US Patent 8935125 Internal cable calibration and compensation

Systems and methods are provided to calibrate and compensate for signal impairments from the use of cables in data communication devices. Signal impairments such as intra-pair skew of differential signals and frequency dependent insertion loss are measured during a calibration phase. One end of the cable is connected to a communication device. The other end of the cable is configured to loop back calibration signals transmitted from the communication device. The calibration signals looped back from the communication device are received and measured by the communication device. The measured impairments are used to determine transmit and receive impairment compensation settings to compensate for impairments caused by the cable. These settings are stored and used to adjust signals transmitted from the communication device to compensate for the transmit impairment. These setting are also used to adjust signals received by the communication device to compensate for the receive impairment.