The VCO 1444 receives the output of the frequency modulator 1442 and generates two output signals G and H. In which, G is a triangle wave, and H is a pulse train having the same frequency as the triangle wave G. The VCO 1444 and part of the outputs of the phase-shift generator 1445 commonly decide the phase angles and frequencies of the four output signals I, J, K, and L. In which, the phase-shift