# Modelling a Resistance Transferfunction in Tina

#### DavidFelder1998

Joined Oct 12, 2022
1
Hello everyone

I currently have a small problem in a student work. I have a transfer function (PT1) which describes the resistance value of a component. Since I would like to simulate with this component in Tina or similar in combination with other electronics, I have the question how to get this resistance transfer function into the software TINA TI. Has anyone of you already done something like this? I could imagine that it would be possible with a simple LC or RC element. However, I just can't imagine how to model the whole thing. I don't have any experience with SPICE components but I would be willing to learn this topic.

David

PS.: I don't know if I have found the right subforum.

#### Papabravo

Joined Feb 24, 2006
19,617
It is an undocumented feature in LTspice.

Resistors
Behavioral Resistors
Create a behavioral resistor by right-mouse-button clicking on its Value field and edit its value to read: R=<expression>. This feature is undocumented, but is considered permissible to use. The expression syntax is the same as for a general behavioral source (see B-sources in Help).
The resistance must not go to zero and negative values can lead to convergence problems, so it is advisable to restrict its values to within a meaningful range as per the following Value example:
R = limit(1,100k,V(1,2)*I(V1)) ; R stays between 1 ohm and 100k
To plot an I-V curve, start by using the differential cursor to plot the voltage across the resistor. First click and hold down the left-mouse-button (red probe icon) on one side of the resistor and then drag and drop the black probe icon on the other side. Finish by dragging the mouse pointer over the x-axis (a ruler icon will appear) and the click the left mouse button to bring up the Horizontal Axis menu. Change the Quantity Plotted from "time" to "I(R1)" (assuming R1 is your behavioral resistor).
You can also specify a resistance with an imaginary part.
I don't know if TINA will allow it.

#### LvW

Joined Jun 13, 2013
1,589
No - you cannot use L or C because theyr impedance is frequency dependent and has phase shift.
In PSpice I can use controlled sources (behavior models)
Questio: What is the function? Depending on temperature or something else?

#### Papabravo

Joined Feb 24, 2006
19,617
No - you cannot use L or C because theyr impedance is frequency dependent and has phase shift.
In PSpice I can use controlled sources (behavior models)
Questio: What is the function? Depending on temperature or something else?
To be clear, for LTspice AFAIK
1. You can make a resistor look like an inductor or a capacitor
2. You cannot make an inductor, or a capacitor look like a resistor.

#### crutschow

Joined Mar 14, 2008
31,156
I have a transfer function (PT1) which describes the resistance value of a component.
What is the transfer function?

#### LvW

Joined Jun 13, 2013
1,589
To be clear, for LTspice AFAIK
1. You can make a resistor look like an inductor or a capacito
I suppose you are referring to an FDNR?

#### eetech00

Joined Jun 8, 2013
3,418
I think its an RC time delay
G/1+T*s

G=gain
T=R*C

laplace function maybe?

#### Papabravo

Joined Feb 24, 2006
19,617
I suppose you are referring to an FDNR?
If FDNR stands for "Frequency Dependent Non-linear Resistor", then it could be but does not have to be.

#### LvW

Joined Jun 13, 2013
1,589
If FDNR stands for "Frequency Dependent Non-linear Resistor", then it could be but does not have to be.
No - it stands for "Frequency-Dependent Negative Resistor".

#### Papabravo

Joined Feb 24, 2006
19,617
No - it stands for "Frequency-Dependent Negative Resistor".
3 out 4 words in an acronym is a pretty good score. That was not what I was talking about. In LTspice you can specify a resistor with a real part and an imaginary part, both of which can be functions.

#### LvW

Joined Jun 13, 2013
1,589
But in this case (real and imag. part) the component would create a phase shift.
Didnt the OP ask for a resistance?

#### Papabravo

Joined Feb 24, 2006
19,617
But in this case (real and imag. part) the component would create a phase shift.
Didnt the OP ask for a resistance?
I don't think it was exactly clear what the TS was asking for. He mentioned a "transfer function(PT1)" with any specification of what that meant. Also unclear what (PT1) refers to. In normal parlance a transfer function is a frequency domain concept which would probably involve phase shifts as a function of frequency. It is entirely possible that he has something else in mind.