Data processing: measuring – calibrating – or testing – Testing system – Of circuit
Reexamination Certificate
2001-09-18
2004-11-30
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Testing system
Of circuit
C324S601000, C324S638000
Reexamination Certificate
active
06826506
ABSTRACT:
FIELD OF THE INVENTION
This application relates to a method and apparatus for characterizing multi-terminal linear devices operating in several modes, and, in particular, to a method and apparatus for measuring devices in any of unbalanced, balanced, and multiple modes of operation.
DESCRIPTION OF THE RELATED ART
It is to be understood that according to this disclosure an unbalanced device has one signal carrying terminal for each single ended input and output of the device and operates in the single ended mode. It is also to be understood that a balanced device has two signal carrying terminals for each balanced input and output pair of the device and operates in one of two modes, either a common mode (even mode) or a differential mode (odd mode).
Signal integrity and its characterization is an issue of growing importance as digital networks increase in speed and bandwidth. Traditionally, RF devices and digital devices have had little in common. However, as digital signals operate higher and higher in speed and approach a 1 gigabit per second (hereinafter “Gb/s”) threshold, the digital signal analysis tools and the RF signal analysis tools begin to overlap in function and requirements. In addition, with higher speed digital signals, the harmonic contents of the digital signals are many times higher than a frequency of a fundamental tone, which results in a need for greater precision in connections between, for example, a device under test (hereinafter “DUT”) and testing devices that characterize these high speed digital DUTs.
A traditional differential time domain reflectometer (hereinafter “TDR”) system, which has been used to test digital DUTs, uses a step function as a driving signal to a DUT. The step function signal is used because there is no commercially available signal source that can generate an impulse function, which is a preferred driving signal for analog circuit characterization.
Due to the harmonic frequencies content in fast-rise-time digital signals, one may think of high-speed digital circuits or interconnections as transmission lines, and consider the effects of, for example, reflected signals on the measurement of these circuits and interconnections. However, frequency domain instruments such as the Vector Network Analyzer (hereinafter “VNA”) that typically consider these effects have not historically been used to measure such digital circuits and interconnections. Instead, the differential TDR has been used to characterize high-speed digital circuits and components.
There are several reasons why the differential TDR has traditionally been used. For one, time-domain representations of digital signals, such as state-to-state transitions, need to be preserved and their signal characteristics as a function of time need to be characterized. In addition, most devices and systems transmitting high-speed digital data use differential signals, while most VNAs are designed for single-ended or unbalanced, 2-terminal devices. However, with increasing data rates, the dynamic range of a very high-speed differential TDR system is often inadequate for analyzing low-level signals such as crosstalk signals or the signal components responsible for generating electromagnetic interference (hereinafter “EMI”). In addition, the parasitic inductances and capacitances that exist in signal lines and interconnections are generally ignored at lower data rates, where traditional TDR systems have been used, but as the data rates become significantly higher they can no longer be ignored. Further, the traditional differential TDR systems do not correct for the systematic sources of error in the measurement equipment, nor do they support de-embedding fixtures or interconnects used to characterize a DUT.
As is known to those of skill in the art, a complete characterization of a single-ended linear 1-terminal or 2-terminal DUT can be achieved by measuring standard S-parameters with a Vector Network Analyzer (hereinafter “VNA”). A standard 2-port S-parameter matrix represents a frequency domain representation of all possible signal paths between any two terminals of a multi-terminal DUT, including forward, reverse, transmission and reflection characteristics of and between the two terminals of the DUT.
One known procedure for measurement of a multi-terminal DUT with a commercially available 2-port VNA, is to connect each port of the VNA to 2-terminals of the multi-terminal DUT, and to terminate the rest of the terminals of the multi-terminal DUT with high quality matching terminations. The 2-port VNA is used to measure or characterize the 2-terminals of the multi-terminal DUT with the remainder of the terminals terminated. This procedure is then repeated wherein two additional terminals of the multi-terminal DUT are measured and the remainder of the terminals are terminated with the high quality matching terminations, until all of the terminals of the multi-terminal DUT have been measured. Once all the terminals of the multi-terminal device have been measured, the plurality of 2-port measurements made by the VNA are then processed to obtain the S-parameters of the multi-terminal DUT. This procedure is described, for example in the related art portion of U.S. Pat. No. 5,578,932 issued to the applicant of this application, which is herein incorporated by reference in its entirety.
As was described in
Combined Differential and Common
-
Mode Scattering Parameters: Theory and Simulation
, David G. Bockelman and William R. Eisenstadt, IEEE Transactions on Microwave Theory and Techniques, Vol. 43, No. 7, Jul. 1995 (hereinafter “the Bockelman IEEE Article”). The standard S-parameters can be extended to mixed-mode S-parameters (hereinafter “S
mm
”) that characterize the linear performance of balanced devices. The mixed-mode S-parameter matrix [S
mm
] are similar to conventional signal-ended S-parameter matrix [S] that the [S
mm
] characterize the stimuli and the response between any two terminals of a DUT. However, the [S
mm
] also considers the stimulus and response mode of operation, in addition to the stimulus and response port.
Referring to FIG.
1
(
a
), as is known to those of skill in the art, the single-ended 2-port [S] are defined in the format S
yz
with yz representing the response and stimulus ports, respectively. Referring now to FIG.
1
(
b
), the mixed-mode S-parameter matrix [S
mm
] for balanced devices are defined as S
wxyz
, with wx representing the additional response and stimulus modes of the DUT. The [S
mm
] of FIG.
1
(
b
) can characterize the linear performance of a balanced 2-terminal device. As with single-ended S-parameters [S], each column represents a different stimulus condition and each row represents a different response. In addition, the [S
mm
] matrix can be divided into four quadrants, and the DUT can be considered a 2-port device operating in pure and conversion modes of operation, as illustrated in FIG.
1
(
b
).
Referring to FIG.
1
(
b
), the upper left-hand quadrant describes the behavior of the DUT when it is stimulated with a differential-mode signal and a differential-mode response is observed. This quadrant consists of four parameters: reflection parameters S
dd11
, S
dd22
on both balanced terminals one and two of the 2-terminal DUT and transmission parameters S
dd21
, S
dd12
in forward and reversed directions between terminals one and two of the 2-terminal DUT. Thus, this quadrant describes the performance characteristics of a 2-terminal DUT operating in the differential mode.
The lower right quadrant describes the behavior of the DUT when it is stimulated with a common-mode signal and a common-mode response is observed. This quadrant also consists of four parameters: reflection parameters S
cc11
, S
cc22
on both balance terminals one and two of the DUT and transmission parameters S
cc21
, S
cc12
in the forward and reverse directions between terminals one and two. This quadrant describes the fundamental performance characteristics of a 2-terminal DUT operating
Adamian Vahe′ A.
Enquist Patrick J.
Phillips Peter V.
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