Abstract: 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.