Patent Grant
7625239
1. Field of the Invention
Embodiments of the present invention relate generally to graphics system hardware and more specifically to a single-to-multiple display adapter utilizing a single cable construction.
2. Description of the Related Art
A typical computer system includes, without limitation, a central processing unit (CPU), a graphics processing unit (GPU), at least one display device, and one or more input devices, such as a keyboard and a mouse. In many common applications, users require two or more display devices to be attached to a single computer system. The display devices are typically attached to the computer system via video cables that connect to one or more graphics adapter cards, installed within the computer system.
To maximize connector area efficiency, a host adapter card may incorporate a high-density connector to transmit two or more standard video signals. The two or more video signals available through the high-density connector need to be separated out into individual standard video connectors in order to properly connect to associated display devices. A cable assembly is typically used to attach two or more display devices to the high-density connector. The cable assembly commonly includes a matching high-density connector and two or more independent cables emerging from the matching high-density connector in a structure known as a “pig-tail.” The loose end of each independent cable is attached to a standard video connector that is configured to deliver a video signal to a single-channel video cable. The single-channel video cable includes a sufficient number of conductive paths to deliver a standard video signal to from a first standard video connector to a second standard video connector, which may be attached to a display device.
The pig-tail cabling structure facilitates the use of high-density connectors, while preserving compatibility with existing single-channel cabling regimes. However, the pig-tail cabling structure is also quite bulky at the exit point of the matching high-density connector and adds an additional cable end connector in the video signal path. Each signal within the cable end connector typically traverses an ungrounded span from the shielded cable to a predefined pin on the connector. This ungrounded span degrades the overall signal integrity of the video signal by interposing an impedance mismatched span in the signal path. Each impedance mismatched span in the signal path introduces noise in the transmitted signal, reducing overall system performance.
One approach to minimizing signal degradation in a pig tail cabling structure is to use high quality, low-loss components and cables. For example, high-quality low-loss cables may be used along with cable end connectors designed to match impedance and minimize connector injection loss. While this approach may help, significant signal degradation nonetheless occurs in the ungrounded span from the cable end to the connector pins. This signal degradation is becoming an important limiting factor in video cable assembly performance as general advances in video technology drive video signals to higher speeds, making the signals more susceptible to impedance mismatches.
As the foregoing illustrates, what is needed in the art is a mechanism for separating video signals from a high-density connector to individual standard connectors that also minimizes impedance mismatching effects.
One embodiment of the present invention sets forth a cable assembly for separating video signals within a high-density connector to individual video connectors. The cable assembly includes a high-density connector, a cable to transmit multiple video signals, and a printed circuit board (PCB) assembly configured to separate the video signals into individual video signals. The individual video signals are advantageously routed under controlled impedance conditions provided by the PCB to individual video connectors attached to the PCB.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The computer system 110 includes, without limitation, a central processing unit (CPU) 120, a system memory 122, and a graphics adapter 124, which incorporates a high-density connector 126. The CPU 120 processes instructions and data stored in the system memory 122 and receives user input from the keyboard 112 and the mouse 114. Additionally, the CPU 120 generates graphics images, either independently or with the assistance of the graphics adapter 124, for display on the display devices 160, 162. The graphics adapter 124 processes the graphics images into two or more video signals that are transmitted through the high-density connector 126 as electrical signals.
A matching high-density connector 132 within the cable assembly 130 receives the two or more video signals. The two or more video signals are separated into two or more independent video signals within the cable assembly 130 and transmitted to independent standard video connectors 134, 136. Each standard video connector 134, 136 may be connected to a corresponding video cable 140, 150, such as a single-channel video cable, configured to transmit video signals to one or more corresponding display devices 160, 162.
Each video cable 140, 150, includes a matching standard video connector 142, 152, a display-side standard video connector 146, 156, and a cable 144, 154. Cable 144 is configured to transmit video signals from matching standard video connector 142 to display-side standard video connector 146. Similarly, cable 154 is configured to transmit video signals from matching standard connector 152 to display-side standard video connector 156.
Display device 160 is configured to receive video signals from the display-side standard video connector 146 of video cable 140. Display device 160 generates visible images for viewing from the video signals. Similarly, display device 162 is configured to receive video signals from the display-side standard video connector 156 of video cable 150 and to generate visible images for viewing from the video signals.
The matching high-density connector 132 includes a set of electrically conductive pins 210, which are connected to wires 212 from cable 220. The cable 220 includes a set of wires 212 and should provide a controlled impedance environment for signals traveling along the wires 212. Each wire 212 spans a certain distance 214 from the cable 220 to the respective pin 210. The distance 214 represents an ungrounded span. As illustrated in greater detail in
The PCB assembly 230 includes a PCB 232, standard video connectors 134, 136, and a cable attach region 234 on the PCB 232. In one embodiment, the cable attach region 234 includes a field of through-holes where wires 212 from the cable 220 may be inserted and soldered to the PCB 232. Distance 216 represents the ungrounded span a wire may take from the cable 220 to the surface of the PCB 232 within the cable attach region 234. Because the field of through-holes may be more tightly packed around the cross section of the cable 220, distance 216 should be significantly smaller than the distance 214 associated with separating wires out to reach pins 210 within the matching high-density connector 132. Thus, noise introduced within the ungrounded span associated with distance 216 should be significantly less than noise introduced within the longer ungrounded span associated with distance 214.
In an ideal scenario 310, the signal path impedance 302 does not change as a signal traverses from the first controlled impedance region 330 to the transition region 332 to the second controlled impedance region 334. In the cable to high-density connector scenario 314, the signal path impedance 302 may increase significantly for longer wire spans within the high-density connector. In the cable to PCB scenario 312, the ungrounded span is negligible or very small and the path impedance 302 does not change dramatically. Furthermore, any path impedance variation associated with this scenario is limited to a relatively short distance. In a high-quality implementation, the cable to PCB scenario 312 should represent a path impedance 302 characteristics close to the ideal scenario 310 and introduce negligible noise, if any, within the video signal path.
The cable attach region 234 includes a field of connection sites 424 situated close to a cable cross section 426, which corresponds to the cross sectional area of cable 220 of
Standard video connector 134 may be electrically attached to the PCB 232 using connection sites 420. Similarly, standard video connector 136 may be electrically attached to the PCB 232 using connection sites 422. In one embodiment, the connection sites 420, 422 are through-holes in the PCB 232.
PCB trace 432 electrically connects at least one connection site 424 within the cable attach region 234 to at least one connection site 422 associated with the standard video connector 136. PCB trace 432 should be a controlled impedance trace to preserve signal integrity for the length of the trace. For example, a 50-Ohm controlled impedance trace should be used for applications requiring a 50-Ohm to ground impedance. Two 50-Ohm traces, routed to matching lengths, may be used where 100-Ohm differential impedance is required. In practical embodiments, a plurality of PCB traces connects a plurality of connection sites 424 to connection sites 422 and 420.
In sum, superior signal quality may be achieved by coupling wires directly from a cable carrying multiple video signals to a PCB and by using PCB traces to transmit individual video signals to individual video connectors. In one embodiment, a cable assembly may be constructed for splitting two video signals transmitted through a standard DMS-59 connector to two independent DVI connectors. The DMS-59 connector attaches to a cable, which is directly attached to a PCB. The PCB contains DVI connectors and impedance controlled PCB traces for connecting the signals transmitted by the cable to two independent DVI connectors.
While the forgoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. For example, aspects of the present invention may be implemented in hardware or software or in a combination of hardware and software. Therefore, the scope of the present invention is determined by the claims that follow.
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