Switched-Capacitor Circuit Zero Crossing Detection
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Solution Overview
Problem
In scaled semiconductor processes, operational amplifiers in sampled-data analog circuits face challenges in achieving sufficient open-loop gain, low noise, and fast settling times due to low power supply voltages and device gain, making it difficult to maintain accurate output voltages in switched-capacitor circuits.
Innovation Solution
A switched-capacitor circuit incorporating a level-crossing detector to generate detection signals for capacitors and sampling switches, which turn OFF when the input signal crosses predetermined levels, allowing for precise sampling and reducing noise and power supply effects through differential signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If operational amplifiers are used in scaled semiconductor processes, then circuit integration is achieved, but open-loop gain and settling time performance deteriorate
Solution Approach 1:
The patent extracts the virtual ground node maintenance function from the operational amplifier and implements it separately using a switched-capacitor circuit with level-crossing detection. This separates the sampling function from the amplification function, allowing the operational amplifier to operate without the burden of maintaining virtual ground continuously, thus improving both integration ease and performance reliability.
Solution Approach 2:
The patent employs periodic switching of the sampling switch synchronized with the clock signal to maintain the virtual ground node at ground potential only at critical sampling instants rather than continuously. This periodic action reduces the burden on the operational amplifier while achieving the necessary performance at integration times, resolving the contradiction between ease of manufacture and reliability.
2Measurement precision
If operational amplifiers provide sufficient open-loop gain and fast settling, then accurate output voltage is achieved, but power consumption and device complexity increase
Solution Approach 1:
The patent uses a level-crossing detector to predict when the input signal will cross zero and pre-positions the sampling switch to capture the signal at the optimal moment. This preliminary detection allows the system to achieve accurate sampling without requiring the operational amplifier to maintain high precision continuously, reducing device complexity while preserving measurement precision.
Solution Approach 2:
The switched-capacitor circuit automatically maintains the virtual ground node at ground potential at sampling instants through the level-crossing detection mechanism, eliminating the need for complex operational amplifier designs to continuously enforce this condition. The system serves itself by using the signal's own characteristics (zero-crossing points) to trigger the sampling action, simplifying the operational amplifier requirements while maintaining accuracy.
3Measurement precision
If virtual ground node is maintained precisely at ground continuously, then accurate output voltage is obtained, but power consumption increases
Solution Approach 1:
The patent implements periodic maintenance of the virtual ground node at ground potential only at critical sampling instants triggered by level-crossing detection, rather than continuous maintenance. This periodic action significantly reduces power consumption while maintaining the precision needed for accurate output voltage sampling, directly resolving the contradiction between measurement precision and energy usage.
4Ease of operation
If sampling occurs at arbitrary times, then circuit operation is simple, but noise and power supply effects increase
Solution Approach 1:
The patent employs feedback through the level-crossing detector that monitors the virtual ground node voltage and generates detection signals to control the sampling switch timing. This feedback mechanism ensures sampling occurs precisely when the signal crosses zero, automatically rejecting noise and power supply interference without complicating the overall circuit operation, thus resolving the contradiction between ease of operation and noise immunity.
Data Source
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AI summary
A sampled-data analog circuit includes a level-crossing detector (30). The level-crossing detector controls sampling switches (S22, S23) to provide a precise sample of the output voltage when the level-crossing detector senses the predetermined level crossing of the input signal. The level-crossing detection may be a zero-crossing detection. An optional common-mode feedback circuit can keep the output common-mode voltage substantially constant.