Linearity Enhancement of VCO-Based Quantizers for SD Modulators by Means of a Tracking Loop

A new approach for mitigating the nonlinearity in the voltage-frequency characteristic of voltage-controlled oscillator (VCO)-based quantizers is proposed in this brief. The signal to be converted is coarsely estimated from the VCO-based quantizer output by digital integration and then subtracted to the input. The VCO only converts a residue of very low level and only with a small-signal component, operating in a narrow region of its voltage-frequency characteristic. The tracking loop so created drastically reduces the harmonic distortion. As compared to other approaches used for the same purpose, the proposed one is simpler and less prone to circuit errors. Simulation results show the feasibility of this approach and validate the theoretical analysis presented in this brief.