High-bandwidth voltage-controlled oscillator-based architectures for analog-to-digital conversion

• Autores: Leidy Mabel Alvero González
• Directores de la Tesis: Eric Gutiérrez Fernández (dir. tes.), Luis Hernández Corporales (tut. tes.)
• Lectura: En la Universidad Carlos III de Madrid ( España ) en 2022
• Idioma: inglés
• Tribunal Calificador de la Tesis: Juan Pablo Alegre Pérez (presid.), Celia López Ongil (secret.), Fernando Cardes García (voc.)
• Programa de doctorado: Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de Madrid
• Materias:
  • Ciencias tecnológicas
    • Tecnología de los ordenadores
      • Convertidores analógico-digitales
    • Tecnología electrónica
      • Diseño de circuitos
• Enlaces
  • Tesis en acceso abierto en: e-Archivo
• Resumen

  • The purpose of this thesis is the proposal and implementation of data conversion open-loop architectures based on voltage-controlled oscillators (VCOs) built with ring oscillators (RO-based ADCs), suitable for highly digital designs, scalable to the newest complementary metal-oxide-semiconductor (CMOS) nodes.

    The scaling of the design technologies into the nanometer range imposes the reduction of the supply voltage towards small and power-efficient architectures, leading to lower voltage overhead of the transistors. Additionally, phenomena like a lower intrinsic gain, inherent noise, and parasitic effects (mismatch between devices and PVT variations) make the design of classic structures for ADCs more challenging. In recent years, time-encoded A/D conversion has gained relevant popularity due to the possibility of being implemented with mostly digital structures. Within this trend, VCOs designed with ring oscillator-based topologies have emerged as promising candidates for the conception of new digitization techniques.

    RO-based data converters show excellent scalability and sensitivity, apart from some other desirable properties, such as inherent quantization noise shaping and implicit anti-aliasing filtering. However, their nonlinearity and the limited time delay achievable in a simple NOT gate drastically limit the resolution of the converter, especially if we focus on wide-band A/D conversion. This thesis proposes new ways to alleviate these issues.

    Firstly, circuit-based techniques to compensate for the nonlinearity of the ring oscillator are proposed and compared to equivalent state-of-the-art solutions. The proposals are designed and simulated in a 65-nm CMOS node for open-loop RO-based ADC architectures. One of the techniques is also validated experimentally through a prototype. Secondly, new ways to artificially increase the effective oscillation frequency are introduced and validated by simulations. Finally, new approaches to shape the quantization noise and filter the output spectrum of a RO-based ADC are proposed theoretically. In particular, a quadrature RO-based band-pass ADC and a power-efficient Nyquist A/D converter are presented and validated by simulations.

    All the techniques proposed in this work are especially devoted for high-bandwidth applications, such as Internet-of-Things (IoT) nodes or maximally digital radio receivers. Nevertheless, their field of application is not restricted to them, and could be extended to others like biomedical instrumentation or sensing.