Signal attenuation using a filter-limiter connection with a threshold setting network
AssigneeHewlett-Packard Company
InventorMichael C. Fischer
Life of this patent
Estimating the term…
Abstract
Method and apparatus for recovering a timing reference signal in an optical storage subsystem. The timing reference signal is recovered by passing it through a zonal bandpass filter coupled to a hard limiter, which feeds a phase locked loop that produces the reference signal.
Claims12
A signal attenuating device for an optical medium data storage apparatus having an optical pickup and a phase locked loop, said signal attenuating device comprising:
- a bandpass filter configured to pass specific frequencies of interest and to attenuate signals outside of said specific frequencies;
- and
- an amplitude limiter coupled to an output of said bandpass filter, said amplitude limiter being configured to shape signals at said output of said bandpass filter, said amplitude limiter including:
- (a) a comparator having first and second inputs and an output that is responsive to a difference of signals at said first and second inputs, said first input being coupled to said output of said bandpass filter;
- and
- (b) a threshold setting network connected to said second input of said comparator, said threshold setting network including a capacitance and including a resistance connected to a fixed source of voltage;
- wherein said bandpass filter and said amplitude limiter are connected between said optical pickup and said phase locked loop to define a timing reference signal input to said phase locked loop.
A method of deriving a reference frequency for processing a signal that is responsive to a laser source having a plurality of power levels comprising the steps of:
- filtering said signal through a bandpass filter to attenuate signals outside of a specified frequency band, including determining a shape factor for said specified frequency band, thereby providing a filtered output signal;
- manipulating said filtered output signal to limit amplitudes of said filtered output signal while preserving zero crossings, thereby providing an amplitude limited filtered output signal, said manipulating including generating a variable threshold input signal that is determined by varying the resistance of a resistor connected to a fixed voltage source and in parallel to a capacitor, said manipulating further including determining a difference between said filtered output signal and said variable threshold input signal;
- and
- passing said amplitude limited filtered output signal for use in defining an output of a phase locked loop.
A signal attenuating device for an information storage system having an optical pickup and phase locked loop, said signal attenuating device comprising:
- a bandpass filter enabled to pass a predetermined range of signal frequencies and attenuate signal frequencies outside said predetermined range of signal frequencies, said bandpass filter being connected to receive signals from said optical pickup;
- and
- a signal amplitude limiter coupled to an output of said bandpass filter, said signal amplitude limiter enabled to alter signal amplitudes exceeding predetermined maximum and minimum values, an output of said signal amplitude limiter being connected to said phase locked loop, said signal amplitude limiter comprising:
- (a) a variable threshold network having a variable threshold setting network that includes an output and a parallel connection of a capacitor and a variable resistor, said variable resistor being connected to a fixed voltage source;
- and
- (b) a comparator having a first input, a second input and an output that is a difference of signals of said first input and said second input, said first input being connected to receive a first signal from said bandpass filter, said second input being connected to said output of said variable threshold setting network.
Dependencies are inferred from the claim text.