Capacitor Scaling for Matched Total Capacitance in DACs
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Solution Overview
Problem
In high-speed data conversion circuits, such as capacitive DACs, achieving optimal performance requires scaling capacitors differently, but existing methods face challenges in maintaining identical total capacitances while varying signal capacitances, leading to suboptimal phase alignment and linearity.
Innovation Solution
The proposed solution involves designing capacitors with different signal capacitances while ensuring identical total capacitances by adjusting parasitic capacitances, allowing for the use of signal drivers of identical drive strength, which maintains phase alignment and improves linearity by ensuring identical input impedances across capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitors are scaled with different signal capacitances to achieve segmentation in DACs, then linearity and far-off-noise performance improve, but phase alignment deteriorates due to mismatched total capacitances
Solution Approach 1:
The patent changes the parasitic capacitance parameter of each capacitor to compensate for differences in signal capacitance. By adjusting the parasitic capacitance value, the total capacitance (signal + parasitic) is made identical across all capacitors, thereby maintaining phase alignment while preserving the beneficial different signal capacitance values for linearity performance.
2Measurement precision
If capacitors are scaled with different signal capacitances, then DAC resolution and performance improve, but driver scaling complexity increases
Solution Approach 1:
The patent applies homogeneity by making all capacitors have identical total capacitance values. This uniformity allows all signal drivers to be designed with identical drive strength and characteristics, eliminating the need for complex driver scaling schemes while still enabling high-resolution DAC operation through segmented capacitor structures.
3Reliability
If total capacitances are made identical across capacitors, then phase alignment and linearity improve, but signal capacitance flexibility is reduced
Solution Approach 1:
The patent segments the capacitor structure into two distinct functional parts: a signal capacitance component that varies according to DAC segment requirements, and a parasitic capacitance component that is adjusted to compensate. This segmentation allows the signal capacitance to provide the necessary flexibility for different DAC resolutions while the parasitic capacitance ensures identical total capacitances for phase alignment.
Data Source
AI summary
The present disclosure addresses a concept for capacitor scaling. A first capacitor is provided with a first signal capacitance between a first electrode and a second electrode of the first capacitor and with a first parasitic capacitance between the first capacitor's first electrode and AC ground. A sum of the first signal capacitance and the first parasitic capacitance yields a first total capacitance. A second capacitor is provided with a second signal capacitance between a first electrode and a second electrode of the second capacitor and with a second parasitic capacitance between the second capacitor's first electrode and AC ground. A sum of the second signal capacitance and the second parasitic capacitance yields a second total capacitance. While the first signal capacitance differs from the second signal capacitance, the first total capacitance equals the second total capacitance.