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Loop Stability Analysis
Setting Up An Analysis
Loop Stability Analysis
Analyses the circuit stability. The classical method for stability analysis is to break the feedback
loop at an appropriate point on AC analysis, while maintaining correct DC conditions. This
means that the loop must be terminated with the appropriate impedance it ‘sees’ looking at the
loop input. Obtaining this impedance value is not always a simple task. Loop stability analysis
measures the loop gain by successive injection (Middlebrook Technique). A zero voltage source
is placed in series in the loop: the first pin of the voltage loop must be connected to the loop
input, the other pin to the loop output. The name of this voltage source is given in the .LSTB
statement, and the loop gain can be displayed.
Two loop stability analysis algorithms are available:
• The default Middlebrook technique with successive injection (default convention
T=AK, with an option to select the M. Tian convention T=−AK).
• The K. Kundert algorithm from “A Test Bench for Differential Circuits.”
Use the .IPROBE command with .LSTB to perform open loop simulations without editing the
device netlists (no need to add a voltage source and nets to create an open loop).
Related Commands
• .LSTB in the Eldo Reference Manual
• .IPROBE in the Eldo Reference Manual
Related Topics
Example 11—Loop Stability of an Opamp
AC Analysis
Eldo® User's Manual, 15.3 229