Method and apparatus for improved servo signal filtering in read channels

A read channel network within a magnetic storage device which receives a servo signal having a bandwidth BWs and a center frequency Fs, and a user data signal, the read channel network comprising:

• A. a servo signal processor, comprising:
• i. a multiplier having at least a first and a second input and at least one output, wherein a servo signal is received at said first input;
• ii. an oscillator in electrical connection with said multiplier second input and that provided on said second input a reference signal at a selectively chosen frequency F0, where Fo is greater than Fs, wherein said multiplier generates at least one sideband signal representative of said servo signal having a center frequency Fo−Fs or Fo+Fs, in response to receipt of said servo signal and said reference signal;
• iii. a band pass filter having an input in electrical connection with said multiplier output, wherein the bandwidth of said band pass filter is substantially centered at the center frequency of the sideband signal and is at least marginally wider than the bandwidth of said sideband signal to produce a filter signal;
• and
• iv. an envelope detector in electrical connection with an output of said bandpass filter and which detects the envelope of said filtered signal;
• and
• B. a user data processor, comprising:
• i. a lowpass filter which receives the user data signal at an input and produces a filtered user data signal therefrom;
• ii. an A/D converter in electrical connection with the lowpass filter and which receives the filtered user data signal at an input and produces a digital user data signal in response;
• and
• iii. a digital filter which receives said digital user data signal and produces a filtered digital representation of said digital user data signal.

A method for processing a servo signal having bandwidth BWs and a center frequency Fs, in a read channel of a magnetic data storage device having a separate path within the read channel for processing user data and servo data, wherein the read channel includes a multiplier, an oscillator, bandpass filter, and envelope detector, the method comprising the steps of:

• A. multiplying said servo signal with a reference signal generated by the oscillator generator at a frequency Fo, where Fo is greater than Fs, to produce at least one sideband signal representative of the servo signal, said sideband signal having a center frequency Fo−Fs or Fo+Fs;
• B. filtering the sideband signal with the bandpass filter, wherein the band pass filter has a bandwidth at least marginally wider than said bandwidth BWs and is substantially centered about the center frequency of the sideband signal to produce a filtered signal;
• and
• C. detecting the envelope of the filtered signal from said bandpass filtering means.