US 7,548,593 B2
Baseband compensation of an offset phase locked loop
Puay Hoe Andrew See, San Diego, Calif. (US); Gary John Ballantyne, Christchurch (New Zealand); James Jaffee, Solana Beach, Calif. (US); and Gurkanwal Kamal Sahota, San Diego, Calif. (US)
Assigned to QUALCOMM Incorporated, San Diego, Calif. (US)
Filed on Sep. 15, 2005, as Appl. No. 11/228,090.
Prior Publication US 2007/0058750 A1, Mar. 15, 2007
Int. Cl. H03C 3/00 (2006.01)
U.S. Cl. 375—302  [375/296; 375/295; 455/73; 455/91] 30 Claims
OG exemplary drawing
 
1. A method comprising:
phase modulating a filtered baseband signal with a quadrature modulator to generate a passband signal, wherein the passband signal has an amplitude and a phase;
limiting the amplitude of the passband signal with a limiter to generate a limited passband signal;
filtering the limited passband signal with a phase-locked loop (PLL) to generate an output signal and thereby introducing a PLL group delay; filtering a baseband signal with a baseband filter to generate the filtered baseband signal, wherein the baseband filter introduces a baseband-filter group delay, and wherein the baseband- filter group delay compensates for the PLL group delay; wherein the output signal is used by a polar transmitter to generate a transmitted signal, wherein the transmitted signal exhibits an amount of spectral energy at an offset frequency, and wherein the baseband-filter group delay compensates for the PLL group delay such that the amount of spectral energy at the offset frequency is reduced; and further wherein the passband signal has a modulation frequency, wherein the baseband-filter group delay has a maximum value when the modulation frequency is zero Hertz, wherein the PLL group delay has a maximum value when the modulation frequency is a first value, and wherein the maximum value of the baseband-filter group delay is approximately equal to the maximum value of the PLL group delay.