Modified frequency modulation
AssigneeElcomatic Limited
InventorArchibald M. Pettigrew
Life of this patent
Estimating the term…
Abstract
There is described methods and circuitry for decoding modified frequency modulated (MFM) information signals as obtained from rotating magnetic storage devices, such as floppy disks and hard disks used in computers. The novel technique involves twice squaring an information carrying data signal mathematically and without saturation, deriving a clock signal from the twice squared data signal using a phase lock loop and thereafter recovering an information signal from said data signal and clock signal.
Claims18
A method of decoding MFM information comprising the steps of deriving an information-carrying data signal from a recording medium, mathematically squaring without saturation said data signal to provide a squared data signal, mathematically squaring without saturation said squared data signal, passing said twice squared data signal to a phase lock loop to derive a coherent clock signal, halving the frequency of said coherent clock signal, multiplying the half frequency clock signal with said data signal, and recovering an information signal from said multiplied signal.
A method as claimed in any preceding claim and further including the step of delaying said data signal prior to multiplication with said half frequency clock signal.
A circuit for decoding MFM information, said circuit including means for deriving an information-carrying data signal from a recording medium, first squaring means for receiving said data signal and mathematically squaring without saturation said data signal to provide a squared data signal, second squaring means for receiving and mathematically squaring without saturation said squared data signal, a phase lock loop for deriving a coherent clock signal from said twice squared data signal, means for halving the frequency of said coherent clock signal, means for multiplying the half frequency clock signal with said data signal, and means for recovering an information signal from said multiplied signal.
A circuit for decoding MFM information, said circuit including means for deriving an information-carrying data signal from a recording medium, a monostable circuit for receiving said data signal and generating a data pulse train from said data signal, a bandpass filter for filtering said data pulse train, a phase lock loop for deriving a coherent clock signal from said filtered data pulse train, means for halving the frequency of said coherent clock signal, a multiplier for multiplying the half frequency clock signal with the data signal, and means for recovering an information signal from said multiplied signal.
Dependencies are inferred from the claim text.