Help explain the capacitance definition in Spice

Click For Summary
SUMMARY

In SPICE, the capacitance between two points x and y is defined mathematically as Cxy = -dQx / dVy for x ≠ y and Cxx = dQx / dVx. This definition aligns with the fundamental relationship of capacitance, C = dQ/dV, but introduces a negative sign for off-diagonal capacitance terms. The discussion highlights confusion regarding this definition, with participants questioning its origins and applicability within SPICE, particularly in relation to other simulation tools like ANSYS.

PREREQUISITES
  • Understanding of basic electrical engineering concepts, specifically capacitance.
  • Familiarity with SPICE simulation software.
  • Knowledge of differential calculus as it applies to electrical charge and voltage.
  • Experience with circuit modeling and simulation tools.
NEXT STEPS
  • Research the mathematical derivation of capacitance in SPICE simulations.
  • Explore the differences between SPICE and ANSYS in modeling capacitance.
  • Study the implications of negative capacitance terms in circuit analysis.
  • Learn about the latest version of SPICE and its updated features related to capacitance modeling.
USEFUL FOR

Electrical engineers, circuit designers, and simulation software users seeking to deepen their understanding of capacitance definitions and applications in SPICE.

anhnha
Messages
179
Reaction score
1
Hi,
In Spice, the capacitance between two points x, y is defined as follows:
Cxy = - dQx / dVy for x != y
Cxx = dQx/dVx

Could anyone help me explain why it is defined like that?
I know that C = dQ/dV but the formula above seems strange to me.

Is my understanding below correct?
Cxy = dQx/d(Vx - Vy)
 
Physics news on Phys.org
anhnha said:
Hi,
In Spice, the capacitance between two points x, y is defined as follows:
Cxy = - dQx / dVy for x != y
Cxx = dQx/dVx

Could anyone help me explain why it is defined like that?
I know that C = dQ/dV but the formula above seems strange to me.

Is my understanding below correct?
Cxy = dQx/d(Vx - Vy)

Could you say more about where you are seeing this in SPICE? Which version of SPICE?

I'll check my SPICE Model Definition Textbook tomorrow at work, but that doesn't ring any bells at the moment. It looks more like an ANSYS or other physical simulator model...?
 

Similar threads

Undergrad Griffith, Electrodynamics, 4th Edition, Example 4.8. (First part)
  • · Replies 6 ·
Replies
6
Views
1K
Undergrad How are the following three definitions subtly different?
  • · Replies 15 ·
Replies
15
Views
2K
Undergrad Griffith, Electrodynamics, 4th Edition, Example 4.8. (Second part)
  • · Replies 3 ·
Replies
3
Views
949
Undergrad Dfns group action & group, written in terms of the other
  • · Replies 26 ·
Replies
26
Views
2K
Graduate Formal definition of Dirac's delta and charge densities
  • · Replies 4 ·
Replies
4
Views
3K
Undergrad Calculating Speed Between Two Cars
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Electric Field & Interplay between Coordinate Systems | DJ Griffiths
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad Understanding the definition of derivative
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad Help understanding conditional expectation identity
  • · Replies 1 ·
Replies
1
Views
3K
Uniform Circular Motion and Projectile Motion Help
  • · Replies 14 ·
Replies
14
Views
3K