Abstract:
A device for Electro-Magnetic Interference (EMI) reduction in an Ethernet system has an Ethernet compatible device. The Ethernet compatible device has a filter for adjusting a signal outputted by the Ethernet compatible device for EMI reduction.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to network systems and, more specifically, to a device and method for reducing EMI issues while retaining compatibility with existing Ethernet based systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ethernet was originally based on the idea of computers communicating over a shared coaxial cable acting as a broadcast transmission medium. Ethernet has evolved into a complex networking technology that today underlies most LANs. The coaxial cable was replaced with point-to-point links connected by Ethernet hubs and or switches. This enabled one to reduce installation costs, increase reliability, and enable point-to-point management and troubleshooting. Ethernet has evolved to become the main network of choice for data communication. 
         [0003]    Ethernet may be connected to devices through Category 5 (CAT5) cables. CAT5 cables comprise a twisted pair of high signal integrity cable housed within a single cable jacket. This use of balanced lines helps preserve a high signal-to-noise ratio despite interference from both external sources and other pairs (i.e., crosstalk). 
         [0004]    Ethernet is capable to connect to devices through CAT5 cable with a span of approximately 100 meters with data rates running at 10, 100 or 1000 M-bit per second. For better margins, it is common that most devices may reach 130 meters or above. Further, the use of switches allows devices to run at full duplex mode without worrying about the collision domain which limits the total cable length and its delay of the network. 
         [0005]    Presently, efforts are being made to expand Ethernet uses to EMI sensitive areas. These may include, but are not limited to areas such as the medical and automotive fields. However, the nature of transmit coding schemes has dictated the EMI performance. Changing the coding schemes may greatly relieve the EMI issue. However, changing the coding scheme will make it incompatible with existing devices. 
         [0006]    Therefore, a need existed to provide a system and method to overcome the above problems. The system and method would reduce EMI issues while remaining compatible with existing Ethernet systems and devices. 
       SUMMARY OF THE INVENTION 
       [0007]    A device for Electro-Magnetic Interference (EMI) reduction in an Ethernet system has an Ethernet compatible device. The Ethernet compatible device has a filter for adjusting the signal output transmitted by the Ethernet compatible device for EMI reduction. 
         [0008]    A data transmission system has a first Ethernet compatible device and a second Ethernet compatible device (referred as link partner). A cable couples the first Ethernet device to and the second Ethernet device (link partner). A filter is coupled to the first Ethernet compatible device for adjusting attenuation of a signal outputted by the first Ethernet compatible device for EMI reduction in the data transmission system. 
         [0009]    The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a simplified functional block diagram of an existing Ethernet system; 
           [0011]      FIG. 2  is a simplified functional block diagram of one embodiment of an Ethernet system of the present invention; 
           [0012]      FIG. 3  is a simplified functional block diagram of another embodiment of an Ethernet system of the present invention; and 
           [0013]      FIG. 3A  is a simplified functional block diagram of an Ethernet device of  FIG. 3 ; and 
           [0014]      FIG. 4  is a simplified functional block diagram of a filter device used in the Ethernet system of  FIG. 3 . 
       
    
    
       [0015]    Common reference numerals are used throughout the drawings and detailed description to indicate like elements. 
       DETAILED DESCRIPTION 
       [0016]    Referring to  FIG. 1 , an existing Ethernet based system  100  is shown. The system  100  may include a first device  102 . The first device  102  may be connected to a second device  104  (hereinafter link partner  104 ). The first device  102  may be connected to the link partner  104  via a cable  106 . In general, the cable  106  may be a CAT5 cable, a CAT5e cable, CAT6, or the like. The listing of the above is given as an example and should not be seen in a limiting manner. Presently, in Ethernet networks, it is generally recommended that the cable  106  runs be limited to a maximum length of approximately 100 m. While passing signals, the cable  106  acts as an attenuator. Thus, as the length of the cable  106  increases, the distortion of the signal traveling through the cable  106  at node  105  also increases. The distortion may be a reduction of amplitude (loss) and phase shift (delay) of the signal traveling through the cable  106 . It has been found that the loss is frequency dependent, broadly rising with frequency, although the actual level of loss is not linearly dependent upon the frequency. 
         [0017]    Referring now to  FIG. 2 , an Ethernet based system  200  in accordance with one embodiment is shown. The system  200  may include a first device  202 . The first device  202  may be connected to a second device  204  (hereinafter link partner  204 ). The second device  204  may be the same as the link partner  104  shown in  FIG. 1 . The first device  202  may be connected to the link partner  204  via cables  206  (external) and  205  (internal). In general, the first device  202  and the link partner  204  may be Ethernet compatible devices These may include but are not limited to network devices such as routers, switches, personal computer, computer peripherals, or the like. The cables  205  and  206  may be a CAT5 cable, a CAT5e cable, CAT6, or the like. The listing of the above is given as an example and should not be seen in a limiting scope. Cable  206 , length L, is similar to cable  106 . Cable  205  is an extra piece of internal cable with its length (100-L), so that the total length is approximately 100 meter between device  102  and its link partner  204 . 
         [0018]    The extra cable  205  acts as a low pass filter with amplitude reduction and phase delay which may be used to reduce EMI issues at node  208  in the system  200 . The amplitude reduction has a direct one to one effect on EMI reduction. The phase delay which slows down the rate of transition edge has even stronger effect in reducing the EMI. Thus, by properly filtering the signal transmitted by the first device  202  and incorporating a portion of the internal cable attenuation  205  in the signal, the system  200  will allow the first device  202  and link partner  204  to communicate within the specification allowed cable length (i.e., 100 meter), with EMI reduced and fully compatible with existing Ethernet systems. 
         [0019]    In the present embodiment, the first device  202  is an Ethernet compatible device which capable of transmitting a signal to the link partner  204 . However, it should be noted that the first device  202  may further be able to receive signals as well as transmit signals. The first device  202  incorporates a programmable portion of the internal cable  205  as part of the first device  202 . In the embodiment shown, corresponding to the external cable length L meters of  206 , (100-L) meters of the internal cable  205  is incorporated as part of the first device  202 . As a result, in system  200 , the total reach of the cable ( 206 + 205 ) is always approximately 100 meters, maximum allowed by the specification. The EMI performance of node  208  in the system  200  is improved by cable  205  attenuation compared with node  108  in the system  100 . Where shorter length of cable  106  and  206  may be used, the system  200  provides better EMI performance than that of system  100  due to the effect of extra cable  205 . 
         [0020]    Referring now to  FIG. 3 , an Ethernet based system  300  in accordance with another embodiment is shown. The system  300  may include a first device  302 . The first device  302  may be connected to a second device  304  (hereinafter link partner  304 ). The second device  304  may be the same as the link partner  104  shown in  FIG. 1 . The first device  302  may be connected to the link partner  304  via a cable  306 . In general, the first device  302  and the link partner  304  may be Ethernet compatible devices. These may include but are not limited to network devices such as routers, switches, personal computers, computer peripherals, or the like. The cable  306  may be a CAT5 cable, a CAT5e cable, CAT6, or the like. The listing of the above is given as an example and should not be seen in a limiting scope. 
         [0021]    In  FIG. 2 , the internal cable  205  acts as a low pass filter with amplitude reduction and phase delay which may be used to reduce EMI. In  FIG. 3 , the cable  205  is replaced by a filter  308  which has the similar characteristic of cable  205  in terms of phase delay and amplitude reduction. 
         [0022]    In the present embodiment, the first device  302  is an Ethernet compatible transmitting device  302 A. However, it should be noted that the first device  302  may further be able to receive signals as well as transmit signals. The transmitting device  302 A incorporates a filter  308  as part of the transmitting device  302 A. The filter  308  may be a programmable filter. The programmable filter  308  may store the cable characteristic into its register to allow the programmable filter  308  to generate a signal having a frequency response similar to the characteristics of the cable  205  ( FIG. 2 ) at any given length. Thus, attenuation and filtering can be a programmable feature based on the length of the cable required. The programmable filter  308  will allow the first device  302  to transmit a waveform similar to the waveform normally transmitted by the first device  102  of  FIG. 1  with the output attenuated by the length of the cable  205  of  FIG. 2 . No modifications are needed for link partner device  304 . Thus, the first device  302  and link partner  304  are able to communicate with a reasonable cable length, with EMI reduced and fully compatible with existing Ethernet systems. 
         [0023]    The first device  302  may take on many different forms based on the type of Ethernet device the first device  302  takes. As in  FIG. 3 , conceptually device  302  is a combination of device  102  and a filter  308  which has a programmable cable characteristic. Referring to  FIG. 3A , in the present embodiment the device  302  is an Ethernet compatible device  302 A. The device  302 A may take on many different forms. In accordance with one embodiment, the device  302 A is comprised of a device  309  to handle both receive (receiving path not shown) and transmit data, registers  310  to store the cable characteristic at various length, a digital processing unit  312  to carry out the filter operation in digital domain, a DAC  314  to convert digital signal into analog form, and a driver device  316  to drive the cable signal. The device  302 A may have other functional blocks without departing from the spirit and scope of the present invention. 
         [0024]    The programmable feature of  302 A will allow the first device  302  to deliver a waveform similar to the waveform normally received by the link partner at node  105  in the system  100  of  FIG. 1 , through cable  106  with a length of 100 meter. The output is first filtered by  308  which has the equivalent length (100-L) of the cable  205 . Then signal passes through cable  306  which has the length of L. Thus, transmitter attenuation and filtering can be a programmable feature based on the length L of the cable run. This allows the first device  302  and link partner device  304  to communicate within a reasonable cable length (100 meter), with EMI reduced and fully compatible with existing Ethernet systems. It is worthwhile to point out that if the cable length is already equal to 100 meter, there will be nothing left to attenuate and therefore the EMI reduction is limited. However, in many applications, such as automotive applications, the cable length required is very short and EMI reduction potential is great. 
         [0025]    Referring to  FIG. 4 , one embodiment of the digital processor programmable filter  312  is shown. In this embodiment, the digital processor programmable filter  312  will have a shift register  320 , a plurality of multipliers  322  depending on the bit resolution required, and an adder  324  to sum the digital signals. The filtered output then connects to the DAC  314 , changing signals to analog waveform and delivers to the cable by the Driver  316 . 
         [0026]    The digital processor programmable filter  312  is capable to adjust its filter performance to match the cable characteristic at various lengths. Based on the actual cable length used between the two link partners, the digital processor programmable filter  312  response can be chosen such that it delivers the least EMI intrusive yet allowed output, and on the receiving end of the link partner it resembles a signal attenuated after 100 meter of cable. This delivers the most optimize EMI performance. That is, it turns the unused receiver capability for the EMI performance enhancement by filtering/attenuating the transmitter signal. 
         [0027]    In accordance with one embodiment, the digital processor programmable filter  312  has its characteristic (amplitude and phase response) closely resemble a CAT5 cable. Furthermore, the digital processor programmable filter  312  is programmable to match the amplitude and frequency response of the CAT5 cable at various cable lengths. The maximum cable reach of Ethernet point to point connection is 100 meter. For any connection that does not require the distance of 100 meter, it is feasible to activate such a filter to reduce the transmitter output according to the unused cable distance and therefore reduce the EMI. 
         [0028]    This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.