Advances in CMOS technologies and circuit techniques have led to the development of continuous-time delta-sigma modulators (CTΔ Σ Ms) that sample at gigahertz (GHz) frequencies and achieve high linearity [-100 dBc and >120 dBFS spurious-free dynamic ranges (SFDRs)] in wide bandwidths (>100 MHz). However, at low frequencies (≤ 10 MHz), their performance is limited by the 1/f noise generated by the near-minimum size devices used in their wide-bandwidth input stages. This, in turn, limits their use in radio receivers intended to cover both the AM and FM bands. In this work, a multi-path multi-frequency chopping scheme is proposed to suppress 1/f noise, while preserving interferer robustness, thermal noise levels, and linearity. Implemented in a CTΔ Σ analog-to-digital converter (ADC) sampling at 6 GHz, it achieves a 22× reduction in 1/f noise, as well as 122-dBFS SFDR and -98.3-dBc THD in a 120-MHz BW.

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Advances in CMOS technologies have led to the development of continuous-time ΔΣ modulators (CTDSMs) with GHz sampling rates that achieve better than-100dBc linearity and bandwidths above 100MHz. However, at low frequencies (below 10MHz), their SNDR is limited by 1/f noise, which limits their use in radio receivers intended to cover both the AM and the FM bands. In this work, a multi-path multi-frequency chopping scheme is proposed to suppress 1/f noise, while maintaining interferer robustness, noise, spurious, and linearity performance. Implemented in a CTDSM sampling at 6GHz, it reduces its 1/f noise corner frequency by 22x and achieves -98.3dBc THD, 122dBFS SFDR in 120MHzBW.

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This paper presents a continuous-Time zoom ADC for audio applications. It combines a 4-bit noise-shaping coarse SAR ADC and a fine delta-sigma modulator with a tail-resistor linearized OTA for improved linearity, energy efficiency, and handling of out-of-band interferers compared to previous designs. In 160 nm CMOS, the prototype chip occupies 0.36 mm2, achieves 107.2 dB SNR, 106.6 dB SNDR, and 107.3 dB dynamic range in a 24 kHz bandwidth while consuming 590 μW from a 1.8 V supply. This translates into a Schreier figure-of-merit (FoMs) of 183.4 dB and a FoMSNDR of 182.7 dB.

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In the pursuit of ever larger bandwidths, in recent years GHz-rate continuous-time (CT) oversampled ADCs have been reported in literature that achieve bandwidths of hundreds of MHz and have even exceeded the GHz barrier [1]-[3]. As impressive as these bandwidths are for CT ADCs, the required ADC architectures are complex, are sensitive to layout parasitics due to the high sampling rates, and most important of all, are power hungry, consuming several hundreds of mW. In this paper, we propose a filtering rnulti-stage noise-shaping (MASH) ΔΣ ADC architecture that overcomes the abovementioned drawbacks. Passive delay compensating filters [4] are used to realize broadband and deep suppression of the input signal component at the internal filter nodes of the ADC. As a result, no interstage DACs are needed, which are commonly required to generate the quantization error replicas in a MASH ΔΣ ADC, saving substantial power and greatly reducing the parasitic load of the high-speed critical nodes. Moreover, because of the absence of signal content at the internal filter nodes, the backend stages of the MASH architecture have relaxed linearity requirements and can be implemented with simple low-power Gm-C filters. Precise excess loop delay and excess phase compensation are accomplished with a partly resistive and capacitive stabilization DAC, enabling very-high-speed operation of the ΔΣ loops. The realized MASH ADC is sampled at 5GHz and achieves 68dB/65dB DR/peak SNDR over a 360MHz bandwidth, -78dBc THD at -1dBFS for a 115MHz input signal, and consumes 158mW. Implemented in a mature 40nm CMOS technology, the ADC occupies only 0.21 mm2 core area, achieves 2× lower power, 5dB higher Schreier FOM and 2× lower Walden FOM compared to state-of-the-art broadband CT ADCs in advanced 16nm-28nm nodes [1]-[3].

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This paper analyzes the error mechanisms that limit the dynamic range (DR) of wide-bandwidth, low-OSR continuous-time (CT) multi-stage noise-shaping (MASH) ΔΣM and proposes a tool, the Signal Leakage Function (SLF), to optimize the architecture, and hence improving DR. The SLF provides new insights on finding the key parameters which influence the inter-stage signal leakage and thus the inter-stage gain (IG). These insights would lead not only to increasing the overall dynamic range in a very power-efficient way, but also decreasing the performance sensitivity to mismatches and other variations.@en

This paper presents a SAR-assisted Continuous-time Delta-Sigma (CT Δ Σ ) ADC, which combines the energy efficiency of SAR ADCs with the relaxed driving requirements of CT Δ Σ ADCs, as well as similar anti-alias filtering. When clocked at 2.4GHz, the ADC achieves 77.5dB SNDR in 40MHz BW. It consumes 3.2mW, resulting in a state-of-the-art Walden FoM of 6.5fJ/cs and a Schreier FOM of 178.5dB.

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This paper presents a 2 GS/s 5-b single-channel SAR ADC in 28 nm CMOS. The ADC uses a gm-boosted StrongARM comparator to achieve the highest reported sampling frequency for a non-time-interleaved SAR ADC. Its high sampling frequency, large input signal capability and one clock cycle latency make the ADC suitable for time-interleaved, multi-stage and feedback ADC architectures. The ADC occupies 900 μm2 and consumes 1.25 mW from a 0.9 V supply. Without calibration, and when operated at 1.5 GS/s it achieves 30.3 dB SNDR (FOMw=31.2 fJ/conv.-step). This drops slightly, to 27.4dB, at the maximum sampling rate of 2 GS/s.
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This book describes techniques for realizing wide bandwidth (125MHz) over-sampled analog-to-digital converters (ADCs) in nano meter-CMOS processes. The authors offer a clear and complete picture of system level challenges and practical design solutions in high-speed Delta-Sigma modulators. Readers will be enabled to implement ADCs as continuous-time delta-sigma (CT∆Σ) modulators, offering simple resistive inputs, which do not require the use of power-hungry input buffers, as well as offering inherent anti-aliasing, which simplifies system integration. The authors focus on the design of high speed and wide-bandwidth ΔΣMs that make a step in bandwidth range which was previously only possible with Nyquist converters. More specifically, this book describes the stability, power efficiency and linearity limits of ΔΣMs, aiming at a GHz sampling frequency.@en

A 4 GHz third-order continuous-time ΔΣ ADC is presented with a loop filter topology that absorbs the pole caused by the input capacitance of its 4-bit quantizer and also compensates for the excess delay caused by the quantizer's latency. The ADC was implemented in 45 nm-LP CMOS and achieves 70 dB DR and -74 dBFS THD in a 125 MHz BW, while dissipating 260 mW from 1.1/1.8 V supply. The ADC occupies 0.9 mm 2 including the modulator, clock circuitry and decimation filter.@en