An interleaved full nyquist high-speed DAC technique

A 9 bit 11 GS/s DAC is presented that achieves an SFDR of more than 50 dB across Nyquist and IM3 below 50 dBc across Nyquist. The DAC uses a two-times interleaved architecture to suppress spurs that typically limit DAC performance. Despite requiring two current-steering DACs for the interleaved architecture, the relative low demands on performance of these sub-DACs imply that they can be implemented in an area and power efficient way. Together with a quad-switching architecture to decrease demands on the power supply and bias generation and employing the multiplexer switches in triode, the total core area is only 0.04 mm2 while consuming 110 mW from a single 1.0 V supply

Wideband CMOS Data Converters for Linear and Efficient mmWave Transmitters

With continuously increasing demands for wireless connectivity, higher\ua0carrier frequencies and wider bandwidths are explored. To overcome a limited transmit power at these higher carrier frequencies, multiple\ua0input multiple output (MIMO) systems, with a large number of transmitters\ua0and antennas, are used to direct the transmitted power towards\ua0the user. With a large transmitter count, each individual transmitter\ua0needs to be small and allow for tight integration with digital circuits. In\ua0addition, modern communication standards require linear transmitters,\ua0making linearity an important factor in the transmitter design.In this thesis, radio frequency digital-to-analog converter (RF-DAC)-based transmitters are explored. They shift the transition from digital\ua0to analog closer to the antennas, performing both digital-to-analog\ua0conversion and up-conversion in a single block. To reduce the need for\ua0computationally costly digital predistortion (DPD), a linear and wellbehaved\ua0RF-DAC transfer characteristic is desirable. The combination\ua0of non-overlapping local oscillator (LO) signals and an expanding segmented\ua0non-linear RF-DAC scaling is evaluated as a way to linearize\ua0the transmitter. This linearization concept has been studied both for\ua0the linearization of the RF-DAC itself and for the joint linearization of\ua0the cascaded RF-DAC-based modulator and power amplifier (PA) combination.\ua0To adapt the linearization, observation receivers are needed.\ua0In these, high-speed analog-to-digital converters (ADCs) have a central\ua0role. A high-speed ADC has been designed and evaluated to understand\ua0how concepts used to increase the sample rate affect the dynamic performance

Design of Energy-Efficient A/D Converters with Partial Embedded Equalization for High-Speed Wireline Receiver Applications

As the data rates of wireline communication links increases, channel impairments such as skin effect, dielectric loss, fiber dispersion, reflections and cross-talk become more pronounced. This warrants more interest in analog-to-digital converter (ADC)-based serial link receivers, as they allow for more complex and flexible back-end digital signal processing (DSP) relative to binary or mixed-signal receivers. Utilizing this back-end DSP allows for complex digital equalization and more bandwidth-efficient modulation schemes, while also displaying reduced process/voltage/temperature (PVT) sensitivity. Furthermore, these architectures offer straightforward design translation and can directly leverage the area and power scaling offered by new CMOS technology nodes. However, the power consumption of the ADC front-end and subsequent digital signal processing is a major issue. Embedding partial equalization inside the front-end ADC can potentially result in lowering the complexity of back-end DSP and/or decreasing the ADC resolution requirement, which results in a more energy-effcient receiver. This dissertation presents efficient implementations for multi-GS/s time-interleaved ADCs with partial embedded equalization. First prototype details a 6b 1.6GS/s ADC with a novel embedded redundant-cycle 1-tap DFE structure in 90nm CMOS. The other two prototypes explain more complex 6b 10GS/s ADCs with efficiently embedded feed-forward equalization (FFE) and decision feedback equalization (DFE) in 65nm CMOS. Leveraging a time-interleaved successive approximation ADC architecture, new structures for embedded DFE and FFE are proposed with low power/area overhead. Measurement results over FR4 channels verify the effectiveness of proposed embedded equalization schemes. The comparison of fabricated prototypes against state-of-the-art general-purpose ADCs at similar speed/resolution range shows comparable performances, while the proposed architectures include embedded equalization as well

CMOS Data Converters for Closed-Loop mmWave Transmitters

With the increased amount of data consumed in mobile communication systems, new solutions for the infrastructure are needed. Massive multiple input multiple output (MIMO) is seen as a key enabler for providing this increased capacity. With the use of a large number of transmitters, the cost of each transmitter must be low. Closed-loop transmitters, featuring high-speed data converters is a promising option for achieving this reduced unit cost.In this thesis, both digital-to-analog (D/A) and analog-to-digital (A/D) converters suitable for wideband operation in millimeter wave (mmWave) massive MIMO transmitters are demonstrated. A 2 76 bit radio frequency digital-to-analog converter (RF-DAC)-based in-phase quadrature (IQ) modulator is demonstrated as a compact building block, that to a large extent realizes the transmit path in a closed-loop mmWave transmitter. The evaluation of an successive-approximation register (SAR) analog-to-digital converter (ADC) is also presented in this thesis. Methods for connecting simulated and measured performance has been studied in order to achieve a better understanding about the alternating comparator topology.These contributions show great potential for enabling closed-loop mmWave transmitters for massive MIMO transmitter realizations

Design Techniques for High-Performance SAR A/D Converters

The design of electronics needs to account for the non-ideal characteristics of the device technologies used to realize practical circuits. This is particularly important in mixed analog-digital design since the best device technologies are very different for digital compared to analog circuits. One solution for this problem is to use a calibration correction approach to remove the errors introduced by devices, but this adds complexity and power dissipation, as well as reducing operation speed, and so must be optimised. This thesis addresses such an approach to improve the performance of certain types of analog-to-digital converter (ADC) used in advanced telecommunications, where speed, accuracy and power dissipation currently limit applications. The thesis specifically focuses on the design of compensation circuits for use in successive approximation register (SAR) ADCs. ADCs are crucial building blocks in communication systems, in general, and for mobile networks, in particular. The recently launched fifth generation of mobile networks (5G) has required new ADC circuit techniques to meet the higher speed and lower power dissipation requirements for 5G technology. The SAR has become one of the most favoured architectures for designing high-performance ADCs, but the successive nature of the circuit operation makes it difficult to reach ∼GS/s sampling rates at reasonable power consumption. Here, two calibration techniques for high-performance SAR ADCs are presented. The first uses an on-chip stochastic-based mismatch calibration technique that is able to accurately compute and compensate for the mismatch of a capacitive DAC in a SAR ADC. The stochastic nature of the proposed calibration method enables determination of the mismatch of the CAPDAC with a resolution much better than that of the DAC. This allows the unit capacitor to scale down to as low as 280aF for a 9-bit DAC. Since the CAP-DAC causes a large part of the overall dynamic power consumption and directly determines both the sizes of the driving and sampling switches and the size of the input capacitive load of the ADC and the kT/C noise power, a small CAP-DAC helps the power efficiency. To validate the proposed calibration idea, a 10-bit asynchronous SAR ADC was fabricated in 28-nm CMOS. Measurement results show that the proposed stochastic calibration improves the ADC’s SFDR and SNDR by 14.9 dB, 11.5 dB, respectively. After calibration, the fabricated SAR ADC achieves an ENOB of 9.14 bit at a sampling rate of 85 MS/s, resulting in a Walden FoM of 10.9 fJ/c-s. The second calibration technique is a timing-skew calibration for a time-interleaved (TI) SAR ADC that calibrates/computes the inter-channel timing and offset mismatch simultaneously. Simulation results show the effectiveness of this calibration method. When used together, the proposed mismatch calibration technique and the timing-skew calibration technique enables a TI SAR ADC to be designed that can achieve a sampling rate of ∼GS/s with 10-bit resolution and a power consumption as low as ∼10mW; specifications that satisfy the requirements of 5G technology

Enabling low cost test and tuning of difficult-to-measure device specifications: application to DC-DC converters and high speed devices

Low-cost test and tuning methods for difficult-to-measure specifications are presented in this research from the following perspectives: 1)"Safe" test and self-tuning for power converters: To avoid the risk of device under test (DUT) damage during conventional load/line regulation measurement on power converter, a "safe" alternate test structure is developed where the power converter (boost/buck converter) is placed in a different mode of operation during alternative test (light switching load) as opposed to standard test (heavy switching load) to prevent damage to the DUT during manufacturing test. Based on the alternative test structure, self-tuning methods for both boost and buck converters are also developed in this thesis. In addition, to make these test structures suitable for on-chip built-in self-test (BIST) application, a special sensing circuit has been designed and implemented. Stability analysis filters and appropriate models are also implemented to predict the DUT’s electrical stability condition during test and to further predict the values of tuning knobs needed for the tuning process. 2) High bandwidth RF signal generation: Up-convertion has been widely used in high frequency RF signal generation but mixer nonlinearity results in signal distortion that is difficult to eliminate with such methods. To address this problem, a framework for low-cost high-fidelity wideband RF signal generation is developed in this thesis. Depending on the band-limited target waveform, the input data for two interleaved DACs (digital-to-analog converters) system is optimized by a matrix-model-based algorithm in such a way that it minimizes the distortion between one of its image replicas in the frequency domain and the target RF waveform within a specified signal bandwidth. The approach is used to demonstrate how interferers with specified frequency characteristics can be synthesized at low cost for interference testing of RF communications systems. The frameworks presented in this thesis have a significant impact in enabling low-cost test and tuning of difficult-to-measure device specifications for power converter and high-speed devices.Ph.D

Design of High-Speed Power-Efficient A/D Converters for Wireline ADC-Based Receiver Applications

Serial input/output (I/O) data rates are increasing in order to support the explosion in network traffic driven by big data applications such as the Internet of Things (IoT), cloud computing and etc. As the high-speed data symbol times shrink, this results in an increased amount of inter-symbol interference (ISI) for transmission over both severe low-pass electrical channels and dispersive optical channels. This necessitates increased equalization complexity and consideration of advanced modulation schemes, such as four-level pulse amplitude modulation (PAM-4). Serial links which utilize an analog-to-digital converter (ADC) receiver front-end offer a potential solution, as they enable more powerful and flexible digital signal processing (DSP) for equalization and symbol detection and can easily support advanced modulation schemes. Moreover, the DSP back-end provides robustness to process, voltage, and temperature (PVT) variations, benefits from improved area and power with CMOS technology scaling and offers easy design transfer between different technology nodes and thus improved time-to-market. However, ADC-based receivers generally consume higher power relative to their mixed-signal counterparts because of the significant power consumed by conventional multi-GS/s ADC implementations. This motivates exploration of energy-efficient ADC designs with moderate resolution and very high sampling rates to support data rates at or above 50Gb/s. This dissertation presents two power-efficient designs of ≥25GS/s time-interleaved ADCs for ADC-based wireline receivers. The first prototype includes the implementation of a 6b 25GS/s time-interleaved multi-bit search ADC in 65nm CMOS with a soft-decision selection algorithm that provides redundancy for relaxed track-and-hold (T/H) settling and improved metastability tolerance, achieving a figure-of-merit (FoM) of 143fJ/conversion step and 1.76pJ/bit for a PAM-4 receiver design. The second prototype features the design of a 52Gb/s PAM-4 ADC-based receiver in 65nm CMOS, where the front-end consists of a 4-stage continuous-time linear equalizer (CTLE)/variable gain amplifier (VGA) and a 6b 26GS/s time-interleaved SAR ADC with a comparator-assisted 2b/stage structure for reduced digital-to-analog converter (DAC) complexity and a 3-tap embedded feed-forward equalizer (FFE) for relaxed ADC resolution requirement. The receiver front-end achieves an efficiency of 4.53bJ/bit, while compensating for up to 31dB loss with DSP and no transmitter (TX) equalization

High-speed Time-interleaved Digital-to-Analog Converter (TI-DAC) for Self-Interference Cancellation Applications

Nowadays, the need for higher data-rate is constantly growing to enhance the quality of the daily communication services. The full-duplex (FD) communication is exemplary method doubling the data-rate compared to half-duplex one. However, part of the strong output signal of the transmitter interferes to the receiver-side because they share the same antenna with limited attenuation and, as a result, the receiver’s performance is corrupted. Hence, it is critical to remove the leakage signal from the receiver’s path by designing another block called self-interference cancellation (SIC). The main goal of this dissertation is to develop the SIC block embedded in the current-mode FD receivers. To this end, the regenerated cancellation current signal is fed to the inputs of the base-band filter and after the mixer of a (direct-conversion) current-mode FD receiver. Since the pattern of the transmitter (the digital signal generated by DSP) is known, a high-speed digital-to-Analog converter (DAC) with medium-resolution can perfectly suppress main part of the leakage on the receiver path. A capacitive DAC (CDAC) is chosen among the available solutions because it is compatible with advanced CMOS technology for high-speed application and the medium-resolution designs. Although the main application of the design is to perform the cancellation, it can also be employed as a stand-alone DAC in the Analog (I/Q) transmitter. The SIC circuitry includes a trans-impedance amplifier (TIA), two DACs, high-speed digital circuits, and built-in-self-test section (BIST). According to the available specification for full-duplex communication system, the resolution and working frequency of the CDAC are calculated (designed) equal to 10-bit (3 binary+ 2 binary + 5 thermometric) and 1GHz, respectively. In order to relax the design of the TIA (settling time of the DAC), the CDAC implements using 2-way time-interleaved (TI) manner (the effective SIC frequency equals 2GHz) without using any calibration technique. The CDAC is also developed with the split-capacitor technique to lower the negative effects of the conventional binary-weighted DAC. By adding one extra capacitor on the left-side of the split-capacitor, LSB-side, the value of the split-capacitor can be chosen as an integer value of the unit capacitor. As a result, it largely enhances the linearity of the CADC and cancellation performance. If the block works as a stand-alone DAC with non-TI mode, the digital input code representing a Sinus waveform with an amplitude 1dB less than full-scale and output frequency around 10.74MHz, chosen by coherent sampling rule, then the ENOB, SINAD, SFDR, and output signal are 9.4-bit, 58.2 dB, 68.4dBc, and -9dBV. The simulated value of the |DNL| (static linearity) is also less than 0.7. The similar simulation was done in the SIC mode while the capacitive-array woks in the TI mode and cancellation current is set to the full-scale. Hence, the amount of cancelling the SI signal at the output of the TIA, SNDR, SFDR, SNDRequ. equals 51.3dB, 15.1 dB, 24dBc, 66.4 dB. The designed SIC cannot work as a closed-loop design. The layout was optimally drawn in order to minimize non-linearity, the power-consumption of the decoders, and reduce the complexity of the DAC. By distributing the thermometric cells across the array and using symmetrical switching scheme, the DAC is less subjected to the linear and gradient effect of the oxide. Based on the post-layout simulation results, the deviation of the design after drawing the layout is studied. To compare the results of the schematic and post-layout designs, the exact conditions of simulation above (schematic simulations) are used. When the block works as a stand-alone CDAC, the ENOB, SINAD, SFDR are 8.5-bit, 52.6 dB, 61.3 dBc. The simulated value of the |DNL| (static linearity) is also limited to 1.3. Likewise, the SI signal at the output of the TIA, SNDR, SFDR, SNDRequ. are equal to 44dB, 11.7 dB, 19 dBc, 55.7 dB