Abstract:
A line driver circuit an method for protecting the line driver circuit from overdrive that includes generating an output signal for a transformer coupled to a load, and comparing a voltage of the output signal to a threshold voltage value. If the comparison indicates overload, the method further includes generating a control signal to reduce an amplitude of the output signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S 
     This application is a divisional of pending U.S. application Ser. No. 12/012,725, filed Feb. 1, 2008, which claims priority to provisional application No. 60/900,180, filed Feb. 7, 2007. These prior applications are incorporated herein by reference, in their entirety, for any purpose. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to electronic communication systems. More particularly, the invention relates to a training pattern to enable recognition of proper wire-pair orientation and correction in electronic communication systems. 
     BACKGROUND 
     In Ethernet 10GBase-T cabling, the data is sent over four pairs of wires. Between the transmitter and receiver, the pairs can be swapped with each other, and the wires in a pair can be swapped. These reconfigurations can result in an inverted signal or the latency of the four pairs can differ. 10GBASE-T, or IEEE 802.3an-2006, is a standard to provide 10 gigabit/second connections over conventional unshielded or shielded twisted pair cables, over distances up to 100 m. This standard mandates specific training patterns to enable recognition of the proper correction, but does not provide a means to find the proper corrections from all the possibilities. Accordingly, there is a need to develop an algorithm to efficiently search the possible corrections and identify the correct one. 
     SUMMARY OF THE INVENTION 
     A line driver circuit and a method for protecting the line driver circuit from overdrive. An exemplary method for protecting the line driver circuit from over drive includes generating an output signal for a transformer coupled to a load, and comparing a voltage of the output signal to a threshold voltage value. If the comparison indicates overload, the method further includes generating a control signal to reduce an amplitude of the output signal. An exemplary line driver circuit may include an output transistor on an integrated circuit chip. The output transistor is configured to provide an output signal to a transformer coupled to a load. The exemplary line driver circuit further includes an overload detector circuit on the integrated circuit chip that is configured to receive the output signal and compare a voltage of the output signal to a threshold voltage value. If the comparison indicates overload, generate a control signal to reduce an amplitude of the output signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exemplary block diagram of a line driver, according to an embodiment of; 
         FIG. 2  is an exemplary block diagram of a line driver; and 
         FIG. 3  depicts an exemplary graph of transmission signals from a line driver circuit. 
     
    
    
     DETAILED DESCRIPTION 
     Details of various embodiments of the present invention are disclosed in the following appendices: 
     Appendix A. 
     Appendix B. 
     Appendix C 
       FIGS. 1 and 2  depict an output overload protection scheme for a line-driver  110  that does not require any external components for reliable operation. The line driver  110  is coupled to an external load ZLOAD  130  via a transformer  120 . 
     The line driver  110  may include a predriver  114  configured to provide output signal TXP to a first line via transistors M 2  and M 4  and output signal TXN to a second line via transistors M 1  and M 3 . The predriver  114  is coupled to respective gates and respective sources of the M 1  and M 2  transistors. The gates of the M 3  and the M 4  transistors are coupled to a bias voltage VBIAS. The M 2  and the M 4  transistors are coupled in series, with a drain of the M 2  transistor coupled to a source of the M 4  transistor, the TXP signal provided from a drain of the M 4  transistor. The M 1  and the M 3  transistors are coupled in series, with a drain of the M 1  transistor coupled to a source of the M 3  transistor, the TXN signal provided from a drain of the M 3  transistor. The predriver  114  is also configured to receive an overload signal. 
     The line driver circuit  110  further includes an overload detector  112  coupled to the predriver circuit  114 . The overload protection circuit  112  is configured to receive a Vthreshold signal and the TXP and TXN signals, and to provide the overload signal to the predriver circuit  114  and to other circuitry. 
     The transformer  120  may include termination resistors  122  and  124  coupled in series between the first line and the second line. A center tap of the primary coil of the transformer  120  may be coupled to a node between the termination resistors Zterm/2  122  and  124 , and may be held at a center tap voltage VCT. 
       FIG. 3  depicts the TXP and the TXN signals. As depicted in  FIG. 3 , the TXP and the TXN signals are complementary to one another. Thus, when the TXP signal has a maximum amplitude of “A” above the VCT voltage, the TXN signal has a maximum amplitude of “A” below the VCT voltage. Additionally, when the TXN signal has a maximum amplitude of “A” above the VCT voltage, the TXN signal has a maximum amplitude of “A” below the VCT voltage. The Vthreshold is less than the VCT. 
     In operation, the overload detector  112  monitors the TXP and the TXN signals. If either the TXP or the TXN signal go below Vthreshold, the overload detector  112  triggers and reduces the transmit amplitude. This is particularly important when the transmitter is transmitting into an open circuit. If Zload  130  is equal to Infinity (open load), then the transmit amplitude will double, causing stress on the output transistors and reducing the lifetime of the part. This invention detects this overload condition and protects the line-driver  110  output transistors. One aspect of this invention is that only one threshold is used and it is easy to implement on the chip. 
     In some cases, the VCT can be equal to the highest power supply voltage. In that case, it is very difficult to generate a voltage reference above the highest power supply. However since this invention detects the lowest potential (low side) of the TXP and the TXN signals, which is below the highest potential voltage on the chip, the threshold detector is easy to implement. 
     In an example:
 
 V peak= VCT=A , where  A=VTX*Z term/( Z term+1)
 
     Normally Zload=Zterm. In that case, Vpeak=VCT+VTX/2. However, if Zterm is equal to Infinity (open circuit case), then Vpeak increases to VCT+VTX, which can overload the output device. While the positive (high) peak voltage increases, the “transformer” action causes the lower side peak voltage to decrease accordingly. Therefore, only one threshold level is required to detect an overload. 
     The output of the threshold detector can go to a digital signal processor (DSP) or a digital or other control circuit. The limit function does not need to be included in the line-driver  110  amplifier or pre-driver  114 . In the case of an overload, the signal to the driver could be shunted outside the transmitter or elsewhere in the transmit data path. 
     An overload can also occur during fink-up. In 802.3, link-pulses are sent between phys. During an “auto-mdix’ auto-negotiation, it is possible for two transceivers to be transmitting on the same pair of wires, causing the signal at the line-driver  110  to increase in amplitude as the two transmitting signals constructively interfere. This invention will also detect this case. 
     In addition, if the transformer has a voltage fault (an open VCT=0), then the integrated circuit will detect this condition therefore recognizing a problem at the transformer. A signal is then sent to the operator of the phy of the open transformer event. 
     As one of ordinary skill in the art will appreciate, various changes, substitutions, and alterations could be made or otherwise implemented without departing from the principles of the present invention. Accordingly, the examples and drawings disclosed herein including the appendix are for purposes of illustrating the preferred embodiments of the present invention and are not to be construed as limiting the invention.