Patent ID: 7146518

Claim:
A filter circuit for a read channel of a storage device in which a cutoff frequency can automatically be set comprising: a low-pass filter wherein the delay time between an input signal and an output signal and cut-off frequency changes corresponding to a control current; a time measuring circuit, which inputs a reference clocking signal, the input signal and the output signal and measures the delay time as a pulse number of the reference clocking signal; a set value changing circuit that either increases or decreases a set value corresponding to a cycle of the input signal and outputs it; a first storage circuit, which, when the pulse number of the reference clocking signal measured by the time measuring circuit reaches a first value, stores the set value output from the set value changing circuit as a first set value; a computing circuit, which obtains a mean value of the first set value stored in the first storage circuit and the set value output from the set value changing circuit; a selective output circuit, which inputs both the mean value output from the computing circuit and the set value output from the set value changing circuit, outputs the mean value when the pulse number of the reference clocking signal measured by the time measuring circuit reaches a second value being greater than the first value, and otherwise, outputs the set value output from the set value changing circuit; and a current supply circuit, which supplies the control current corresponding to either the mean value or the set value output from the selective output circuit to the low-pass filter; wherein the mean value, which is output from the selective output circuit when the pulse number of the reference clocking signal is the second value, is the average of the first set value stored in the first storage circuit and a second set value, which is output from the set value changing circuit when the pulse number of the reference clocking signal is the second value, and the control current is set to a value that corresponds to the value output from the selective output circuit to control a cutoff frequency thereof.