A method and apparatus for producing phase reference signals for use in a
quadrature modulation circuit are disclosed. The quadrature modulation
circuit includes a signal splitter (130), a first and second signal
conditioning circuit (104, 106), a local oscillator (126) and a combiner
(128). The method includes generating a first and second phase reference
signal (111, 113) by the local oscillator. The method also includes
providing a first and second sign information signal (225, 223) to a
corresponding first and second phase modulator (240, 242). Finally, the
method includes modulating the first phase reference signal (111) by the
first phase modulator (240) to produce a first modulated phase reference
signal (131), and modulating the second phase reference signal (113) by
the second phase modulator (242) to produce a second phase modulated
reference signal (133). The phase modulated reference signals (131, 133)
are then amplitude modulated and combined for subsequent transmission.