Is there an issue with annotating BSIM4 capacitances using xschem and ngspice? In the screen capture...
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stefanoaz
06/29/2021, 11:26 PMIs there an issue with annotating BSIM4 capacitances using xschem and ngspice? In the screen capture I tried annotating csd of the nmos device, but no value appears (I also tried cds). The syntax I used in the save statement was .save @m.x1.XM47.msky130_fd_pr__nfet_01v8_lvt[csd]. And for the ngspice_get_value symbol, I used this syntax:
name=r119 node=v(@m.x1.XM47.msky130_fd_pr__nfet_01v8_lvt[csd])
descr="csd"
Other BSIM4 capacitances fail to be passed as well.
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Stefan Schippers
06/30/2021, 6:45 AMI will dig in more detail this afternoon. In the mean time can you please check if the csd capacitance exists in the .raw file ? open the .raw file created by ngspice and look for the capacitance value. If it is missing you must tell ngspice to save these values.
Stefan Schippers
06/30/2021, 1:27 PMI think you must use the ngspice_get_value.sym component and use an expression like:
@m.x1.xm1.msky130_fd_pr__nfet_01v8[csd]
(replace x1.xm1 with correct path for your circuit or use ${path} followed by mos instance name, like: ${path}xm1).
You must explicitly save the required parameters, like:
.control...save @m.x1.xm1.msky130_fd_pr__nfet_01v8[csd]....endcs
stefanoaz
06/30/2021, 2:38 PMHi Stefan. I am saving these with the correct paths and they are working for the other parameters, as is seen in the screen capture. But I will check to see if the rawfile contains the csd (I suspect it does not). If not, it may be an ngspice behavior.
If it's a confirmed bug in ngspice, I'll report that in this thread.
stefanoaz
06/30/2021, 2:49 PMStefan: it was in fact my error. I did not notice that in the get_value.sym expression, i surrounded the node with v( ), which was needed for the symbol I copied it from. You can see this in my original comment. When I removed the v( ), the capacitance was reported.
User error.
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