Keithley S530 User Manual

S530 Parametric Test System Test Subroutine Library User's Manual Section 3: Test subroutine library reference
S530-907-01 Rev. A / September 2015 3-73
vtext
This subroutine estimates the extrapolated gate-source threshold voltage of a metal-oxide field-effect transistor
(MOSFET).
Usage
double vtext(int d, int g, int s, int sub, char type, double vlow, double vhigh,
double vds, double vbs, double ithr, double vstep, int nmax, 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
The forced 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
nmax
Input
The maximum number of steps
slope
Output
The calculated slope
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
Gate-source voltage threshold, in volts.
Details
This subroutine estimates the extrapolated threshold voltage of a MOSFET using the maximum slope
method. Maximum slope refers to the common technique of numerically differentiating the I
DS
versus
V
GS
curve. Slope refers to the FET transconductance (g
m
).
This subroutine uses a two-step method of finding V
T
. First, a binary search is done on the V
GS
to find
a drain current (I
DS
) that is within 0.25 of the estimated threshold current (for most enhancement
devices this value is 1 μA). If the measured I
DS
value is within tolerance, the routine continues with a
sliding five-point linear least-squares (LLSQ) analysis of the I
DS
-V
GS
curve.

Keithley S530 Specifications

General

Brand	Keithley
Model	S530
Category	Test Equipment
Language	English