Patent ID: 8212515

Claim:
A microcomputer which obtains a rotor position signal from a biphase signal delivered by a resolver mounted on an electric motor according to a rotation phase of a rotor relative to a stator, thereby controlling the motor based on the rotor position signal, the microcomputer comprising a digital signal converter which is configured by hardware and converts the biphase signal delivered from the resolver into a digital data position signal, the digital signal converter being mounted on a single chip, wherein the digital signal converter includes: a first multiplier which multiplies a first phase signal delivered from the resolver by a signal shifted in phase by π/2 relative to an excitation signal by which the first phase signal is multiplied; a second multiplier which multiplies a second phase signal delivered from the resolver by a signal in phase with an excitation signal by which the second phase signal is multiplied; an adder which adds results of calculation by the first and second multipliers; a high-pass filter which passes predetermined higher frequencies as a result of addition by the adder, thereby delivering an output signal; and a phase comparison section which compares a phase of the output signal of the high-pass filter with a phase of signal having a frequency twice as high as the excitation signal thereby to obtain data further obtained by counting a phase difference between the compared signals by the counter, thereby delivering the obtained data as a position signal.