Switched Capacitor Common-Mode Feedback for Stable Output Potential
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Solution Overview
Problem
Delta-sigma modulators experience fluctuations in output potential due to varying capacitance values during phase changes in common-mode feedback circuits, leading to asymmetry and errors in signal amplification and integration processes.
Innovation Solution
A switched capacitor circuit with a main circuit and control circuit that synchronizes switch operations to maintain consistent total capacitance values across different phases, using synchronized control signals to balance capacitance connections and stabilize output potentials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the common-mode feedback circuit switches capacitance connections during phase changes, then the feedback control is improved, but the output potential fluctuates due to varying capacitance values
Solution Approach 1:
The patent applies asymmetry by introducing a dummy capacitor that compensates for the capacitance change during phase transitions. The dummy capacitor is configured to provide an equal but opposite capacitance change, thereby balancing the total capacitance and preventing output potential fluctuations while maintaining effective feedback control switching.
Solution Approach 2:
The patent changes the capacitance parameter dynamically by switching between different capacitor connections during phases. The dummy capacitor's capacitance is specifically designed to offset the parameter change in the main feedback capacitor, allowing the system to maintain stable total capacitance while still achieving phase-based feedback control improvement.
2Adaptability or versatility
If the capacitance value varies during phase changes, then the feedback control adapts to different phases, but asymmetry and errors occur in signal amplification and integration
Solution Approach 1:
The dummy capacitor acts as a counterweight to the capacitance variation in the feedback path. By configuring the dummy capacitor to provide an equal and opposite capacitance change during phase transitions, it neutralizes the asymmetry introduced by switching, thereby maintaining accurate signal amplification and integration without compromising phase adaptability.
Solution Approach 2:
The dummy capacitor creates a compensating copy of the capacitance variation effect. Instead of directly controlling the main feedback capacitor to be perfectly symmetric, the system uses the dummy capacitor to replicate and invert the variation, achieving error cancellation and maintaining precision while preserving adaptability.
3Stability of the object's composition
If switch operations are synchronized to maintain consistent capacitance, then output potential stability is improved, but the circuit complexity increases
Solution Approach 1:
The patent merges the dummy capacitor into the existing feedback circuit topology, integrating it with the main feedback capacitor and switch network. This combining approach allows the compensation function to be achieved without adding completely separate control mechanisms, thereby limiting the increase in circuit complexity while maintaining output potential stability.
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
The solution stabilizes output potentials, reduces errors caused by asymmetry, and ensures accurate signal amplification and integration by maintaining consistent capacitance values, thereby improving the precision of delta-sigma modulators.
Implementation Method 1
a first capacitor that is connected between an output of the operational amplifier and a node to which a current-biasing potential is applied from the operational amplifier; a second capacitor that is connected in parallel to the first capacitor via a first switch group
Data Source
AI summary
A switched capacitor circuit includes main, common-mode feedback, and control circuits. The main circuit includes a sampling capacitor and an operational amplifier. The sampling capacitor samples an input signal with first and second control signals. The common-mode feedback circuit includes: a first capacitor connected between an output of the operational amplifier and a node; a second capacitor connected in parallel to the first capacitor via a first switch group; a third capacitor connected in parallel to the first capacitor via a second switch group; and a third switch group and a fourth switch group. The control circuit turns on the first switch group and the fourth switch group in synchronization with a first common control signa based on the first control signal, and turns on the second switch group and the third switch group in synchronization with a second common control signa based on the second control signal.