PSF Utilities - Read Spectre Data Files

Ken Kundert






psf_utils is a library allows you to read data from a Spectre PSF ASCII file. Spectre is a commercial circuit simulator produced by Cadence Design Systems. PSF files contain signals generated by Spectre. This package also contains two programs that are useful in their own right, but also act as demonstrators as to how to use the library. They are list-psf and plot-psf. The first lists the available signals in a file, and the other displays them.

Accessing the Results

You can use the PSF class to read ASCII Parameter Storage Format files. When instantiating the class you pass in the path to the file and then the resulting PSF object contains a dictionary that containing the signals. For example, the following lists is a:

from psf_utils import PSF
from inform import Error, display

kinds = {
    'float double': 'real',
    'float complex': 'complex',

    psf = PSF('adc.raw/tran.tran')

    for signal in psf.all_signals():
        kind = signal.type.kind
        kind = kinds.get(kind, kind)
        display(f'{<15}  {signal.units:<12}  {kind}')
except Error as e:

This example plots the output signal:

from psf_utils import PSF
from inform import Error, display
import matplotlib.pyplot as plt

    psf = PSF('adc.raw/tran.tran')
    sweep = psf.get_sweep()
    out = psf.get_signal('out')

    figure = plt.figure()
    axes = figure.add_subplot(1,1,1)
    axes.plot(sweep.abscissa, out.ordinate, linewidth=2,
    axes.set_title('ADC Output')
    axes.set_xlabel(f'{} ({PSF.units_to_unicode(sweep.units)})')
    axes.set_ylabel(f'{} ({PSF.units_to_unicode(out.units)})')
except Error as e:

abscissa and ordinate are NumPy arrays. As such, you can perform computation with them:

out = out_p.ordinate - out_n.ordinate

from numpy import sin
sine = sin(sweep.abscissa)

Utility Programs

Two utility programs are installed along with the psf_utils library: list-psf and plot-psf. The first lists the signals available from a PSF file, and the second displays them. They both employ caching to speed up access to the data. They also cache the name of the PSF file so that it need not be given every time. plot-psf also caches its arguments, so if you run it again with no arguments it will simply repeat what it did last time. For example, here is a typical session:

# display signals in PSF file
> list-psf -f resistor.raw/pnoise.pnoise
Using pnoise.raw/pnoise.pnoise.
    R1:flicker  R1:total    R2:fn       out
    R1:thermal  R2:rn       R2:total

# display them again, this time in long form
> list-psf -l
Using pnoise.raw/pnoise.pnoise.
    R1:flicker  A²/Hz  real  (12042 points)
    R1:thermal  A²/Hz  real  (12042 points)
    R1:total    A²/Hz  real  (12042 points)
    R2:fn       A²/Hz  real  (12042 points)
    R2:rn       A²/Hz  real  (12042 points)
    R2:total    A²/Hz  real  (12042 points)
    out         A/√Hz  real  (12042 points)

# display only those that match R1:* (assumes nonomatch variable is set in shell)
> list-psf -l R1:*
Using pnoise.raw/pnoise.pnoise.
    R1:flicker  A²/Hz  real  (12042 points)
    R1:thermal  A²/Hz  real  (12042 points)
    R1:total    A²/Hz  real  (12042 points)

# display a graph containing signals that start with R1:
> plot-psf R1:*

# display the thermal noise of R1, and then the total noise minus the flicker noise
> plot-psf R1:thermal R1:total-R1:flicker

# display a graph containing only out
> plot-psf out

> plot-psf        # display out again

Converting to PSF ASCII

psf_utils only supports PSF ASCII files. As an alternative, libpsf is a Python package that can read both ASCII and binary PSF files. Or, you can use the Cadence psf program to convert various types of simulation results files into PSF ASCII format. To use it, simply specify the input and output files:

> psf -i adc.raw/tran.tran -o adc.raw/tran.psfascii
> list-psf -f adc.raw/tran.psfascii

In this example there is nothing special about the ‘psfascii’ suffix, it is simply mnemonic. Rather, the output is in ASCII format because the -b (binary) option is not specified.


Flicker Noise is a simulation script that shows how to write simple Python scripts that run Spectre and use psf_utils to extract and display the desired results.


Latest development release:
Version: 0.5.0
Released: 2020-01-08
0.5 (2020-01-08):
  • beta release

0.4 (2019-09-26):
  • Allow glob patterns to be passed to both list-psf and plot-psf.

0.3 (2019-09-25):
  • Fix import errors in plot-psf command.

0.2 (2019-09-25):
  • Fix dependencies.

0.1 (2019-09-25):
  • Initial version