| 摘要 |
PURPOSE:To obtain a digital signal without influence of switching noise, by generating the start signal, which starts A/D conversion, while avoiding the rise or fall time of switching pulses of an electric power source circuit. CONSTITUTION:Analogue signal A1 input to chopper circuit 1 is chopped according to chopper pulses 32 from photo coupler 33, and signal 11 with switching noise superposed is input to synchronous rectifying circuit 2, and signal 22 subjected to rectification smoothing according to synchronizing pulses 31 is applied to sample hold circuit 5. The input signal voltage of circuit 5 is held at the fall of sampling hold signal 85 from control circuit 8. Signal 85 is synchronized with the rise or the fall of switching pulses 43 and 44 according to A/D conversion command signal 84. By A/D conversion start signal 86 synchronized with the rise of signal 85 and avoiding the rise and the fall of pulses 43 and 44, output signal 51 of circuit 5 is digitized by A/D converter 6. Thus, the influence of noise at a switching pulse switching time is eliminated. |
