Error-correction of stored television signals

Details Error-correction of stored television signals Error-correction of stored television signals

1989-08-18

1991-11-19

Shepperd, John W.

Excavating

371 215, G06F 1110, H04N 5907

Patent

active

050671332

DESCRIPTION:

BRIEF SUMMARY
This invention concerns the storage of digital television signals in solid state random access memory chips.
A means for storing digital television signals in a solid state memory is described in co-pending Patent Application No. filed concurrently herwith.
It is known that in the storage of digital data in a random access solid state memory, deterioration of the stored data can occur as a result of failure of a memory cell to store the value of a data bit assigned thereto. Such failures may occur as a result of ambient atomic radiation which may cause a value stored in an individual cell to change in response to bombardment of the corresponding cell with an atomic particle. Normal levels of ambient radiation are such that errors of the kind described are infrequent, but when such an error occurs in a digital television image signal, the result can be a visible blemish in a reproduced picture image.
Accordingly it is an object of the present invention to provide means for overcoming this disadvantage.
The invention provides a method of storing a digital television picture image in a solid-state store, wherein a code is generated from the data contained in each line of the video raster, and a corresponding code value is stored in association with the data relating to each line of the picture signal, the code value being derived from the stored data in such a manner that an error occurring in any bit of the data relating to a given line, following storage thereof, can be detected by re-computing a code value from data retrieved from the store in relation to said line, and comparing the re-computed code value with that originally stored in relation to the same line. By providing that the algorithm utilised in computing the code value will provide not only an indication of an error, but also the location of the bit containing the error, means may be provided for correcting the error in any such data bit before the picture signal is reproduced.
The invention is illustrated by way of example in the accompanying drawings, in which:
FIG. 1 is a block circuit diagram of a circuit for error check code generation, and
FIG. 2 is a similar view of a circuit for error correction.
Referring to the drawings, the circuit of FIG. 1 includes an input 10 for receiving a sampled digital television picture signal and an output 11 for providing to a memory store a composite signal comprising the original picture signal and an accompanying error check code. The input 10 is coupled to the output 11 via two signal paths 12 and 13 that are optionally selectable via an electronic switch 14. the signal path 13 includes a function generator 15, an adder 16 and an accumulator 17, the latter receiving at its input the output of the adder 16 and providing at its output a signal coupled on the one hand to one side of the electronic switch 14 and on the other hand to an input of the adder 16, another input of which receives the output from the function generator 15. In the operation of the circuit of FIG. 1, the electronic switch 14 is arranged to couple the output 11 to the input 10 via the signal path 12 during the transmission of the data bits corresponding to each line of the digital television signal. Between consecutive lines of the signal, the switch 14 is actuated to couple the output 11 to the accumulator 17, so that the value provided at the output of the latter is inserted in the composite signal as an error check code. This code is generated by summing for every byte in the line a function that is provided by the function generator 15 and is the sum of every bit in the byte multiplied by the portion of that bit in the line. The first byte contains bits 1 to 8, the second 9 to 16 and so on. The summing is performed by the adder 16 and accumulator 17. In general the code value provided by the accumulator 17 will occupy about four bytes in the data stream.
In the writing of picture information into a memory store, two modes of operation are available, namely normal mode in which all of the picture data is written and long play in w

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