Infinite impulse response filter circuit and magnetic disk drive

摘要

Embodiments in accordance with the present invention provide an infinite impulse response (IIR) filter circuit which can operate stably even when the coefficients are adaptively changed. The IIR filter circuit in accordance with an embodiment of the present invention has transfer function coefficients that are adaptively changed. Wherein using a Nth-order polynomial A(z) and a polynomial B(z) whose order is not higher than N, the transfer function is defined by $L\left(z\right)=\frac{B\left(z\right)}{A\left(z\right)};$ $\mathrm{where}$ $\prod _{i=0}^{-1}\left(z^2+1-2k_{i}z\right)=1$ is also defined. The polynomial A(z) is transformed to make the term of the Nth power of z equal to 1. If the order of the polynomial A(z) is even, the polynomial A(z) is determined so as to satisfy the condition: $A\left(z\right)=\frac{1}{1+l}\left(\prod _{i=0}^{N/2-1}\left(z^2+1-2k_{2i}z\right)+l\left(z^2-1\right)\prod _{i=0}^{N/2-2}\left(z^2+1-2k_{2i+1}z\right)\right)$ If the order N is odd, the polynomial A(z) is determined so as to satisfy the condition: $A\left(z\right)=\frac{1}{1+l}\left(\left(z+1\right)\prod _{i=0}^{\left(N-1\right)/2-1}\left(z^2+1-2k_{2i}z\right)+l\left(z-1\right)\prod _{i=0}^{\left(N-1\right)/2-1}\left(z^2+1-2k_{2i+1}z\right)\right)$ where l and k_i (i=0, 1, 2 , , , ) are real numbers.