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I am performing PSRR analysis in LTSpice from this online tutorial. It shows PSRR analysis of LT 3042.

enter image description here

Here is my LTSpice schematic: enter image description here

The thing is no matter how much I try, I only get data till 10kHz. What am I doing wrong?

P.S. Let me know, I will attach my .asc file if needed.

EDIT 1: When I change the .tran stop time to 2 sec, it shows the initial missing data, still the range is stuck at 10kHz. enter image description here

enter image description here

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  • \$\begingroup\$ It would help a lot if you'd supply your netlist/.asc file. \$\endgroup\$ Jul 25, 2023 at 6:04
  • \$\begingroup\$ [link] (mega.nz/file/…) \$\endgroup\$ Jul 25, 2023 at 6:49

2 Answers 2

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The problem is your .step statement

.step dec param freq 10kHz 80MHz 100

In the SPICE Error Log (see below) you can see that the freq starts from 0.08 which is not what you intended. 80MHz seems to be interpreted as 80mHz i.e., 0.08 and the frequency starts at 0.08Hz and goes upto 10kHz. This is the problem.

enter image description here

enter image description here

To fix this, change the statement to
.step dec param freq 10e3 80e6 100

You can then simulate and see that the sweep starts from freq = 10kHz and goes higher like what you want

enter image description here

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  • \$\begingroup\$ thanks for such an elaborate explanation! \$\endgroup\$ Jul 25, 2023 at 11:26
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    \$\begingroup\$ e6 works great, but if the questioner is starting to get into SPICE they should really start using meg. \$\endgroup\$
    – Ste Kulov
    Jul 25, 2023 at 14:12
  • \$\begingroup\$ Yes, I do use that now. \$\endgroup\$ Jul 26, 2023 at 7:04
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In LTSpice, 'M' is not a recognised suffix, you have to use 'meg'.

So your sim statement should say .step dec param freq 10kHz 80meg 6

Correction from @qrk: 'm' gets recognised as e-3, which is why you have to use 'meg'

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    \$\begingroup\$ As a suffix, "m" or "M" is recognized as e-3. "meg" or "MEG" is recognized as e6. \$\endgroup\$
    – qrk
    Jul 25, 2023 at 15:01
  • \$\begingroup\$ Yes, this worked well. \$\endgroup\$ Jul 26, 2023 at 7:05

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