Wave transmission lines and networks – Coupling networks – Equalizers
Reexamination Certificate
2001-04-20
2003-09-09
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Equalizers
C333S172000
Reexamination Certificate
active
06617939
ABSTRACT:
BACKGROUND OF THE INVENTION
One embodiment of the present invention generally relates to a connector or cable connector assembly, and more particularly, to a connector or cable connector assembly with an equalization circuit board for performing signal conditioning.
Conventional cable assemblies have been proposed that include an electrical cable with multiple electrical contacts and a housing attached to the cable. Signal conditioning circuit elements have been provided, such as resistors, capacitors and inductors, that are mounted in the housing as discrete individual components connected to contacts within the housing. U.S. Pat. No. 5,766,027 describes a cable assembly with an equalization board, on which the discrete signal conditioning circuitry is mounted. The circuitry on the equalization board is aligned with and joined to electrical contacts and cable conductors.
FIG. 1
illustrates a conventional equalization circuit board
10
having conductive pads
12
along one edge and a separate array of conducting pads along the opposite edge of the opposite side. The circuit board
10
may include multiple layers, such as upper, central and bottom layers. The central layer may include a conducting ground plane referenced to electrical ground with plating lined apertures (vias)
14
. The plating lined vias
14
extend between the upper layer and bottom layer. The plating within the vias
14
establishes electrical connections on the upper and lower layers to the ground plane. Signal conditioning circuitry is included on the upper or lower layer in the form of multiple conducting pads
16
and multiple relatively narrow circuit paths
18
interconnecting various conducting pads
16
and various plating lined vias
14
. Each conducting pad
16
is identified with an impedance symbol, such as R or L or C to indicate electrical elements that provide signal conditioning.
High speed data signals are conveyed at a desired data rate from a cable through the cable connector assembly. The data rate includes a known fundamental frequency. The data signals are comprised of multiple frequency components, each frequency component of which is attenuated to a differing degree by the cable.
FIG. 2
illustrates an exemplary graph of an attenuation characteristic curve
24
over an operating frequency range exhibited by high speed data signals. The curve
24
of
FIG. 2
may also be considered a cable loss curve. The horizontal axis of the graph in
FIG. 2
represents frequency, while the vertical axis represents “decreasing” attenuation. Attenuation increases in the direction of arrow
20
. Thus, low frequency components of data signals experience less attenuation due to cable loss than high frequency components of the data signals. The curve
24
corresponds to a data signal that is transmitted at a known desirable data rate having a fundamental frequency f
FND
. The data rate similarly has a frequency component at a second harmonic f
2nd
. Heretofore, it was considered desirable to maintain the level of attenuation for all frequency components of a data signal within a close tolerance (i.e., substantially constant). Heretofore, it was believed that the variations in attenuation introduced undesirable signal characteristics into the data stream.
In the past, signal conditioning circuits, such as disclosed in the '027 patent, were proposed for adjusting the cable loss characteristic to maintain substantially constant attenuation over the entire operating frequency range of the connector assembly.
FIG. 2
illustrates (through a dashed line) a signal conditioning equalization attenuation curve
22
, that is attained by conventional signal conditioning circuits. The signal conditioning circuit creates an attenuation curve that mirrors, but is inverted with respect to, the cable loss curve
24
to add exponentially decreasing attenuation to the data signal over frequency. The combined effects of the signal conditioning circuit and cable form equalization curve
22
. The equalization curve
22
represents the attenuation characteristic of the data signal output from the connector assembly once the data signals have traveled through the signal conditioning circuitry on equalization board
10
(FIG.
1
). As illustrated in
FIG. 2
, conventional signal conditioning circuitry is designed to offset the portion of the cable loss curve
24
below the second harmonic f
2nd
, such that frequency components of the data signal below the second harmonic f
2nd
, or fundamental frequency f
FND
exhibit constant attenuation. Thus, conventional signal conditioning circuitry introduced additional attenuation corresponding to region
26
above the equalization curve
22
and below the cable loss curve
24
up to the second harmonic f
2nd
, or fundamental frequency f
FND
.
Conventional signal conditioning circuits used multiple signal conditioning components including several capacitors, several resistors and several inductors to attain the desired equalization curve
22
. In many systems, ten or more components were required. The components were then organized on an equalization board in a layout dictated by the efficient use of the surface area of the equalization board. The components were distributed and arranged across the surface of the equalization board in a layout needed to maximize the useable area on the board, in order to minimize the size of the board. The most space efficient layouts for the multiple circuit components required that the components be interconnected through curved traces running in multiple directions and including multiple bends. Conventional signal conditioning circuit layouts have failed to realize that the shear complexity of the circuit layout introduces additional sources of interference into the data signals being transmitted. For instance, conventional signal conditioning circuit layouts introduce reflectance, cross-talk and other interference sources that adversely affect the signal integrity. Heretofore, these additional factors affecting signal integrity were not recognized nor accounted for in connection with the design of equalization circuitry.
Moreover, conventional equalization circuits for cable assemblies offer poor signal integrity at high frequencies and are therefore lossy in nature. These equalizing circuits not only introduce attenuation at low frequencies, they also introduce attenuation at high frequencies. In order for existing equalization circuits to be affective, they are only useful with long length cable assemblies (e.g., greater than 20 meters at 1.0 GBPS data rates). By limiting equalization circuits to use with long length cable assemblies, the added attenuation introduced by the equalization circuit at high frequencies is small relative to the amount of attenuation introduced by the length of the cable at high frequencies. Thus, while existing equalization circuits introduce undesired attenuation at high frequencies, the amount of attenuation relative to attenuation introduced by the cable itself is minimal. However, such equalization circuits were not useful with shorter length cables nor with cable assemblies having low attenuation at high frequencies relative to the attenuation of the equalization circuit at the same high frequencies.
A need remains for an improved equalization circuit design. It is an object of at least one embodiment of the present invention to meet the foregoing needs and other objectives that will become apparent from the detailed description, drawings and claims presented hereafter.
BRIEF SUMMARY OF THE INVENTION
In accordance with at least one embodiment of the present invention, an equalizer design has been developed that improves the signal integrity of long length and short length cable assemblies. Improvements in the signal integrity are detectable through examination and measurement of eye pattern openings, jitter and other signal “goodness qualities”. The equalizer design in accordance with at least one embodiment of the present invention affords the ability to easily modify a cable assembly to account for changes
Jones Stephen E.
Pascal Robert
Tyco Electronics Corporation
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