VCO-ADC Linearization by Switched Capacitor Frequency-to-Current Conversion

The main limitation of voltage-controlled oscillator based analog-to-digital converters (VCO-ADC) is the VCO non-linear voltage-to-frequency response, especially with ring-oscillators. This issue strongly restricts the final resolution we are able to get from the converter. In addition, flicker noise is a limitation for low-bandwidth applications. We propose a novel way of compensating both the VCO non-linearity and the phase noise effects. By means of a time varying switched-capacitor circuit, we build a purely analog compensation loop where jitter clock and DAC non-linearity do not suppose a limitation. The loop is closed with an opamp that provides gain to the compensation operation. The idea is proposed theoretically and tested by simulations, showing a good performance for audio or sensing applications.