Hi,

I am trying to figure out a way to plot gm/Id for a transistor within LTspice. I am using as a starting point the schematic in the example MOSFET parameter sweep, MOS_gm_gmb_gds_ro.asc , within Examples\Examples\Educational\MOSFET parameter sweep\ .

In short, I am stepping the W/L and biasing sources and running .OP and .AC LIST 1 analysis . The example computes gm, gmb, gds, using the small-signal values from the AC analysis.

To plot gm/Id I would need to obtain the bias current of the NMOS transistor, either from the DC current through the voltage sources or through the device itself. Is there a way to refer to this current from the waveform viewer, maybe a trick I am missing ? The Spice Log file lists the device operating point for just one iteration, so I don't see how to extract the bias information for the steps, which is obviously being computed prior to the each AC analysis.

In short, given a sequence of AC analysis, how can I obtain/extract the bias point information for the circuit/devices, and if possible refer/use it within the waveform view when plotting ?

Helmut, can you help ? Mike, are you out there ? Fellow users, any ideas/work arounds ?

Thanks in advance for any help!

--- In LTspice@..., "f0xwm" <yfuji@...> wrote:

Hi,

I am trying to figure out a way to plot gm/Id for a
transistor within LTspice. I am using as a starting
point the schematic in the example MOSFET parameter
sweep, MOS_gm_gmb_gds_ro.asc , within
Examples&#92;Examples&#92;Educational&#92;MOSFET parameter sweep&#92; .

In short, I am stepping the W/L and biasing sources
and running .OP and .AC LIST 1 analysis . The example
computes gm, gmb, gds, using the small-signal values
from the AC analysis.

To plot gm/Id I would need to obtain the bias current
of the NMOS transistor, either from the DC current
through the voltage sources or through the device
itself. Is there a way to refer to this current from
the waveform viewer, maybe a trick I am missing ?
The Spice Log file lists the device operating point
for just one iteration, so I don't see how to extract
the bias information for the steps, which is obviously
being computed prior to the each AC analysis.

In short, given a sequence of AC analysis, how can I
obtain/extract the bias point information for the
circuit/devices, and if possible refer/use it within
the waveform view when plotting ?

Helmut, can you help ? Mike, are you out there ?
Fellow users, any ideas/work arounds ?

Thanks in advance for any help!

Hello,

You should use the .DC analysis in this case. Please take a
look the examples.

Files > Tut > Transconductance Gm and Gds



Best regards,
Helmut

--- In LTspice@..., "f0xwm" <yfuji@...> wrote:

Hi,

I am trying to figure out a way to plot gm/Id for a transistor
within LTspice. I am using as a starting point the schematic in the
example MOSFET parameter sweep, MOS_gm_gmb_gds_ro.asc , within
Examples&#92;Examples&#92;Educational&#92;MOSFET parameter sweep&#92; .

In short, I am stepping the W/L and biasing sources and running .OP
and .AC LIST 1 analysis . The example computes gm, gmb, gds, using
the small-signal values from the AC analysis.

To plot gm/Id I would need to obtain the bias current of the NMOS
transistor, either from the DC current through the voltage sources
or through the device itself. Is there a way to refer to this
current from the waveform viewer, maybe a trick I am missing ? The
Spice Log file lists the device operating point for just one
iteration, so I don't see how to extract the bias information for
the steps, which is obviously being computed prior to the each AC
analysis.

In short, given a sequence of AC analysis, how can I
obtain/extract the bias point information for the circuit/devices,
and if possible refer/use it within the waveform view
when plotting ?

Helmut, can you help ? Mike, are you out there ?
Fellow users, any ideas/work arounds ?

Thanks in advance for any help!

A while ago, I wanted to plot quantities like gm and gm/Id,
and uploaded:



Files:
mos18u.plt
mos18u.asc
gm_over_go.mos18u.plt
gm_over_go.mos18u.asc
TSMC18u_T77A.mod
[among others]

I'm using ideal controlled sources to let the simulation figure out reasonable bias points, and math functions in the plot to obtain derivatives in DC sweeps (if I recall correctly).

Hope that helps
CM

开云体育

Hello, this is a very good thread I am trying to learn from.

However the links in the post are non functioning. Is there a way to know where are they now?

The links got broken when this group moved from Yahoo! to groups.io.

If you know the file or folder name from any of the links, you should be able to find it you go to Files and type in the name in the search box in the top right.

For example, for this link:

..you can search for "Transconductance Gm and Gds" and you will get one hit: the correct folder.

Notes:

1. "%20" in any links should be replaced with a space.
2. Include the quotation marks in the search terms because you're looking for the exact file or folder name.

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