From Open-Loop to Closed-Loop Single-VCO-Based Sensor-to-Digital Converter Architectures: theoretical analysis and comparison

Sacco, Elisa; Vergauwen, Johan; Gielen, Georges

doi:10.1109/iwasi.2019.8791296

Cited by 6 publications

(6 citation statements)

References 14 publications

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“…The SNDR is relatively independent of OSR for low f bw , suggesting that phase noise dominates the achievable SNDR rather than quantization noise. To verify this assumption, we utilize the analytical equations which describe the VCO-based ADCs [25], [26], where the SNDR takes into account both quantization noise and STNO's phase noise:…”

Section: Resultsmentioning

confidence: 99%

“…A sensor connected to the ADC input generates a voltage v in (t) which is used as a control signal for the VCO. The VCO converts the voltage v in (t) to time/phase domain where the conversion relationship (to a first-order approximation) is given by [26]:…”

Section: B Vco Adcmentioning

confidence: 99%

“…However, this quantization error (residual phase) inherently becomes the inital phase of the next sampling period, thus the VCO acts like an integrator. The combination of this time-domain integration, and the delta operation performed by the differentiator resemble a first-order Delta-Sigma (∆Σ) modulator with a noise transfer function (NTF) [25], [26]:…”

Section: B Vco Adcmentioning

confidence: 99%

“…in z-domain. Additionally, the VCO's phase noise has the same NTF as the quantization noise [25], [26]. This is an important feature for the STNO-based magnetic field-to-digital converter since typical STNOs have shown phase noise in the range from -55 dBc/Hz to -72 dBc/Hz at 1 MHz offset, limiting their applications [15].…”

Section: B Vco Adcmentioning

confidence: 99%

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A Magnetic Field-to-Digital Converter Employing a Spin-Torque Nano-Oscillator

Albertsson

Åkerman

Rusu

2020

IEEE Trans. Nanotechnology

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In this work, a novel magnetic field-to-digital converter based on emerging spin-torque nano-oscillators (STNOs) is proposed. The architecture is inspired by voltage controlled oscillator (VCO)-based analog-to-digital converters (ADCs) which have shown inherent first-order noise shaping of both quantization-and phase-noise without the need for feedback. In the proposed architecture, the STNO acts both as a magnetic field sensor and VCO. The architecture's performance is evaluated in terms of signal-to-noise and distortion ratio (SNDR) utilizing Verilog-AMS modeling, where a macrospin model fitted to experimental data is employed for accurate description of the STNO operation. The presented simulation results demonstrate the potential of the STNO-based magnetic field-to-digital converter architecture.

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Section: Resultsmentioning

confidence: 99%

Section: B Vco Adcmentioning

confidence: 99%

Section: B Vco Adcmentioning

confidence: 99%

Section: B Vco Adcmentioning

confidence: 99%

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A Magnetic Field-to-Digital Converter Employing a Spin-Torque Nano-Oscillator

Albertsson

Åkerman

Rusu

2020

IEEE Trans. Nanotechnology

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“…1(b) is usually employed [20]. Although the VCO in a loop ensures higher linearity, the frequency operating range is narrowed and the additional feedback network results in a low conversion speed, a larger area, and an increased power budget [24]. The limiting factor in these close-loop time-based interfaces is the VCO phase noise [20].…”

Section: Introductionmentioning

confidence: 99%

A Low-Phase-Noise CMOS Ring Voltage-Controlled Oscillator Intended for Time-Based Sensor Interfaces

2022

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We describe in this paper an improved ring voltage-controlled oscillator (VCO) showing a reduced phase noise while allowing an extended frequency tuning range. The phase noise improvement is obtained through the minimized contribution of tuning line noise while maintaining a rail-to-rail swing. The proposed VCO features a linear tuning characteristic yielding a constant gain over a wide range of operating frequencies. An analytical model is extracted resulting in closed-form expressions for the VCO phase noise. Employing the analytical expressions, the contributed noise and phase noise limitations are fully addressed, and all the effective factors are investigated. The VCO prototype was fabricated in a 0.35 µm CMOS process. It consumes 0.903 mW from a 3.3 V supply when running at its maximum oscillation frequency of 9.37 MHz. The measured VCO phase noise is -147.57 dBc/Hz at 1 MHz offset from the 9.37 MHz oscillation frequency, and the circuit occupies a silicon area of 0.005 mm 2 . A state-variable Matlab ® model of a timebased sensor interface has been developed including the impact of phase noise nonideality. The system-level simulations demonstrate that the PLL-based sensor interface exploiting the proposed VCO characteristics can achieve a 88.43 dB signal-to-noise ratio over a 1-kHz bandwidth.

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