Electrical connectors – Preformed panel circuit arrangement – e.g. – pcb – icm – dip,... – Distinct contact secured to panel circuit
Reexamination Certificate
1999-11-23
2001-08-21
Nguyen, Khiem (Department: 2839)
Electrical connectors
Preformed panel circuit arrangement, e.g., pcb, icm, dip,...
Distinct contact secured to panel circuit
Reexamination Certificate
active
06276945
ABSTRACT:
BACKGROUND OF THE INVENTION
Modern backplanes, also referred to as motherboards, serve as communication media for the exchange of electronic signals between a plurality of daughter cards. The daughter cards generate communication signals, for example, data signals, address signals, and control signals which are distributed to daughter card connectors mounted on one or both sides of each daughter card. The daughter card connectors register with a corresponding set of backplane connectors on the backplane, which in turn distributes the signals between daughter cards along various communication paths.
Each connector pair includes an array of conductive interconnects in the form of mating male pins and female contacts which couple by frictional contact. The interconnects each provide a separate electrical path for the transmission of signals between, boards typically with some providing the transmission of signals in one direction and the others providing the transmission of signals in the other direction. Within a connector, the interconnect paths run substantially parallel.
As communication technology improves, there is increasing demand on connectors to channel more data through a given area. An obvious solution is to reduce the distance between signal paths, allowing for more data channels. This, however, increases the likelihood of electromagnetic coupling between signals. Such coupling generally takes on two forms, namely electric field E (capacitive) coupling and magnetic field H (inductive) coupling. The influence of either form of coupling between signals is generally referred to in the art as crosstalk. Crosstalk corrupts the waveform of an affected signal, which, in turn, can cause data errors, timing errors or other anomalies which interfere with proper data communication.
The danger of crosstalk is most significant where signals converge in a densely-populated region as in a connector. This passage of signals through connector pins in close proximity to each other makes crosstalk inevitable in prior art connector configurations, for example the configuration shown in the perspective view of Prior Art FIG.
1
A and the side view of Prior Art FIG.
1
B. This configuration includes a male connector housing
30
having an array of male pins
36
mounted to a, backplane
32
and a corresponding female connector housing
34
having a corresponding array of female contacts
38
bonded to a printed circuit board daughter card
42
. The female contacts
38
connect to the printed circuit board
42
by metal rods
40
which are bent approximately at right angles
44
contacting the printed wiring through plated through-holes
46
or surface mount pads.
Such an arrangement is sufficient for transporting signals of moderate speeds. However, in modern systems having faster signal clocks and increased data throughput, crosstalk interferes with system performance. In particular, the length of the paths between the backplane
32
and the daughter card
42
and the coupling between them introduces delays, distortions and unwanted couplings which seriously degrade the information transmitted.
Prior Art
FIG. 1B
illustrates the path of a signal, represented by arrow
48
, propagating between a backplane
32
and a daughter card
42
through a prior art connector assembly
30
,
34
. It is apparent that the path length of the conductive medium between boards, including male pin
36
A, female contact
38
A and metal rod
40
A, is extended and linear. It is also apparent that this path is parallel to adjacent paths defined by male pin
46
B, female contact
38
B and metal rod
40
B over its entire length. The behavior of the signal current
48
and its responsibility in inducing crosstalk are illustrated in Prior Art FIG.
2
and FIG.
3
.
Prior Art
FIG. 2
illustrates signal current
48
propagating through a male pin
36
, entering a female contact
38
at contact point
52
and passing to conducting rod
40
. As the signal propagates, it generates an H field
53
represented in the drawing in exemplary fashion as entering the plane of the page at points
49
and exiting the plane of the page at points
51
. The H field
53
is illustrated in the perspective view of Prior Art
FIG. 3. E
fields are not shown, but they are also generated by the voltages on the conductors.
In Prior Art
FIG. 3
, H fields
53
A,
53
B,
53
C respectively generated by signal currents
48
A,
48
B,
48
C emanate in a generally cylindrical orientation about the signal path, with the circles representing each field at a particular axial location along the conductive paths as shown. Depending on the magnitude and frequency of the current and the relative proximity of the signal paths, the resultant H field
53
A generated by one signal
48
A may extend spatially far enough to influence a signal
40
B of an adjacent path and a signal
40
C of a non-adjacent path. This form of coupling is referred to in the art as inductive coupling. Furthermore, the electric field created by the first signal
48
A, for example, may couple to nearby signal paths
48
B,
48
C. This is known in the art as capacitive coupling. In this manner each of signals
48
A,
48
B,
48
C may influence adjacent or non-adjacent signals.
It is well known in the art that a conductive medium has an inherent inductance caused by an H field generated about the medium by the current flowing through it. The closer a first medium is placed in proximity to a second medium, the more likely their respective H fields will influence each other. This, in turn, leads to an increased likelihood of crosstalk between media.
The theory of crosstalk in transmission lines is somewhat involved, but for printed circuit board connectors, the transmission line paths between a backplane and daughter card through male pins and female contacts are sufficiently short such that the signal propagation time is currently generally less than one-half of the rise time of the digital signals transmitted thereon. For this condition, the crosstalk amplitude increases as the signal rise time or frequency component increases. For the same reason, crosstalk increases with connector path length. Furthermore, the male pin/contact paths are characteristically inductive, causing increased signal attenuation as frequency increases. To accommodate high frequencies, or fast rise times, it is common to insert coaxial contact pairs in backplane to daughter card connectors. However, because coaxial pairs are expensive and bulky, they are used only in extraordinary circumstances.
The controlled-impedance lines of predominantly inductive prior art connectors are generally not matched between the backplane and daughter card, causing reflections when signal rise times approach the propagation delay of the connector paths. This causes signal distortion and attenuation and increases crosstalk due to multiple reflections, limiting high-frequency throughput. Shielded connectors are available to enhance throughput, but generally are expensive to produce and have relatively poor contact density per unit area. To achieve reduction of H and E fields at high frequencies, a shield is typically placed between each row of contacts on eat side (male and female) of the connector, a very complicated and expensive configuration. In this configuration, H field attenuation is provided by providing ground return paths adjacent each forward signal path E field attenuation is not fully effective because the resultant shield geometry is suboptimal. This phenomenon is detailed in Hybricon's Technology Focus publication H89107, incorporated herein by reference, which explains crosstalk for two parallel conductive paths.
Prior Art
FIG. 15A
is a side view of a conventional shielded connector, illustrating current flow in adjacent signal paths. For purposes of example, a backplane
32
includes a male connector
30
and a daughter card includes a corresponding female connector
34
. Planar shields
202
are inserted between rows or columns (for example along the vertical cross section of
FIG. 1B
) of mated contacts
Hayward C. Michael
Rehlander Richard N.
Hybricon Corporation
Mills & Onello LLP
Nasri Javaid
Nguyen Khiem
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