Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Reexamination Certificate
1999-01-06
2001-10-16
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
Reexamination Certificate
active
06304071
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to phase detectors and more particularly to phase detectors for determining an error value dependent on the relative phase between a local oscillator signal and an input signal received over a channel having a class of partial response denoted as PR(a, b, b, a).
BACKGROUND OF THE INVENTION
To recover data from noisy channels, such as for example magnetic data carriers having high data densities, it is known to class the write/read channel of the data carrier in accordance with a partial response characteristic which approximates to the frequency response characteristics of the channel, and the arrangement or design of a digital data recovery circuit is selected to optimise data recovery from a channel with that partial response characteristic. As the correct recovery of data is so dependent on how well the channel characteristics are matched by the form of data recovery circuit selected, it is common to provide an equaliser circuit on the input of the data recovery circuit to compensate for any difference between the actual and the approximated channel characteristics.
The data recovery circuit contains a phase-lock loop circuit arrangement which receives an analogue read signal, from the equaliser circuit if there is one, and operates to control an oscillator at the phase and an integer multiple frequency of components of interest of the incoming data stream. Signals generated by this oscillator are used to sample the incoming analogue signal at appropriate sampling points, from which samples data recovery is performed. Correct phase alignment of the oscillator signals and the components of interest of the analogue read signal are critical in performing correct data recovery.
To assist the phase lock loop circuit arrangement in achieving fast initial frequency and phase alignment, the data carrier will usually have one or more regions in which VFO field data has been intentionally written. The VFO field data is a regular data pattern which, when being read, provides an analogue signal which in approximately sinusoidal and periodic in nature. In using these data channels, it is known for the data to be encoded to contain a minimum of two consecutive like bits in the data stream, and the VFO field data may for example comprise a succession of pairs of like data bits.
It is widely appreciated that certain types of optical data carrier channels currently being investigated for development will have a response characteristic approximating that of equation (1).
F(D)=a+bD+bD
2
+aD
3
Eqn. (1)
Here, a and b are constant coefficients and D is a unit delay operator. This type of channel can be referred to as a class of partial response PR(a, b, b, a) channel.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the present invention, a phase detector, for determining an error value dependent on the relative phase between a local oscillator signal and an input signal received over a PR (a, b, b, a) channel, which received signal is sampled at regular intervals, which intervals are dependent upon the local oscillator signal, comprises:
means to select an ideal sample value for a sampling point;
means to determine a difference value corresponding to a difference between the ideal sample value and the actual sample value for that sampling point;
means to determine the sense of change to the ideal sample value from a ideal sample value for a preceding sampling point;
a means to determine the sense of change to the ideal sample value for a preceding sampling point from a ideal sample value for a twice preceding sampling point; and
a means responsive to at least one of said senses of change so determined and to said difference value to provide said error value.
The sign of the difference value may be operated on in dependence on at least one of the senses of change so determined. Alternatively or in addition, the difference between the ideal sample value and the actual sample value for the preceding sampling point may be used to provide said error value.
The difference value may be provided as the error value only at a sample time when both of said senses of change are determined to be the same and each non-zero. Here, the phase detector may further comprise a means responsive when said senses of change are different or at least one of said senses of change is zero to provide a preceding error value as the error value. In this case, the phase detector may further comprise a means responsive when in a track mode and when said senses of change are different or at least one of said senses of change is zero to provide a predetermined fraction of a preceding error value as the error value. Said predetermined fraction may be one half.
Preferably, the magnitude of the error value is equal to the magnitude of the difference value.
In accordance with a second aspect of the present invention, a method, for determining an error value dependent on the relative phase between a local oscillator signal and an input signal received over a PR(a, b, b, a) channel, which signal is sampled at regular intervals which are dependent upon the local oscillator signal, comprises:
selecting an ideal sample value for a sampling point;
determining a difference value corresponding to a difference between the ideal sample value and the actual sample value for a sampling point;
determining the sense of change to the ideal sample value from a ideal sample value for a preceding sampling point;
determining the sense of change to the ideal sample value for a preceding sampling point from a ideal sample value for a twice preceding sampling point; and
providing said error value dependent on said difference value and at least one of said senses of change so determined.
Here, the sign of the difference value may be operated on in dependence on at least one of the senses of change so determined. In either case, the difference between the ideal sample value and the actual sample value at the preceding sampling point may be used to provide said error value.
Advantageously, the difference value is provided as the error value only when both of said senses of change are determined to be the same and each non-zero for a sampling point. Here, the method may further comprise providing a preceding error value as the error value when said senses of change are different or at least one of said senses of change is zero. In this case, the method may still further comprise providing a predetermined fraction of a preceding error value as the error value when in a track mode and when said senses of change are different or at least one of said senses of change is zero. Said predetermined fraction may be one half.
In accordance with a third aspect of the present invention, a phase-locked loop incorporates any of the above phase detectors.
REFERENCES:
patent: 4620147 (1986-10-01), Niki
patent: 5038096 (1991-08-01), Obie et al.
patent: 5990673 (1999-11-01), Forsberg
Popplewell Andrew
Williams Stephen
Kerveros J
Metjahic Safet
NeoMagic Corp.
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