Browse Prior Art Database

Test Site for Common-Collector S-Parameter Measurements

IP.com Disclosure Number: IPCOM000101932D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Crabbe, E: AUTHOR [+4]

Abstract

The disclosed test site eliminates parasitic effects which cannot be corrected for by the calibration. For Common-Collector measurements, it is important to AC-ground the subcollector of the device under test. A conventional collector opening of a few mu m2 . will provide a good short between the AC-grounded pad of the test site and the subcollector at low frequencies but not at high frequencies. The constriction of the AC current flowing in the ground loop through this small opening leads to an inductance. This inductance and the pad capacitance cause the S-parameter measurements to be dominated by anomalous resonances.

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Test Site for Common-Collector S-Parameter Measurements

       The disclosed test site eliminates parasitic effects
which cannot be corrected for by the calibration.  For
Common-Collector measurements, it is important to AC-ground the
subcollector of the device under test.  A conventional collector
opening of a few mu m2 . will provide a good short between the
AC-grounded pad of the test site and the subcollector at low
frequencies but not at high frequencies. The constriction of the AC
current flowing in the ground loop through this small opening leads
to an inductance. This inductance and the pad capacitance cause the
S-parameter measurements to be dominated by anomalous resonances.

      The test site illustrated in Fig. 1 solves the problem by
AC-clamping the subcollector to ground with a large contact under the
ground pad.  This ground pad provides a path between the grounds of
the input and output ports, and it can be much larger than the signal
pads for measurements in the common collector configuration.  The
contact window has approximately the dimensions of this pad (although
it can be smaller), and the substrate is implanted in that region at
the same time as the collector to reduce the resistance.  The
dimensions of the two signal pads are in addition minimized to reduce
the pad capacitances.  Their minimum size is set by the
high-frequency probes which require pads of at least 50 mu m on a
side.