characterization, modeling, and design of esd protection circuits

2.2. Transmission Line Pulsing 21
(a)
(b)
Power Supply
Ri =1MΩ
+
V in
-
+
V in
-
R L =50Ω
DUT
V dev
DUT
S
I dev
Transmission Line
Scope
Probe
Scope
Probe
I dev = (V in - V dev ) / R L
t pulse = 2L/v
R L =50Ω
Fig. 2.5 (a) TLP schematic: a transmission line of length L is charged
to voltage V in and then discharged through the device under
test (DUT) when switch S closes. An oscilloscope voltage
probe across the DUT monitors the circuit response. (b)
Equivalent circuit of the TLP setup: the input is a square pulse
of height V in and duration 2L/v, where v is the phase velocity
of the line.
supply pin grounded and other pins open. This method is much like the HBM in that a
capacitor is charged and then discharged into a circuit. However, for TLP the capacitance
is distributed, thus creating a simple square-wave input on the order of 100ns long with a
rise time of about 2ns. The height of the pulse is Vin , the power-supply voltage, and the
width of the pulse is 2L/v, where L is the length of the transmission line and v is the
propagation (phase) velocity of the line. If the impedance of the circuit is constant, the
transmission line delivers a constant current pulse. An oscilloscope probe measures the
voltage across the device; the current may also be probed or may be calculated from the
input and device voltages:
L
Idev =
( Vin – Vdev) ⁄ RL . (2.1)