Circuit and method for compensation if high-frequency signal loss on a transmission line

Abstract

A circuit and method that maintains the impedance matching characteristics of a common output driver while compensating for the high-frequency signal attenuation inherent in printed circuit board traces and other integrated circuit signal transmission media are disclosed. The circuit includes a pre-emphasis driver configured in parallel with a standard output driver. The pre-emphasis driver is a tri-statable device which mirrors a received logic input when in an “on” state and provides a high output impedance with no signal content when in an “off” state. The pre-emphasis driver is controlled by a pre-emphasis control signal configured such that the pre-emphasis driver can inject high-frequency signal components into a transmission line for a portion of a clock cycle. The pre-emphasis control signal is configured such that the pre-emphasis driver turns “on” in close approximation with data signal transitions and is turned “off” before a reflected signal caused by the impedance mismatch between the pre-emphasis driver and downstream elements (i.e., a transmission line and a receiver) appears at the parallel driver output. In its broadest terms the method includes: providing a data signal at a matched-impedance driver; placing a low-impedance driver in parallel with the matched-impedance driver; using a control signal to turn “on” the low-impedance driver when the data signal transitions and turn “off” the low-impedance driver before an impedance mismatch induced reflected signal returns at the output of the matched-impedance driver.

Dependencies are inferred from the claim text.