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Technique for Measuring the Instantaneous Current Drawn by a VLSI Circuit Using E-Beam Testing

IP.com Disclosure Number: IPCOM000099669D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 3 page(s) / 125K

IBM

Related People

Franch, RL: AUTHOR [+2]

Abstract

Disclosed is a technique for measuring the instantaneous current drawn by a circuit, using an E-beam tester.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Technique for Measuring the Instantaneous Current Drawn by a VLSI Circuit Using E-Beam Testing

Disclosed is a technique for measuring the instantaneous
current drawn by a circuit, using an E-beam tester.

For purposes of noise analysis it is important that the
instantaneous currents provided by power supply de-coupling
capacitors, and their time derivatives, be known in some detail
during the operating cycle of integrated circuits (*).  Part of the
internal waveform timing analysis is the timing analysis of the IDD
current waveform and the location of the peak current within the
cycle, with respect to the other internal waveforms.  While it is
easy to measure the average currents drawn, there is no convenient
way of measuring the instantaneous current waveform for modern ICs,
whose cycle times can be as short as 20 nS.  It is particularly
difficult to measure currents through lines which cannot be attached
to an oscilloscope ground.

The principle used in the invention is to measure the
difference in voltage, using an E-beam tester, across a sensing
resistor which is inserted into the power supply line near the
circuit under test.  The value of the resistor is to be determined by
factors described below, but it must be fairly small compared to the
chip under test, so as not to cause a significant voltage drop.  A
value of less than 5 ohms is typical.  Also, the series inductance of
the sensing resistor must be extremely small, so as not to cause
significant L di/dt drop.  Since the voltage waveform across a
sensing resistor is used to obtain R I(t), it is desirable that the
voltage be only R I(t), and not R I(t) L di/dt. Metal film chip
resistors used in this application have calculated self-inductance of
much less than one nanohenry.

The E-beam tester is used to measure the voltage on either side
of the resistor.  The power supply voltage of interest is brought to
the circuit under test via a power plane.  This can be part of a
printed circuit board, or inserted in a wiring board, as shown in
Fig. 1.  The power is interrupted by a small gap in the metal.  The
power is delivered to the circuit by the resistor, which bridges the
gap.  The E-beam tester measures the voltage on either side of the
gap, Va and Vb, as shown, while the circuit is operated.  The
measured voltage difference between the two points is related to the
current drawn simply by I = (Vb-Va)/R.  As E-beam testers typically
have pulse widths of 1 nsec or less, the current measured has
comparable time resolution.

Modern DRAMs have peak currents on the order of 10...