Multistage Voltage Comparator With Precharge for Accurate Switching
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Solution Overview
Problem
Existing voltage comparators in switching power supplies face challenges in accurately comparing voltages due to supply voltage variations, especially when the difference in comparison voltages is minute, leading to inefficiencies and potential damage from premature or delayed switching.
Innovation Solution
Implementing differential amplifiers in the first two stages of a multistage voltage comparator, followed by inverter stages, allows for a more accurate comparison by charging capacitors with voltage thresholds during a precharge phase and propagating the comparison through stages, thereby reducing the impact of supply voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single-ended multistage comparators are used, then device complexity is reduced, but measurement precision deteriorates due to supply voltage variations affecting the comparison accuracy
Solution Approach 1:
The comparator is divided into multiple stages, with the first two stages implemented as differential amplifiers and subsequent stages as inverters. This segmentation allows the early differential stages to reject supply voltage variations while later stages provide signal amplification, resolving the contradiction between simplified structure and measurement precision.
Solution Approach 2:
Different stages of the comparator are given different functional qualities: the first two stages use differential amplifiers with high power supply rejection ratio for accurate voltage comparison, while subsequent stages use inverters for signal amplification. This local differentiation of functional quality enables both structural simplicity and measurement precision.
2Productivity
If the comparison is performed during phases when supply voltage varies, then productivity is improved by continuous operation, but measurement precision deteriorates due to inaccurate comparison results
Solution Approach 1:
The comparator operates in periodic phases: a precharge phase where capacitors are charged to reference voltage thresholds, and a comparison phase where the actual voltage comparison occurs. This periodic operation allows the comparison to be performed at optimal moments while maintaining continuous productivity through structured timing.
Solution Approach 2:
During the precharge phase, capacitors are precharged to voltage thresholds before the comparison phase begins. This preliminary action prepares the comparator for accurate measurement by establishing reference levels in advance, ensuring that the subsequent comparison is not affected by supply voltage variations.
Data Source
AI summary
A circuit that includes a voltage comparator for comparing two voltages. The comparator includes a first in series stage with a differential amplifier, a second in series stage with a differential amplifier, and one or more subsequent inverter stages. Each of the stages includes one or more switches for connecting the inputs of the comparison devices of the stages to their outputs during a precharge phase to charge capacitors with voltages based on the voltage thresholds of the comparison devices. In a subsequent comparison phase, the one or more switches are open, where a comparison between the two voltages is propagated through the stages.