Mesfets not supported in LT?

[Paul Burridge]

Hi,

Does LT support/recognise Mesfets (or GaAsFets)? I don't see any
category within the standard library that appears to, unless they're
just processed as Mosfets with different parameters...
And while we're about it, what's the significance of the Lambda
parameter in the Jfet model? I know it's "channel length modulation"
but what exactly does that mean?

Thanks,

p.
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Mike Engelhardt]

Paul,

Does LT support/recognise Mesfets (or GaAsFets)? I don't see any
category within the standard library that appears to, unless they're
just processed as Mosfets with different parameters...
And while we're about it, what's the significance of the Lambda
parameter in the Jfet model? I know it's "channel length modulation"
but what exactly does that mean?

A MESFET is maybe more similiar to a JFET than a MOSFET,
but a distinct device none the less. There is a symbol, mesfet,
that will netlist as a MESFET, but you will have to supply your
own foundry models. For the parameter's supported in LTspice
MESFET's see the help section

(key F1)=>LTspice=>Circuit Elements=>Z. MESFET transistor

--Mike

 

[Kevin Aylward]

Paul Burridge wrote:

Hi,

And while we're about it, what's the significance of the Lambda
parameter in the Jfet model? I know it's "channel length modulation"
but what exactly does that mean?

Channel length modulation is equivalent to the early effect in
transistors. It makes the output a non ideal current source, that is
there is a finite output resistance. That is, there is a slope on the
Ids verses vds output curve. e.g. Idr=Id.(1+Vds.lambda)

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[Paul Burridge]

On Thu, 09 Sep 2004 06:52:14 GMT, "Kevin Aylward"
<salesEXTRACT@anasoft.co.uk> wrote:

Channel length modulation is equivalent to the early effect in
transistors. It makes the output a non ideal current source, that is
there is a finite output resistance. That is, there is a slope on the
Ids verses vds output curve. e.g. Idr=Id.(1+Vds.lambda)

Ta, Kev.
On a largely unrelated matter, I was carrying out these parameter
variations with LT by taking one of the stock models as a base,
changing Beta and Vto and renaming the stock model with a suffix (a),
(b), (c) and so forth. LT complained about the unrecognised character,
so I renamed them without the brackets. So a 2N2222 became a 2N2222A
for example. This time LT didn't complain, but changed the model
numbers to 2N2223, 2N2224 & 2N2225! Bloody confusing that was! Now I
think I know why Helmut said it's best not to place your own models in
with the stock ones!
--

"What is now proved was once only imagin'd." - William Blake, 1793.