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iamxo
Joined: 22 Mar 2006
Posts: 976
Helped: 559
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 28 Aug 2008 10:09 hspice & hsim gets different simulation results |
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I'm simulating an 1k SRAM, with spice netlist.
At first, I use hsim(due to its high speed) and get the expected result.
However, when I change the tool to Hspice(more accurate than hsim), the result was totally wrong. the input clock to the SRAM through the driver buffer is no clock waveform, just waveform like steps.
but I find that the hspice converges successfully.
So, anyone meets the same problem or like that?? Give some advice or explainations, I have searched in google and gets nothing useful.
Thanks in advance.
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jbeniston
Joined: 05 May 2005
Posts: 85
Helped: 8
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| 28 Aug 2008 10:11 hspice & hsim gets different simulation results |
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| hsim has different levels of optimisation, making the results less accurate, the more you optimise. Try running with no optimisations, and see what result you get. It will be slower of course.
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iamxo
Joined: 22 Mar 2006
Posts: 976
Helped: 559
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| 29 Aug 2008 7:54 Re: hspice & hsim gets different simulation results |
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| jbeniston wrote: |
| hsim has different levels of optimisation, making the results less accurate, the more you optimise. Try running with no optimisations, and see what result you get. It will be slower of course. |
Thanks, in my simulation, the optimization is little, so I got the same result after omiting the options.
Someone said the version of the hspice maybe the reason because I use tsmc90nm process, is it possible??
Added after 5 hours 53 minutes:
I find the problem, it's due to the clock input terminal, where a reverse connected diode is put between clock and gnd.
Does this cause the problem as I first posted?
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apallix
Joined: 07 Aug 2008
Posts: 19
Helped: 2
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| 29 Aug 2008 9:25 Re: hspice & hsim gets different simulation results |
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The reverse biased diode is probably an antenna diode. It shouldn't be an issue in my opinion.
If the clock waveform is completely out of whack, I would suspect some thing more basic like some input pins floating etc. Hsim automatically assumes that inputs that are not driven by an input stimulus and left floating are at '0' where as hspice makes no such assumptions.
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iamxo
Joined: 22 Mar 2006
Posts: 976
Helped: 559
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| 31 Aug 2008 6:15 Re: hspice & hsim gets different simulation results |
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| apallix wrote: |
The reverse biased diode is probably an antenna diode. It shouldn't be an issue in my opinion.
If the clock waveform is completely out of whack, I would suspect some thing more basic like some input pins floating etc. Hsim automatically assumes that inputs that are not driven by an input stimulus and left floating are at '0' where as hspice makes no such assumptions. |
Thank you, apallix. but in my sram circuit, no input is floating during simulation.
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iamxo
Joined: 22 Mar 2006
Posts: 976
Helped: 559
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| 01 Sep 2008 8:30 Re: hspice & hsim gets different simulation results |
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I found the problem.
It's due to the antenna diode in my circuit, which is not found in my model file.
The simulation is correct when I get rid of the antenna diode from my circuit.
~~~
Thanks all for your help.
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