PURPOSE: To easily make variable a filter characteristic in a software in accordance with the object to be used by mounting a switched capacitor filter, a clock signal oscillator and a microprocessor on the same semiconductor substrate.
CONSTITUTION: A phase comparator 4 takes out a phase difference between a reference signal 1 having a reference phase and a signal 9 to show the number of the rotations of a present motor 8 outputted from a signal processing circuit 64 as an error signal and outputs it to a switched capacitor filter SCF 6. The SCF 6 executes a filter processing and outputs to the inputted error signal and thereafter, the signal outputted from the SCF 6 is impressed to the motor 8. To an MPU 7, a parameter for a filter characteristic from a controller 70 through a data bus 3. Based on the parameter, the MPU 7 controls the SCF 6 and an oscillator 5, changes the filter characteristic of the SCF 6 and always the motor 8 becomes the optimum rotation condition, in accordance with the error signal from the phase comparator 4.
TAKEDA KATSUMI
MATSUNAGA TOSHIHIRO
HITACHI VIDEO ENG