Resolver digital converter

A resolver digital converter that converts a detection signal that is an analog signal output from a resolver that detects rotation of a rotor into a signal of a digital angle, the resolver digital converter comprising:

• an analog-to-digital converter that converts a resolver sine value signal and a resolver cosine value signal, which are the detection signals, and an excitation signal of the resolver, which is an analog signal, into digital signals;
• a conversion unit that converts the signal of the digital angle into a sine value signal and a cosine value signal;
• a multiplication unit that calculates a first multiplication value signal by multiplying the resolver sine value signal converted into the digital signal by the analog-to-digital converter and the cosine value signal of the digital angle together and calculates a second multiplication value signal by multiplying the resolver cosine value signal converted into the digital signal by the analog-to-digital converter and the cosine value signal of the digital angle together;
• a subtraction unit that calculates a subtraction value signal by subtracting the second multiplication value signal from the first multiplication value signal;
• a synchronous detection unit that performs synchronous detection of the subtraction value signal by using the excitation signal and outputs a detection signal acquired through the synchronous detection;
• a control unit that adjusts the digital angle such that the detection signal is zero;
• a band pass processing unit that is disposed between the analog-to-digital converter and the multiplication unit and performs band pass processing, in which only a signal of a predetermined band out of the digital signal is passed, with a period that is shorter than a sampling period of the analog-to-digital converter;
• and
• a correction unit that sets gain correction values based on a maximum value and a minimum value of each one of digital signals of the resolver sine value signal and the resolver cosine value signal that have passed the band pass processing unit, corrects gains of the digital signals of the resolver sine value signal and the resolver cosine value signal by using the gain correction values, and outputs the digital signals to the multiplication unit.