Lucent Technologies Inc.

Per Magnusson

Patrik Larsson

Bryan D Ackland

Information can be communicated back from a receiver to a transmitter over a serial link designed for communication to be essentially only in one direction without requiring a separate feedback path with an extra wire. This is achieved by changing at least one characteristic of the receiver input. For example, the receiver input impedance, the receiver input voltage, or both, may be altered. The change in a characteristic of the receiver input can be detected by an appropriately designed transmitter, and such detection can be used to trigger a change in the behavior of the transmitter. Advantageously, only simple alterations are required in conventional serial link circuits to provide a low bandwidth reverse communication path over the same wires. Such a change in a receiver input characteristic can also be employed to inform a transmitter of the existence of a receiver that is on a card that is hot-plugged into system.

Serial communication technique

The amount of jitter that results in a serial receiver having a parallel architecture Can is reduced by insuring that the edges specifically introduced by the code are actually received by the phase detector. In particular, the code is designed to increase the probability that the edges it introduces are actually received by the phase detector. In a preferred embodiment of the invention, all the edges introduced by the code are actually received by the phase detector. This is achieved by guaranteeing that the edges introduced by the code are evenly spaced in the data stream at a rate corresponding to the phase detector sampling rate. For example, if the receiver consists of N data samplers, e.g., N=5, and one phase detector, the edges introduced by the code are arranged to be N symbols apart. This may be done by inserting as the Nth symbol an overall symbol that has a dummy component so that an edge results between the N-1 symbol and the overall Nth symbol. Thus, the data stream is arranged into repeating frames of N symbols. Alternatively, the frame could be arranged to be a multiple X of N, e.g., the frame is K symbols long, K=XN, with the partially redundant data symbol being the K-1, i.e., XN-1, symbol.

Redundant codes for clock recovery in serial links

For certain high-speed applications, where high-precision is not required analog-to-digital conversion may be performed by employing several comparators, each having their own offset. Each such comparator with an offset may be constructed by employing a differential amplifier with an offset followed by a conventional comparator. Advantageously, the time to obtain a conversion to digital of an analog sample is reduced in comparison to prior art converters, thus enabling high-speed operation.

Analog-to-digital converter for differential signals

The problem that signal levels may change slowly over time, e.g., as a result of ranges in temperature, is overcome by employing an automatic gain control feedback loop using a comparator, hereinafter referred to as a feedback slicer, connected to the output of a programmable gain amplifier to determine whether the output of the programmable gain amplifier is higher or lower than the desired signal level to which it is known to correspond. In particular, the decision level for the feedback slicer is set so that it is equal to the desired amplitude of a correctly amplified symbol. The gain of the programmable gain amplifier is adjusted, e.g., slowly over time, so that the amplitude of the amplified symbol hovers about that level. More than one signal level may be tracked. If so, each level tracked employs its own feedback slicer. Advantageously, the hardware for performing the automatic gain control is simplified, providing a cost reduction, and if implemented on a chip, a real estate savings may be realized as well.

Growing community of inventors

Hazlet, NJ, United States of America

Per Magnusson