Double-Sampled Delta-Sigma Converter Reference Charge Compensation
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Solution Overview
Problem
Switched-capacitor delta-sigma data converters experience inter-channel crosstalk and non-linearity due to variations in reference voltage, particularly in two-phase applications where changes in reference capacitance and quantizer output codes affect the accuracy and noise levels across multiple converter channels.
Innovation Solution
Incorporating a compensation switched-capacitor network that draws dummy load charge quanta from the voltage reference output, ensuring a constant total charge is drawn regardless of input voltage variations, thereby stabilizing the reference voltage and reducing cross-talk and non-linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a two-phase reference application is used in switched-capacitor delta-sigma data converters, then the conversion accuracy is improved by separating coarse and fine reference phases, but inter-channel crosstalk and non-linearity increase due to reference capacitance variations
Solution Approach 1:
A compensation switched-capacitor network is introduced as an intermediary element between the voltage reference output and the integrator. This network draws dummy load charge quanta that compensates for the charge not provided to the integrator, acting as a mediator to balance the reference voltage and eliminate the harmful effects of capacitance variations while preserving the benefits of two-phase reference application
Solution Approach 2:
The invention changes the parameter of total charge drawn from the voltage reference output by dynamically adjusting the compensation network's charge quanta. By modifying the charge transfer parameter to remain constant regardless of input voltage variations, the system eliminates reference voltage variations and their associated harmful effects while maintaining conversion accuracy
2Reliability
If the fine reference is supplied from a filter capacitor disconnected from the voltage reference buffer, then noise from the buffer is eliminated, but voltage variations occur due to changes in reference capacitance at each cycle
Solution Approach 1:
The compensation switched-capacitor network implements a feedback mechanism by monitoring the charge requirements of the reference feedback network and drawing corresponding dummy load charge quanta from the voltage reference output. This feedback loop ensures that the total charge drawn remains constant, stabilizing the reference voltage while maintaining the noise isolation benefits of the disconnected filter capacitor configuration
3Device complexity
If multiple converter circuits share a common fine reference from a filter capacitor, then component count is reduced, but cross-talk between channels increases due to exacerbated voltage variations
Solution Approach 1:
The compensation network serves as a shared intermediary for multiple converter circuits, providing a common solution to the cross-talk problem. By drawing dummy load charge quanta that compensate for the combined charge requirements of all shared converters, it stabilizes the common fine reference voltage and eliminates cross-talk while allowing multiple channels to share the same filter capacitor infrastructure
Data Source
AI summary
A switched-capacitor delta-sigma data converter circuit includes compensation for voltage reference error that may cause non-linearity and inter-channel crosstalk. The circuit includes a voltage reference circuit, an integrator, a quantizer that quantizes the output of the integrator and a reference feedback switched-capacitor network that provides feedback charge quanta to the integrator that represents an output of the quantizer, so that the output of the quantizer, on average, represents an input signal provided to the integrator. In addition, a compensation switched-capacitor network is included for drawing dummy load charge quanta from the voltage reference output that is not provided to the integrator so that a total charge drawn from the voltage reference output when the reference feedback switched-capacitor network is coupled to the voltage reference output does not vary as the input voltage varies.