Waveform generator for use in IQ modulation
AssigneeFreescale Semiconductor, Inc.
InventorNadim Khlat
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Abstract
A waveform generator for use in IQ modulation in a wireless cellular device having an FM waveform generator (104) that is programmable to generate a desired FM frequency deviation; a digital accumulator (108, 110, 112) to provide phase generation. First and second look-up tables 114 and 116 use the 6 MSBs and the 6 LSBs of 12-bit digital accumulator values to look up phase-space values that are combined in complex multipliers (130, 140), which are re-used from other parts of the circuit. This provides the following advantage(s): Support of both FM and I/Q modulation techniques for constant envelope modulation; low cost implementation; and flexibility to address multimode systems.
Claims11
A waveform generator (100) for use in IQ modulation, comprising:
- digital frequency modulation waveform generator means (104) for generating digital values representative of any of a predetermined range of desired frequency modulation schemes;
- digital accumulator means (108, 110, 112) for accumulating digital values produced by said digital frequency modulation waveform generator means;
- first look-up means for receiving only a most significant group of bits produced by the digital accumulator means and for looking up in a first look-up table (114) phase-space values (cos(φMSB), sin (φMSB)) associated with the received most significant group of bits;
- second look-up means for receiving only a least significant group of bits produced by the digital accumulator means and for looking up in a second look-up table (116) phase-space values (cos(φLSB), sin(φLSB)) associated with the received least significant group of bits;
- and
- combining means (130, 140) for combining the phase-space values produced by the first and second look-up means to produce in-phase and quadrature-phase values (I, Q) for transmission modulation.
A waveform generator (100) for use in IQ modulation, comprising:
- digital frequency modulation waveform generator means (104) for generating digital values representative of any of a predetermined range of desired frequency modulation schemes;
- and
- digital accumulator means (108, 110, 112) for accumulating digital values produced by said digital frequency modulation waveform generator means and for producing values comprising N bits,
- look-up means for receiving only the most significant M bits of values produced by the accumulator means and for looking up in a first look-up table (114) phase-digital space values (cos(φMSB), sin(φMSH)) associated with the received most significant M bits;
- approximating means for receiving only the least significant N–M bits produced by the digital accumulator means and for deriving therefrom phase-space values (cos(φLSB), sin(φLSB)) associated therewith by approximating to unity a cosine value associated therewith and approximating to the value of the least significant N–M bits a sine value associated therewith;
- and
- combining means (130, 140) for combining the phase-space values produced by the look-up means and the approximating means to produce in-phase and quadrature-phase values (I, Q) for transmission modulation.
Dependencies are inferred from the claim text.