Signal History Controlled Slew-Rate Transmission Method and Bus Interface Transmitter

Abstract

A signal history controlled slew-rate transmission method and bus interface transmitter provide an improved channel equalization mechanism having low complexity. A variable slew-rate feed-forward pre-emphasis circuit changes the slew rate of the applied pre-emphasis in conformity with the history of the transmitted signal. The pre-emphasis circuit may be implemented by a pair of current sources supplying the output of the transmitter, and having differing current values. The current sources are controlled such that upon a signal value change, a high slew rate is provided and when the signal value does not change for two consecutive signal periods, the slew rate is reduced. A current source having a controlled magnitude may be employed to provide a slew rate that changes over time and is continuously reduced until another transmission value change occurs.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field[0002]The present invention relates generally to electrically connected bus interface circuits, and more particularly, to bus interface circuits having signal history controlled pre-emphasis.[0003]2. Description of the Related Art[0004]Interfaces between present-day system devices and also between individual circuits have increased in operating frequency and complexity. In particular, high speed serial bus interfaces typically require sophisticated signal processing in order to achieve maximum bandwidth over cost-effective channel interconnects.[0005]Numerous signaling and reception techniques have been employed to extract the maximum possible data rate from a given channel, for example, feed-forward equalization (FFE) such as signal-history based pre-emphasis / de-emphasis on the transmission side, distributed equalization within the channel in or discrete equalization with respect to the channel characteristics, and receiver-side eq...

AI Technical Summary

Benefits of technology

The patent is about improving the equalization of a bus interface transmitter by using a feed-forward pre emphasis circuit with a variable slew rate. The slew rate is adjusted based on the history of the transmitted signal to provide better equalization. The method involves using a pair of current sources with different current levels, where the weaker current source has a slower slew rate and is controlled by the previous transmission value, while the stronger current source has a faster slew rate and is controlled by the present transmission value. This results in a lower overall transmitter output slew rate when the same value is transmitted consecutive. The weaker current source also has a dual rate controlled magnitude to slow down the change in its magnitude when the transmission value changes. The technical effect of this invention is improved equalization of the bus interface transmitter.

Problems solved by technology

Interfaces between present-day system devices and also between individual circuits have increased in operating frequency and complexity.

All of the above techniques, although effective, have significant costs in terms of die area, power consumption and complexity.

Although relatively simple to implement, the transmitter-side FFE current switching scheme yields less than optimal results, in that overshoot typically occurs at the receiver side of the interface for certain data patterns.

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