[SI-LIST] Re: Impulse vs. Step Response?
- From: Tracy Barclay <Tracy.Barclay@xxxxxxxxxxxx>
- To: David Banas <DBanas@xxxxxxxxxx>
- Date: Fri, 2 Sep 2011 08:00:06 -0700
Hi David,
For your transient analysis, I do not see a transient waveform defined in your
netlist. The source Vin only defines a DC voltage and a AC voltage. I would
expect to see something like:
Vin in 0 DC 1 AC 1 PWL(0 1 0.05n 1 0.06n 0)
Where the PWL definition defines the desired unit step.
------------------------------------------------
Tracy Barclay
CAE
Synopsys, Inc.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of David Banas
Sent: Thursday, September 01, 2011 17:40
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Impulse vs. Step Response?
Hi all,
I've got a puzzler. I'm using this HSpice deck:
.TITLE AC Sweep vs. Transient Correlation
.OPTION
+ POST
+ PROBE
+ RUNLVL = 5
Rin in out r=1K
Cout out 0 c=1pF
Rout out 0 10MEG
Vin in 0 DC 1 AC 1
.IC V(out) = 0
.AC DEC 10 1 1G
.TRAN 0.05n 1u 0 0.05n UIC
.PROBE AC V(in) V(out)
.PROBE TRAN V(in) V(out)
.END
to get both the transfer function, H(w), (.AC command) and the unit step
response, u(t), (.TRAN command) of a simple RC LPF.
Then, I take the FFT of the .TRAN output and compare it to the .AC output.
And they match!
I wasn't expecting a match, since all my textbooks say there's a `jw' factor
relating the impulse response and the step response. That is:
U(w) = H(w)/jw
So, when I compared the 2 spectra, I was expecting the FFT of my .TRAN output
to have an extra 6dB/octave roll-off, as compared to the .AC output, due to the
`w' in the denominator, above.
Can anyone shed some light on this?
Thanks,
David Banas
Sr. Member Technical Staff
Altera
+1-408-544-7667 - desk
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