| Author |
Message |
peterlau1984
Joined: 11 Dec 2008
Posts: 18
|
 07 Jan 2009 2:18 Why simulation result is so different with my spec. ?? |
|
|
|
|
Dear all,
I designed a cascode current mirror with the relation
rout = gm4*ro4*ro2= 10 Mohm.
However, I got the simulation result that gm was 1 mA/V and ro2, ro4 was about 1 Kohm from "DC opation points" of Spectre , after runing dc analysis. The result of rout is apparently much less than my specification.
Why would this come out?
Is there anything wrong with my simulation??
|
|
| Back to top |
|
 |
Google
AdSense
|
07 Jan 2009 2:18 Ads |
|
|
|
|
|
|
| Back to top |
|
|
LvW
Joined: 07 May 2008
Posts: 1466
Helped: 242
Location: Germany
|
07 Jan 2009 10:34 Re: Why simulation result is so different with my spec. ?? |
|
|
|
|
| peterlau1984 wrote: |
Dear all,
I designed a cascode current mirror with the relation
rout = gm4*ro4*ro2= 10 Mohm.
However, I got the simulation result that gm was 1 mA/V and ro2, ro4 was about 1 Kohm from "DC opation points" of Spectre , after runing dc analysis. The result of rout is apparently much less than my specification.
Why would this come out?
Is there anything wrong with my simulation?? |
I´m not familiar with SPECTRE, however, for each simulator there are severe differences between dc and ac analyses (of course !!) as far as resistances are concerned. I suppose, you are interested in a dynamic/differential rout of several Mohms. But the dc analysis gives you information only about dc properties.
Try to verify the value of rout via an ac analysis.
|
|
| Back to top |
|
|
DenisMark
Joined: 16 Sep 2005
Posts: 324
Helped: 66
Location: Russia
|
11 Jan 2009 6:06 Why simulation result is so different with my spec. ?? |
|
|
|
|
The same thing you can also check by DC sweep analysis by sweeping of output voltage (Rout=1/deriv(Iout)).
Do you sure that you saw "gds" parameter in "DC operation point"? May be you have been confised by "ron" which is output resistance in triode region?
|
|
| Back to top |
|
|
