Digital-to-analog converter using pulse-width modulation

Claim 2

A digital-to-analog converter for converting input digital data having a predetermined sampling period into an analog signal, comprising: pulse-width modulated signal generation means for generating a pulse-width modulated signal having a pulse width corresponding to said input digital data; and low-pass filter means for eliminating high-frequency components of said pulse-width modulated signal to thereby output said analog signal; wherein said pulse-width modulated signal generation means is operative to divide the sampling period of said input digital data into an integral even number of divided sampling periods and to generate a pulse-width modulated signal in each divided sampling period, said sampling period including at least two pulses having equal pulse widths symmetrically arranged about a point a predetermined interval from the center of said sampling period and corresponding to said input digital data.

Claim 3

A digital-to-analog converter according to claim 1, wherein said pulse-width modulated signal generation means comprises: ROM means coupled to receive the input digital data as address data for outputting parallel data representing the at least two pulses of said pulse-width modulated signal in a respective one of said sampling periods; and parallel-to-serial converter means for converting said parallel data to a serial data signal corresponding to the at least two pulses of said pulse-width modulated signal.

Claim 4

A digital-to-analog converter according to claim 2, wherein said pulse-width modulated signal generation means further comprises: buffer means and inverter means arranged in parallel and having inputs commonly coupled with the parallel-to-serial converter means for providing said serial data signal and an inverted version of said serial data signal, respectively, at corresponding outputs thereof; and differential amplifier means for providing said pulse-width modulated signal at an output thereof by producing said pulse-width modulated signal as a difference between said serial data signal and said inverted version of said serial data signal; the output of said differential amplifier means being coupled to said low-pass filter means to supply said pulse-width modulated signal thereto.

Claim 5

A digital-to-analog converter according to claim 1, wherein said pulse-width modulated signal generation means comprises: first ROM means coupled to receive said input digital data as address data for outputting first parallel data representing said pulse-width modulated signal; second ROM means coupled to receive said input digital data as address data for outputting second parallel data representing an inverted version of said first parallel data; first parallel-to-serial converter means for converting said first parallel data to serial data supplied at an output thereof and representing said pulse-width modulated signal; second parallel-to-serial converter means for converting said second parallel data to serial data supplied at an output thereof and representing an inverted version thereof; and differential amplifier means having a noninverting input and an inverting input coupled with respective ones of the output of said first parallel-to-serial converter means and the output of said second parallel-to-serial converter means for providing said pulse-width modulated signal at an output thereof, wherein the output of said differential amplifier means is coupled with said low-pass filter means to supply said pulse-width modulated signal thereto.