fig3 a and the rectangular wave of fig3 b results in the waveform as illustrated in fig3 c which shifts sides from vertices to the next vertices of the triangular wave upward or downward fig1 illustrates another method of generating the modulation waveform indicated by the solid lines in fig2 a fig1 a shows a pure triangular wave as shown in fig3 a fig1 b shows a rectangular wave for an offset which has transition points at the same timing as the vertices of the triangular wave although the rectangular wave of fig3 b has a fixed signal level with its polarization reversed at the transition points the rectangular wave of fig1 b has its signal level changed at the transition points without the polarization reversal accordingly adding the triangular wave of fig1 a and the rectangular wave of fig1 b results in the waveform as illustrated in fig1 c which shifts sides from vertices to the next vertices of the triangular wave upward or downward in accordance with the signal levels fig1 illustrates still another method of generating the modulation waveform indicated by the solid lines in fig2 a fig1 a shows a pure triangular wave as fig3 a fig1 b shows a rectangular wave for an offset which has the transition points at the same timing as the vertices of the triangular wave but has the opposite polarity to that of fig3 b specifically the rectangular wave in fig1 b has the negative polarity in regions in which the rectangular wave in fig3 b has the positive polarity and has the positive polarity in regions in which the rectangular wave in fig3 b has the negative polarity thus adding the triangular wave of fig1 a and the rectangular wave of fig1 b results in the waveform which.