Patent ID: 7702012

Claim:
An infinite impulse response filter circuit whose transfer function's coefficients 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 ⁡ ( z ) = B ⁡ ( z ) A ⁡ ( z ) where ∏ i = 0 - 1 ⁢ ⁢ ( z 2 + 1 - 2 ⁢ k i ⁢ z ) = 1 when 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 ⁡ ( z ) = 1 1 + l ⁢ ( ∏ i = 0 N / 2 - 1 ⁢ ⁢ ( z 2 + 1 - 2 ⁢ k 2 ⁢ i ⁢ z ) + l ⁡ ( z 2 - 1 ) ⁢ ∏ i = 0 N / 2 - 2 ⁢ ⁢ ( z 2 + 1 - 2 ⁢ k 2 ⁢ i + 1 ⁢ z ) ) ; ⁢ and if the order N is odd, the polynomial A(z) is determined so as to satisfy the condition A ⁡ ( z ) = ⁢ 1 1 + l ⁢ ⁢ ( ( z + 1 ) ⁢ ∏ i = 0 ( N - 1 ) / 2 - 1 ⁢ ⁢ ( z 2 + 1 - 2 ⁢ k 2 ⁢ i ⁢ z ) + l ⁡ ( z - 1 ) ⁢ ∏ i = 0 ( N - 1 ) / 2 - 1 ⁢ ⁢ ( z 2 + 1 - 2 ⁢ k 2 ⁢ i + 1 ⁢ z ) ) wherein l and k i (i=0, 1, 2,,,) are real numbers; wherein the infinite impulse response filter circuit is in communication with a voice coil motor to control a position of a magnetic head actuator relative to a magnetic recording medium.