Section 3: Test subroutine library reference
S530 Parametric Test System Test Subroutine Library User's Manual
3-34
S530-907-01 Rev. A / September 2015
gm
This subroutine estimates transconductance of a metal-semiconductor field-effect transistor (MESFET) at a
specified drain voltage (V
DS
) and gate voltage (V
GS
).
Usage
double gm(int
d
, int
g
, int
s
, int
sub
, double
vds
, double
idlim
, double
vgs
,
double
vgstep
, double
iglim
, int
*iflag
)
d
Input
The drain pin of the device
g
Input
The gate pin of the device
s
Input
The source pin of the device
sub
Input
The substrate pin of the device
vds
Input
Drain voltage, in volts
idlim
Input
Drain current limit, in amperes
vgs
Input
Gate voltage, in volts
vgstep
Input
V
GS
step size, in volts
iglim
Input
Gate current limit, in amperes
iflag
Output
Return status flag:
0 = Normal completion
1 = Not enough valid data for LLSQ
2 = Current limit reached (98 % of
iglim
or
idlim
)
Returns
Output
Estimated MESFET transconductance
Details
This subroutine estimates the transconductance of a MESFET at a specified V
DS
and V
GS
. A drain
voltage is forced, and then five V
GS
to I
DS
(drain-source current) data points are taken around the
specified V
GS
(the V
GS
step size is defined by the input parameter
vgstep
). Then a linear least
squares (LLSQ) line is fit through the data and the transconductance is estimated from the slope of
the line.
V/I polarities
N-cV
DS
, +V
GS
P channel -V
DS
,- V
GS
Source-measure units (SMUs)
SMU1: Forces
vds
, programmable current limit, measures I
DS
SMU2: Sweeps
vgs
, programmable current limit
