Modulators – Phase shift keying modulator or quadrature amplitude modulator
Patent
1994-10-07
1995-12-19
Grimm, Siegfried H.
Modulators
Phase shift keying modulator or quadrature amplitude modulator
329308, 329357, 348639, 348642, 348727, 348641, 375261, 375298, 375301, 375321, 375324, H03C 160, H03D 124, H04L 2736, H04L 2738
Patent
active
054771994
ABSTRACT:
A synchronous detector for demodulating and decoding a digital data signal modulated either according to a vestigial sideband or a quadrature amplitude modulation scheme is based upon the principle of recognizing that a vestigial sideband signal may be regarded and treated as an offset-keyed QAM signal. The detector comprises a tuner for tuning to a center frequency symmetrically displaced within the transmitted digital data signal frequency spectrum and a decoder circuit selectively operating to reconstruct the transmitted digital data stream according to the duration of a transmitted data symbol. A related method of demodulating and decoding a modulated digital data stream comprises analogous steps of tuning to a center carrier frequency and selectively switching between in phase and quadrature arms of the demodulator such that the switch resides in one position or the other for a duration equal to half the duration of a transmitted data symbol. A related modulator for modulating a digital data signal either according to a vestigial sideband or quadrature amplitude modulation scheme comprises a switch for selectively switching an input digital data signal between real and imaginary arms and a modulator for modulating at center frequency. In one modulator embodiment, a noise cancellation circuit may be coupled between the real and imaginary arms.
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Grimm Siegfried H.
Scientific-Atlanta, Inc.
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