| 摘要 |
PURPOSE:To detect the speed signal of a driving coil in high efficiency by driving the coil by a constant-current driving circuit, and producing the speed signal by a speed electromotive force generated at the coil by a high input impedance amplifier. CONSTITUTION:Since the equivalent impedance of a constant-current driving circuit 12 becomes infinitive when a driving coil L is driven by the driving circuit 13, a speed electromotive force Ev generated in the coil L appears at a point P1 as it is. The voltage of the point P1 is led by a high input impedance amplifier A2 to assume the same waveform as the driving current waveform of the coil L through an RC low pass filter 14. The output signal of the filter 14 is added at its input voltage Vi in reverse phase by an adder 17. Thus, the applied voltage of the coil L is cancelled to produce only the speed signal of the speed electromotive force by the Ev. |
