Combined angle demodulator and digitizer
First Claim
1. A frequency-to-digital converter that operates on an input signal and generates a digital output signal at an output sample-rate, f, comprising:
- a modulator loop means for generating a coarsely quantized digital representation of the frequency modulation of said input signal at a modulator loop sample-rate of Nf where N is a positive number, wherein the component of said digital output signal corresponding to quantization error has a spectrum that occupies primarily high frequencies; and
,a decimation filter coupled to said modulator loop means, said decimation filter for providing lowpass digital filtering and for reducing the modulator loop sample rate, Nf, to said output sample rate f.
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Accused Products
Abstract
A new technology for simultaneously performing the previously separate functions of analog phase-tracking and A/D conversion, represented by a family of systems referred to as delta-sigma frequency-to-digital converters (ΔΣFDCs). Each system uses coarse analog phase measurements, quantization noise shaping, and decimation filtering to perform instantaneous frequency-to-digital conversion. Because they operate on instantaneous frequency in the manner that ΔΣ modulators operate on amplitude, they share many of the benefits enjoyed by ΔΣ modulator-based A/D converters such as reduced analog circuit requirements and amenability to VLSI implementation.
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Citations
22 Claims
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1. A frequency-to-digital converter that operates on an input signal and generates a digital output signal at an output sample-rate, f, comprising:
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a modulator loop means for generating a coarsely quantized digital representation of the frequency modulation of said input signal at a modulator loop sample-rate of Nf where N is a positive number, wherein the component of said digital output signal corresponding to quantization error has a spectrum that occupies primarily high frequencies; and
,a decimation filter coupled to said modulator loop means, said decimation filter for providing lowpass digital filtering and for reducing the modulator loop sample rate, Nf, to said output sample rate f. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method of operating on an input signal of the form:
- ##EQU10## where A is a constant amplitude, fc is a constant carrier frequency, φ
(t) is a frequency modulation signal, and n(t) is undesired noise; and
producing a digital representation of φ
(t);
comprising the steps of;generating a quantized digital representation of φ
(t) with a sample rate greater than the Nyquist rate of φ
(t), said quantized digital representation of φ
(t) having an error associated therewith, wherein said error is predominantly at high frequencies; andlowpass filtering and reducing said sample rate of said quantized digital representation of φ
(t) by providing lowpass digital decimation filtering;where said step of generating comprises the steps of; performing phase measurements of xr (t) relative to a feedback signal; performing quantization on data generated from said phase measurements; and generating said feedback signal using data from said step of quantization. - View Dependent Claims (13, 14)
- ##EQU10## where A is a constant amplitude, fc is a constant carrier frequency, φ
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15. A frequency-to-digital converter for processing a frequency modulated input signal and generating a digital signal representing the frequency modulation of the input signal at an output sample-rate, f, comprising:
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a plurality of modulator loop means each having an input and an output and a feedforward path and a feedback path, wherein each modulator loop means generates a coarsely quantized digital representation of the frequency modulation of said input signal with a sample-rate greater than said output sample-rate, f, and the component of said digital output signal corresponding to quantization error has a spectrum that occupies primarily high frequencies; means for coupling said feedforward path of one of said plurality of modulator loop means to said feedback path of another one of said plurality of modulator loop means; means for coupling said outputs of said plurality of modulator loop means together according to a predetermined functional relationship between said outputs of said plurality of modulator loop means; and a decimation filter coupled to said commonly coupled outputs, said decimation filter for providing lowpass digital filtering and for reducing the sample-rate of said digital outputs of the modulator loops to said output rate f. - View Dependent Claims (16, 17)
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18. A method of frequency-to-digital conversion of a frequency modulated input signal at an output frequency rate of f comprising the steps of:
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generating a coarsely quantized digital signal representing the frequency modulation of said input signal in a plurality of modulator loop circuits, each modulator loop circuit having an input and an output, said coarsely quantized digital signal being generated at a sample rate greater than said output frequency rate of f so that said digital signal has a component corresponding to quantization error with a spectrum which occupies primarily high frequencies; coupling a feedforward signal from one of said plurality of modulator loop circuits to be used as a feedback signal in another one of said plurality of modulator loop circuits; combining output signals from each of said plurality of modulator loop circuits together according to a predetermined functional relationship between said outputs of said plurality of modulator loop circuits; and decimation filtering to said commonly coupled outputs to provide lowpass digital filtering and to reduce said sample rate of said digital output of said modulator loop circuits to said output rate f. - View Dependent Claims (19, 20, 21, 22)
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Specification