Analogue-to-digital converters, digital-to-analogue converters, and digital modulators

Claim 1

An analog-to-digital converter comprising: an input for analog signals; filter means having an input for receiving, from a summing node, an error signal; first quantizing means for producing a first digital signal from a signal derived from the output of the filter means; a feedback loop for feeding a signal derived from the first digital signal to be combined in analog form with a signal derived from the analog input signal at the summing node, so that the filter means in use receives the error signal representing the total error between the signal derived from the analog input signal and the analog representation of the first digital signal; means for filtering the error signal to remove noise outside the passband of the analog-to-digital converter; second quantizing means for producing a second digital signal representative of the filtered error signal; means for combining the first and second digital signals to produce a digital output signal representative of the analog input signal; an equalization network for offsetting phase and amplitude errors introduced by the filtering means and by the second quantizing means before the first and second digital signals are combined; and means for calibrating the equalization network by means of a test signal at intervals of time.