Help explain the capacitance definition in Spice

In summary, the conversation is about the definition of capacitance in Spice. The formula for capacitance between two points x and y is given as Cxy = - dQx / dVy, and for the same point x and y, it is Cxx = dQx / dVx. The person is seeking clarification on why the formula is defined in this way and is wondering if their understanding, Cxy = dQx / d(Vx - Vy), is correct. They also ask for more information about where this formula can be found in Spice and mention checking a SPICE Model Definition Textbook.
  • #1
anhnha
181
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)
 
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  • #2
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...?
 

What is capacitance?

Capacitance is the ability of a material or component to store electrical energy in the form of an electric charge. It is measured in farads (F).

How is capacitance defined in Spice?

In Spice, capacitance is defined as the ratio of the change in electric charge on a component to the change in voltage across the component. It is represented by the letter "C" in circuit diagrams and equations.

How is capacitance calculated in Spice?

In Spice, capacitance is calculated using the formula C = Q/V, where C is the capacitance in farads, Q is the change in electric charge in coulombs, and V is the change in voltage in volts.

What is the significance of capacitance in circuit design?

Capacitance plays a crucial role in circuit design as it affects the behavior of components and circuits. It can be used to store energy, filter signals, and stabilize voltages, among other applications.

How does capacitance impact circuit performance in Spice simulations?

In Spice simulations, capacitance can impact circuit performance by affecting the voltage and current levels, as well as the frequency response of the circuit. It is important to accurately model capacitance in order to obtain realistic simulation results.

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