Analog Devices,inc.

Analog Devices International Unlimited Company

Gil Engel

Jialin Zhao

Steven C Rose

Martin Clara

Hajime Shibata

Gabriele Manganaro

Yunzhi Dong

Matthew Louis Courcy

Shawn S Kuo

Lawrence A Singer

Bernd Schafferer

Hao Luo

Yunchu Li

Paul S Wilkins

Yuhu Chen

Techniques that enable calibration of digital-to-analog Converters (DACs) with minimal processing overhead. A single frequency bin can be used to calibrate errors between bits. A low frequency feedback path can be included into a low frequency low power ADC to determine the error signal that exists in the calibration bin. The bits are calibrated when this error signal is minimized. The calibration techniques described provide an extremely efficient and optimal calibration at the DAC output of both static and dynamic errors.

Calibration of digital-to-analog converters

Digital to analog converter generates an analog output corresponding to a digital input by controlling DAC cells using bits of the digital input. The DAC cells individually make a contribution to the analog output. Due to process, voltage, and temperature variations, the DAC cells may have duty cycle error or mismatches. To compensate for the duty cycle error of a DAC cell, a small amount of charge is injected into a low-impedance node of a DAC cell when the data signal driving the DAC cell transitions, or changes state. The small amount of charge is generated using a capacitive T-network, and the polarity of the charge injected is opposite of the error charge caused by duty cycle error. The opposite amount of charge thus compensates or cancels out the duty cycle error, and duty cycle error present at the output of the DAC cell is reduced.

DAC duty cycle error correction

Digital to analog conversion generates an analog output corresponding to a digital input by controlling unit elements or cells using data bits of the digital input. The unit elements or cells individually make a contribution to the analog output. Due to process, voltage, and temperature variations, the unit elements or cells may have mismatches and/or errors. The mismatches and/or errors can degrade the quality of the analog output. To extract the mismatches and/or errors, a transparent dither can be used. The mismatches and/or errors can be extracted by observing the analog output, and performing a cross-correlation of the observed output with a switching bit stream of the dither. Once extracted, the unit elements or cells can be adjusted accordingly to reduce the respective mismatches and/or errors.

Background duty cycle error measurement for RF DAC

Digital to analog conversion generates an analog output corresponding to a digital input by controlling unit elements or cells using data bits of the digital input. The unit elements or cells individually make a contribution to the analog output. Due to process, voltage, and temperature variations, the unit elements or cells may have mismatches. The mismatches can degrade the quality of the analog output. To extract the mismatches, a transparent dither can be used. The mismatches can be extracted by observing the analog output, and performing a cross-correlation of the observed output with the dither. Once extracted, the unit elements or cells can be adjusted accordingly to reduce the mismatches.

Background static error measurement and timing skew error measurement for RF DAC

A multi-path dual-switch DAC refers to implementing multiple paths in a switch driver and only two switches in a DAC stack of a DAC unit. In addition to multiple paths configured to improve the driving ability of the input signals, the switch driver of a multi-path dual-switch DAC unit includes two or more logic gates configured to act as multiplexers combining some of the output signals from different paths. The use of such logic gates enables using only two switches in the DAC stack unit to receive the data. Furthermore, optionally, additional logic gates may be used to combine some other output signals from different paths to generate dummy signals, thus providing internal dummy logic. The multi-path dual-switch DACs described herein may advantageously use half-clock rate and reduce or eliminate supply modulation issues, while also reducing power consumption and improving linearity compared to traditional DAC architectures.

Multi-path dual-switch digital-to-analog converter

A time-interleaved digital-to-analog converter (DAC) uses M DAC cores to convert a digital input signal whose digital input words are spread to different DAC cores to produce a final analog outputs. The M DAC cores, operating in a time-interleaved fashion, can increase the sampling rate several times compared to the sampling rate of just one DAC. However, sequential time-interleaving DAC cores often exhibit undesirable spurs at the output. To spread those spurs to the noise floor, the time-interleaving DAC cores can be selected at a pseudo randomized manner or in a specific manner which can break up the sequential or periodic manner of selecting the DAC cores.

Randomized time-interleaved digital-to-analog converters

Embodiments of the present invention may provide non-invasive techniques for adjusting timing in multistage circuit systems. A multistage circuit system according to embodiments of the present invention may include a plurality of circuit stages coupled to signal lines that carry signals. The system may also include a plurality of load circuits, one provided in for each circuit stage. The load circuits may have inputs coupled to the signal lines that carry the input signals. Each load circuit may include a current source programmable independently of the other load circuits that propagates current through an input transistor in the respective load circuit that receives the signal. The current propagating through the input transistor may provide a load on the corresponding signal line, allowing fine timing adjustment for each circuit stage.

Fine timing adjustment method

Differential clock phase imbalance can produce undesirable spurious content at a digital to analog converter output, or interleaving spurs on an analog-to-digital converter output spectrum, or more generally, in interleaving circuit architectures that depend on rising and falling edges of a differential input clock for triggering digital-to-analog conversion or analog-to-digital conversion. A differential phase adjustment approach measures for the phase imbalance and corrects the differential clock input signals used for generating clock signals which drive the digital-to-analog converter or the analog-to-digital converter. The approach can reduce or eliminate this phase imbalance, thereby reducing detrimental effects due to phase imbalance or differential clock skew.

Differential phase adjustment of clock input signals

Reducing distortions in a digital-to-analog converter is a challenge for circuit designers. For current steering digital-to-analog converters (DACs), a quad switching scheme has been used to remove code-dependent glitching which is otherwise present in dual switching schemes. However, due to various impairments in the circuit, e.g., mismatches in the transistors, some code-dependent distortions remain even when a quad switching scheme is implemented. To address this issue, the quad switching scheme can be randomized to improve dynamic linearity while relaxing driving circuitry design and power constraints. Advantageously, randomization reduces the code dependency of the distortions and makes the distortions appear more noise-like at the output of the DAC.

Randomized quad switching

The present disclosure provides embodiments of an improved current steering switching element for use in a digital to analog (DAC) converter. Typically, each current steering switching element in the DAC converter provides a varying set of currents for converting a digital input signal. Generally, the switches and drivers in the current steering switching elements are scaled down proportionally to the current being provided by the current steering switching element according to a ratio as less and less current is being driven by the switching element in order to overcome timing errors. However, device sizes are limited by the production process. When a switch is not scaled proportionally to the current, settling timing errors are present and affects the performance of the DAC. The improved current steering switching element alleviates this issue of timing errors by replacing the single switch with two complementary current steering switches.

Complementary switches in current switching digital to analog converters

A method for generating a data signal for synchronizing one or more electrically coupled digital receivers is disclosed. A data signal having a data rate is modulated with a pseudo-noise (PN) code having a data rate greater than the data rate of the data signal. The modulated data signal is demodulated by a receiver using the PN code. A correlation value is generated and is compared to a predetermined value to indicate phase synchronization. If the receiver is in phase synchronization with the transmitter, the received demodulated data signal is passed.

Spread spectrum communication and synchronization

A modified pipeline architecture allows the simple implementation of a foreground calibration technique with the continuous calibration benefits of the background calibration techniques. To calibrate a stage in the pipeline, a calibration voltage is presented to the input instead of the output from the previous stage. To prevent loss of information, the output data of the previous stage is passed on to a stage further down.

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Lexington, MA, United States of America

Gil Engel