Avtech AVR-EB2A-B, Instructions Manual

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This is the key equation for relating the observed voltage waveform to the DUT current.
SETTING THE AMPLITUDE LEVELS
The test jig contains a “bias tee” circuit to combine a DC forward bias with a reverse
bias pulse.
An adjustable DC voltage of up to +115V is generated in the mainframe. This DC
voltage is controlled by the front-panel OS menu, or by the “source:voltage:low”
command. The DC voltage source has R
DC
= 950 Ω in series with it, inside the
mainframe. The DC forward bias current through the DUT is then given by:
I
F
= (V
DC
– V
DIODE
) / (R
DC
+ R
SCOPE
)
I
F
= (V
DC
– V
DIODE
) / 1000 Ω
where V
DIODE
is the diode forward voltage drop (typically 0.7V).
The reverse bias pulse is capacitively coupled “on top” of this DC bias current. The
pulse generator has an adjustable amplitude of up to -24V, controlled by the front-panel
AMP menu, or by the “source:voltage” command. The pulse generator has 50 Ω in
series with it, inside the mainframe, as well as the 50 Ω of the oscilloscope, so the size
of the current change will be V
PULSE
/ (50 Ω + 50 Ω). Thus, the reverse current will given
by:
I
R
≈ I
F
+ V
PULSE
/ 100 Ω
In this equation, I
F
is positive, V
PULSE
is negative, and V
PULSE
must be set sufficiently high
such that I
R
is negative. This equation is only approximate, because the diode itself may
introduce some poorly-defined parasitic resistance during the switching transient.
This basic arrangement of DC and pulse sources is specified by MIL-STD-750E Method
4031.4 Test Condition A.
AMPLITUDE ACCURACY
The amplitude settings should not be relied upon for any degree of accuracy , because
the diode characteristics (forward voltage drop, reverse parasitic resistance) are not
known accurately in advance. Instead the voltage at the OUT terminal on the test jig
should be
measured with a calibrated oscilloscope.
CURRENT MONITOR
The AVR-EB2A-B monitors the actual forward bias current through the DUT. If the DUT
has been incorrectly seated, and the forward bias current can not flow properly, the
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