Keithley S530

Section 3: Test subroutine library reference S530 Parametric Test System Test Subroutine Library User's Manual
3-76 S530-907-01 Rev. A / September 2015
vtext2
This subroutine estimates the extrapolated gate-source threshold voltage of a metal-oxide field-effect transistor
(MOSFET) using a modified version of the vtext subroutine method.
Usage
double vtext2(int d, int g, int s, int sub, char type, double vlow, double vhigh,
double vds, double vbs, double ithr, double vstep, int npts, double *slope, int
*kflag)
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
type
Input
Type of transistor: "N" or "P"
vlow
Input
The start of the gate-source voltage (V
GS
) binary search, in volts
vhigh
Input
The end of the V
GS
binary search, in volts
vds
Input
Drain voltage, in volts
vbs
Input
Substrate bias, in volts
ithr
Input
Drain-source trigger current (I
DS
), in amperes
vstep
Input
V
GS
step size, in volts
npts
Input
The number of points in the sweep
slope
Output
The calculated transconductance (g
m
)
kflag
Output
Return status flag:
 0 = Normal operation
 1 = The ithr parameter is too high; indicates that the vlow
parameter is above the voltage threshold (V
T
) and the slope is
constantly decreasing
 2 = Did not find peak slope; indicates that the vhigh parameter
was below V
T
(maximum slope was the last value)
 3 = Binary search on V
GS
failed; may indicate that the vlow and
vhigh parameters were below V
T
and the device never turned on
 4 = The type parameter was not specified as "N" or "P"
 5 = V
GS
step size is 0.0
Returns
Output
The estimated threshold voltage
Details
This subroutine is a modified version of the vtext (on page 3-73) subroutine. The differences are:
 All setup parameters must have the correct sign (polarity)
 An initial binary search is done with LPTLib trigi and searchv subroutines
 The I
DS
-V
GS
data is measured at one time (LPTLib sweepv, smeasi)
 The vlow parameter must be algebraically smaller than the vhigh parameter