eldo_user

Examples
Example 22—Extract Gain and Phase Margin of a 2-Stage Opamp
• .EXTRACT—Extract characteristics from the simulator results.
• .PARAM—Global parameter setting.
• .STEP—Sweeping parameters.
Netlist Explanation
.param pCX=0.2p
.step param pCX DEC 10 0.01p 1p
The .STEP statement is used to observe the impact of the compensation capacitance upon
stability. The .EXTRACT quantities (see below) such as phase and margins are automatically
plotted versus the swept parameter, pCX.
.option nobound_phase
The nobound_phase option can be used if you prefer a continuous phase plot. By default the
phase plots are displayed modulo 360.
.AC DEC 1000 1 100E6
The above specifies a .AC statement to sweep the frequency from 1Hz to 100MHz.
.PLOT AC VDB(OUT)
.PLOT AC VP(OUT)
The above lines specify that the output response is plotted in Bode format.
.EXTRACT AC LABEL=MAX MAX(VDB(OUT))
The above line specifies to extract the open loop gain.
.EXTRACT AC LABEL=bandwidth 'CROSSING(VDB(OUT), -3)'
The above line specifies to extract the 3db bandwidth.
.EXTRACT ac label=phase_margin_1 {180 + xycond(vp(OUT), vdb(OUT) == 0)}
.EXTRACT ac label=gain_margin_1 -xycond(vdb(OUT), vp(OUT) < -180)
The above lines show the first compact method to extract the Gain and Phase margins, using the
XYCOND() function.
.EXTRACT AC label=unit_gain_freq crossing(vdb(OUT), 0)
.EXTRACT AC label=phase_margin_2 180 - yval(vp(OUT), 1) + yval( vp(OUT),
unit_gain_freq )
.EXTRACT AC label=opp_phase_freq crossing(vp(OUT), -180)
.EXTRACT AC label=gain_margin_2 -yval(vdb(OUT), opp_phase_freq)
The above lines show the second method to extract the Gain and Phase margins, using explicit
extraction of the zero-crossing and -180°-crossing frequencies.
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Eldo® User's Manual, 15.3