Output Hold Circuit for Precise Zero-Crossing Sampling
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Solution Overview
Problem
In sampled-data analog circuits, operational amplifiers face challenges in maintaining accurate output voltages due to low power supply voltages and device gain, especially in achieving sufficient open-loop gain, fast settling times, and large output swing, which are exacerbated by noise and the need to maintain a virtual ground node at precise levels.
Innovation Solution
A switched-capacitor circuit incorporating a level-crossing detector and a waveform generator to generate a predetermined waveform, allowing the amplifier to hold the output voltage at a constant level when the node voltage crosses a predetermined level, thereby reducing noise and increasing signal range through differential signal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If operational amplifiers are used to maintain virtual ground node at precise levels for accurate integration, then measurement precision is improved, but device complexity increases due to requirements for sufficient open-loop gain, low noise, and fast settling times
Solution Approach 1:
The patent extracts the voltage maintenance function from the operational amplifier and implements it separately using a dedicated circuit that activates only when needed. This separates the sampling function from the ground maintenance function, reducing the complexity requirements of the operational amplifier while maintaining measurement precision at the critical sampling instant.
Solution Approach 2:
The patent applies preliminary action by establishing the virtual ground node at the correct voltage level before the sampling operation occurs. The circuit prepares the ground node in advance so that when sampling happens, the voltage is already correct, eliminating the need for continuous high-performance operational amplifier operation during the entire time period.
2Measurement precision
If operational amplifiers provide sufficient open-loop gain and fast settling time to maintain virtual ground, then measurement precision is improved, but use of energy increases due to continuous operation requirements
Solution Approach 1:
The patent implements periodic action by making the voltage maintenance circuit operate only during specific intervals when sampling occurs, rather than continuously. The circuit is activated periodically at the moment of sampling and remains inactive otherwise, significantly reducing the energy consumption of the operational amplifier while maintaining precision only when needed.
Solution Approach 2:
The patent extracts the energy-intensive voltage maintenance function from continuous operational amplifier operation and implements it as a periodic, on-demand function. This separation allows the system to achieve high measurement precision at sampling moments while dramatically reducing overall power consumption during non-sampling intervals.
3Measurement precision
If operational amplifiers provide large output swing for high dynamic range, then measurement precision is improved, but device complexity increases with technology scaling
Solution Approach 1:
The patent extracts the output swing requirement from the operational amplifier and implements it through a separate voltage maintenance circuit that operates independently. This allows the operational amplifier to focus on its core function while the additional circuit handles the dynamic range requirements, reducing overall device complexity despite technology scaling constraints.
Solution Approach 2:
The patent segments the functional requirements into separate circuits: one for sampling, one for voltage maintenance, and one for ground node control. This segmentation allows each circuit to be optimized independently for its specific function, reducing the complexity burden on any single circuit including the operational amplifier.
4Measurement precision
If virtual ground node is maintained continuously at ground level, then measurement precision is improved, but device complexity increases due to continuous control requirements
Solution Approach 1:
The patent applies periodic action by maintaining the virtual ground node at the correct voltage level only during the sampling interval rather than continuously. The circuit is designed to activate precisely when sampling occurs and remains inactive otherwise, reducing control complexity while maintaining precision only when measurement is required.
Solution Approach 2:
The patent uses preliminary action to establish the correct virtual ground voltage before sampling occurs. The circuit prepares the ground node in advance during a setup phase, so that when sampling begins, the voltage is already correct. This eliminates the need for continuous real-time control during the entire operation period.
Data Source
AI summary
A sampled-data analog circuit uses zero-crossing detector. A waveform generator produces a plurality of segments of ramp at the output. An output of a zero crossing detector controls a sampling switch, thereby causing a precise sample of the output voltage to be taken at the instant the zero crossing detector senses the zero crossing of the input signal. The waveform generator further includes a output hold function to maintain the output voltage.