Wave transmission lines and networks – Coupling networks – Balanced to unbalanced circuits
Reexamination Certificate
2001-01-31
2002-12-10
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Balanced to unbalanced circuits
C333S025000, C333S260000
Reexamination Certificate
active
06492881
ABSTRACT:
BACKGROUND
1. Technical Field
The present invention relates generally to device interfacing; and, more particularly, it relates to interfacing a single ended device to a device employing differential inputs.
2. Related Art
There is a movement in the art towards devices that use or require differential inputs. There have been some conventional approaches that have sought to perform the interfacing of a single ended signal to a device necessitating differential inputs. One conventional approach seeks to isolate signals. This is done by separating traces on a printed circuit board (PCB) and by providing extra ground paths through connectors or in and out of integrated circuit (IC) packages. One deficiency in this approach is that isolating these signals does not eliminate shared paths altogether. Cross-talk between the signals is reduced, but it may not be completely eliminated.
Another conventional approach uses a differential driver that provides source and return connections for every signal. This second conventional approach allows cross-talk problems to be somewhat minimized, since each signal has its own dedicated return path. However, using these differential drivers necessitates special devices and more pins within a system, thereby increasing real estate consumption, cost, and complexity within a system. In certain applications where these constraints are rigid, the incremental addition of cost and complexity may make it impracticable to use such a conventional solution. The use of these differential drivers requires the use of other special devices more pins to perform the proper interfacing. This conventional approach is exemplary of a brute force method that puts little emphasis on cost savings in any number of terms including: money, real estate, and complexity.
Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.
SUMMARY OF THE INVENTION
Various aspects of the present invention can be found in a single to differential interface. The single to differential interface includes a first isolated power and ground plane and a second isolated power and ground plane. The first isolated power and ground plane generates a single ended source output having a first current magnitude. The second isolated power and ground plane is communicatively coupled to the first isolated power and ground plane via a substantially transmission-like connection. The second isolated power and ground plane receives a pair of differential signals. The first isolated power and ground plane receives a return signal via a single return path, the return signal having a second current magnitude.
In certain embodiments of the invention, the substantially transmission-like connection includes a number of transmission lines. One of the transmission lines has a first characteristic impedance and at least one other of the transmission lines has a second characteristic impedance. The first current magnitude and the second current magnitude are substantially of a common magnitude. The substantially transmission-like connection includes a number of connection types including a trace on a printed circuit board. The substantially transmission-like connection is operable across a predetermined frequency range at which the single ended source output is operable to be modulated. The predetermined frequency range spans from DC to a maximum switching frequency. One of the differential signals of the pair of differential signals is referenced through a resistance to a voltage logic level.
Other aspects of the present invention can be found in a single to differential interface. The single to differential interface includes a single ended source, a single to differential interface circuitry, and a differential receiver. The single ended source emits a single ended source output. The single to differential interface circuitry is operable to convert the single ended source output to a pair of differential outputs. The differential receiver receives the pair of differential outputs. The single to differential interface circuitry employs a substantially transmission-like connection between the single ended source and the differential receiver.
In certain embodiments of the invention, the substantially transmission-like connection includes a number of connection types including a trace on a printed circuit board. The differential receiver includes a printed circuit board trace having a first characteristic impedance, and the substantially transmission-like connection includes an interface trace having a second characteristic impedance. The second characteristic impedance is larger than the first characteristic impedance. One of the differential outputs of the pair of differential outputs is referenced through a resistance to a voltage logic level. The single to differential interface also includes a floating power supply that biases the single ended source. In other embodiments, a current being transmitted from the single ended source includes a magnitude that is substantially equal to a magnitude of a current that is received by the single ended source.
Other aspects of the present invention can be found in a single to differential interface method. The method includes referencing a single ended source output signal to a floating single ended source ground, implementing a differential interface that is referenced to a system ground, and referencing a number of differential signals to a number of receiver power supply voltages.
In certain embodiments of the invention, one of the differential signals is referenced to one of a voltage logic level low or a voltage logic level high. The method also includes using uniform impedance control, and the uniform impedance control is operable to ensure a single return current path. The method also includes connecting a first isolated power and ground plane to a second isolated power and ground plane via a substantially transmission-like connection. The substantially transmission-like connection includes a number of connection types including an interface trace on a printed circuit board.
Other aspects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
REFERENCES:
patent: 5534830 (1996-07-01), Ralph
patent: 5628057 (1997-05-01), Phillips et al.
patent: 5781078 (1998-07-01), Jones
Cleon Petty and Todd Pearson, 2/98, Motorola, Inc., “Designing With PECL (ECL at +5.OV)” AN1406 Application Note, (pp. 1-7, 8 pages total), AN1406/D Figure 6, Generic Driver/Receiver Pair.
National Semiconductor, Nov. 1996, “DS90CR281/DS90CR282 28-Bit Channel Link”, 1996 National Semiconductor Corporation TL/F/13638, (pp. 1-13, 14 pages total), Physical Dimensions (millimeters).
Stoddard Joe D.
Wright Mitchel E.
Akin Gump Strauss Hauer & Feld & LLP
Compaq Information Technologies Group L.P.
Glenn Kimberly E
Lee Benny
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