Hi Daisy,
It seems that the simulator does not identify what f is. When I try your .measure card. It report the following warning message in the listing file.
**warning** could not identify variable type f
I simulate successfully with the following cards.
Code:.meas ac gainmax max vdb(vout)
.meas ac f3db when vdb(vout)='gainmax-3'
Please note that time or frequency are independent variables in a HSPICE simulator. However, we have never quote a variable like frequency or time in SPICE.
The .measure syntax is
.measure <DC|TRAN|AC> result when out_var=val where result is time for TRAN and frequency for AC. They are independent variables.
Best regards,
Yawei