Charge-Mode Comparator Circuit for Stable ADC Signal Comparison
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Solution Overview
Problem
Comparators in ADC circuitry face challenges in maintaining consistent performance under varying conditions, particularly in accurately comparing close voltage levels within a limited time frame, which affects the overall performance of sub-ADC units and analogue-to-digital circuitry.
Innovation Solution
The implementation of charge-mode circuitry that utilizes bounded charge packets to control the flow of charge between input signals, allowing for the stabilization of voltage levels and accurate comparison, while being insensitive to common-mode voltage and threshold voltage variations, using a controllable charge pump and switching circuitry synchronized with a clock signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional voltage-mode comparators are used, then the comparator can operate with simple circuitry, but the performance becomes inconsistent under varying common-mode voltage and threshold voltage conditions
Solution Approach 1:
The patent transforms the comparator from voltage-mode operation to charge-mode operation by changing the fundamental parameter being compared. Instead of directly comparing input voltages, the circuit converts voltages to charge packets and compares the charge quantities. This parameter transformation makes the comparison immune to common-mode voltage variations and threshold voltage mismatches, achieving consistent performance without requiring complex compensation circuitry.
Solution Approach 2:
The patent replaces the direct voltage comparison mechanism with a charge transfer and comparison mechanism. By using controlled charge packets that are transferred through switching circuitry and stored in capacitors, the system substitutes the voltage-based comparison with a charge-based comparison. This substitution eliminates sensitivity to voltage variations while maintaining comparability through the fundamental charge relationship Q=CV.
2Speed
If the comparator operates with high speed, then the conversion rate increases, but noise and sensitivity to voltage variations increase
Solution Approach 1:
By changing from voltage comparison to charge comparison, the system achieves high-speed operation with reduced noise sensitivity. The charge packets are transferred and compared in a controlled manner during the comparison phase, allowing rapid decision-making without the noise amplification problems of high-speed voltage comparators. The charge-based approach provides inherent noise rejection because charge transfer is a precise, controlled process less susceptible to electromagnetic interference.
Solution Approach 2:
The comparator operates in periodic phases: a reset phase where charge packets are prepared and stored, and a comparison phase where the charge packets are transferred and compared. This periodic operation allows the circuit to stabilize between operations, reducing noise accumulation while maintaining high effective comparison speed through the regular rhythm of charge transfer and comparison cycles.
3Measurement precision
If the comparator uses precise voltage comparison, then measurement accuracy improves, but the circuit becomes sensitive to process and voltage variations
Solution Approach 1:
The patent achieves precise measurement of voltage differences by transforming the measurement parameter from voltage to charge. The charge packets are proportional to the voltage differences being measured, and comparing charge quantities provides precise measurement that is inherently reference-independent. This charge-based measurement approach maintains high precision while eliminating sensitivity to process variations and voltage drifts that plague voltage-mode comparators.
Solution Approach 2:
The patent introduces charge packets as an intermediary between the voltage inputs and the comparison operation. Instead of directly comparing input voltages, the voltages are first converted to charge packets through controlled charging of capacitors. This intermediary charge representation provides a stable, measurable quantity that accurately reflects voltage differences while being immune to the variations that affect direct voltage comparison.
Data Source
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AI summary
There is disclosed herein charge-mode circuitry for use in a comparator to capture a difference between magnitudes of first and second input signals, the circuitry comprising: a tail node configured during a capture operation to receive a charge packet; first and second nodes conductively connectable to said tail node along respective first and second paths; and control circuitry configured during the capture operation to control such connections between the tail node and the first and second nodes based on the first and second input signals such that said charge packet is divided between said first and second paths in dependence upon the difference between magnitudes of the first and second input signals.