Level-locked loop: a technique for broadband quadrature signal generation

A method for precise wideband quadrature signal generation is presented. A divide-by-2 stage forms an adjustable phase quadrature signal generator. Its output phase error is converted to an error signal, which feeds back to the quadrature signal generator through an integrator, to correct the output phase difference. Using this method, a phase accuracy better than 0.5/spl deg/ is achieved over 40 MHz to 500 MHz of output frequency without any external tuning. The loop compensates for any circuit and layout mismatches, is not sensitive to distorted input LO signals, and has no inherent high frequency limitation.