The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 21, 2002
Filed:
Oct. 30, 2000
Alan R. Desroches, San Jose, CA (US);
Hewlett-Packard Company, Palo Alto, CA (US);
Abstract
A driver circuit compensates for skin effect losses in a transmission line by using a lower impedance when data switches at the maximum switching rate, and using a higher output impedance when data switches at less than the maximum switching rate. As is known in the art, skin-effect resistance causes the impedance of a transmission line to be higher for high-frequency components. A driver in accordance with the present invention compensates for this effect by lowering the output impedance of the driver when transmitting high-frequency components having alternating data values, and using a higher output impedance when transmitting low frequency components having consecutive data values. When transmitting low-frequency consecutive high or low data values using a higher output impedance, the resulting voltage divider formed by the output impedance of the driver at the beginning of the transmission line and the termination resistors at the end of the transmission line causes the high and low DC levels at the end of the transmission line to move closer to the detection threshold of the receiver circuit, thereby causing the next isolated low or high pulse, respectively, to start from a point closer to the threshold. Furthermore, when transmitting high-frequency alternating values at the maximum switching rate using a lower output impedance, the resulting voltage divider produces a larger signal swing in the signal received by the receiver circuit. The result is that all pulses cross the receiver threshold with an excellent “eye opening”, thereby ensuring detection by the receiver circuit.