Apparatus for digital-to-analogue conversion

Claim 2

Apparatus for digital-to-analogue conversion comprising: a dither generator; an adder for adding dither from said dither generator to a digital input signal to produce an added output; a noise shaping circuit having an output, for performing noise shaping on said added output; said noise shaping circuit including a quantizer with certain threshold levels; a digital-to-analogue (D/A) converter converting said output from said noise shaping circuit to an analog signal; and control means for widening said threshold levels as a level of said digital input signal becomes zero, and for attenuating an input signal to said digital-to-analogue converter by substantially 1K times when said threshold levels are increased by K times, where K is a number.

Claim 3

Apparatus for digital-to-analogue conversion according to claim 1, wherein K=2 n where n is an integer, and wherein said attenuating and widening are performed by bit shifting in said control means.

Claim 4

Apparatus for digital-to-analogue conversion according to claim 1, wherein said D/A converter includes a One-Bit digital-to-analogue converter.

Claim 5

Apparatus for digital-to-analogue conversion according to claim 1, wherein said control means fixes a pulse duty cycle of an output from said D/A converter to 50% at a point where an AC component of said dither becomes zero and when more than four consecutive samples of output data from said noise shaping circuit equal zero.

Claim 6

Apparatus for digital-to-analogue conversion according to claim 1, wherein said control means fixes a pulse duty cycle of an output from said D/A converter to 50% at a point where an AC component of said dither becomes zero.

Claim 7

Apparatus for digital-to-analog conversion according to claim 1, wherein said control means fixes an output from said D/A converter to 50% pulse duty cycle when more than four consecutive samples of output data from said noise shaping circuit equal zero.

Claim 8

Apparatus for digital-to-analogue conversion according to claim 1, wherein K=2 n where n is an integer.

Claim 9

Apparatus for digital-to-analogue conversion according to claim 1, further comprising memory means for storing a lookup table with a plurality of sets of input and output values stored therein for each of a plurality of values of K.

Claim 10

Apparatus for digital-to-analogue conversion comprising: a dither generator; an adder for adding dither from said dither generator to a digital input signal to produce an added output; a noise shaping circuit having an output, for performing noise shaping on said added output; said noise shaping circuit including a quantizer with certain threshold levels; a one bit digital-to-analogue (D/A) converter converting said output from said noise shaping circuit to an analog signal; control means for widening said threshold levels as a level of said digital input signal becomes zero, and for attenuating an input signal to said digital-to-analogue converter by substantially 1/K times when said threshold levels are increased by K times where K=2 n with n being an integer, said control means performing said attenuating and said widening by bit shifting; and wherein said control means fixes a pulse duty cycle of an output from said D/A converter to 50% at a point where an AC component of said dither becomes zero and when more than four consecutive samples of output data from said noise shaping circuit equal zero.

Claim 11

Apparatus for digital-to-analogue conversion comprising: a dither generator; an adder for adding dither from said dither generator to a digital input signal to produce an added output; a noise shaping circuit having an output, for performing noise shaping on said added output; said noise shaping circuit including a quantizer with certain threshold levels; a one bit digital-to-analogue (D/A) converter converting said output from said noise shaping circuit to an analog signal; control means for widening said threshold levels as a level of said digital input signal becomes zero, and for attenuating an input signal to said digital-to-analogue converter by substantially 1/K times when said threshold levels are increased by K times where K=2 n with n being an integer, said control means performing said attenuating and said widening by bit shifting; and wherein said control means fixes a pulse duty cycle of an output from said D/A converter to 50% at a point where an AC component of said dither becomes zero and when more than four consecutive samples of output data from said noise shaping circuit equal zero.

Claim 14

The method of claim 10, further comprising the step of converting said output signal to an analog signal.

Claim 15

The method of claim 11, wherein said converting step is carried out by a one bit digital-to-analog converter.

Claim 16

The method of claim 10, wherein K=2 n , where n is an integer.

Claim 17

The method of claim 13, wherein said widening and attenuating steps are carried out by bit shifting.

Claim 18

The method of claim 11, further comprising the steps of fixing a pulse duty cycle of an output from said D/A converter to 50% at a point where an AC component of said dither signal becomes zero and when more than four consecutive samples of said output signal equal zero.