U.S. Philips Corporation

Robertus W Groen

Henri Cloetens

Antonius H Akkermans

Johannes C Van Lier

Cornelis A De Jonge

Lawrence M Schwartz

A phase locked loop includes a capture aid circuit to pull the frequency of the oscillator towards the bit frequency of a data signal HF.sub.in consisting of pulses of variable lengths, each length being an integral multiple of a single bit basic length unit. The capture aid circuit includes a pulse length detector for measuring and rounding pulse length to the nearest integral number of basic length units, and determining the difference (.DELTA.RL) between the measured and rounded length value (RL). For small frequency deviations the rounding error (.DELTA.RL) signal is used as a frequency deviation control signal for increasing or decreasing the oscillator frequency. For larger frequency deviations the minimum pulse length will be either more or less than a predetermined number of length units. That is detected by supplying the rounded pulse length signal (RL) signal to a pulse length decoder which determines the presence of pulses having a minimum length below the predetermined number of units or the absence of pulses having such minimum length. From signals indicative of those conditions further control signals are derived in a frequency deviation detector, which further control signals adjust the oscillator frequency so as to bring the frequency deviation within the range in which the rounding error (.DELTA.RL) signal can be used to precisely adjust the oscillator frequency to the bit frequency of the data signal.

Phase locked loop with frequency deviation detector and decoder circuit

An information track on a record carrier (2) is read by a read head which includes detectors producing detection signals (IA, IB, IC and ID) which correspond to the information pattern on the track. The respective detection signals are converted by analog-to-digital converters (16a, 16b, 16c and 16d) into respective series of n-bit digital signal values (ua, ub, uc and ud). From such signal values a data signal (SD) is derived which is representative of the information being read. The signal values are also applied to respective cascade arrangements of a quantizing circuit (21a, 21b, 21c and 21d) and a decimating filter (22a, 22b, 22c and 22d), which convert them into respective series of signal values (va, vb, vc and vd) which represent only the low frequency portion of the information in the detection signals produced by the read head and include control information relating to tracking by the read head. Those series of signal values are supplied to a microprocessor which derives therefrom control signals (Sr, Sf) for controlling the read head to maintain accurate tracking.

Apparatus for reading an information pattern from a record carrier and

A read and/or write device for a record carrier having tracks which extend substantially parallel to each other. A read and/or write head for scanning the tracks is moved by a positioning system in a direction transverse to the tracks. During such movement a counter derives the number of tracks traversed per unit time from the number of reference level crossings of a periodic signal V.sub.sp having a frequency corresponding to the track crossing frequency. Counting of spurious level crossings is inhibited by blocking the counter during a blocking interval (tbl) following each level crossing which is counted. The speed of the read and/or write head is controlled on the basis of the counted level crossings.

Read and/or write device

Optical scanning apparatus which includes an A/D converter control circuit for matching the conversion range of an A/D converter to the range of an analog signal produced by a photo-sensitive detector in response to radiation originating from a radiation source such as a laser. The converter produces a binary overflow signal which signifies whether the analog signal is within or above the conversion range of the converter. Depending on the binary value of the overflow signal, a control signal generator produces either an increasing or decreasing control signal which is returned in a feedback loop to the radiation source to control the radiation intensity or to the converter to adjust its conversion range.

Optical scanning apparatus with control circuit for optimizing the

The invention relates to a video-disc player in which by controlling a pivotal mirror rapid jumps over a large number of tracks can be made substantially within the field-blanking interval. In order to minimize the picture disturbance the jump is always started at the instant at which the duration of the remaining period until just before the address code within the next field blanking interval is equal to the anticipated duration of the jump to be performed in particular by measuring the time which has elapsed since the previous read-out of an address code.

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Eindhoven, Netherlands

Robertus W Groen