VCO-based ADC with a simplified DAC for non-linearity correction

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Institution of Engineering and Technology (IET)
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The performance of open-loop ADCs implemented with VCOs is limited by VCO non-linearity and first-order noise shaping. The resolution limitation imposed by first-order noise shaping can be compensated by a ring oscillator VCO with many output phases. Linearity can also be improved by using a feedback loop around the VCO closed with a DAC. However, a long ring oscillator may require a DAC with a prohibitive number of bits if feedback is used to compensate distortion. This Letter proposes an ADC architecture based on the Leslie-Singh Sigma-Delta (Σ∆) modulator that allows to implement a distortion correction loop around a VCO with a simplified DAC of few levels, yet keeping a large number of output quantisation levels to maintain resolution. The Letter discusses the system-level architecture and shows an implementation circuit example to verify the effective correction of distortion.
Voltage-controlled oscillators, Digital-analogue conversion, Circuit feedback, Distortion, Compensation, Sigma-delta modulation, Quantisation (Signal), VCO-based ADC, Simplified DAC, Nonlinearity correction, Open-Loop ADC performance, Vco nonlinearity, First-order noise shaping, Resolution limitation, Ring oscillator VCO, Feedback loop, Distortion compensation, Leslie-singh sigma-delta modulator, Leslie-singh sigma-delta modulator, Distortion correction loop, Quantisation levels, System-level architecture
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Quintero, A., Pérez, C., Gutiérrez, E. & Hernández, L. (2018). VCO-based ADC with a simplified DAC for non‐linearity correction. Electronics Letters, 54(13), 813-815.