Signal Equalizer for Balanced Transmission Line-Based Video Switching

Abstract

A method of equalizing signals from a plurality of balanced transmission line cables having different lengths includes providing a first cable having a first length and a second cable having a second length, the first cable coupled to a variable resistor. A first signal is transmitted along the first cable to the variable resistor such that the first signal is attenuated to assume a first frequency domain characteristic. A second signal is transmitted along the second cable such that the second signal is attenuated to assume a second frequency domain characteristic. A voltage of the first signal is divided in the variable resistor such that the first signal assumes substantially the second frequency domain characteristic. The first signal having the second frequency domain characteristic is outputted.

1 . A method of equalizing signals from a plurality of balanced transmission line cables having different lengths, the method comprising:
 providing a first cable having a first length and a second cable having a second length, the first cable coupled to a variable resistor;   providing a cable filter coupled to the first cable;   transmitting a first signal along the first cable to the variable resistor such that the first signal is attenuated to assume a first frequency domain characteristic;   transmitting a second signal along the second cable such that the second signal is attenuated to assume a second frequency domain characteristic;   dividing a voltage of the first signal in the variable resistor;   receiving the first signal from the variable resistor to the cable filter and applying a reciprocal transfer function through the cable filter such that the first signal assumes substantially the second frequency domain characteristic; and   outputting the first signal having the second frequency domain characteristic.   
     
     
         2 . The method of  claim 1 , wherein the dividing comprises:
 comparing the first length and the second length;   if the first length is greater than the second length, dividing the voltage to decrease attenuation of the first signal; and   if the second length is greater than the first length, dividing the voltage to increase attenuation of the first signal.   
     
     
         3 . The method of  claim 1 , wherein the balanced transmission line cable is a unshielded twisted pair cable. 
     
     
         4 . The method of  claim 1 , wherein the balanced transmission line cable is a shielded twisted pair cable. 
     
     
         5 . The method of  claim 1 , wherein the signals are video signals. 
     
     
         6 . The method of  claim 1 , further comprising:
 applying skew compensation to the first signal.   
     
     
         7 . A signal equalizer for equalizing a signal transmitted along a balanced transmission line cable, the equalizer comprising:
 a first variable resistor for receiving the signal and dividing a voltage of the signal;   a cable filter for receiving the signal from the variable resistor and applying a reciprocal transfer function to the signal;   an amplifier having an inverted input for receiving the inverted signal from the cable filter and a non-inverted input for receiving a signal ground, the amplifier having a shunt between the inverted input and the non-inverted input; and   a dynamic stabilizer coupled to the amplifier, the dynamic stabilizer controlled by a second variable resistor.   
     
     
         8 . The signal equalizer of  claim 7 , wherein the balanced transmission line cable is a unshielded twisted pair cable. 
     
     
         9 . The signal equalizer of  claim 7 , wherein the balanced transmission line cable is a shielded twisted pair cable. 
     
     
         10 . The signal equalizer of  claim 7 , further comprising:
 a delay line for receiving the signal from the amplifier and applying skew compensation to the signal.   
     
     
         11 . The signal equalizer of  claim 7 , further comprising:
 wherein the reciprocal transfer function is applied according to the following equation in dB/ft, where f is frequency in MHz:
   reciprocal transfer function≈0.003012(1.97 √f )+(0.023 f )+0.05 /√f ) 
   
     
     
         12 . The signal equalizer of  claim 7 , wherein the first variable resistor is set to add loss to the signal. 
     
     
         13 . The signal equalizer of  claim 7 , wherein the signal equalizer provides unity gain. 
     
     
         14 . A balanced transmission line based signal switching system comprising:
 a signal switch coupled to at least one balanced transmission line video receiver;   a plurality of first signal transmitters each coupled to the signal switch by a respective first balanced transmission line cable with a first length;   at least one second signal transmitter coupled to the signal switch by a second balanced transmission line cable with a second length different from the first length;   at least one equalizer coupled between a respective one of the at least one second signal transmitter and the signal switch, and having a variable resistor for dividing a voltage of a signal received from a respective one of the at least one second signal transmitter and a cable filter for applying a reciprocal transfer function to the signal received from the respective one of the at least one second signal transmitter, the variable resistor and the cable filter capable of providing negative equalization to the signal such that loss is added to the signal;   a display coupled to the video receiver.   
     
     
         15 . The system of claim of  14 , wherein a number of the plurality of first signal transmitters is greater than a number of the at least one second signal transmitter. 
     
     
         16 . The system of  claim 14 , wherein the at least one equalizer is capable of providing positive equalization to the signal. 
     
     
         17 . The system of  claim 14 , wherein the at least one equalizer is capable of providing positive equalization, negative equalization and no equalization to the signal. 
     
     
         18 . The system of  claim 17 , wherein the at least one equalizer is adjustable to provide between −500 feet to 500 feet of equalization to the signal. 
     
     
         19 . The system of  claim 14 , wherein the balanced transmission line cable is a shielded twisted pair cable. 
     
     
         20 . The system of  claim 14 , wherein the balanced transmission line cable is a unshielded twisted pair cable.