Digital-to-analog converter with delta-sigma modulation

Claim 1

A digital-to-analog conversion apparatus operative according to a system clock signal for converting a digital input into a corresponding analog output, comprising: clock means for generating a system clock signal having a given basic frequency and a relatively short period; dividing means for frequency-dividing the system clock signal to produce a divided clock signal having a frequency one-fourth or less of the basic frequency and a relatively long period; oversampling means for oversampling a digital input containing a sequence of multi-bit data; delta-sigma modulating means operative in synchronization with the system clock signal for effecting delta-sigma modulation of the oversampled digital input to produce a requantized digital signal containing, every short period timed by the system clock signal, a requantized data comprised of a lesser number of bits than the multi-bit data; pulse forming means including first means operative in response to the divided clock signal having the frequency one-fourth or less of the basic frequency during each long period timed by the divided clock signal for effecting a detection of a set of the requantized data occurring during each long period of the detection, and second means operative in response to each detection for effecting pulse modulation of each set of the requantized data to form a pulse signal corresponding to the requantized digital signal according to results of the detection; and filtering means for filtering the pulse signal to produce an analog output corresponding to the digital input.