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.

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.

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].