Adding note on gmid data generation testbench

content/_sec_sizing.qmd

@@ -18,6 +18,10 @@ The $\gmid$ methodology has the huge advantage that is catches MOSFET behavior q
 
 In order to get the required tabulated data we use a testbench in Xschem which sweeps the terminal voltages, and records various large- and small-signal parameters, which are then stored in large tables. The testbench for the LV NMOS is shown in @fig-techsweep-nmos-tb, and the TB for the LV PMOS is shown in @fig-techsweep-pmos-tb.
 
+::: {.callout-note title="Note on Characterization Testbench"}
+The testbenches are relatively straightforward, with one exception: The drain current noise is sensed via the drain voltage source `vd` and converted to a noise voltage (node `n`) using a current-controlled voltage source (CCVS). This is necessary as the `.noise` simulation statement works with voltages.
+:::
+
 ![Testbench for LV NMOS $\gmid$ characterization.](./xschem/techsweep_sg13g2_lv_nmos.svg){#fig-techsweep-nmos-tb}
 
 ![Testbench for LV PMOS $\gmid$ characterization.](./xschem/techsweep_sg13g2_lv_pmos.svg){#fig-techsweep-pmos-tb}