Switched-Capacitor Four-Phase Charging for Low-Noise Integration
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Solution Overview
Problem
Switched-capacitor circuits face issues with signal-dependent charge modulation from reference voltage sources, leading to integrator gain errors and undesirable linearity errors in analog-to-digital converters, due to the dependence of charge transfer on previous cycle charges and noise introduction from signal-conditioning circuits.
Innovation Solution
The implementation of a switched-capacitor circuit operating in four phases, where a capacitor is initially charged to a common mode signal to mask residual charges, then charged with an input signal, followed by a high-bandwidth auxiliary reference signal, and finally with a noiseless reference signal, reducing signal-dependent charge modulation and improving signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a capacitor is charged with an input signal in a switched-capacitor circuit, then the input signal is processed, but signal-dependent charge modulation occurs from the reference voltage source
Solution Approach 1:
The charging process is divided into multiple phases: a first charging phase where the capacitor is charged to a common mode signal, and a second charging phase where the capacitor is charged with the input signal. This segmentation separates the reference signal charging from the input signal charging, reducing signal-dependent charge modulation from the reference voltage source.
Solution Approach 2:
The capacitor is preliminarily charged to a common mode signal before being charged with the input signal. This preliminary charging action establishes a baseline charge that masks residual charges and reduces the impact of signal-dependent charge modulation during subsequent processing.
2Duration of action of stationary object
If charge transfer depends on previous cycle charges, then circuit operation continues, but integrator gain errors occur
Solution Approach 1:
The capacitor is preliminarily charged to a common mode signal at the beginning of each cycle, independent of previous cycle charges. This preliminary action resets the charging baseline, ensuring that charge transfer in the current cycle does not depend on residual charges from previous cycles, thereby eliminating integrator gain errors.
Solution Approach 2:
The common mode signal serves as a reference template that is applied to the capacitor at the start of each cycle. By copying this standardized charging pattern repeatedly, the circuit achieves continuous operation while maintaining consistent charging conditions that prevent gain errors.
3Device complexity
If a standard reference signal is used, then circuit simplicity is maintained, but linearity errors occur in analog-to-digital converters
Solution Approach 1:
The reference signal application is segmented into two distinct phases: first applying a common mode reference signal to establish a baseline, then applying the input signal for processing. This segmentation allows the use of simple reference signals while achieving high linearity accuracy by preventing signal-dependent charge modulation.
Solution Approach 2:
The common mode signal acts as an intermediary between the reference voltage source and the input signal processing. It mediates the charging process by establishing a stable baseline that eliminates the direct coupling between input signal variations and reference signal charging, thereby reducing linearity errors.
4Adaptability or versatility
If signal-conditioning circuits are used, then signal processing is enhanced, but noise is introduced into the circuit
Solution Approach 1:
The harmful noise component is extracted and separated from the useful signal processing function. By dedicating the first charging phase solely to applying the common mode signal without signal-conditioning circuitry, the circuit eliminates noise introduction while maintaining enhanced signal processing capability in the second phase.
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 reduces the dependence on previous cycle charges, minimizes reference signal modulation, and enhances the signal-to-noise ratio by applying a high-bandwidth auxiliary reference signal, resulting in improved accuracy and reduced noise in the output signal.
Implementation Method 1
a capacitor (502) connected to an integrating circuit (506, 504)
Data Source
AI summary
Techniques for operating a switched-capacitor circuit to reduce input and feedback dependence and/or reduce reference modulation. A switched-capacitor circuit can be operated in four phases. In a first phase at a start of a cycle, the capacitor is charged/discharged by a common mode signal to mask any residual charge stored in the capacitor from a previous cycle. In a second phase, the capacitor is charged with an input signal. During a third phase, the capacitor is charged with a wide-bandwidth auxiliary reference signal, and during a fourth phase the capacitor is charged with a reference signal. During the third and fourth phases, the capacitor may be coupled to an integrating circuit to integrate a difference between the input signal and the reference signal.