Digital filter circuit, signal processing device, and digital filter processing method

A digital filter circuit comprising:

• a separating circuit implemented in hardware and configured to separate a first complex-number signal in a frequency domain, into which a complex-number signal in a time domain has been transformed through a Fourier transform, into a second complex-number signal in the frequency domain and a third complex-number signal in the frequency domain, the second complex-number signal corresponding to a real part of the complex-number signal in the time domain, and the third complex-number signal corresponding to an imaginary part of the complex-number signal in the time domain;
• a filter coefficient generating circuit implemented in the hardware and configured to accept inputted first, second, and third input filter coefficients that are complex-numbers, and generating a first frequency-domain filter coefficient that is a complex number from the first input filter coefficient and third input filter coefficients, and generating a second frequency-domain filter coefficient that is a complex number from the second input filter coefficient and the third input filter coefficient;
• a first filter implemented in the hardware and for performing a filtering process on the second complex-number signal with the first frequency-domain filter coefficient and outputting a fourth complex-number signal;
• a second filter implemented in the hardware and for performing a filtering process on the third complex-number signal with the second frequency-domain filter coefficient and outputting a fifth complex-number signal;
• and
• a combining circuit implemented in the hardware and configured to combine the fourth complex-number signal with the fifth complex-number signal and generating a sixth complex-number signal,
• wherein performing filtering by the digital filter circuit in a frequency domain instead of in the time domain reduces circuit size and power consumption.