I would not trust the values, since Cadence's GPDK is a fictitious technology with models close to real technology and does have bugs in it and this could be one of the bugs.
Thanks for your reply. I had tried using NCSU FreePDK and NCSU CDK. However they don’t have spectre model files (.scs files) for simulations. Both of the PDKs have HSPICE compatible model files only. This is strange as at least NCSU CDK (CDK Stands for Cadence Design Kit) should have spectre model files. (I downloaded NCSU CDK ver. 1.6.0 Beta – compatible for IC6.1 and above). I need a pdk for learning purpose. I had written to their help email ID but there is no reply from their side.I would love to recommend Skywater 130 nm which is open source https://github.com/google/skywater-pdk
but there is currently no install instructions for use in Cadence. If you are in a university then maybe ask any professors if they are willing to give you access to a real technology which they use for research. You will have to sign an NDA though.
However, currently you can also use https://eda.ncsu.edu/
This also have install instructions and working with certain cadence versions.
However, I have not personally used them as of now.
Hope it helps
Thanks for your reply.1. Read about model used by this PDK in Spectre model reference guide.
2. Did you check if your drain current is "pure" drain current (is it equal to source, source-drain, is bulk current negligible)?
3. Did you check how simulator options affecting dc simulation and dcOP computation?
4...
Spectre documentation you can find in your spectre installation directory. Inside is a /doc directory consisting of plenty documents.1.Read about model used by this PDK in Spectre model reference guide.
There is not much spectre model documentation available in with the pdk. Atleast could not find anything relevant to the issue.
DC op functions are not part of primitives, nor the direct measurements. You can learn more in "Component Description Language user guide" inside the Virtuoso documentation.2. Did you check if your drain current is "pure" drain current (is it equal to source, source-drain, is bulk current negligible)?
Since I am using the the ‘gmoverid’ function to directly plot this graph, there should not be any error on this case. See the snapshot in my first post
Errpreset is used by transient analysis.3. Did you check how simulator options affecting dc simulation and dcOP computation?
No. In the DC simulation setup form, I kept the accuracy settings to ‘moderate’. What other simulation settings do you recommend pls?
It depends to many things. Usually sweep should be done within operating range (0 to vdd), however results around zero might not be reliable.Also wanted to ask one thing: While sweeping Vgs, should I sweep the value starting from zero or any other value such as 0.2 etc.
Thanks for your reply. Unfortunately, I dont have HSPICE. Also if it is a CDK (Cadence Design Kit), I suppose it should support a Cadence Simulator (Spectre etc).Hi, let me see if I can replicate the same results on my setup.
Also if you are using just for purposes of learning I would still recommend using NCSU CDK.
it works with cadence as a front end and HSPICE as a simulator in the backend which you have to set from the ADE environment. HSPICE and Spectre might use different numerical ways to compute and simulate circuits but one isn’t right or wrong. So you are good to go.
the following document is from the above page. And it shows how to use HSPICE with Cadence ADE.
So to conclude, don’t wait for me to verify the GPDK is correct use something which does not have any reported bugs as of now. The reason why I am asking you to not use GPDK is because while designing a LNA for our college project 45nm has bug regarding flicker noise not going away even if you keep on increasing transistor width by changing fingers but does reduce when you increase multiplicity . Something, which does not happen in real devices. I am personally tired of cadence’s shizz since I spent a good chunk of time understanding a bug!
hope this helps
Try GPDK45nm or GPDK130nm. You might have access to them actually.Hi all,
Just checking back if anyone has a solution to my problem. I just need a PDK having Spectre support with near-to-real parameters (the one I have - gpdk90 is far away from a real pdk: gm/Id for pmos is above 41).
Thanks and Regards,
Arvind Gupta.
Thanks for your reply. I dont have access to these PDKs. If I did, I would not have asked. I just need a PDK with which I can try out gm/Id technique.Try GPDK45nm or GPDK130nm. You might have access to them actually.
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