Patent Publication Number: US-2011072064-A1

Title: Reduce interference for kvm system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to transmission of electrical signals, and more specifically to filtering of electrical signals in a Keyboard, Video, and Mouse (KVM) device. 
     2. Description of the Related Art 
     Modern organizations, be it schools, businesses, governments, or the like, rely heavily on computer systems to perform a wide variety of day to day tasks. In some cases, each person affiliated with an organization may have an assigned desktop computer, laptop computer, or the like. Each computer may communicate with a plurality of servers that store data and programming necessary to perform the day to day functions of the organization. 
     As the use of computer systems proliferates, modern organizations often find it difficult to find enough physical space to store all the equipment that forms the computer system. In general, the space occupied by a server is typically greater than or equal to that of a desktop or laptop computer. Furthermore, a variety of other equipment such as input and output devices must be provided to operate each of the computers and servers. Due to increasing costs for maintaining office space, most organizations find it desirable to reduce the area occupied by the computer system. Some organizations may maintain hundreds, and even thousands of servers. Accordingly, computer server management and space utilization become even more critical in such organizations. 
     Typically, servers are assembled on standard server racks, allowing the racks to be centrally managed and easily stacked. KVM switches may be used to effectively monitor and control the computer servers. For example, by means of a KVM switch, it is possible to manage multiple computers with only one set of keyboard, video monitor and mouse, which saves both space and cost. The KVM switches are usually mounted in the standard server rack. A KVM switch may also be integrated with a flat panel display, a keyboard, and a cursor control device. In such an integrated KVM module, usually called a LCD KVM or a KVM drawer, the KVM switch is usually stationary and the flat panel display, the keyboard and the cursor control device can be slid out from the system rack to an extend position for operation and slid back into the system rack to a closed position for storage. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to transmission of electrical signals, and more specifically to filtering of electrical signals in a Keyboard, Video, and Mouse (KVM) device. In one embodiment, a method for designing a filter for filtering an electric signal transmitted between a Keyboard, Video, and Mouse (KVM) switch and at least one device includes determining a filter architecture, wherein the filter architecture defines a desired type of frequency response for the filter, determining one or more parameters of the filter, wherein the parameters define one or more performance characteristics of the filter, and optimizing the one or more parameters to achieve a specific desired frequency response of the filter. 
     In another embodiment, a computer readable storage medium comprising a program product which, when executed is configured to perform an operation for designing a filter for filtering an electric signal transmitted between a Keyboard, Video, and Mouse (KVM) switch and at least one device includes determining a filter architecture, wherein the filter architecture defines a desired type of frequency response for the filter, determining one or more parameters of the filter, wherein the parameters define one or more performance characteristics of the filter, and optimizing the one or more parameters to achieve a specific desired frequency response of the filter. 
     In yet another embodiment, a system includes a memory comprising a program for designing a filter for filtering an electric signal transmitted between a Keyboard, Video, and Mouse (KVM) switch and at least one device, and at least one processor which, when executing the program is configured to determine a filter architecture, wherein the filter architecture defines a desired type of frequency response for the filter, determine one or more parameters of the filter, wherein the parameters define one or more performance characteristics of the filter, and optimize the one or more parameters to achieve a specific desired frequency response of the filter. 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary system according to an embodiment of the invention. 
         FIG. 2  illustrates another exemplary system according to an embodiment of the invention. 
         FIG. 3  is a flow diagram of exemplary operations performed while designing a filter, according to an embodiment of the invention. 
         FIG. 4  illustrates yet another exemplary system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention generally relates to transmission of electrical signals, and more specifically to filtering of electrical signals in a Keyboard, Video, and Mouse (KVM) device. Embodiments of the invention provide methods and apparatus for designing a filter configured to reduce the effects of noise in an electrical signal transferred between a KVM device and another device. Designing the filter may involve determining a filter architecture, wherein the filter architecture defines a desired type of frequency response for the filter, determining one or more parameters of the filter, wherein the parameters define one or more performance characteristics of the filter, and optimizing the one or more parameters to achieve a specific desired frequency response of the filter. 
     In the following, reference is made to embodiments of the invention. However, it should be understood that the invention is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the invention. Furthermore, although embodiments of the invention may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the invention. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
       FIG. 1  illustrates an exemplary computer system  100 , according to an embodiment of the invention. As illustrated in  FIG. 1 , the system  100  may include a switching device  110 , a plurality of servers  120  (for example, two servers  120  are shown), a computer display screen  130  (hereinafter referred to simply as monitor  130 ), a keyboard  140 , and a scrolling device  150 . In one embodiment of the invention, the switching device may be a Keyboard, Video, and Mouse (KVM) switch. As illustrated in  FIG. 1 , the switching device  110  may be coupled with the servers  120  via an interface  121 . In one embodiment of the invention, the interface  121  may be a signal converting interface. 
     The monitor  130  may be coupled with the switching device  110  via a video interface  131 , as illustrated in  FIG. 1 . The video interface  131  may be configured to transfer video signals to the monitor  130 . For example, in one embodiment, video signals from one of the servers  120  may be transferred to the monitor  130  by the switching device  110  via the video interface  131 . 
     An input interface  141  may couple the keyboard  140  and the scrolling device  150 , such as a mouse, to the switching device. The keyboard  140  and scrolling device  150  may be used to provide input, for example, commands to manipulate data in one of the servers  120 . In one embodiment of the invention, the switching device may be configured to couple the keyboard  140 , monitor  130 , and the scrolling device  150  to one of the servers  120  at any given time. The user may be configured to change the specific server  120  to which the switching device is coupled by, for example, issuing one or more commands using the keyboard  140  and/or the scrolling device  150 . 
     As illustrated in  FIG. 1 , a plurality of connecting cables, for example, the cables  160 ,  170 , and  180  may coupled the servers  120 , keyboard  140 , scrolling device  150 , and monitor  130  to the switching device  110 . In one embodiment, one or more of the cables may be configured to carry video signals. For example, the cables  160  and  170  may be configured to carry video signals and other associated input and output commands to and from the switching device  110 . 
     In a particular embodiment of the invention, the cables carrying video signals may include a Category 5 (CAT5) cable. In one embodiment the category 5 cable may include four twisted pairs in a single cable jacket. This use of balanced lines helps preserve a high signal-to-noise ratio. However, category 5 cables often suffer from interference from both external sources and other pairs, commonly referred to as crosstalk. 
       FIG. 2  illustrates a category 5 cable  200  that may be configured to transfer video signals between devices  210  and  220 , according to an embodiment of the invention. In one embodiment, the devices  210  and  220  may represent at least the switching device (for example, the switching device  110  of  FIG. 1 ) and any one of the servers  120  and the monitor  130  illustrated in  FIG. 1 . As illustrated in  FIG. 2 , the category 5 cable may include four twisted pairs  201 - 204 . In one embodiment of the invention, the first pair  201  may be configured to carry a red video signal (R), the second pair  202  may be configured to carry a green video signal (G), and the third pair  203  may be configured to carry a blue video signal (B). 
     The fourth pair  204  may be configured to carry data signals. In one embodiment, the fourth pair  204  may be configured to carry one or more commands from peripheral video, keyboard and/or scrolling device connected to the system  100 . Furthermore, the transmission of the data signals in the fourth pair  204  may be a bidirectional transmission transmitted between devices  210  and  220 . In another embodiment, a horizontal synchronous signal (Hsync), a vertical synchronous signal (Vsync) as well as the polarity signal (of the horizontal synchronous signal and the vertical synchronous signal) may be carried on the red video signal (R), a green video signal (G), and a blue video signal (B) respectively. 
     As illustrated in  FIG. 2 , each of the devices  210  and  220  may include a respective termination device  211  and  221 . The termination devices  211  and  221  may terminate each wire in the twisted pairs  201 - 204 . In a particular embodiment of the invention, the termination devices  211  and  221  may be RJ45 connectors. 
     As illustrated further in  FIG. 2 , the termination devices  211  and  221  may be configured to couple the R, G, and B video signals from respective twisted pairs  201 - 203  with a driver circuit  212  of the device  210  and a receiver circuit  222  of the device  220 . In other words, the twisted pairs  201 - 203  may be configured to transfer video signals in a single direction, i.e., from the device  210  to the device  220 , in one embodiment. Accordingly, the driver circuit  212  may be configured to assert R, G, and B video signals what may be transmitted via the termination device  211 , the twisted pairs  201 - 203 , and termination device  212 , to the receiver  222 . 
     While the first to third twisted pairs  201 - 203  may be configured to transfer signals in a single direction, the fourth twisted pair  204  may be a bidirectional pair configured to exchange data in any direction between the devices  210  and  220 . Accordingly, the twisted pair  204  is shown connected to a transmitter/receiver circuits  213  and  223 , respectively, at device  210  and  220  via the termination devices  211  and  212 . 
     As discussed above, category 5 cables may be prone to cross talk interference. The twisted pair  204  may be especially prone to cross talk interference because it is bidirectional. In other words, the unidirectional transmission of video signals on the first to third twisted pairs  201 - 203  may generate a relatively greater noise on the bidirectional fourth twisted pairs  204 . For example, as the unidirectional transmission of video signals on the first to third twisted pairs  201 - 203  transmitted from the first device  210  to the second device  220 , signals in the bidirectional fourth twisted pairs  204  may be concurrently transmitted from the second device  220  back to the first device. In this configuration, signals transmitted in different directions in the twisted pairs  201 - 204  may result in undesired higher cross talk interference. 
     Accordingly, in one embodiment, a filter may be provided in at least one of the devices  210  and  220  to filter out the noise in the signals transferred on the twisted pair  204 . As illustrated in  FIG. 2 , filters  214  and  224  may be provided within the transmitter/receiver circuits  213 / 223 , however in alternative embodiment, the filters  214 / 224  may be separate circuits provided at an interface between the transmitter/receiver circuits  213 / 223  and the termination devices  211 / 212 . 
     The filters  214  and  224  may be designed to effectively remove noise in signals transferred on the twisted pair  204 .  FIG. 3  illustrates exemplary steps that may be performed during design of a filter for the devices  210  or  220  to filter noise on the twisted pair  204 . As illustrated in  FIG. 3 , the operations may begin in step  310  by determining a filter architecture. Exemplary filter architectures may include the Butterworth filter architecture, the Chebyshev filter architecture, Bessel Filter architecture, and the like, which are described in greater detail below. 
     In step  320 , parameter specifications for the filters may be determined. The parameter specifications may determine one or more performance characteristics of the filters  214  and/or  224 . Exemplary parameters that may be determined may include, for example, filter order, pass band, impedance, and the like. In step  330 , the filter design may be optimized. Optimizing the filter design may involve adjusting one or more filter parameters to obtain a specific performance or frequency response from the filter. Exemplary optimization operations may include, for example, optimizing roll-off speed, optimizing return loss, optimizing insertion loss, and the like. 
     In one embodiment of the invention, the particular type of filter architecture that is used to design the filters  214  and  224  may be determined based on one or more desired operational characteristics of the filters. For example, in a particular embodiment, it may be desirable to get a maximally flat response in a pass band region of the filter. The passband refers to a range of frequencies or wavelengths that can pass through a filter without being attenuated. In such embodiments, a Butterworth type filter architecture may be utilized. 
     The Butterworth filter is a type of electronic filter design configured to have a frequency response which is as flat as possible in the pass band. The Butterworth filter is also commonly referred to as the maximally flat magnitude filter. The frequency response of the Butterworth filter has no ripples in the passband, and rolls off towards zero in the stopband. A stopband is a band of frequencies, between specified limits, in which a filter attenuates or does not let signals through. When viewed on a logarithmic Bode plot, the response of a Butterworth filter slopes off linearly towards negative infinity. Butterworth filters have a monotonically changing magnitude function with frequency, unlike other filter types that have non-monotonic ripple in the passband and/or the stopband. 
     Compared with Chebychev filters or an elliptic filter, the Butterworth filter has a slower roll-off, and thus will require a higher order to implement a particular stopband specification. However, Butterworth filter will have a more linear phase response in the passband than the Chebyshev and elliptic filters. 
     In some embodiments of the invention, it may be desirable to have a fast roll off speed in the stopband. In such embodiments, a Chebyshev filter may be used. Chebyshev filters can be analog or digital filters having a steeper roll-off and more passband ripple or stopband ripple than Butterworth filters. 
     In some embodiments of the invention, it may be desirable to have a filter having a linear phase response. In such embodiments, a Bessel type filter may be used. Bessel filters that have a maximally flat magnitude and linear phase response in the passband of the filter. While embodiments of the invention are disclosed with reference to Butterworth, Chebyshev, and Bessel filters, in alternative embodiments, any reasonable type of filter architecture, for example, elliptical filters, comb filters, or the like, may be used. The particular architecture may be selected based on a desired frequency response characteristic of the filter. 
     As described above with reference to  FIG. 3 , after selecting a desired filter architecture, one or more parameter specifications for the filter may be selected. For example, in one embodiment, an order of the filter may be determined during the filter design process. A first order filter will only have a single frequency-dependent component. Accordingly, the slope of the frequency response may be limited to 6 dB per octave. In some embodiments, to achieve steeper slopes, higher order filters may be defined. 
     In one embodiment of the invention determining an order of the filter may require balancing a cost of the filter with the desired performance. In general, higher order filters may perform better than lower order filters. However, higher order filters may require more components, and therefore may be much more costly to implement. Accordingly, during the filter design process, the order of the filter may be determined based on the cost of the filter and the desired performance. 
     The pass band may be another parameter that is defined during the filter design process. As described above, the pass band determines a range of frequencies or wavelengths that can pass through a filter without being attenuated. Frequencies that are outside the range defined by the passband may be blocked by the filter. In one embodiment of the invention, the passband may be defined based on a desired data rate for transferring signals across a twisted pair. For example, in a particular embodiment, if a maximum data rate of 5 megabits/sec (Mbps) is desired, the passband may be at least 10 MegaHertz (MHz). 
     Another parameter that may be defined during the filter design process is the ripple response. A ripple refers to the periodic variation in insertion loss with frequency of a filter. Not all filters exhibit ripple, some have monotonically increasing insertion loss with frequency such as the Butterworth filter. Common classes of filters which exhibit ripple are the Chebyshev filters and the Elliptical filters. The ripple is not usually strictly linearly periodic. 
     The amount of ripple may be traded for other parameters in the filter design. For instance, the rate of roll-off from the passband to the stopband can be increased at the expense of increasing the ripple without increasing the order of the filter (that is, the number of components has stayed the same). On the other hand, the ripple can be reduced by increasing the order of the filter while at the same time maintaining the same rate of roll-off. In a particular embodiment, the ripple response may be determined to be 0.5 dB. 
     Yet another parameter that may be determined is impedance seen at terminals of the filter. The impedance that is determined may include both, an input impedance and an output impedance. Input impedance may be the impedance that is seen across input terminals of the filter. The input impedance may be measured by terminating the output terminals of the filter. In contrast to the input impedance, the output impedance may be the impedance seen across output terminals of the filter. The output impedance may be measured by terminating the input terminals of the filter. In one embodiment of the invention, the output impedance seen by output terminals of the filter may be around 100 Ohms, which is typical of CAT 5 cables. 
     Once the filter parameters have been determined, filter design process may involve optimizing the one or more parameters to achieve one or more specific desired filter characteristics. For example, in one embodiment, if a faster roll off speed is desired, then an attenuation value of the filter may be adjusted. The higher the attenuation value, the greater may be the roll off speed at any given frequency. For example, at 15 MHz, the roll off speed at an attenuation value of −30 dB may be greater than at an attenuation value of −20 dB. 
     Another example of optimization may involve adjusting the return loss of the filter. Return loss or reflection loss is the reflection of signal power resulting from the insertion of a device in a transmission line or optical fiber. It is usually expressed as a ratio in dB relative to the transmitted signal power. Reflections of a signal traveling down a conductor generally occur at a discontinuity or impedance mismatch. For example, the signal reflections may occur at an interface between a CAT 5 cable and the filter input. 
     A large return loss may distort signals being transmitted in the passband. Accordingly, it may be desirable to reduce the return loss. In one embodiment, the return loss may be determined at a cut-off frequency. In one embodiment, an acceptable return loss may be around −20 dB. 
       FIG. 4  depicts a block diagram of a computer system  400  according to an embodiment of the invention. In general, the computer system  400  may include a Central Processing Unit (CPU)  411  connected via a bus  471  to a memory  412 , storage  416 , an input device  417 , an output device  418 , and a network interface device  419 . The input device  417  can be any device to give input to the computer system  400 . For example, a keyboard, keypad, light-pen, touch-screen, track-ball, or speech recognition unit, audio/video player, and the like could be used. 
     The output device  418  can be any device to give output to the user, e.g., any conventional display screen. Although shown separately from the input device  417 , the output device  418  and input device  417  could be combined. For example, a display screen with an integrated touch-screen, a display with an integrated keyboard, or a speech recognition unit combined with a text speech converter could be used. 
     The network interface device  419  may be any entry/exit device configured to allow network communications between the computer system  400  and one or more other devices via a network. For example, the network interface device  419  may be a network adapter or other network interface card (NIC). 
     Storage  416  is preferably a Direct Access Storage Device (DASD). Although it is shown as a single unit, it could be a combination of fixed and/or removable storage devices, such as fixed disc drives, floppy disc drives, tape drives, removable memory cards, or optical storage. The memory  412  and storage  416  could be part of one virtual address space spanning multiple primary and secondary storage devices. 
     The memory  412  is preferably a random access memory sufficiently large to hold the necessary programming and data structures of the invention. While memory  412  is shown as a single entity, it should be understood that memory  412  may in fact comprise a plurality of modules, and that memory  412  may exist at multiple levels, from high speed registers and caches to lower speed but larger DRAM chips. 
     Illustratively, the memory  412  contains an operating system  413 . Exemplary operating systems, which may be used to advantage, include Linux (Linux is a trademark of Linus Torvalds in the US, other countries, or both) and Microsoft&#39;s Windows®. More generally, any operating system supporting the functions disclosed herein may be used. 
     Memory  412  may also include an application  414 . Applications  414  may be software products comprising a plurality of instructions which, when executed by the CPU  411  are capable of performing operations for designing a filter, according to an embodiment of the invention. For example, the application  414  may perform, or support performance of one or more steps outlined in  FIG. 2 . 
     While the foregoing 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, and the scope thereof is determined by the claims that follow.