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I can be more specific when I am at my computer but find 'add curve' in the plot menu. That allows you to plot almost any function. If you want a node voltage in the equation simply click on the node then add a divide symbol and click on the next node. For a current you hold down shift while clicking. There is also a dropdown list of voltages and currents as well.
By the way, once you have entered a curve equation once, the next time you do 'add curve' you can pick earlier equations from the drop down box - you don't have to type it in again.
Also, check out the scripts in SIMetrix. I couldn't see one for gm but there are other useful ones there such as one for doing a curve trace of a MOS - it is called mos_is_vds.sxscr and is in the script|examples directory.
OK. I have attached a simple schematic & the results.
It is a simple MOSFET with a DC sweep for the gate. In order to avoid a divide by zero error when plotting, I have swept the gate from 1mV rather than zero.
There are two plots on the graph: the "static" gm i.e. simply the drain current divided by gate voltage and the dynamic version of the same which is the derivative of that.
If that doesn't help, maybe you could show what you haver done and explain where it goes wrong.
it says
Error : Cannot find vector of name 'Q4#D'
the reason is that in the netlist it does not save the point that i need for plot the gm
how can i say SIMetrix to save the volatage and current of Desired point in the netlist.
By default SIMetrix saves all node voltages & currents. Just to be sure, with the schematic loaded hit F11 function key. Then in the window that opens up at the bottom check there aren't any ".keep" statements. If your circuit is within a subcircuit, the nodes may not be saved. Add:
it gives the same error
i deleted the other .keep in the netlist and added .keep /SUBS
is it true that for plotting gm i should devide the Drain current of M4 to gate voltage of M9(refer to the picture) maye be the error is here!
OK, thanks. The problem is you are trying to do measure gm in an AC analysis. What I explained earlier was how to plot gm for a single transistor. It can also be done for a complete circuit, if that is what you want, but it needs to be done with a DC analysis.
OK. I think this will do what you want. I have broken the current between Q4 & Q6 and added a current controlled voltage source. The output of that will be AC current (although it will be plotted as a voltage where 1V=1A).
Actually, the solution to the problem is simpler than that. When you select the AC analysis ("Choose Analysis") to set the frequency etc there is a check box lower down "Save all currents". I am not sure why the .keep doesn't have the desired effect, but the "Save all currents" in the AC analysis puts:
in the shematic without a current controlled voltage source if i want to input the direct command in the netlist for plotting gm what is the plot command?
Added after 10 minutes:
it means that i want to plot gm with the other gragphs Simultaneously when i run the shematic
Try this. I have simply changed the AC settings to save AC currents (see attached image) and added a current probe to the drain of Q4. I also edited the current probe so it plots on a new grid to save the first graph being too cluttered.
i could not get 100db gain(like in the paper) for moderate inversion region
with 4mv offset voltage the gain is 80db
and also for strong inversion:with 200uv offset voltage,gain is 35dB
any way to increase the gain?
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