| 摘要 |
PURPOSE:To increase an S/N ratio greatly by shifting the phase of an input rectangular wave by 90 deg. by connecting low-pass filters in series for conversion from the input rectangular wave to a triangular wave. CONSTITUTION:In order that a pilot signal and a triangular wave VT are completely in phase, namely, in order that a 19kHz rectangular wave is shifted in phase by 90 deg., the wave is shifted in phase by about 87 deg. through a low pass filter LPF1 and further shifted by about 3 deg. through a low-pass filter LPF2, thus converting the rectangular wave into the triangular wave. A cutoff frequency for setting the extent of a phase shift to about 87 deg. is set five times as high as that for obtaning the extent of a 90 deg. phase shift and the extent of signal attenuation is reduced by about 20dB. Further, the low-pass filter LPF2 reduce the extent of signal attenuation by about 6dB, so an S/N ratio is greatly increased. |
