Rambus Inc.

Semtech Corporation

Kamran Farzan

Dongyun Lee

Aaron Ali

David J Cassan

Angus William McLaren

Mehrdad Ramezani

Saman Sadr

A signal transmitter circuit includes an output driver circuit configured to transmit a signal using a multi-level pulse amplitude modulation (PAM) scheme comprising a plurality of discreet signal levels. During operation, the output driver initiates a first transition of the signal to a first level of the multi-level PAM scheme from a second level of the multi-level PAM scheme, and initiates a second transition of the signal to the first level from a third level of the multi-level PAM scheme. The signal transmitter further includes a control circuit configured to control a slew rate of the signal transmitter circuit to cause the signal to reach a threshold voltage level at a first time, the first time occurring a first duration of time after the first transition is initiated, and to cause the signal to reach the threshold voltage level at a second time, the second time occurring the first duration of time after the second transition is initiated.

Edge enhancement for signal transmitter

An apparatus including a signal generation circuitry to provide a stream of digital signals carrying data. The apparatus includes a storage circuitry to provide a plurality of transmit levels corresponding to respective predetermined equalization levels; selection circuitry to select a transmit level from among the plurality of transmit levels based on the digital signals carrying data. Each of the plurality of transmit levels is a respective input signal to the selection circuitry. The apparatus includes a digital-to-analog converter (DAC) circuitry configured to receive the selected transmit level and convert the selected transmit level to an analog signal of the selected transmit level.

Transmit driver architecture

A hybrid voltage mode (VM) and current mode (CM) four-level pulse amplitude modulation (PAM-4) transmitter circuits (a.k.a. drivers) is calibrated using a configurable replica circuit and calibration control circuitry. The replica circuit includes an on-chip termination impedance to mimic a receiver's termination impedance. The amount of level enhancement provided by the current mode circuitry is calibrated by adjusting the current provided to the output node and sunk from the output node by the replica current mode circuitry while the replica voltage mode circuitry is driving an intermediate PAM-4 level. After the level enhancement has been set, the non-linearity between levels is calibrated by adjusting the amount of current provided to the output node by the replica current mode circuitry while the replica voltage mode circuitry is driving a maximum output voltage level.

PAM-4 calibration

A method and related apparatus for outputting an analog signal are disclosed. A plurality of transmit levels corresponding to respective predetermined equalization levels is provided. A stream of digital signals carrying data is provided. A transmit level from among the plurality of transmit levels based on the digital signals carrying data is selected. The selected transmit level is received, the selected transmit level is converted to an analog signal of the selected transmit level, and the analog signal of the selected transmit level is output over a signal interface.

A high speed transmit driver is provided, along with methods to improve driver slew rate, decrease transmit jitter, improve termination accuracy, and decrease sensitivity to supply noise.

Growing community of inventors

Toronto, Canada

Kamran Farzan