# Two port impedance, negative inductance?

In summary, the speaker is discussing their simulations of decoupling capacitor parasitic inductance and how they have used two port measurements in Mentor's Hyperlynx to obtain s2p files that were converted to normalized z-parameters in MATLAB. They are now trying to extract inductance from the complex impedance using a formula, but are getting a negative value and are trying to figure out what went wrong with their conversion. They mention finding a mistake in the conversion that caused the imaginary part to have the opposite polarity.
Hi
I'm doing simulations in preparation for experimental measurements of decoupling capacitor parasitic inductance. I've done simulations of two port measurements, in mentors hyperlynx, of parallel capacitors on small power planes. These have given me s2p files that I've converted to normalized z-parameters in matlab.
So, I want to extract inductance from the complex impedance. To do this I use
$L = \frac{\Im(z12)}{2\pi f}$
Taking a measurement in f=1.326e8Hz, where inductance dominates, gives me L = -0.3982/(2*pi*1.326e8)=-4.78e-10H. So, negative inductance! What am I missing here? Figure 1 and 2 shows |z| and re(z) and im(z).

#### Attachments

• z.png
2.3 KB · Views: 490
• z-ir.png
2.2 KB · Views: 486
OK, I found it, there is something wrong with my conversion between S and Z, causing imaginary part to become opposite polarity.

## 1. What is a two port impedance?

A two port impedance is a measure of the electrical resistance and reactance of a circuit with two input/output ports. It is used to characterize the relationship between voltage and current in a circuit.

## 2. What is negative inductance in a two port impedance?

Negative inductance in a two port impedance occurs when the inductive reactance of the circuit is greater than the capacitive reactance, resulting in a negative net reactance. This can happen when the circuit contains elements such as negative inductors or negative capacitors.

## 3. How is negative inductance represented in a two port impedance?

Negative inductance is typically represented by a negative sign in front of the inductive reactance value in the impedance equation. It can also be represented by a negative imaginary component in the complex impedance.

## 4. What are some applications of negative inductance in two port impedance?

Negative inductance can be used in electronic filters to achieve frequency selectivity, in oscillators to control frequency stability, and in impedance matching networks to improve signal transfer between different components. It can also be used in metamaterials to achieve unique electromagnetic properties.

## 5. How is negative inductance different from regular inductance in two port impedance?

Negative inductance is essentially the opposite of regular inductance, as it results in a negative net reactance instead of a positive one. This can affect the behavior of the circuit, such as the phase shift between voltage and current, and can be used to achieve specific circuit characteristics not possible with regular inductance.

• Electrical Engineering
Replies
14
Views
2K
• Electrical Engineering
Replies
7
Views
2K
• Electrical Engineering
Replies
2
Views
4K
• Engineering and Comp Sci Homework Help
Replies
20
Views
3K
• Electrical Engineering
Replies
2
Views
3K
• Engineering and Comp Sci Homework Help
Replies
26
Views
2K
• Electrical Engineering
Replies
8
Views
10K
• Electrical Engineering
Replies
7
Views
6K
• Introductory Physics Homework Help
Replies
3
Views
898
• Introductory Physics Homework Help
Replies
2
Views
1K