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US 5,055,843 AGranted
Sigma delta modulator with distributed prefiltering and feedback
AssigneeAnalog Devices, Inc.
InventorsPaul F. Ferguson, Jr., Apparajan Ganesan, Robert W. Adams
Life of this patent
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Abstract
A separate filter circuit is inserted between the D/A converter and the summing junction in the feedback path of a conventional sigma delta modulator. This additional filter allows control of the quantization noise transfer function profile independently of the forward signal transfer function. By proper tailoring of the transfer functions a third or higher order modulator can be constructed without instability developing.
Claims27
A sigma delta modulator for generating an output digital data stream from an analog signal, said modulator comprising:
- a plurality of filter modules for receiving and processing an error signal;
- means connecting said filter modules in series;
- means for injecting a signal between each pair of filter modules;
- an analog-to-digital converter responsive to an output of said plurality of filter modules for generating said output data stream;
- a digital-to-analog converter responsive to said output stream for generating a feedback signal;
- means for summing said analog signal and said feedback signal to generate said error signal;
- means responsive to said feedback signal for applying a partial feedback signal to each of said injecting means and to said summing means;
- a plurality of prefilters connected in parallel to said analog input, each of said prefilters generating a partial prefilter signal;
- and
- means for applying a partial prefilter signal to each of said injecting means and to said summing means.
7 more elements
A sigma delta modulator for generating an output digital data stream from an analog signal at an analog input, said modulator comprising:
- a plurality of filter circuits connected as a cascade filter for receiving and processing an error signal;
- a plurality of summing junctions, one of said plurality of summing junctions being located between each pair of filter circuits in said cascade filter;
- an analog-to-digital converter responsive to an output of said cascade filter for generating said output data stream;
- a digital-to-analog converter responsive to said output stream for generating a feedback signal;
- a plurality of feedback circuits connected as a cascade feedback circuit for receiving and processing said feedback signal, each of said plurality of feedback modules generating one of a plurality of partial feedback signals,
- means for applying one of said plurality of partial feedback signals to one of said summing junctions;
- a plurality of prefilters connected in parallel to said analog input, each of said prefilters generating a partial prefilter signal;
- and
- means for applying one of said plurality of partial prefilter signals to one of said summing junctions.
6 more elements
A sigma delta modulator for generating an output digital data stream from an analog signal at an analog input, said modulator comprising:
- a first summing junction responsive to said analog signal for generating a first error signal;
- an integrator responsive to said error signal for generating an integrated error signal;
- a second summing junction responsive to said integrated error signal for generating a second error signal;
- a resonator network responsive to said second error signal for generating an output error signal;
- a comparator responsive to said output error signal for generating said output data stream;
- a selection switch responsive to said output stream for selecting one of two reference voltages as a feedback signal;
- a first feedback circuit responsive to said feedback signal for generating a first partial feedback signal;
- means for applying said first partial feedback signal to said second summing junction to be summed with said integrated error signal to generate said second error signal;
- a second feedback circuit responsive to said first partial feedback signal for generating a second partial feedback signal;
- means for applying said second partial feedback signal to said first summing junction to be summed with said analog signal to generate said first error signal;
- a first prefilter connected between said analog input and said first summing junction;
- and
- a second prefilter connected between said analog input and said second summing junction.
10 more elements
A sigma delta modulator for generating an output digital data stream from an analog signal, said modulator comprising:
- a filter network for receiving and processing an error signal;
- an analog-to-digital converter responsive to an output of said filter network for generating said output data stream;
- a digital-to-analog converter responsive to said output stream for generating a feedback signal;
- means for summing said analog signal and said feedback signal to generate said error signal;
- means responsive to said feedback signal for injecting a partial feedback signal into a first plurality of predetermined points in said filter network;
- a plurality of prefilters connected in parallel to said analog input, each of said prefilters generating a partial prefilter signal;
- and
- means for applying a partial prefilter signal into a second plurality of predetermined points in said filter network.
5 more elements
A sigma delta modulator for generating an output digital data stream from an analog signal, said modulator comprising:
- a plurality of filter modules for receiving and processing an error signal;
- means connecting said filter modules in series;
- means for injecting a signal between each pair of filter modules;
- at least one resonator feedback network connecting an output of a resonator pair of filter modules to an input of said resonator pair of filter modules to form a resonator;
- an analog-to-digital converter responsive to an output of said plurality of filter modules for generating said output data stream;
- a digital-to-analog converter responsive to said output stream for generating a feedback signal;
- means for summing said analog signal and said feedback signal to generate said error signal;
- and
- means responsive to said feedback signal for applying a partial feedback signal to each of said injecting means and to said summing means.
6 more elements
A sigma delta modulator for generating an output digital data stream from an analog signal at an analog input, said modulator comprising:
- a first summing junction responsive to said analog signal for generating a first error signal;
- a first integrator responsive to said error signal for generating a first integrated error signal;
- a second summing junction responsive to said first integrated error signal for generating a second error signal;
- a second integrator responsive to said second error signal for generating a second integrated error signal;
- a third summing junction responsive to said second integrated error signal for generating a third error signal;
- a third integrator responsive to said third error signal and having an output;
- a resonator feedback network connected between said third integrator output and said second summing junction to form a resonator;
- means responsive to said third integrator output for generating an output error signal;
- a comparator responsive to said output error signal for generating said output data stream;
- a selection switch responsive to said output stream for selecting one of two reference voltages as a feedback signal;
- a first feedback circuit responsive to said feedback signal for generating a first partial feedback signal;
- means for applying said first partial feedback signal to said second summing junction to be summed with said integrated error signal to generate said second error signal;
- a second feedback circuit responsive to said first partial feedback signal for generating a second partial feedback signal;
- and
- means for applying said second partial feedback signal to said first summing junction to be summed with said analog signal to generate said first error signal.
12 more elements
Dependencies are inferred from the claim text.