Modulators – Frequency modulator
Patent
1991-05-06
1992-05-05
Grimm, Siegfried H.
Modulators
Frequency modulator
332120, 375 44, 455 42, 455110, H03C 340
Patent
active
051111632
ABSTRACT:
A digital FM modulator (10) which functions to modulate a fixed frequency, e.g. RF, reference signal f.sub.r 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 f.sub.s, and converts it into a digital signal S.sub.D comprised of successive digital words representative of a prescribed parameter (e.g. amplitude) of the analog signal v(t) at corresponding, successive sampling times t.sub.i. This digital signal S.sub.D 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 I.sub.A and Q.sub.A components disposed in phase quadrature relation to each other. The DDS output signal components I.sub.A and Q.sub.A are coupled to respective first and second mixers (62, 68) of an I/Q hybrid circuit (59), with the I.sub.A and Q.sub.A DDS output signal components serving to modulate the reference RF carrier signal f.sub.r, which is also coupled to the mixers (62, 68) in phase quadrature, to thereby ultimately produce, after summation of the resultant IF.sub.A and IF.sub.B 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).
REFERENCES:
patent: 4540958 (1985-09-01), Neyens et al.
patent: 4990867 (1991-02-01), Ogura et al.
Denson-Low Wanda K.
Grimm Siegfried H.
Hughes Aircraft Company
Lindeen III Gordon R.
Mitchell Steven M.
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