Voltage-controlled oscillator (VCO) as first stage in an analog-to-digital converter (ADC) in combination with a digital filter for second or higher-order

摘要

A delta-sigma modulation analogue-to-digital converter (ADC) is formed by combining a first stage comprising a VCO and a first order filter, with a second stage comprising a digital loop filter which may be of higher order. In an embodiment, an ADC 400 receives an analogue input signal Vin, forms an analogue error signal between the input signal and the output of the ADC, and integrates the error signal in a first stage circuit VCO 204 comprising a voltage-controlled oscillator and an integrator 404. The first stage circuit VCO 204 implements a first order noise-shaping function. The output of the first stage is quantised by quantiser 406 and passes to the second stage digital loop filter 206 which implements a noise-shaping function of first, second or higher order. A second quantiser 208 receives the output of the digital filter and provides the output of the converter. The output of the first stage may be quantised at a higher resolution than the output of the output of the second stage, improving accuracy of conversion. Higher order noise shaping improves the quality of an ADC by better attenuating noise in the input signal.