Capacitor SPICE Model with DC Bias Extraction
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Solution Overview
Problem
Existing circuit simulation models for capacitors with DC bias applied are inconvenient to use due to the lack of a valid theoretical basis for frequency-dependent and temperature-dependent changes, leading to inaccurate results when integrated into SPICE simulators, and they fail to account for the complex changes caused by actual voltage signals including DC bias, signal voltages, and noise voltages.
Innovation Solution
A method is developed to construct a circuit simulation model for capacitors with DC bias by configuring a basic equivalent circuit, deriving circuit equations, measuring characteristics changes, representing them as polynomials, and replacing circuit elements with nonlinear voltage-dependent voltage sources, and using a low-pass filter to extract the DC bias component for accurate simulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing equivalent circuit models are used for capacitors with DC bias, then the model can be integrated into SPICE simulators, but the frequency characteristics and accuracy are inaccurate due to lack of valid theoretical basis
Solution Approach 1:
The patent applies parameter changes by transitioning from fixed nominal capacitance values to voltage-dependent capacitance models. The equivalent circuit parameters (capacitance, resistance, inductance) are made variable based on applied voltage conditions, allowing accurate representation of frequency characteristics across different operating ranges. This resolves the contradiction by enabling both SPICE integration and high-frequency accuracy through dynamic parameter adjustment.
Solution Approach 2:
The patent implements dynamics by creating a dynamic equivalent circuit model where circuit elements change their characteristics based on the applied voltage signal. The model dynamically adjusts capacitance, resistance, and inductance values according to the voltage magnitude and frequency, enabling accurate simulation from DC to high-frequency bands while maintaining SPICE compatibility through systematic modeling approaches.
2Ease of operation
If simple equivalent circuits with nominal capacitance are used, then the circuit analysis is simple, but the results greatly differ from actual circuit characteristics when DC bias is applied
Solution Approach 1:
The patent applies segmentation by dividing the capacitor's frequency response into distinct bands (low-frequency, mid-frequency, high-frequency) and modeling each band with appropriate circuit elements. This segmented approach maintains analytical simplicity while improving accuracy, as each segment can be treated independently with standard SPICE elements, avoiding the need for complex unified models.
Solution Approach 2:
The patent uses parameter changes to transition from simple nominal capacitance models to voltage-dependent models. By making circuit parameters variable based on operating conditions, the model maintains ease of use through systematic parameter adjustment while significantly improving accuracy in representing actual capacitor behavior under DC bias and varying frequency conditions.
3Device complexity
If frequency-dependent characteristics are considered only for ESR, then the model is simpler, but other elements are not accurately represented
Solution Approach 1:
The patent applies universality by creating a unified equivalent circuit model that accurately represents frequency-dependent characteristics across all circuit elements (capacitance, resistance, inductance), not just ESR. This multi-functional model provides comprehensive accuracy while maintaining manageable complexity through systematic application of SPICE elements that can be integrated into existing circuit analysis workflows.
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 allows for accurate representation of capacitor characteristics under DC bias, enabling precise circuit design and simulation, particularly in high-frequency bands, and improves the usability of SPICE models by providing a stable and accurate wide-band equivalent circuit model for capacitors.
Implementation Method 1
a low-pass filter for extracting a DC bias component from an applied voltage
Data Source
AI summary
Provided is a circuit simulation model that can suitably represent capacitor characteristics, thereby realizing accurate circuit design and circuit analysis. A SPICE model is constituted of a capacitor unit in which a capacitor is replaced with a linear voltage dependent current source, a low-pass filter unit that has a function of extracting a DC bias voltage, a calculation circuit unit that is configured by combining an adder, a multiplier, and the like to perform a calculation of a circuit equation derived from an equivalent circuit for a capacitor such as an idealized C circuit model, an RC circuit model, or the like, and a linear voltage dependent voltage source that applies a total voltage applied across the capacitor to the calculation circuit.