# LTSpice - varying frequency along time

Discussion in 'General Electronics Chat' started by atferrari, Feb 14, 2015.

1. ### atferrari Thread Starter AAC Fanatic!

Jan 6, 2004
2,826
920
LTSpice simulation.

I could not find a way to implement this:

a) Testing a circuit fed with a fixed amplitude sinusoidal voltage source varying frequency along a certain period. Say, in 2 seconds, between 6KHz to 450 Hz with 0.5 V amplitude.

b) Later I would like to test the same circuit in the same period at a fixed frequency with a varying amplitude.

c) And last, eventually, mixing both options.

Is such a thing possible? I fear I am out of luck here.

I am not trying to do a .tran simulation; my test is in one pass along time and stepping a parameter is not what I need either (well, the way I know to use it, at least...).

Suggestions appreciated.

Edit:

Yes, it is a .tran simulation. My bad.

/Edit

Last edited: Feb 15, 2015
2. ### MrAl Distinguished Member

Jun 17, 2014
3,592
754
Hi,

There is a VCO in there. Use a ramp as control.

3. ### atferrari Thread Starter AAC Fanatic!

Jan 6, 2004
2,826
920
Didn't know of a VCO.

Off to look for it. Gracias.

4. ### Alec_t AAC Fanatic!

Sep 17, 2013
7,000
1,445
I think the VCO MrAl referred to is the 'modulate' device.

atferrari likes this.
5. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,070

V(in) goes from 0V to 2V (because time goes from 0s to 2s) and V(B1) = V(in) = time.

V(F) is 10Hz when V(in) is 0V specified by space=10).
V(F) is 50Hz when V(in) is 1V specified by mark=50).
V(F) is 90Hz when V(in) is 2V because the slope is 40Hz per volt.

Last edited: Feb 14, 2015
JohnInTX likes this.
6. ### MrAl Distinguished Member

Jun 17, 2014
3,592
754
Hi,

Yes, that's it.

7. ### atferrari Thread Starter AAC Fanatic!

Jan 6, 2004
2,826
920
Gracias Mike. Using it now. Doing what I needed.