Altera Corporation

Mei Luo

Sergey Yuryevich Shumarayev

Wilson Wong

Thungoc M Tran

Chong H Lee

Rakesh H Patel

Kazi Asaduzzaman

Tim Tri Hoang

Weiqi Ding

Allen K Chan

Simardeep Maangat

Tin H Lai

Hiep The Pham

Mingde Pan

Shou-Po Shih

Wing Liu

Vinh Van Ho

Among other things, the present invention addresses timing issues related to a polarity control scheme in DFE implementation. Multiplexing that may be necessary for implementing a polarity control scheme is incorporated into multiplexing that may be required to convert half rate data into full rate data in a delay element of a DFE. Clocking signals are provided to a multiplexer that are encoded with polarity information. The various clock signals are generated using a clock generation circuit that incorporates polarity control.

Apparatus and method for polarity tap control

An integrated circuit includes a duty cycle detection circuit, a comparator circuit, and a tuning circuit. The duty cycle detection circuit receives a clock signal, such as a system clock signal, and detects the level of duty cycle distortion in the clock signal. The comparator circuit then generates an output based on the level of duty cycle distortion that is detected in the clock signal. The tuning circuit may accordingly adjust the clock signal based on the output generated by the comparator circuit to produce an adjusted clock output signal. As an example, the clock output signal produced by the tuning circuit after the adjustment may have a 50% (or significantly close to 50%) duty cycle.

Clock duty cycle calibration circuitry

In an embodiment of the present invention, a feedback technique is used to track a reference signal with a DFE summing node common mode voltage. For example, in an embodiment implemented in CML, the feedback signal shifts both differential signals (e.g., the summing node common voltage and the reference voltage) by the same amount. In such an embodiment, the feedback technique preferably changes the reference common mode but not its differential mode.

Apparatus and method for common mode tracking in DFE adaptation

A circuit includes a receiver circuit, a decision feedback equalizer circuit, and a control loop circuit. The receiver circuit receives a data signal and generates an input signal in response to the data signal. The decision feedback equalizer circuit includes a tap driver and a first current source coupled to the tap driver. The tap driver drives the input signal based on a tap weight. The control loop circuit varies a current through the first current source based on variations in the input signal to reduce changes in the tap weight that are caused by the variations in the input signal.

Techniques for decision feedback equalization that reduce variations in the tap weight

Circuits and a method for tuning an integrated circuit (IC) are disclosed. The IC includes a storage circuit coupled to receive a data signal, a clock input signal and a reset signal. The storage circuit may be used to generate a clock signal. The reset signal is supplied by a reset circuit. The reset circuit may include one or more logic gates to generate the reset signal. The reset circuit receives a phase shifted version of the clock input signal and the reset signal is generated based on the phase shifted version of the clock input signal. In one embodiment, the reset signal is a series of pulses generated at specific intervals to shift the output of the storage circuit from logic high level to logic low level.

Duty cycle correction circuitry

Methods and apparatus are provided for selectively setting a CM voltage for a transceiver, reducing the effect of current mismatch, and generating a voltage step that can be used for receiver detection. A circuit of the invention can include voltage generator circuitry operable to generate a plurality of voltage signals of substantially different voltages. The circuit can also include multiplexer circuitry with voltage inputs coupled to the voltage signals. The multiplexer circuitry can be operable to select a reference signal from among the voltage inputs. In addition, the circuit can include operational amplifier ('op-amp') circuitry with a first input coupled to the reference signal and a second input coupled to an output signal of the op-amp circuitry.

Versatile common-mode driver methods and apparatus

Systems and methods are provided using dynamically adjustable differential output drivers. Integrated circuits such as programmable logic devices may be provided with adjustable differential output drivers for transmitting high-speed data to other integrated circuits. The peak-to-peak output voltage and common-mode voltage of the output drivers may be adjusted. Dynamic control circuitry may be used to control the settings of current sources, programmable resistors, and voltage source circuitry in the adjustable differential output driver automatically in real time. The adjustable components in the differential output driver may be adjusted by the dynamic control circuitry based on feedback information received from the integrated circuit to which the data is transmitted.

Dynamically-adjustable differential output drivers

Serial data transmitter circuitry on a PLD includes a number of features that enable the transmitter to support many different communication protocols under a wide range of circuit conditions. Examples of features that the transmitter may include are (1) multiple pre-emphasis circuits of selectable strength and polarity, (2) selectable VOD, (3) selectable slew rate, (4) calibratable termination, (5) selectable common mode voltage, and (6) electrical idle mode.

High-speed serial data transmitter architecture

In level-shifting circuitry for shifting low-voltage-domain signals to a high-voltage domain, one of two output transistors is driven with one of the low-voltage-domain signals, thereby reducing loading on the output and increasing output speed and bandwidth. The circuitry can be mirrored for differential operation. When included in a serial interface of a programmable logic device, the circuitry can be programmably selectable between single-ended and differential operation.

High-speed level-shifting circuit

Transmitters or other devices coupled to transmission links may be required to detect the presence of receivers (or other devices) on the links before starting signal transmission. Methods and apparatus are provided for a transmitter to detect the presence of a receiver on a link. The detection relies on measuring changes in the electrical characteristics of the link at the output of the transmitter. Changes in capacitive or other loading at the transmitter output, caused by the coupling of a link and receiver to the transmitter, may be estimated by determining the rise time of a signal at the transmitter output. The rise time may be estimated in response to applying a common-mode voltage step at the transmitter output, for example. The transmitter may be able to determine the presence of a receiver on the link from changes in rise-time. Increasing transmitter output impedance, or measuring common-mode driver rise time, may increase the accuracy of the detection process.

Method and apparatus for detection of devices on a transmission link

The on-chip impedance termination circuits can be dynamically adjusted to match transmission line impedance values. A network of termination resistors on an integrated circuit provides termination impedance to a transmission line coupled to an IO pin. The termination resistors are coupled in series and in parallel with each other. Pass gates are coupled to the resistors. The pass gates are individually turned ON or OFF to couple or decouple resistors from the transmission line. Each pass gate is set to be ON or OFF to provide a selected termination resistance value to the transmission line. The termination resistance of the resistor network can be increased or decreased to match the impedance of different transmission lines. The termination resistance can also be varied to compensate for changes in the resistors caused by temperature variations on the integrated circuit or other factors.

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San Jose, CA, United States of America

Mei Luo