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Linear Charge Application Circuit

IP.com Disclosure Number: IPCOM000115856D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 140K

Publishing Venue

IBM

Related People

Riggio Jr, SR: AUTHOR

Abstract

Disclosed is a test circuit for detecting leakage path fault conditions in the individual wiring nets of a multi-layer device carrier. Using this circuit, an electrical charge is applied between a test point of the wiring net under test and a reference point, so that a high voltage appears between these two points. If there is a nearly open circuit between these two points, this voltage will remain for a period of time. If this voltage decays rapidly, a leakage path fault condition must exist, and thus has been detected. Also, a leakage path fault condition between the originally charged net and any net adjacent to this net can be detected by measuring the voltage between a point on the adjacent net and the reference point after the original net has been fully charged.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 45% of the total text.

Linear Charge Application Circuit

      Disclosed is a test circuit for detecting leakage path fault
conditions in the individual wiring nets of a multi-layer device
carrier.  Using this circuit, an electrical charge is applied between
a test point of the wiring net under test and a reference point, so
that a high voltage appears between these two points.  If there is a
nearly open circuit between these two points, this voltage will
remain for a period of time.  If this voltage decays rapidly, a
leakage path fault condition must exist, and thus has been detected.
Also, a leakage path fault condition between the originally charged
net and any net adjacent to this net can be detected by measuring the
voltage between a point on the adjacent net and the reference point
after the original net has been fully charged.  If a voltage appears
at the point on the adjacent net, a leakage path fault condition is
known to exist between the original net and the adjacent net.

      Using this test circuit, a charge is linearly applied to the
net under test, with current being injected into the net according to
a "ramp" function, as voltage increases linearly with time.  If a
voltage step is instead applied to the net through a switch, the
voltage response is non-linear, resulting in a non-repeatable and
unreliable test as the measured voltage assumes the form of a
decaying sine wave according to the resistive, capacitive, and
inductive elements within the net being tested.

      Fig. 1 is a block diagram showing major portions of the test
circuit.  The net 1 being tested is connected to a constant current
source 2 and to a scaling network 3, which feeds a differential
amplifier 4 through a set of voltage followers 4a.  The output of
differential amplifier 4 is connected to a hysteresis comparator 5
having an output signal indicating when the maximum voltage is
reached between the net 1 under test and the reference point.  A
third voltage follower 6 is connected to the scaling network to
provide a point at which a reduced equivalent of the resulting
voltage can be monitored.

      Fig. 2 is a schematic diagram of the test circuit.  Constant
current source 2 is formed with a constant current sink 7, voltage
references 8 and 9, and a pair of transistors 11 and 12, which are
connected in series with current sense resistor 13.  The constant
current sink 7, including resistors 14 and 15, voltage reference 16,
and transistor 17, sets a constant bias current through voltage
references 8 and 9, while providing proper base drive currents for
series transistors 11 and 12.

      Using constant current sink 7 in this way, instead of using a
resistor to provide the bias current of voltage references 8 and 9
and the drive currents for transistors 11 and 12, minimizes the power
that would otherwise be lost in heat between the base of transistor
12 and ground.  Since the supply voltage applied to terminal 18 can
be varied between +40 volts...