TL072: How to setup a transient Fourier (THD) analysis?

Tony Damore

Part Number: TL072

Tool/software:

Hi there,

As the title says I'm trying to run a distortion analysis on a waveform from an amplifier. I know how to get to this point (similar to PSPICE) but don't know how to add an Output Variable for analysis. I can't seem to figure out how to rename a net or to apply that name here.

Thanks in advance

7 months ago

0 Tony Damore 7 months ago

Prodigy 10 points

To clarify, I am trying to setup this analysis in PSPICE for TI

0 Gerasimos Madalvanos 7 months ago in reply to Tony Damore

TI__Mastermind 31576 points

Hey Tony,

The output variable here would be a voltage value, and if your output net is labeled something like "out", you can just declare the output variable to be V(out).

However, there will be some distortion induced by the simulator, as it creates essentially a piecewise linear approximation of the output voltage, so for very low THD values, you will need to decrease your step size to be very small, which will be either very processor intensive, time intensive, or both. A longer discussion on this can be found in the thread linked below.

In addition to the simulator needing to run a very granular simulation for "correct" results, there may be some characteristics of the amplifier that are not present in the SPICE model that will give an optimistic THD figure. The slew rate vs input voltage differential is not modeled, the slew rate is present, but it is a constant value from the smallest voltage differential up until the full slew rate.

https://e2e.ti.com/support/tools/simulation-hardware-system-design-tools-group/sim-hw-system-design/f/simulation-hardware-system-design-tools-forum/198744/calculating-thd

Unfortunately it doesn't seem that SPICE simulations are a great substitute for real life THD measurements.

Best
Jerry

0 Tony Damore 7 months ago in reply to Gerasimos Madalvanos

Prodigy 10 points

Thanks for your help Jerry. I agree with everything you said here. I guess my sticking point is I don't know how to name the output net. Seems like on old PSPICE I could just double click the net and name it.

+1 Gerasimos Madalvanos 7 months ago in reply to Tony Damore

TI__Mastermind 31576 points

Hey Tony,

You can name a net by pressing "n" on your keyboard, or by going to place, Net Alias. This opens up a dialogue box where you can name the net. Now just hit OK and place it on the wire you want to name.

Best,
Jerry

0 Tony Damore 7 months ago in reply to Gerasimos Madalvanos

Prodigy 10 points

ah! got it, thank you!

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TL072: How to setup a transient Fourier (THD) analysis?