Preweighted Linearized VCO Analog-to-Digital Converter

Abstract

A linearization technique of voltage-to-frequency characteristics of voltage-controlled oscillator (VCO) analog-to-digital converters (ADCs) is presented. In contrast to previous works, the proposed technique is an open-loop calibration-free configuration, so it can operate at higher frequencies. It is also independent of the delay element structure, so it can be applied to various VCO ADC topologies. The analog input signal is first mapped through a preweighted resistor network in which every delay element experiences a different version of the input and produces the corresponding delay. As a result, the proposed approach suppresses the impact of $V/F$ nonlinearity on the ADC performance by expanding a linear region of the transfer curve over the full rail-to-rail input. This technique shows substantial improvement results by keeping nonlinearity within ±0.5% over the full input scale (dBFS) and achieves a peak signal-to-noise and distortion ratio (SNDR) of 75.7 and 60.4 dB for input of −8 and 0 dBFS, respectively.