| 摘要 |
PURPOSE:To obtain a sinusoidal wave stable with high harmonic attenuation, by processing a step waveform through the combination with a Miller integrator and plurality of CR filters where the phase is operated in a stable region. CONSTITUTION:Two digital signals outputted from FFs 7, 8 in a step waveform generating circuit are synthesized via resistors R1, R2 and become a signal of symmetrical step waveform. This signal is inputted to a Miller integrator consisting of an operational amplifier 10, the resistors R1, R2 and a capacitor C1, where harmonics are eliminated. The signal of step waveform eliminated with the harmonics is given to an LPF connecting CR filters 11, 12, and the harmonics are further eliminated. The time constant of the CR of the filters 11, 12 is selected so that the phase change amount is present near 0 deg. or 90 deg. at the cut-off frequency of the LPF, and the change in the amount of phase is less against the frequency change. The output of the LPF is fed back to an inverting terminal of the amplifier 10. Since the phase lead of the Miller integrator is 90 deg., the feedback of 0 deg. can be performed. |
