OhmSpiceOpen simulator

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Op-amp loop gain and phase margin

Measure gain and phase margins, then compare them with step-response ringing.

Analog

Compare the Closed-loop AC, Loop gain, and Small-step transient views to connect phase margin with ringing.

Editor showing the Op-amp loop gain and phase margin SPICE example as an unsaved schematic.
Op-amp loop gain and phase margin opens as an editable, unsaved schematic.

Open and run

  1. Open Examples from the Home ribbon.
  2. Choose Op-amp loop gain and phase margin.
  3. Open Simulate and choose Setup to review the analyses.
  4. Choose Run for one analysis or Run All for the complete configured set.
  5. Select a matching Scope view after the run. Use Save as sheet to keep the example or Discard to close it.

Sheets, analyses, and Scope

Non-inverting amp and loop gain

#

Setup: Loop-gain lab

AnalysisConfiguration
Small-step transientTransient
  • Step 5n
  • Stop 4u
Closed-loop ACAC
  • Sweep dec
  • Points 100
  • Start 100
  • Stop 20Meg
Loop gain (voltage injection)AC
  • Sweep dec
  • Points 80
  • Start 1
  • Stop 20Meg

Scope views and expected results

Closed-loop AC
AC Response
Waveforms
  • V(vin)
  • V(vout)
Loop gain T (voltage injection)

Analysis: Loop gain (voltage injection)

AC Response
Waveforms
  • T = −V(vfb)/V(vinv)-V(vfb) / V(vinv)
Step response (ringing)

Analysis: Small-step transient

Transient
Waveforms
  • V(vin)
  • V(vout)
  • V(vload)
Readouts
  • Maximum outputMaxV(vout)
  • Minimum outputMinV(vout)

Python scripts

No Python scripts are included with this example.

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