eldo_user

Setting Up An Analysis
Pole Zero Analysis
Pole Zero Analysis
This topic describes the usage of the pole-zero post-processor.
Eldo is able to obtain the locations of poles and zeros for analog circuits following a small
signal analysis. This data is useful for obtaining stability and phase margin information as well
as predicting closed loop performance from an open loop response. As a lot of closely spaced
poles or zeros are not easily discernible via a Bode plot, the interactive post processor and its
textual output clearly help to identify such singularities and evaluate the most important areas in
a circuit's behavior.
The pole-zero data is obtained by linearizing the circuit about an operating point and outputting
information about circuit matrix description and AC response. This data will be analyzed by the
Eigenvalue QZ algorithm, one of the most accurate techniques available.
The pole-zero post-processor enables the designer to detect all the roots of the analyzed circuit
and to simplify this information, extracting the most meaningful of these roots. Moreover, a
high-level model of the reduced circuit—equivalent for AC and small signal analysis—is
calculated and given in the form of an FNS device that can replace the original circuit when
used as part of a more complex design.
The pole-zero post-processor may be activated for circuits that have been simulated using the
.PZ and .AC commands. The .PZ command can take either the voltage at a node, the voltage
between two nodes, or the current through a voltage source as parameters. The pole-zero
analysis determines the transfer function relationship—expressed as complex poles and zeros—
between the input at which the AC voltage source is applied and the output specified as a
parameter in the .PZ command.
Pole-zero only works on quasi-static devices.
Tip
See “.AC” and “.PZ” in the Eldo Reference Manual.
Pole-Zero Analysis Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
Running Pole-Zero Analysis in Batch Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
Running Pole-Zero Analysis in Interactive Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
Pole-Zero Analysis Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
FNS Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Pole-Zero Numerical Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
Pole-Zero Analysis Flow
To obtain the poles and zeros you must first run an analysis, then use the pole-zero postprocessor.
230
Eldo® User's Manual, 15.3