Browse Prior Art Database

Variable-Capacitance Adapter Card for Bus Testing

IP.com Disclosure Number: IPCOM000112966D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Elles, MC: AUTHOR [+4]

Abstract

Disclosed is a variable-capacitance tool for verifying the effects of changes in the capacitive loading of one or more signal lines in a personal computer, such as a group of signal lines in a system bus, and for assisting in the analysis of various signal quality problems. Voltage Variable Capacitance Diodes are used to apply a variable capacitive load to the signal trace.

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Variable-Capacitance Adapter Card for Bus Testing

      Disclosed is a variable-capacitance tool for verifying the
effects of changes in the capacitive loading of one or more signal
lines in a personal computer, such as a group of signal lines in a
system bus, and for assisting in the analysis of various signal
quality problems.  Voltage Variable Capacitance Diodes are used to
apply a variable capacitive load to the signal trace.

      In Fig. 1, an individual capacitive cell circuit 10 includes a
back-to-back pair of Motorola MV104 Silicon EPICAP diodes 12, which
produce a capacitive load variable between 7 and 23 pf on output line
14 as the voltage on input line 16 is varied between +2 and +30
volts.  For automated test procedures, the voltage on input line 16
may be supplied, for example, by a digital to analog convertor 17.
In the testing of individual circuit lines, only one circuit line can
be connected to output line 14, but a number of cell circuits 10 may
be tied to digital to analog convertor 17 by means of input line 18.
In this way, the various cell circuits 10 are switched and varied in
capacitance simultaneously.

      A pair of capacitors are connected between input line 16 and
electrical ground to filter noise within the circuit.  A ceramic
capacitor 19 is used to filter out high frequencies, while a tatalum
capacitor 20 is used to filter out relatively low frequencies.

      A different diode, or diodes in parallel, may be used in plac...