Switched Capacitor Circuit Current Control
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Solution Overview
Problem
Switched capacitor circuits rely on unit capacitors for matching and programmability, which requires complex layout analysis and parasitic extraction, limiting dynamic range and accuracy due to parasitic capacitances and charge injection mismatches.
Innovation Solution
A switched capacitor circuit with multiple capacitors and current sources, where the current sources are enabled at the beginning of the charge cycle and disabled when a reference potential is reached, allowing for nodal control of charge transfer and scaling of currents rather than capacitors, simplifying the design and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If unit capacitors are used for matching and programmability, then the circuit achieves programmable gain and filtering functions, but the layout complexity and parasitic extraction requirements increase significantly
Solution Approach 1:
The patent changes the fundamental parameter used for gain control from capacitor ratios to current ratios. By using current sources with programmable ratios (achieved through current mirrors and switching networks), the circuit maintains programmability while eliminating the need for complex capacitor array layouts and parasitic extraction procedures.
Solution Approach 2:
The patent substitutes the mechanical/physical arrangement of unit capacitors (which requires careful layout and parasitic management) with an electrical system based on current sources and current mirrors. This substitution maintains the programmable function while dramatically simplifying the layout requirements.
2Measurement precision
If unit capacitors are used for matching, then the circuit achieves accurate gain control, but parasitic capacitances and charge injection mismatches limit accuracy
Solution Approach 1:
The patent replaces the capacitor-based charge transfer mechanism with a current-based mechanism. By using current sources and current mirrors, the circuit achieves accurate gain control through current ratios rather than capacitor ratios, thereby eliminating sensitivity to parasitic capacitances and charge injection mismatches that plague capacitor-based designs.
Solution Approach 2:
The patent changes the controlling parameter from capacitor values (which are susceptible to parasitic effects) to current values (which can be precisely controlled through current mirrors). This parameter change fundamentally improves accuracy by removing the circuit's sensitivity to parasitic capacitances.
3Measurement precision
If capacitor ratios are used to control voltage gain, then the circuit achieves the desired gain control, but the dynamic range and programmability are limited
Solution Approach 1:
The patent changes the gain control parameter from capacitor ratios to current ratios. Current sources can be programmed over a much wider dynamic range using standard CMOS current mirrors and switching networks, thereby expanding the programmable gain range while maintaining precise voltage gain control.
Solution Approach 2:
The patent creates a more universal circuit architecture that can achieve a wide range of gain values through current programming. The current-based approach allows the same circuit topology to be programmed for different gains, dynamic ranges, and even different transfer functions (such as logarithmic or exponential), making it more versatile than capacitor-ratio-based designs.
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 reliance on unit passives, simplifies the layout, and enhances accuracy by controlling currents at a nodal level, making the circuit more efficient and saving silicon area while maintaining high precision in applications like gain circuits, filters, and data converters.
Implementation Method 1
the current from one current source charges at least two of the capacitors in series during the charge portion of the cycle
Implementation Method 2
a comparator comparing a node whose potential varies with the charging of the two or more of the switched capacitors
Data Source
AI summary
A switched capacitor circuit including two or more capacitors arranged in a switched capacitor circuit configuration with a comparator comparing a node whose potential varies with the charging of one or more of the switched capacitors. The switched capacitor circuit also has two or more current sources scaled relative to one another coupled to the capacitors and to the comparator, where the current from one current source charges at least two of the capacitors in series during the charge portion of the cycle, and the other current source charges at least one of but at least one fewer of the capacitor(s) during the charge portion of the cycle, and where the current sources are enabled at the beginning of the charge portion of the cycle, but where the comparator disables the current sources once the node reaches a reference potential.