Apparatus for providing a carrier signal with two digital data streams I-Q modulated thereon

Abstract

A digital I-Q modulator provides an analog signal at a desired frequency .omega..sub.1 with in-phase I and quadrature-phase Q modulation sidebands provided responsive to different associated ones of in-phase I and quadrature-phase Q digital data streams, each having the same number N of data bits. A multiplexer alternatingly selects a different one of the data streams to provide a first N-bit-wide data signal during each of a successive multiplicity of time intervals of duration T essentially equal to the reciprocal of the carrier signal frequency .omega..sub.1. The bits of the data signal are inverted to provide another data signal during every other one of a multiplicity of inversion time intervals of duration T/2, with each commencing at one of the beginning and midpoint of each time interval T. A single digital-to-analog converter (DAC) uses the sequentially inverted data stream to provide an analog signal having an amplitude substantially established by the digital value of the second data signal during each of another multiplicity of conversion time intervals of duration T/4, each commencing at one of the beginning and midpoint of each inversion time interval T/2. A bandpass filter, having a center frequency substantially equal to the carrier signal frequency F and a bandpass of at least twice the baseband signal bandwidth of the digital data streams effectively removes all frequency components except those of the desired modulation envelopes at the desired carrier frequency.

Dependencies are inferred from the claim text.