A Coarse-Fine VCO-ADC for MEMS Microphones With Sampling Synchronization by Data Scrambling

Quintero, Andrés; Buffa, Cesare; Pérez, Carlos; Cardes, Fernando; Straeussnigg, Dietmar; Wiesbauer, A.; Hernández, Luis

doi:10.1109/lssc.2020.2964158

Cited by 34 publications

(35 citation statements)

References 7 publications

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“…11), driving twin VCOs with differential input signals. This structure also has the benefit of achieving excellent PSRR values way above common belief [9]. Alternative solutions aim at limiting the signal swing using canceling feedforward paths or closed-loop feedback structures, as will be discussed in part 2.…”

Section: B Distortionmentioning

confidence: 99%

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Time-Encoding Analog-to-Digital Converters: Bridging the Analog Gap to Advanced Digital CMOS-Part 1: Basic Principles

Gielen

Hernández

Rombouts

2020

IEEE Solid-State Circuits Mag.

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I. MOTIVATION FOR TIME ENCODINGThe scaling of CMOS technology deep into the nanometer range has created challenges for the design of high-performance analog integrated circuits. The shrinking supply voltage and the presence of mismatch and noise restrain the dynamic range, causing analog circuits to be large in area and have a high power consumption in spite of the process scaling. Analog circuits based on time encoding [1], [2] and hybrid analog/digital signal processing [3] have been developed to overcome these issues. Realizing analog circuit functionality with highly digital circuits results in more scalable design solutions that can achieve excellent performance. This article reviews the basic principles of time encoding, in particular applied to analog-to-digital converters (ADCs) based on Voltage-Controlled Oscillators (VCOs), one of the most successful time-encoding techniques to date. Although VCO-based ADCs have been around for a long time [4], [5] they really received a significant boost in interest after Straayer and Perrotts highly cited 2008 paper [6]. Since then, many other advancements from different research groups worldwide have been published, in application domains such as sensor readout [7]-[10], telecom [11]-[13], wideband wireless [14]-[18], Internet of Things [19], automotive [20], [21], biomedical [22]-[24], to name a few. Note that the integrating properties of VCOs have also been used to implement continuous-time filters, time to digital converters and other analog signal processing blocks [25]-[27].This overview article is divided in two parts. This first part will introduce the basic principles of time encoding with emphasis on VCO-based ADCs, and will compare them to traditional analog circuits. The follow-up article (part 2) will describe and compare different time-encoding circuit architectures for analog-to-digital converters, and will discuss the corresponding design challenges of the building blocks. Together, they will demonstrate how time-encoding circuits can overcome many of the problems encountered when designing high-performance analog circuits that fully take advantage of advanced digital CMOS technologies, rather than suffering from it, hence bridging the analog gap to advanced CMOS. The main idea behind time encoding consists of representing an analog signal with a modulated square wave, where the signal information is encoded in the transitions instead of the instantaneous amplitude. Such a signal is easy to handle with digital circuits and is robust against noise and distortion. Representing the signal is then done through pulse modulations, known since long ago. Pulse Width Modulation (PWM) is one of the best examples, and used extensively in, for instance, power electronics. The typical block diagram of a time-encoding ADC is shown in Fig. 1. The analog input signal is applied to a pulse modulator that encodes the information in the pulse width, frequency or position of a signal (or set of signals) with two levels only. This two-level signal, which is still analog, ...

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Section: B Distortionmentioning

confidence: 99%

“…To illustrate the above concepts and as example of the different design methodology needed for VCO-based ADCs, we now describe the circuit shown in [9], which is intended for audio applications. It is a very simple VCO-based ADC, yet it shows the full potential of time encoding.…”

Section: Practical Design Examplementioning

confidence: 99%

Time-Encoding Analog-to-Digital Converters: Bridging the Analog Gap to Advanced Digital CMOS-Part 1: Basic Principles

Gielen

Hernández

Rombouts

2020

IEEE Solid-State Circuits Mag.

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“…This would be the case of the first ring-oscillator in Figure 7 which is out of the loop. Nevertheless, this is not a problem in audio applications because of the low amplitude of the input signal [13]. On the other hand, the purpose of using single-ended cells in the ring-oscillators is saving power.…”

Section: Circuit Impairmentsmentioning

confidence: 99%

“…On the other hand, the purpose of using single-ended cells in the ring-oscillators is saving power. Although in the literature it is stated that this might suppose not enough PSRR performance, with a pseudo-differential architecture and a proper layout design, the PSRR will not become a limitation [12,13,23].…”

Section: Circuit Impairmentsmentioning

confidence: 99%

“…In this manuscript, we propose a "hybrid" approach for VADs applications that makes use of voltage-controlled-oscillators based ADCs (VCO-based ADCs) to perform the feature extraction of audio signals [10]. It is known that VCO-based ADCs are suitable for audio applications due to their low power consumption and dynamic range well-suited to human hearing [11][12][13]. VCOs can be also used to implement band-pass filters, such as in [14][15][16].…”

Section: Introductionmentioning

confidence: 99%

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Time-Encoding-Based Ultra-Low Power Features Extraction Circuit for Speech Recognition Tasks

et al. 2020

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Current trends towards on-edge computing on smart portable devices requires ultra-low power circuits to be able to make feature extraction and classification tasks of patterns. This manuscript proposes a novel approach for feature extraction operations in speech recognition/voice activity detection tasks suitable for portable devices. Whereas conventional approaches are based on either completely analog or digital structures, we propose a “hybrid” approach by means of voltage-controlled-oscillators. Our proposal makes use of a bank a band-pass filters implemented with ring-oscillators to extract the features (energy within different frequency bands) of input audio signals and digitize them. Afterwards, these data will input a digital classification stage such as a neural network. Ring-oscillators are structures with a digital nature, which makes them highly scalable with the possibility of designing them with minimum length devices. Additionally, due to their inherent phase integration, low-frequency band-pass filters can be implemented without large capacitors. Consequently, we strongly benefit from power consumption and area savings. Finally, our proposal may incorporate the analog-to-digital converter into the structure of the own features extractor circuit to make the full conversion of the raw data when triggered. This supposes a unique advantage with respect to other approaches. The architecture is described and proposed at system-level, along with behavioral simulations made to check whether the performance is the expected one or not. Then the structure is designed with a 65-nm CMOS process to estimate the power consumption and area on a silicon implementation. The results show that our solution is very promising in terms of occupied area with a competitive power consumption in comparison to other state-of-the-art solutions.

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Time Based and VCO-ADCs from a Signal Processing Perspective

Gielen

Hernandez-Corporales

Rombouts

2022

Time-Encoding VCO-ADCs for Integrated Systems-on-Chip

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A Coarse-Fine VCO-ADC for MEMS Microphones With Sampling Synchronization by Data Scrambling

Cited by 34 publications

References 7 publications

Time-Encoding Analog-to-Digital Converters: Bridging the Analog Gap to Advanced Digital CMOS-Part 1: Basic Principles

Time-Encoding Analog-to-Digital Converters: Bridging the Analog Gap to Advanced Digital CMOS-Part 1: Basic Principles

Time-Encoding-Based Ultra-Low Power Features Extraction Circuit for Speech Recognition Tasks

Time Based and VCO-ADCs from a Signal Processing Perspective

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