The invention relates to a signal source (S) which comprises a local oscillator (5) for generating a reference frequency signal fo. The signal source comprises: a frequency divider by N (6) connected to the local oscillator (5) and delivering two quadratic square-wave signals (Id, Qd) at a frequency fo/N,N being equal to 2 or 4.times.n, and n being an integer number, and a multiphase filter (7) which supplies two sinusoidal quadratic signals (Is, Qs) at a frequency equal to mfo/N on the basis of the quadratic signals (Id, Qd) issued by the frequency divider, m being an odd number. The invention finds its application in direct frequency conversion circuits and transmission circuits used in the field of telecommunication.
