Abstract: In one embodiment, a segmented digital-to-analog converter (DAC) has two configurations (i.e., sub-DACs) with overlapping operating ranges and a data mapper that maps the digital input signal into two different digital signals, one for each sub-DAC. The currents generated by the sub-DACs are combined and then used to generate the corresponding analog output signal. Because the sub-DACs have overlapping operating ranges, the DAC can be calibrated to account for process variations that result in the actual current ratio between the two sub-DACs being different from the ideal, designed current ratio. Calibration algorithms generate calibration constants that are applied by the data mapper when mapping the digital input signal into the two digital signals respectively applied to the two sub-DACs. In this way, high-precision DACs can be implemented without requiring expensive circuitry to handle undesirable current mismatch resulting from process variations.

Abstract: In one embodiment, a constant-current generator is connected in series with a dependent (e.g., tail) device. A switched capacitor circuit connected to the gate of the dependent device is operated to (i) charge at least one capacitor of the switched capacitor circuit, (ii) use the at least one charged capacitor to adjust the gate voltage of the dependent device to drive the dependent current through the dependent device to be equal to the constant current through the constant-current generator, and (iii) direct the dependent and constant currents through source and sink current nodes.

Abstract: An amplifier circuit includes differential input nodes, a differential amplifier stage having differential input terminals and differential output terminals, and an input common-mode voltage adaptation circuit connected between the differential input nodes of the amplifier circuit and the differential input terminals of the differential amplifier stage. During an input common-mode adaptation phase, the input common-mode voltage adaptation circuit forces the differential input terminals of the differential amplifier stage to a common-mode voltage equal to an adaptive reference voltage, independent of a common-mode voltage applied to the differential input nodes of the amplifier circuit during the input common-mode adaptation phase.

Abstract: A digital-to-analog converter (DAC) has a pulse-width encoder that generates a charging pulse having a pulse width proportional to the DAC's digital input value. The charging pulse controls a charging switch that selectively connects a current source to a capacitor for the duration of the charging pulse. At the end of the charging pulse, a voltage corresponding to the charge stored in the capacitor forms the DAC's analog output signal. Such DACs can be configured (1) with negative-gain amplifiers across the capacitor to form a negative feedback loop, (2) with multiple parallel current sources, and/or (3) in differential architectures.

Abstract: In one embodiment, a constant-current generator is connected in series with a dependent (e.g., tail) device. A switched capacitor circuit connected to the gate of the dependent device is operated to (i) charge at least one capacitor of the switched capacitor circuit, (ii) use the at least one charged capacitor to adjust the gate voltage of the dependent device to drive the dependent current through the dependent device to be equal to the constant current through the constant-current generator, and (iii) direct the dependent and constant currents through source and sink current nodes.

Abstract: A digital-to-analog converter (DAC) has a pulse-width encoder that generates a charging pulse having a pulse width proportional to the DAC's digital input value. The charging pulse controls a charging switch that selectively connects a current source to a capacitor for the duration of the charging pulse. At the end of the charging pulse, a voltage corresponding to the charge stored in the capacitor forms the DAC's analog output signal. Such DACs can be configured (1) with negative-gain amplifiers across the capacitor to form a negative feedback loop, (2) with multiple parallel current sources, and/or (3) in differential architectures.

Abstract: In one embodiment, a bootstrap switch circuit has (i) a switch device that selectively provides a input signal as an output signal and bootstrap circuitry that provides a relatively high-voltage control signal to the gate of the switch device to turn on the switch device while preventing any over-voltage conditions from being applied to the switch device. The bootstrap circuitry includes a capacitor and a number of transistors configured as either switches or inverters. The circuit has two operating phases: one in which the capacitor gets charged while the switch device is turned off and the other in which the charged capacitor is isolated and used to generate the high-voltage control signal to be a fixed voltage difference above the current voltage level of the input signal applied to the switch device, thereby preventing an over-voltage condition.

Abstract: Signal processing circuitry having parallel processing channels has clock-generation circuitry that generates (i) high-speed clock signals used to drive the channels and (ii) synchronization signals used to reset the processing of the channels. In one embodiment, the signal processing circuitry has multiple multiplexing channels arranged in one or more macrocells, each macrocell having one or more channels and a phase-locked loop (PLL) that generates a high-speed PLL clock signal and a synchronization signal for the macrocell's channels. Each channel has a counter that implements a state machine used to drive the multiplexing processing, where the state machine is reset to a specified state upon receipt of each synchronization pulse in the synchronization signal.

Abstract: A system for a backplane that employs i) an adjustment of positive-to-negative (P-N) driver skew of a transmit signal of a relatively high-speed differential driver to reduce far-end crosstalk, ii) a high-speed differential subtraction circuit combining a gain-adjusted replica of at least one transmit signal with a received signal to reduce near-end crosstalk, and iii) a phase-locked loop (PLL) synchronization circuit to align timing events between a set of near-end and far-end high-speed interfaces.

Abstract: Methods and apparatus are provided for sigma-delta delay control in a Delay-Locked-Loop that employs a delay line to generate a clock signal based on a reference signal. A first value is generated if a clock signal has a time lead relative to a reference signal; and a second value is generated if a clock signal has a time lag relative to a reference signal. The first and second values are accumulated to generate an N bit digital word; and the N bit digital word is reduced to an M bit digital word, where M is less than N. Thereafter, the M bit digital word can be converted to an analog bias signal. The reducing step can be performed, for example, by a sigma-delta modulator. The high frequency quantization noise generated by the sigma-delta modulator can be filtered using a low pass filter. The converting step can be performed by a digital-to-analog converter, such as a master/slave digital-to-analog converter.

Abstract: A method and apparatus is provided to assure that a delay line control loop will only lock at a desired phase difference—e.g., 360 degrees (and not at the desired phase difference plus a multiple of 360 degrees), between its input and output signals. The phase delay detector of the invention samples multiple signals, from internal stages of the delay line, which are then logically combined to assure that the VCDL will only lock at the desired phase difference.

Abstract: Methods and apparatus are provided for sigma-delta delay control in a Delay-Locked-Loop that employs a delay line to generate a clock signal based on a reference signal. A first value is generated if a clock signal has a time lead relative to a reference signal; and a second value is generated if a clock signal has a time lag relative to a reference signal. The first and second values are accumulated to generate an N bit digital word; and the N bit digital word is reduced to an M bit digital word, where M is less than N. Thereafter, the M bit digital word can be converted to an analog bias signal. The reducing step can be performed, for example, by a sigma-delta modulator. The high frequency quantization noise generated by the sigma-delta modulator can be filtered using a low pass filter. The converting step can be performed by a digital-to-analog converter, such as a master/slave digital-to-analog converter.

Abstract: A system for a backplane that employs i) an adjustment of positive-to-negative (P-N) driver skew of a transmit signal of a relatively high-speed differential driver to reduce far-end crosstalk, ii) a high-speed differential subtraction circuit combining a gain-adjusted replica of at least one transmit signal with a received signal to reduce near-end crosstalk, and iii) a phase-locked loop (PLL) synchronization circuit to align timing events between a set of near-end and far-end high-speed interfaces.

Abstract: Signal processing circuitry having parallel processing channels has clock-generation circuitry that generates (i) high-speed clock signals used to drive the channels and (ii) synchronization signals used to reset the processing of the channels. In one embodiment, the signal processing circuitry has multiple multiplexing channels arranged in one or more macrocells, each macrocell having one or more channels and a phase-locked loop (PLL) that generates a high-speed PLL clock signal and a synchronization signal for the macrocell's channels. Each channel has a counter that implements a state machine used to drive the multiplexing processing, where the state machine is reset to a specified state upon receipt of each synchronization pulse in the synchronization signal.