| 摘要 |
PURPOSE:To reduce memory quantity by storing a rotation factor required for FFT(fast Fourier transformation) in a memory without overlapping. CONSTITUTION:As aiming at the deviation of a phase between a cos function and a sin function and the symmetric property of positive and negative of these in respect of the rotation factor, only the positive value of the trigonometric function is stored beforehand in the memory 2 without overlapping the rotation factor, and an address (m) in the memory 2 is obtained by an address generation circuit 3 on the basis of the value of the index (k) of the rotation factor, and on the other hand, data obtained from the memory 2 in conformity with this address (m) is sign-inverted selectively by a sign inversion circuit 4. By controlling the operation of the address generation circuit 3 and the sign inversion circuit 4 by a control circuit 7 by inputting a select signal to designate whether the rotation factor intended to obtain is a real part or an imaginary part and the value of the most significant bit of the index (k), a negative value is obtained by sign-inverting a corresponding positive value. |
