Fredrik Feyling

As a generalization of the continuous-time pipeline (CTP), we present a theoretical model that can be used to analyze any conventional continuous-time (CT) analog-to-digital converter (ADC). In addition to providing a unified approach for deriving reconstruction filter coefficients, the general model enables new ADC architectures that do not fit in the framework of neither the cascaded continuous-time sigma-delta modulators (CT-Σ∆Ms), nor the CTP ADCs. As an example exploiting this design flexibility, we present a 7th order Leapfrog ADC. The aggressive 7th order filter enables a low oversampling ratio (OSR), while stability is ensured by local digital feedback with single-bit quantizers. The modular structure makes it well-suited for a programmatic design methodology, and the layout of the ADC is generated using a custom-made Python tool for analog layout compilation. Implemented in a 130nm CMOS technology, the prototype achieves a dynamic range of 82 dB with an OSR of 11, while consuming 2.5 mW from a 1.5 V supply. The resulting Schreier figure-of-merit (FOM) is 168 dB.

In this paper, the design flexibility of the control-bounded analog-to-digital converter principle is demonstrated. A band-pass analog-to-digital converter is considered as an application and case study. We show how a low-pass control-bounded analog-to-digital converter can be translated into a band-pass version where the guaranteed stability, converter bandwidth, and signal-to-noise ratio are preserved while the center frequency for conversion can be positioned freely. The proposed converter is validated with behavioral simulations on several filter orders, center frequencies, and oversampling ratios. Additionally, we consider an op-amp circuit realization where the effects of first-order op-amp non-idealities are shown. Finally, robustness against component variations is demonstrated by Monte Carlo simulations.

The paper considers the calibration of control-bounded analog-to-digital converters. It is demonstrated that variations of the analog frontend can be addressed by calibrating the digital estimation filter. In simulations (both behavioral and transistor level) of a leapfrog analog frontend, the proposed calibration method restores essentially the nominal performance. Moreover, with digital-filter calibration in mind, the paper reformulates the design problem of control-bounded converters and thereby clarifies the role of sampling, desired filter shape, and nominal conversion error.

In this paper, the design flexibility of the control-bounded analog-to-digital converter principle is demonstrated. A band-pass analog-to-digital converter is considered as an application and case study. We show how a low-pass control-bounded analog-to-digital converter can be translated into a band-pass version where the guaranteed stability, converter bandwidth, and signal-to-noise ratio are preserved while the center frequency for conversion can be positioned freely. The proposed converter is validated with behavioral simulations on several filter orders, center frequencies, and oversampling ratios. Additionally, we consider an op-amp circuit realization where the effects of first-order op-amp non-idealities are shown. Finally, robustness against component variations is demonstrated by Monte Carlo simulations.

In this paper, behavioural circuit simulations are used to compare the leapfrog control-bounded analog-to-digital converter to relevant continuous-time sigma-delta modulators in terms of nominal performance and sensitivity to component variations, clock jitter and finite gain-bandwidth product. Simulations show that the nominal performance of the leapfrog is similar to that of a continuous-time sigma-delta modulator of the same loop filter order and with the same number of quantization levels. Component variations in the leapfrog's analog system will introduce errors in the final output, unless the coefficients of the reconstruction filter are modified accordingly. Nevertheless, the simple, modular structure, analytical stability guarantee and single-bit quantizers make the leapfrog an interesting alternative to conventional continuous-time sigma-delta modulators.