eldo_user

Setting Up An Analysis
Transfer Function
Symptoms
The .PZ command generates G and C matrices. The pole-zero post-processor computes poles
and zeros, and generates approximated FNS to be used. It uses a QZ algorithm to solve the
generalized Eigenvalue system:
GX = λCX
The CPU cost of the QZ algorithm is approximately n 3 , where n is the size of the G and C
matrices. When n > 500, the CPU time is large, and numerical issues may arise. This is a
constraint of the QZ algorithm.
Solution
Use a two-step S-parameter block approach:
1. Extract the S-parameters of the circuit (using .FFILE and .AC commands).
This generates a .s2p file containing the S-parameters.
2. Use this S-parameter file in one of two ways:
o
o
Use this S-parameter file (.s2p) as a macromodel of the circuit (using an FBLOCK
model). This is more accurate than the FNS pole-zero approach.
Alternatively, specify the .PZ command with the S-parameter file (.s2p) (using an
FBLOCK model). The pole-zero post-processor can then be used to compute the
poles and zeros as before, avoiding any numerical issues.
Related Topics
Tip
See “.AC,” “.FFILE” and “.PZ” in the Eldo Reference Manual.
Pole-Zero Analysis Flow
Pole-Zero Analysis Output
FNS Model
Working with S, Y, Z Parameters
Transfer Function
The .TF command calculates the small signal transfer function by linearizing around a bias
point. The gain from the input voltage source to the output node or source is calculated and
output to the .chi file together with the input and output impedances.
Tip
See “.TF” in the Eldo Reference Manual.
Eldo® User's Manual, 15.3 237