Switched-Capacitor Calibration Circuit for Duty-Ratio-Independent RC Tuning
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Solution Overview
Problem
Conventional calibration circuits for RC time constants are affected by unbalanced duty ratios of sampling clocks, leading to inaccuracies in resistance and capacitance calibration, which can result in errors in filter characteristics and RC time constant adjustments.
Innovation Solution
A calibration circuit that uses a switched capacitor with a charging switch for a constant voltage and a discharging switch for a reference voltage, alternately supplied during each cycle of the sampling clock, allowing for precise calibration of capacitance or resistance values without requiring a precise duty ratio in the sampling clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional calibration circuit uses a sampling clock with unbalanced duty ratio for charging and discharging the capacitance, then the calibration process can be simplified, but the calibration accuracy of the RC time constant deteriorates
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary component to generate a compensation voltage that counteracts the error caused by unbalanced duty ratio. The op-amp measures the voltage difference caused by unequal charging/discharging times and generates a corrective voltage to compensate for this error, thereby maintaining calibration accuracy without requiring a precisely balanced sampling clock.
Solution Approach 2:
The patent implements a feedback mechanism where the operational amplifier continuously monitors the voltage across the capacitance during charging and discharging phases. Based on this feedback, the op-amp adjusts the compensation voltage to equalize the effective charging and discharging voltages, thereby correcting the RC time constant calibration error caused by duty ratio imbalance.
2Measurement precision
If the sampling clock duty ratio is made precise to ensure accurate calibration, then the RC time constant calibration accuracy improves, but the device complexity and difficulty of clock generation increase
Solution Approach 1:
Instead of requiring the sampling clock itself to have precise duty ratio, the patent uses an operational amplifier as an intermediary to compensate for duty ratio imbalances. This mediator generates a correction voltage that effectively equalizes the charging and discharging conditions, allowing the use of simple, easily generated sampling clocks while maintaining high calibration accuracy.
Solution Approach 2:
The patent changes the voltage parameter dynamically during the calibration process. The operational amplifier adjusts the compensation voltage based on the actual duty ratio of the sampling clock, thereby compensating for parameter variations. This allows the system to maintain accuracy despite variations in clock duty ratio, simplifying clock generation requirements.
3Adaptability or versatility
If automatic switching of resistance or capacitance values is implemented for time constant adjustment, then the adaptability improves, but the device complexity and potential for switching errors increase
Solution Approach 1:
The patent replaces mechanical switching mechanisms with an electrical compensation approach using an operational amplifier. Instead of physically switching between different resistance or capacitance values, the system uses voltage compensation to achieve continuous time constant adjustment. This substitution eliminates switching errors and reduces mechanical complexity while maintaining adaptability.
Solution Approach 2:
The patent transitions from static switching between discrete values to dynamic continuous adjustment. The operational amplifier provides continuous voltage compensation that dynamically adapts to duty ratio variations, enabling smooth and precise time constant adjustment without the discontinuities and errors associated with switching mechanisms.
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 enables stable filter characteristics in semiconductor integrated circuits independent of fabrication process variations, ensuring accurate RC time constant calibration without relying on precise duty ratios, thus improving the reliability of RC filter performance.
Implementation Method 1
a first capacitance to be calibrated in the switched capacitor is effectively charged to a first constant voltage during a charging period and effectively discharged to a first reference voltage during a discharging period in each cycle of a sampling clock
Data Source
AI summary
A first constant voltage is supplied to a variable capacitance in a switched capacitor, and the variable capacitance is effectively charged to the first constant voltage in each cycle of a sampling clock. A current generated by charging the calibration resistance is averaged, and a resultant current is compared against a current generated by applying a second constant voltage to a resistance. The capacitance value of the variable capacitance is adjusted in accordance with a result of the comparison. Thus the variable capacitance is calibrated so as to have a target value.