Qualcomm Incorporated

Puay Hoe Andrew See

Gurkanwal Singh Sahota

Gary John Ballantyne

Brett Christopher Walker

James Ian Jaffee

Steven M Mollenkopf

A phase modulator faithfully reproduces higher frequency modulation using an offset phase-locked loop (OPLL) without passing excessive noise through an increased bandwidth of the OPLL. A quadrature modulator modulates information from a baseband signal onto a passband IF signal and, after a limiter strips away amplitude variations, the OPLL reproduces the phase modulation on an RF signal. The OPLL introduces a group delay that does not vary linearly with the modulation frequency and that consequently causes distortion when uncompensated. A baseband filter filters the amplitude of the baseband signal and introduces a complementary group delay that compensates for the OPLL group delay and results in a combined group delay of the baseband filter, quadrature modulator, limiter and OPLL that remains substantially constant as modulation frequency varies. Compensating for the OPLL group delay reduces distortion and the spectral energy at offset frequencies from the carrier frequency of the RF signal.

Baseband compensation of an offset phase locked loop

A transmitterconverts a digital baseband signal inputfor transmission by an antennato support multiple communication standards. An over-deviation phase multiplierincreases signal phase deviation by a factor of M. A digital phase modulatorapplies trigonometric lookup tables. A digital intermediate frequency up-converterup-shifts frequencies of desired signal content. First and second digital-to-analog converters (DACs)anduse relatively low-bit operations, which add DAC noise. First and second low pass filtersandapply rejection above frequencies of desired signal content. An analog I/Q modulatorconverts from complex to real signals, adding an unwanted signal spaced from the desired signal content by an intermediate frequency multiple. A limiterreduces amplitude modulated noise. An over-deviation phase dividerdivides signal phase deviation by 1/M to reduce phase modulated noise.

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San Diego, CA, United States of America

Puay Hoe Andrew See