Altera Corporation

Tin H Lai

Sergey Yuryevich Shumarayev

Wilson Wong

Tim Tri Hoang

Rakesh H Patel

Simardeep Maangat

Thungoc M Tran

Wei-Jen Huang

Tony K Ngai

Kazi Asaduzzaman

Shou-Po Shih

Doris Po Ching Chan

Chong H Lee

Allen K Chan

Arch Zaliznyak

Mei Luo

John Dung-Ngoc Lam

An integrated circuit ('IC') may include clock and data recovery ('CDR') circuitry for recovering data information from an input serial data signal. The CDR circuitry may include a reference clock loop and a data loop. A retimed (recovered) data signal output by the CDR circuitry is monitored by other control circuitry on the IC for a communication change request contained in that signal. Responsive to such a request, the control circuitry can change an operating parameter of the CDR circuitry (e.g., a frequency division factor used in either of the above-mentioned loops). This can help the IC support communication protocols that employ auto-speed negotiation.

Clock and data recovery circuitry with auto-speed negotiation and other possible features

An integrated circuit ('IC') may include clock and data recovery ('CDR') circuitry for recovering data information from an input serial data signal. The CDR circuitry may include a reference clock loop and a data loop. A retimed (recovered) data signal output by the CDR circuitry is monitored by other control circuitry on the IC for a communication change request contained in that signal. Responsive to such a request, the control circuitry can change an operating parameter of the CDR circuitry (e.g., a frequency division factor used in either of the above-mentioned loops).

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

Equalization of an incoming data signal can be controlled by sampling that signal at times when data values in that signal should be stable ('data samples') and when that signal should be in transition between successive data values that are different ('transition samples'). A transition sample that has been taken between two successive differently valued data samples is compared to a reference value (which can be one of those two data samples). The result of this comparison can be used as part of a determination as to whether to increase or decrease equalization of the incoming data signal.

Digital adaptation circuitry and methods for programmable logic devices

Adaptation convergence in an adaptive dispersion compensation engine (ADCE) of a high-speed serial interface is detected by monitoring the output of the error amplifier of one or more adjustment loops of the ADCE. Adaptation convergence is considered to have been detected upon detection of a predetermined number of transitions in the error amplifier output, each of which occurs within a preselected interval following the previous transition. The detector may be implemented with a timer that times the preselected interval and a counter that counts transitions in the error amplifier output. The timer restarts each time a transition occurs, and the counter outputs a convergence signal when it reaches the predetermined number, but is reset each time the timer reaches the preselected interval. The serial interface may be part of a programmable integrated circuit device and in any case the preselected interval and the predetermined number may be programmable.

Programmable adaptation convergence detection

A method, and circuitry, for choosing the correct equalization curve in adaptive equalization uses a feedback loop in which the incoming high-speed serial data are digitized and deserialized for use in the remainder of the device, and also are used by an adaptive state machine to both extract the reference levels for digitization and to control the equalization curve. Detection of the reference level and selection of the equalization curve may be performed at a different rates to avoid interfering with one another. The state machine preferably is programmable. This is useful in any device, but is particularly well-suited for a programmable device, such as a PLD or other programmable integrated circuit device, where conditions may vary according a user logic design.

Adaptive equalization using data level detection

A method and apparatus is provided for standby voltage offset cancellation at inputs to a comparator within a receiver channel. Each of a first comparator input and second comparator input is isolated from an input signal such that each of the first and second comparator inputs attains a respective standby voltage level. A voltage level on one of the first and second comparator inputs is incrementally changed, while the output signal of the comparator is monitored. Upon detecting a state transition in the output signal of the comparator, the incremental changing of the voltage level on the one comparator input is stopped at a final voltage level setting. The final voltage level setting is stored in a computer memory for reference in setting of the voltage level at the one comparator input so as to compensate for the standby voltage offset at the inputs to the comparator.

Method and apparatus for standby voltage offset cancellation

An equalization circuitry that includes a digital-to-analog converter having a voltage divider and a multiplexer coupled to the voltage divider is described. In one implementation, the digital-to-analog converter provides a control signal to a plurality of single-stage equalizer control logic circuits. Also, in one implementation, the multiplexer receives a plurality of inputs from the voltage divider and selects an output from the plurality of inputs. Furthermore, in one implementation, the voltage divider includes a plurality of resistors coupled in series. Also, in one implementation, the voltage divider further includes a first resistor coupled to the plurality of resistors, ground, and a lowest voltage input terminal of the multiplexer, where a voltage across the first resistor is an input voltage to the lowest voltage input terminal. Additionally, in one implementation, the voltage divider further includes a second resistor coupled to the plurality of resistors and a supply voltage, where the supply voltage minus a voltage across the second resistor and a voltage across a resistor of the plurality of resistors is an input voltage to a highest voltage input terminal of the multiplexer. In one implementation, the first and second resistors are programmable in user mode.

Equalization circuitry including a digital-to-analog converter having a voltage divider and a multiplexer

Techniques and circuitry are provided for programmably controlling signal offsets in integrated circuitry. In one embodiment, an integrated circuit includes a signal offset cancellation circuit that is programmably selected to control the offset of signals on either one input/output or another input/output of an amplifier circuit. In one embodiment, a logic circuit is used to selectively couple a bank of current sources to one input/output or another input/output of a differential amplifier through a switching circuit. The bank of current sources may employed to control the signal offset on either input/output, or may be decoupled from all of the inputs/outputs when signal offset cancellation is not required.

Signal offset cancellation

Methods and circuits are presented for providing equalization, including decision feedback equalization (DFE), to high data-rate signals. Half-rate delay-chain circuitry produces delayed samples of an input signal using two or more delay-chain circuits operating at a fraction of the input signal data-rate. Two delay-chain circuits operating at one-half the input signal data-rate may be used. More generally, n delay-chain circuits operating at 1/n the input signal data-rate may be used. Multiplexer circuitry combines the outputs of the delay-chain circuits to produce an output signal including samples of the input signal at the input signal data-rate. Duplicate path DFE circuitry includes two paths used to provide DFE equalization while reducing the load of the DFE circuitry on the circuitry that precedes it. A first path produces delayed samples of a DFE signal, while a second path produces the DFE output signal from the delayed samples.

Half-rate DFE with duplicate path for high data-rate operation

Equalization circuitry may be used to compensate for the attenuation of a data signal caused by a transmission medium. The control circuitry for the equalization circuitry may generate control inputs for equalization stages that control the amount of gain provided to the data signal. A comparator may determine whether the gain from the equalization circuitry is less than or more than the desired amount of gain. A programmable up/down counter may adjust the counter value based on the output of the comparator. The counter value may be converted into one or more analog voltages using one or more digital-to-analog converters. These analog voltages may be provided to the equalization stages as control inputs. The control circuitry may also include hysteresis circuitry that prevents the counter value from being adjusted when the gain produced by the equalization stages is close to the desired amount of gain.

Programmable digital equalization control circuitry and methods

Systems and methods for adjusting a signal received from a communication path are disclosed. A receiver can receive a signal from a communication path which attenuates at least some frequency components of the signal. The receiver can include an equalization block that adjusts at least some of the frequency content of the received signal, a signal normalization block that provides a normalized signal amplitude and/or a normalized edge slope, and a control block. In one embodiment, the control block controls frequency adjustment in the equalization block for high frequencies but not for low frequencies. For low frequency adjustment, the control block controls the normalized signal amplitude in the signal normalization block. In this manner, controlled adjustment for low frequency content is performed in the signal normalization block.

Signal adjustment receiver circuitry

Systems and methods for adjusting a signal received from a communication path are disclosed. A receiver can receive a signal from a communication path which attenuates at least some frequency components of the signal. The receiver can include an equalization block that adjusts at least some of the frequency content of the received signal, a signal normalization block that provides a normalized signal amplitude and/or a normalized edge slope, and a control block. In one embodiment, the control block controls frequency adjustment in the equalization block for high frequencies. For low frequency adjustment, user-programmable parameters control the normalized signal amplitude in the signal normalization block and the low frequency adjustment in the equalization block.

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San Jose, CA, United States of America

Tin H Lai