One-bit sigma-delta modulator with improved signal stability

A method for one-bit sigma-delta modulating an input signal, the method comprising the steps of:

• (a) producing a first filter signal by first anti-alias filtering the input signal, the first anti-alias filtering step providing:
• (1) a flat gain over a baseband of frequencies, the absolute values of which are less than or equal to some pre-selected input frequency fi;
• and
• (2) a first cutoff frequency fl;
• (b) producing a chopper signal by chopping the first filter signal at a chopping frequency fc determined by a clock generator, the clock generator being connected to produce a sampling signal at a sampling frequency fs, and fc being characterized by fl being less than 2fc-2fi and by fc being an exact integer submultiple of fs;
• and
• (c) producing a modulator output signal by one-bit modulating the chopper signal with the sampling signal.

An apparatus for one-bit sigma-delta modulating an input signal, the apparatus comprising:

• (a) means for producing a first filter signal, comprising means for first anti-alias filtering the input signal, the first anti-alias filtering means providing:
• (1) a flat gain over a baseband of frequencies, the absolute values of which are less than or equal to some pre-selected input frequency fi;
• and
• (2) a first cutoff frequency fl;
• (b) means for producing a chopper signal, comprising means for chopping the first filter signal at a chopping frequency fc determined by a clock generator, the clock generator being connected to produce a sampling signal at a sampling frequency fs, and fc being characterized by fl being less than 2fc-2fi;
• (c) means for producing a second filter signal, comprising means for second anti-alias filtering the chopper signal, the second anti-alias filtering means providing:
• (1) a flat gain over a band of frequencies from fc-fi to fc+fi;
• and
• (2) a second cutoff frequency f2 which is less than fs-fc-2fi;
• and
• (d) means for producing a modulator output signal, comprising means for one-bit modulating the second filter signal with the sampling signal.

An apparatus for one-bit sigma-delta modulating an input signal, the apparatus comprising:

• (a) means for producing a first filter signal, comprising means for first anti-alias filtering the input signal, the first anti-alias filtering means providing:
• (1) a flat gain over a baseband of frequencies, the absolute values of which are less than or equal to some pre-selected input frequency fi;
• and
• (2) a first cutoff frequency fl;
• (b) means for producing a chopper signal, comprising means for chopping the first filter signal at a chopping frequency fc determined by a clock generator, the clock generator being connected to produce a sampling signal at a sampling frequency fs, and fc being characterized by fl being less than 2fc-2fi and by fc being an exact integer submultiple of fs;
• and
• (c) means for producing a modulator output signal, comprising means for one-bit modulating the chopper signal with the sampling signal.