Switched Capacitor ADC Kick-Back Correction Using Dither Correlation
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Solution Overview
Problem
Switched capacitor networks in analog-to-digital converters (ADCs) experience non-linear kick-back, where residual charge distorts sampled signals and degrades performance, as the amount of charge injected back is not a linear function of the input signal, making it difficult to correct using only the input value.
Innovation Solution
A system incorporating a random number generator, correlation circuit, and correction circuit that uses dither injection to determine and correct for kick-back by correlating a pseudo-random noise signal with the ADC output, allowing for digital subtraction of kick-back contributions from the ADC output, thereby reducing distortion and performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If switched capacitors are connected to reference voltage during hold phase, then charge is stored for amplification, but residual charge is injected back into input during next sample phase causing non-linear kick-back distortion
Solution Approach 1:
The patent extracts the harmful kick-back charge from the main signal path by introducing a separate dither injection path. The dither signal is injected through dedicated capacitors (Ccal) rather than through the main signal capacitors, allowing the kick-back effect to be measured and corrected without interfering with the primary signal amplification function.
Solution Approach 2:
The patent implements feedback by measuring the kick-back effect through correlation of the dither signal with the ADC output, then using this measured information to correct the ADC output. The correction circuit subtracts the calculated kick-back contribution from the ADC output, creating a closed-loop system that continuously compensates for the harmful effect.
2Ease of operation
If kick-back correction is attempted using only input value scaling, then correction is simple, but it fails because kick-back is non-linear and depends on previous ADC output
Solution Approach 1:
The patent introduces a dither signal as an intermediary to measure the kick-back effect. This dither signal serves as a probe that allows the system to characterize the non-linear kick-back behavior without directly manipulating the main input signal. The correlation between dither and ADC output provides information about the kick-back that would be impossible to obtain through simple input scaling.
Solution Approach 2:
The patent replaces the mechanical approach of direct charge neutralization with an electronic/software-based correction system. Instead of physically preventing kick-back charge injection through hardware modifications, the system uses digital signal processing techniques (correlation and subtraction) to remove the kick-back effect from the output, substituting complex hardware modification with more flexible electronic correction.
3Object-affected harmful factors
If additional capacitors are added to reduce kick-back, then kick-back distortion is reduced, but device complexity and component count increase
Solution Approach 1:
The patent makes the dither injection capacitors (Ccal) multi-functional by using them both for kick-back measurement and for the primary signal path. During the calibration phase, these capacitors measure kick-back through dither injection. During normal operation, they function as part of the signal amplification network. This eliminates the need for completely separate additional capacitors dedicated solely to kick-back reduction.
Solution Approach 2:
The patent merges the kick-back measurement function with the existing capacitor network. Rather than adding entirely separate measurement capacitors, the system utilizes the existing switched capacitor structure and combines it with dither injection through the same or overlapping capacitor elements, thereby reducing the total component count compared to fully separate measurement and signal paths.
Data Source
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AI summary
A method and device involve a circuit having a switched capacitor network that is switchably connected to an input signal. A randomly determined amount of dither is injected into a circuit having a switched capacitor network that is switchably connected to an input signal. After injecting the dither, at least one correlation value is determined. The correlation value(s) indicates a degree of correlation between the injected dither and an output of the circuit. Distortion caused by an amount of charge kicked back into the circuit when the switched capacitor network is reconnected to the input signal may then be reduced. The reduction is calculated as a function of the correlation value(s).