Problem with .step in LTSpice

[Paul Burridge]

Hi,

I've come across an odd problem in the simplified circuit I'm posting
to a.b.s.e under the same subject title as this message.
I can't seem to get LT to step through 3 drain resistor values whilst
performing a DC sweep of Vgs. It should amount to just 30 iterations
in total, but LT is sweeping through over 22,000 when I include "oct"
in the .step statement. I can't get it to run at all without "oct" in
that line and I've never had to use "oct" at all for a step run
before. Can anyone tell me if the syntax for this kind of check has
changed recently and/or what the correct syntax should be?

Thanks,

p.

 

[Mike Engelhardt]

Paul,

I've come across an odd problem in the simplified circuit I'm posting
to a.b.s.e under the same subject title as this message.
I can't seem to get LT to step through 3 drain resistor values whilst
performing a DC sweep of Vgs. It should amount to just 30 iterations
in total, but LT is sweeping through over 22,000 when I include "oct"
in the .step statement. I can't get it to run at all without "oct" in
that line and I've never had to use "oct" at all for a step run
before. Can anyone tell me if the syntax for this kind of check has
changed recently and/or what the correct syntax should be?

..step param R 1k 5k 1k ; step from 1K to 5K in 1K steps
..step oct param R 1K 5K 10 ; step from 1K to 5K in 10 steps per octave

BTW, LTspice files aren't binary, they're ASCII:

--Mike

--- step.asc ---
Version 4
SHEET 1 880 680
WIRE 368 32 368 208
WIRE 144 80 144 32
WIRE 144 32 368 32
WIRE 144 160 144 192
WIRE 144 288 144 384
WIRE 16 368 16 384
WIRE 16 384 112 384
WIRE 112 384 144 384
WIRE 368 384 368 288
WIRE 112 384 112 400
WIRE 96 256 16 256
WIRE 16 256 16 288
WIRE 144 384 368 384
FLAG 112 400 0
SYMBOL njf 96 192 R0
SYMATTR InstName J1
SYMATTR Value 2N3819
SYMBOL voltage 368 192 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 20
SYMBOL voltage 16 272 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 1
SYMBOL res 128 64 R0
SYMATTR InstName R1
SYMATTR Value {R}
TEXT -80 144 Left 0 !;op
TEXT -256 448 Left 0 ;.step param R 1k 5k 1k
TEXT -208 264 Left 0 !.dc V2 5 -5 1m
TEXT -256 480 Left 0 !.step oct param R 1K 5K 10

 

[Paul Burridge]

.step param R 1k 5k 1k ; step from 1K to 5K in 1K steps
.step oct param R 1K 5K 10 ; step from 1K to 5K in 10 steps per octave

Great; thanks, Mike.
Is there a comprehensive manual on LTS anywhere on the 'net or in
print form that covers all the functionality of the program? A help
file alone doesn't really do it justice.

 

[Mike Engelhardt]

Paul,

Great; thanks, Mike.
Is there a comprehensive manual on LTS anywhere on the 'net
or in print form that covers all the functionality of the
program? A help file alone doesn't really do it justice.

The help file is only officially supported document, but you
can get that as a printable .pdf from

http://LTspice.linear-tech.com/software/scad3.pdf

Another good source of info is the independent users' group
at http://groups.yahoo.com/group/LTspice

--Mike