Abstract: A circuit includes a delay locked loop (DLL), a calibration circuit and an output delay chain controlled by the calibration circuit. The DLL comprises a plurality of series-coupled first delay elements each of which has substantially the same first delay. The calibration circuit comprises a plurality of series-coupled second delay elements, each of which has substantially the same second delay that is less than the first delay, a first delay element, and a circuit for determining the minimum number of second delay elements that are needed to produce the first delay. The output delay chain comprises a plurality of series-coupled second delay elements, an input for receiving the input signal, and a circuit for selectively tapping the output delay chain at a plurality of taps in the output delay chain so as to produce in the input signal different delays of integral multiples of the second delay.

Abstract: Circuits, methods, and apparatus for memory interfaces that compensate for skew between a clock signal and DQ/DQS signals that may be caused by a fly-by routing topology. The skew is compensated by clocking the DQ/DQS signals with a phase delayed clock signal, where the phase delay has been calibrated. In one example calibration routine, a clock signal is provided to a receiving device. A DQ/DQS signal is also provided and the timing of their reception compared. A delay of the DQ/DQS signal is changed incrementally until the DQ/DQS signal is aligned with the clock signal at the receiving device. This delay is then used during device operation to delay a signal that clocks registers providing the DQ/DQS signals. Each DQ/DQS group can be aligned to the clock, or the DQS and DQ signals in a group may be independently aligned to the clock at the receiving device.

Abstract: Method and circuitry for implementing high speed multiple-data-rate interface architectures for programmable logic devices. The invention partitions I/O pins and their corresponding registers into independent multiple-data rate I/O modules each having at least one pin dedicated to the strobe signal DQS and others to DQ data signals. The modular architecture facilitates pin migration from one generation of PLDs to the next larger generation.

Abstract: An integrated circuit may include memory interface circuitry that is used to communicate with off-chip memory. The memory interface circuitry may include data strobe (DQS) enable circuitry that receives DQS signals from the off-chip memory and that outputs a gated version of the DQS signals. The DQS enable circuitry may include an input buffer, a comparator, a latch, a flip-flop, a counter, and a gating circuit. The input buffer may receive an incoming DQS signal. The comparator may be used to determine when the incoming DQS signal starts to toggle. The latch may be used to control when a gating signal is asserted. The flip-flop controls the counter, which limits the duration that the gating signal is asserted. The gating circuit receives the DQS signal from the buffer and the gating signal and passes the DQS signal through to its output only when the gating signal is asserted.

Abstract: Circuits and a method for correcting duty cycle distortions in an integrated circuit (IC) are disclosed. The IC includes a splitter circuit that is coupled to receive a clock signal. The clock signal is split into two different clock signals. One of the clock signals is an inverted version of the other. A delay circuit is coupled to each of the clock signals. Each of the delay circuits generates a delayed version of the corresponding clock signal. A corrector circuit is coupled to receive both the delayed versions of the clock signals. The corrector circuit generates a clock output signal with a corrected duty cycle.

Abstract: Circuits and techniques for operating an integrated circuit (IC) with a level shifter circuit are disclosed. A level shifter circuit with input and output terminals is operable to shift an input signal that ranges from a ground voltage to a first positive voltage to an output signal that ranges from the ground voltage to a second positive voltage. The level shifter circuit further includes a first kicker transistor having a first source-drain terminal operable to receive a buffered version of the input signal and having a second source-drain terminal coupled to the output terminal. The first kicker transistor may receive gate signals that turn on the first kicker transistor when the input signal is at the ground voltage and may pull the output terminal to the first positive voltage as the input signal transitions from the ground voltage to the first positive voltage.

Abstract: A programmable memory interface circuit includes a programmable DLL delay chain, a phase offset control circuit and a programmable DQS delay chain. The DLL delay chain uses a set of serially connected delay cells, a programmable switch, a phase detector and a digital counter to generate a coarse phase shift control setting. The coarse phase shift control setting is then used to pre-compute a static residual phase shift control setting or generate a dynamic residual phase shift control setting, one of which is chosen by the phase offset control circuit to be added to or subtracted from the coarse phase shift control setting to generate a fine phase shift control setting. The coarse and fine phase shift control settings work in concert to generate a phase-delayed DQS signal that is center-aligned to its associated DQ signals.

Abstract: Method and circuitry for implementing high speed multiple-data-rate interface architectures for programmable logic devices. The invention partitions I/O pins and their corresponding registers into independent multiple-data rate I/O modules each having at least one pin dedicated to the strobe signal DQS and others to DQ data signals. The modular architecture facilitates pin migration from one generation of PLDs to the next larger generation.

Abstract: Integrated circuits with clock generation and distribution circuitry are provided. Integrated circuits may include phase-locked loops configured to generate multiple clock signals that are delayed versions of one another. The clocks signal may be distributed to various regions on an integrated circuit using serially connected clock buffer blocks. Each buffer block may include bidirectional pairs of buffer circuits coupled in parallel. Each buffer circuit may have a first input configured to receive an input clock signal, an output at which a corrected version of the input clock signal is provided (e.g., an output at which an output clock signal with desired duty cycle is provided), a second input that receives a first delayed clock signal for setting the desired duty cycle for the output clock signal, and a third input that receives a second delayed clock signal that is high at least when the first delayed clock signal rises high.

Abstract: Methods and apparatus for providing either high-speed, or lower-speed, flexible inputs and outputs. An input and output structure having a high-speed input, a high-speed output, a low or moderate speed input, and an low or moderate speed output is provided. One of the input and output circuits are selected and the others are deselected. The high-speed input and output circuits are comparatively simple, in one example having only a clear signal for a control line input, and are able to interface to lower speed circuitry inside the core of an integrated circuit. The low or moderate speed input and output circuits are more flexible, for example, having preset, enable, and clear as control line inputs, and are able to support JTAG boundary testing. These parallel high and lower speed circuits are user selectable such that the input output structure is optimized between speed and functionality depending on the requirements of the application.

Abstract: Integrated circuits may include memory interface circuitry operable to communicate with system memory. The memory interface circuitry may receive data and data strobe signals from system memory during read operations. The memory interface circuitry may include de-skew circuitry and dynamic variation compensation circuitry. The de-skew circuitry may be configured during calibration procedures to reduce skew between the data and data strobe signals. The dynamic variation compensation circuitry may be used in real time to compensate for variations in operating conditions.

Abstract: One embodiment relates to a programmable output buffer which includes first and second programmable variable-impedance single-ended driver circuits and first and second termination circuits. The first termination circuit is coupled to a first output pin which is driven by the first programmable variable-impedance single-ended driver circuit, and the second termination circuit is coupled to a second output pin which is driven by the second programmable variable-impedance single-ended driver circuit. The first and second termination circuits are programmable to either provide parallel termination for a differential signal or drive single-ended signals with the parallel termination turned off. Other embodiments and features are also disclosed.

Abstract: Methods and apparatus for providing either high-speed, or lower-speed, flexible inputs and outputs. An input and output structure having a high-speed input, a high-speed output, a low or moderate speed input, and an low or moderate speed output is provided. One of the input and output circuits are selected and the others are deselected. The high-speed input and output circuits are comparatively simple, in one example having only a clear signal for a control line input, and are able to interface to lower speed circuitry inside the core of an integrated circuit. The low or moderate speed input and output circuits are more flexible, for example, having preset, enable, and clear as control line inputs, and are able to support JTAG boundary testing. These parallel high and lower speed circuits are user selectable such that the input output structure is optimized between speed and functionality depending on the requirements of the application.

Abstract: Integrated circuits with clock generation and distribution circuitry are provided. Integrated circuits may include phase-locked loops configured to generate multiple clock signals that are delayed versions of one another. The clocks signal may be distributed to various regions on an integrated circuit using serially connected clock buffer blocks. Each buffer block may include bidirectional pairs of buffer circuits coupled in parallel. Each buffer circuit may have a first input configured to receive an input clock signal, an output at which a corrected version of the input clock signal is provided (e.g., an output at which an output clock signal with desired duty cycle is provided), a second input that receives a first delayed clock signal for setting the desired duty cycle for the output clock signal, and a third input that receives a second delayed clock signal that is high at least when the first delayed clock signal rises high.

Abstract: Integrated circuits with clock generation and distribution circuitry are provided. Integrated circuits may include phase-locked loops configured to generate multiple clock signals that are delayed versions of one another. The clocks signal may be distributed to various regions on an integrated circuit using serially connected clock buffer blocks. Each buffer block may include bidirectional pairs of buffer circuits coupled in parallel. Each buffer circuit may have a first input configured to receive an input clock signal, an output at which a corrected version of the input clock signal is provided (e.g., an output at which an output clock signal with desired duty cycle is provided), a second input that receives a first delayed clock signal for setting the desired duty cycle for the output clock signal, and a third input that receives a second delayed clock signal that is high at least when the first delayed clock signal rises high.

Abstract: A circuit comprises first and second differential pairs and first and second switch circuits. The first differential pair includes first and second transistors operable to generate a first output signal based on a first input signal in a single-ended mode. The second differential pair includes third and fourth transistors operable to generate a second output signal based on a second input signal in the single-ended mode. The first switch circuit is operable to block current through the second transistor in a differential mode. The second switch circuit is operable to block current through the third transistor in the differential mode. The first and the fourth transistors are operable to generate a third output signal based on a third input signal in the differential mode.

Abstract: Circuits and techniques for operating an integrated circuit (IC) with a configurable input-output circuit are disclosed. A disclosed circuit includes a single-ended input-output buffer coupled to an output terminal. The single-ended input-output buffer is operable to transmit an input signal to the output terminal as an output signal. A pre-emphasis circuit that is operable to sharpen a first edge and a second edge of the output signal is coupled between the single-ended input-output buffer and the output terminal. The first edge of the output signal is sharpened when the input signal switches from a first logic level to a second logic level while the second edge of the output signal is sharpened when the input signal switches from the second logic level to the first logic level.

Abstract: An adjustable delay circuit includes first and second transistors each having a control input coupled to an input node of the adjustable delay circuit and an output coupled to an output node of the adjustable delay circuit. The adjustable delay circuit includes a first pass gate coupled between first and second capacitors and the output node of the adjustable delay circuit. The first and the second capacitors are coupled between a node at a high voltage and a node at a low voltage. The first pass gate is operable to be controlled by a first delay control signal.

Abstract: A circuit includes a phase adjustment circuit and a dead zone detect circuit. The phase adjustment circuit is operable to receive periodic signals and is operable to provide one of the periodic signals as a selected periodic signal based on a phase comparison between a data signal and the selected periodic signal. Each of the periodic signals has a different phase. The dead zone detect circuit is operable to cause the phase adjustment circuit to shift a phase of the selected periodic signal if the dead zone detect circuit determines that the data signal is in a dead zone. The dead zone detect circuit defines the dead zone based on two of the periodic signals. The phase adjustment circuit is operable to adjust a phase range of the dead zone.

Abstract: A programmable integrated circuit may have a memory controller that interfaces between master modules and system memory. The memory controller may receive memory access requests from the masters via ports that have associated priority values and fulfill the memory access requests by configuring system memory to respond to the memory access requests. To dynamically modify the associated priority values while the memory controller receives and fulfills the memory access requests, a priority value update module may be provided that dynamically updates priority values for the memory controller ports. The priority value update module may provide the updated priority values with update registers that are updated based on an update signal and a system clock. The priority values may be provided by shift registers, memory mapped registers, or provided by masters along with each memory access request.