any other instantaneous error, such as high-frequency noise) present on the reference voltage is captured by the sampling switching network at the end of the reference sampling period. At that time the reference charge is captured on the reference sampling capacitor along with the instantaneous value of the noise and error
Implementation Method 2
The ADC selectively couples a terminal of a reference capacitor to a summing node of the input integrator depending on the output of the quantizer and/or the value at the input of the feedback digital-to-analog converter (DAC)
Data Source
AI summary
A delta-sigma analog-to-digital converter (ADC) circuit improves performance by reducing the amount of noise and other error sampled by the reference switching circuit. The reference is operated such that one or more reference capacitors remain coupled to an input summing node of the ADC input integrator when an input value to a feedback digital-to-analog converter (DAC) indicates that their contribution is not required to apply a reference in the next quantization period. The reference switching network can select from two or more of the following reference options: 1) switch the reference capacitor to apply a charge quanta as per an ordinary switched-capacitor cycle, 2) switch the reference voltage on a second terminal of the reference capacitor to apply an opposite polarity charge quanta, or 3) leave the first terminal of the reference capacitor coupled to the integrator without changing the voltage at the second terminal of the reference capacitor.