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Technique for Testing Decoupling Capability of a Computer System

IP.com Disclosure Number: IPCOM000050340D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Kostenko, WP: AUTHOR [+2]

Abstract

The effect of varying decoupling capacitance or other components in the power distribution on a computer system can be determined by exercising the computer with a repetitive program.

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Technique for Testing Decoupling Capability of a Computer System

The effect of varying decoupling capacitance or other components in the power distribution on a computer system can be determined by exercising the computer with a repetitive program.

The processor, channels, or memory, etc., is cycled with a program which loads zeros and ones into available general purpose registers or another appropriate facility of the element. This program repeats at its fundamental rate and generates strong harmonics of this through out the frequency spectra. By recording the magnitude of the power voltage noise harmonics with a spectrum analyzer, the noise generated by the constant and repetitive switching activity (DI) is characterized according to frequency. This initial noise characterization can be performed anywhere along a power supply line; however, the closer to the computer switching circuits the more relevant is the data.

Once the base spectral noise curve is established, for example, capacitors which are used for decoupling can be added or subtracted. After each addition or subtraction, a new noise curve can be established at the same point of interest as measured for the original or base curve. The result of dividing the latter noise curve by the original noise curve is a noise voltage ratio. This noise voltage ratio can be derived at any or many locations of interest. Each location's noise curves must be divided by its own original or base noise curve.

A reasonable decoupling system does not allow a proportionately large power supply voltage variation within the frequency range of interest. Therefore, the program-initiated switching of the machine's logic, generates a relatively constant noise current versus frequency spectrum for all reasonable power configurations. The constancy of the noise current allows interpreting the noise voltage ratio of two different power or decoupling schemes as, effectively, the noise transfer impedance ratio versus frequency at the point monitored. Such an interpretation allows studying the relative effects of different areas such as bus i...