Digital FM modulator
First Claim
1. A digital FM modulator, comprising:
- digital converter means for converting an AM analog input signal into a digital signal representative thereof;
digital signal processing means for processing said digital signal;
digital synthesizer means responsive to said processed digital signal for generating first and second variable frequency synthesizer output signals, I1 and Q1, respectively, disposed in phase quadrature relation with each other;
signal generating means for generating a fixed frequency reference signal;
I/Q hybrid circuit means, including;
signal splitter means for splitting said reference signal into first and second reference signal components I2 and Q2, respectively, disposed in phase quadrature relation with each other;
first mixer means for mixing said first reference signal component I2 with said first synthesizer output signal I1, to thereby produce a first intermediate frequency output signal IF1;
second mixer means for mixing said second reference signal component Q2 with said second synthesizer output signal Q1, to thereby produce a second intermediate frequency output signal IF2;
summer means for combining said first intermediate frequency output signal IF1 and said second intermediate frequency output signal IF2, to thereby produce an FM modulator output signal.
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Accused Products
Abstract
A digital FM modulator (10) which functions to modulate a fixed frequency, e.g. RF, reference signal fr with an incoming AM analog signal v(t) by way of utilization of digital signal processing circuitry (14, 18, 22, 26, 28, 38, 48). The digital FM modulator 10 includes a digital encoder, e.g. a codec 14, which samples the incoming analog signal v(t) at a prescribed sampling rate fs, and converts it into a digital signal SD comprised of successive digital words representative of a prescribed parameter (e.g. amplitude) of the analog signal v(t) at corresponding, successive sampling times ti. This digital signal SD is a digital data stream which is subsequently conditioned for input to a direct, digital synthesizer (DDS) (48), which, in response to this input, synthesizes an output signal having IA and QA components disposed in phase quadrature relation to each other. The DDS output signal components IA and QA are coupled to respective first and second mixers (62, 68) of an I/Q hybrid circuit (59), with the IA and QA DDS output signal components serving to modulate the reference RF carrier signal fr, which is also coupled to the mixers (62, 68) in phase quadrature, to thereby ultimately produce, after summation of the resultant IFA and IFB mixer output signals, a modulated FM signal P(t). The modulated FM signal P(t) is essentially equivalent to a modulated FM signal generated by an analog FM modulator, wherein the incoming analog signal v(t) modulates a voltage controlled oscillator (VCO).
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Citations
20 Claims
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1. A digital FM modulator, comprising:
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digital converter means for converting an AM analog input signal into a digital signal representative thereof; digital signal processing means for processing said digital signal; digital synthesizer means responsive to said processed digital signal for generating first and second variable frequency synthesizer output signals, I1 and Q1, respectively, disposed in phase quadrature relation with each other; signal generating means for generating a fixed frequency reference signal; I/Q hybrid circuit means, including; signal splitter means for splitting said reference signal into first and second reference signal components I2 and Q2, respectively, disposed in phase quadrature relation with each other; first mixer means for mixing said first reference signal component I2 with said first synthesizer output signal I1, to thereby produce a first intermediate frequency output signal IF1; second mixer means for mixing said second reference signal component Q2 with said second synthesizer output signal Q1, to thereby produce a second intermediate frequency output signal IF2; summer means for combining said first intermediate frequency output signal IF1 and said second intermediate frequency output signal IF2, to thereby produce an FM modulator output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification