Zero-Crossing Sampled-Data Circuit for Precise Low-Noise Sampling
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Solution Overview
Problem
In scaled semiconductor processes, operational amplifiers in sampled-data analog circuits face challenges in maintaining accurate integration and reducing noise, particularly due to low power supply voltages and device gain, which affects the performance of switched-capacitor circuits.
Innovation Solution
A switched-capacitor circuit incorporating a level-crossing detector and sampling switches that turn OFF when the input signal crosses predetermined levels, allowing for precise sampling and reducing noise by using differential signal paths and capacitors to manage virtual ground nodes effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If operational amplifiers are used to maintain accurate integration and virtual ground levels, then measurement precision is improved, but device complexity and power consumption increase due to requirements for high open-loop gain and fast settling time
Solution Approach 1:
The patent extracts the virtual ground maintenance function from the operational amplifier and implements it separately using a dedicated virtual ground generation circuit. This circuit uses a level-crossing detector to monitor when the output voltage crosses zero and controls switches to maintain the virtual ground node at ground potential only during critical sampling moments, rather than continuously requiring high-gain operational amplifier control.
Solution Approach 2:
The virtual ground maintenance is implemented periodically rather than continuously. The level-crossing detector triggers switch actions only when the output voltage crosses zero, creating periodic virtual ground enforcement at critical sampling instants. This eliminates the need for continuous high-gain operational amplifier control while maintaining measurement precision at required moments.
2Measurement precision
If operational amplifiers with high open-loop gain are used to reduce noise and maintain virtual ground, then measurement precision is improved, but power consumption increases due to low power supply voltage constraints
Solution Approach 1:
The virtual ground maintenance is activated periodically only when needed for accurate sampling, triggered by the level-crossing detector when the output voltage crosses zero. This eliminates continuous power consumption of high-gain operational amplifiers while maintaining noise reduction and measurement precision at critical moments.
Solution Approach 2:
The circuit uses the signal itself (output voltage crossing zero) to trigger the virtual ground maintenance mechanism. The level-crossing detector monitors the output voltage and automatically activates the virtual ground enforcement when crossing occurs, making the system self-regulating without requiring continuously powered high-gain amplification.
3Measurement precision
If continuous virtual ground maintenance is implemented using operational amplifiers, then measurement precision is improved, but loss of time occurs due to slow settling time affecting fast operation
Solution Approach 1:
Virtual ground maintenance is performed periodically at critical sampling instants triggered by level-crossing detection, rather than continuously. This allows the circuit to achieve virtual ground stability only when needed for accurate measurement, eliminating time loss from continuous settling while maintaining precision at required moments.
Solution Approach 2:
The virtual ground enforcement is activated in advance of the critical sampling moment by detecting when the output voltage approaches and crosses zero. This preliminary action ensures the virtual ground is established before the sampling operation requires it, eliminating settling time delays during the actual sampling process.
Data Source
AI summary
A sampled-data analog circuit includes a level-crossing detector. The level-crossing detector controls sampling switches 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.