Yan Zhang - IEEE Xplore Author Profile

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Combining the noise-shaping (NS) technique with the SAR converter enables high resolution while maintaining state-of-the-art power efficiency and minimal area occupation [1]. However, the performance of existing NS SAR ADCs drops significantly for bandwidths higher than a few MHz, making the NS SAR unattractive for high-speed applications such as wireless communications. Single-core wideband solut...Show More
Time-interleaved (TI) analog-to-digital converters (ADCs) are an established architecture, but fundamental problems still exist that prevent replicating the performance of each sub-ADC to the overall TI ADC. This article presents different techniques to overcome the main challenges in implementing an interleaved converter: 1) driving the ADC with sufficient linearity and bandwidth; 2) avoiding the...Show More
This brief presents a linearity enhancement method, named charge linearization technique (CLT), for top-plate input successive approximation register (SAR) data converters. The proposed CLT removes the linearity degradation due to the non-linear parasitic capacitance of the comparator. Consequently, the constraint on the size of the comparator is relieved. An 11-bit redundant SAR converter featuri...Show More
In this paper, we present a novel input buffer based on the push-pull architecture for an 11-bit 2-GS/s 8x time-interleaved ADC. The proposed buffer features an auxiliary follower which is used to drive the body terminals of the main push-pull output transistors, removing their non-linear contribution at the output node, with a negligible overhead in terms of power consumption. The ADC features a ...Show More
A 2GS/s 11b 8x-interleaved ADC is presented where flipped-voltage-follower-based reference buffers attenuate channel interactions and a set of on-chip background digital calibrations mitigate channel mismatches. A high-linearity input buffer is included which does not degrade ADC performances. Implemented in a 28nm CMOS technology, the ADC achieves 57.3dB SNDR and 69.9dB SFDR close to the Nyquist ...Show More
An LO phase-shifting system based on digital fractional- ${N}$ bang-bang phase-locked loops (PLLs) in the 8.5–10.0-GHz range is presented. A direct phase modulation method is leveraged to perform LO phase-shifting directly within the frequency synthesizer, leading to an inherently linear phase-shifting characteristic, even in the presence of digital-to-time converter (DTC) nonlinearities. Synchro...Show More
The quest of increasingly higher mobile uplink/downlink data-rates has recently driven the communication industry to set extremely challenging requirements on the integrated jitter of local oscillators [1]. In fractional-N PLLs, the adoption of a digital-to-time-converter (DTC) has become ubiquitous to meet performance targets, as it greatly improves integrated jitter by re-aligning the edges of t...Show More
This work presents a low-jitter and low out-of-band noise two-core fractional- $N$ digital bang-bang phase-locked loop (PLL). Two novel techniques are introduced to efficiently suppress the quantization noise (QN) of the digitally controlled oscillator (DCO) and to achieve an optimal trade between power consumption and PLL noise. The digital period averaging technique, working in background of th...Show More
This paper analyses for the first time from a quantitative standpoint the effectiveness of redundancy in successive approximation register (SAR) analog-to-digital converters (ADCs) that employ the conventional and monotonic switching algorithms. It is shown that the redundancy tolerance window is one-sided in the case of conventional switching algorithm, thus only underestimations of the input sig...Show More
In this work, a 12-bit, 150-MS/s, 13-steps redundant asynchronous SAR ADC achieving better than 63-dB SNDR and 72-dB SFDR with a 100-MHz Equivalent Resolution Bandwidth (ERBW) is presented. To achieve a high conversion rate without impairing accuracy, the implemented ADC features a custom sub-fF unit capacitance with mismatch calibration in the digital domain, a sub-radix-2 CDAC which introduces r...Show More
This brief presents a 12-bit successive approximation register (SAR)-based time-interleaved (TI) analog-to-digital converter (ADC) with a fully programmable interleaving factor. A total of six SAR sub-ADCs can be time-interleaved. The interleaving factor is programmable from 2 to 6, resulting in an overall sampling rate from 300 to 900MS/s. On-chip offset, gain, and timing skew background calibrat...Show More
Sub-100fs fractional-N PLLs in the tens of GHz range are required by modern wireless standards such as 5G [1]. The main factors limiting jitter and spot-noise in a digital PLL (DPLL) are on one hand the phase noise of the digitally controlled oscillator (DCO) and, on the other hand, the quantization noise (QN) introduced by the DCO frequency granularity. Though several approaches, such as multi-co...Show More
Automatic bandwidth control based on least mean-square adaptive filters has been demonstrated to desensitize the loop gain of a phase-locked loop (PLL) from process spreads, environmental variations, and channel frequency. This work extends this concept to low-jitter designs that adopt aggressive out-of-band filtering, by introducing multitap adaptive filtering. The method requires no injection of...Show More
This paper presents a novel technique to reduce the locking time in Digital Phase-Locked Loop (DPLL) based on Bang-Bang Phase Detector (BB-PD). The implemented 65-nm CMOS fractional-N frequency synthesizer generates an output signal between 3.7 and 4.1 GHz from a 52 MHz reference clock and improves the trade-off between phase noise, due to the loop quantization, and locking time, exploiting a digi...Show More
This article presents a fractional-N sampling type-I phase-locked loop (PLL). To overcome the impairments of a conventional type-I PLL, namely the frequency-tuning-dependent time offset and the narrow range of the sampling phase detector (SPD), which would prevent fractional-N synthesis, a novel digital phase error correction (DPEC) technique, operating in the background, is introduced, which prov...Show More
This work introduces a bang-bang fractional- $N$ phase-locked loop with quantization noise shaping that overcomes the classical noise limit of a standard bang-bang phase detector. An adaptive algorithm, working in the background of the main system, guarantees optimal noise shaping across process and environmental variations. The prototype, implemented in a standard 28-nm CMOS process, has a core ...Show More
Digital PLLs (DPLLs) have demonstrated to be a promising candidate to implement frequency synthesizers in wireless transceivers, thanks to their scaling-friendly architecture and to the possibility of implementing powerful background adaptive calibration algorithms to compensate the system non-idealities. The combination of these features leads to an inherently faster time-to-market than tradition...Show More
Digital PLLs are nowadays recognized as a viable approach for the design of high-performance frequency synthesizers in scaled CMOS technologies. Latest implementations allow achieving at low power both state-of-the-art rms jitter, between 50fs and 100fs, and highly linear fast frequency modulation capability, thus enabling both high-efficiency communications systems and radar applications in CMOS....Show More
This work presents a very compact self-biasing dynamic startup circuit for class-C voltage-controlled oscillators (VCOs). Using a referenceless nonlinear inverting stage, the solution has been implemented in a 28-nm CMOS technology 14-GHz oscillator, leading to a VCO startup time better than 20 ns, at par with the fastest startup circuits in literature, with an extremely compact area of 0.003 mm2.Show More
This article presents a fractional-N frequency synthesizer architecture that is able to overcome the limitations of conventional bang-bang phase-locked loops. A digital frequencyerror recovery technique is introduced to enable fast lock, at no significant power or circuit overhead. A digital-to-time converter design with reduced static and dynamic nonlinearity is proposed, which allows for low-jit...Show More