JP2557375B2 - Field discriminating circuit of television receiver - Google Patents

Description

Description: [Object of the invention] (Field of industrial application) The present invention relates to a television receiver, and more particularly to a field discrimination circuit of a television receiver using a liquid crystal device.

(Prior Art) Interlaced scanning is performed in broadcasting systems such as NTSC (National Television System Committee).
In a conventional receiver using a cathode ray tube, no particular field discrimination is required. However, since a television receiver using a liquid crystal device has a matrix structure, when a display corresponding to interlaced scanning is attempted, the scanning electrode groups selected for each field alternate with each other, so that field discrimination is not possible. You will need it. Then, if the technology of PLL (Phase-Locked Loops) is applied here, sufficient operation can be expected, but if the number of scanning lines or the scanning frequency changes, adjustment or resetting is not necessary. it is obvious.

In addition, normally, in the liquid crystal device, in order to prevent device deterioration, the polarity of the drive voltage is inverted every frame and AC drive is performed. At this time, the field identification is wrong,
If the discrimination signals continuously indicate the same field, the voltages of the same polarity are applied again to the liquid crystals corresponding to the pixels on the same scanning electrode group, which is not preferable. Further, if it is determined that the fields are always the same, every other field is displayed, and this must be avoided. When the received signal contains noise and the temporal positional relationship between the vertical sync signal and the horizontal sync signal is unstable, the field is erroneously or cannot be distinguished.
However, even in such a case, the field discrimination signal needs to change periodically for the above reason.

(Problems to be Solved by the Invention) As described above, in the television receiver using the liquid crystal device, the received signal contains noise and the temporal positional relationship between the vertical synchronizing signal and the horizontal synchronizing signal is Even when unstable, the field discrimination signal needs to change periodically. Further, it is desirable to operate even when the number of scanning lines or the scanning frequency changes.

An object of the present invention is to provide a simple field discriminating circuit that satisfies such a condition.

[Configuration of the Invention] (Means for Solving the Problems) It is detected for each field whether it is an odd field or an even field from the temporal positional relationship between the vertical synchronizing signal and the horizontal synchronizing signal, that is, the vertical synchronizing signal is input. Field detection circuit detects the field detection result only when the vertical sync signal and the horizontal sync signal are detected temporally each time, and when the odd field and the even field are alternately detected a plurality of times in succession. The output of the field discriminating circuit is inverted when it is not continuously detected. That is, if the previous output indicates an odd field, the signal indicating an even field is used, and if the previous output indicates an even field, it is output from the signal field determination circuit indicating an odd field.

(Working) Use the detected field signal only if the field is estimated to be correctly detected, ie if the odd and even fields are detected alternately, otherwise it is estimated from the previous state Since the field signal is used, a correct field discrimination output can be expected even if an error sometimes occurs in the field signal detected every time the vertical synchronization signal is input due to noise contained in the received signal. Further, since there is no part depending on the number of scanning lines, it is possible to cope with a video signal having a different number of scanning lines without any change in the field estimation unit.

(Example) Hereinafter, the details of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the field discriminating circuit of the present invention. In the figure, a field detection unit (10) is a part that detects whether the field following the vertical synchronization signal is an odd field or an even field each time the vertical synchronization signal is input, and outputs (field detection signal ) Is established at the back porch of the vertical sync signal. The field estimation unit (20) estimates and determines whether the field following the vertical synchronization signal is an odd field or an even field based on the field detection signal output from the field detection unit (10) for each field. The state is updated at the leading edge of the vertical sync signal each time the vertical sync signal is input. In the field estimation section (20), the storage section 1 (21) is a section for storing the output signal (field detection signal) of the field detection section (10) for a plurality of fields, and in this example, for two fields. The storage unit 2 (22) stores the output of the field estimation unit (20), and the gate circuit 1 (23) stores the field in the storage unit 2 (22) according to the field detection signal and the stored field detection signal. This is the part that stores the odd number. That is, only when the field detection signals are alternately different in the order in which they are detected, a signal obtained by inverting the even and odd of the latest detection signal is output, and in other cases, the output of the currently stored field estimation unit (20) is output. This is a part for storing a signal obtained by inverting even and odd. Here, the reason why the latest field detection signal is inverted is that the output of the field estimation unit (20) is delayed by one time with respect to the output of the field detection unit (10). It takes advantage of the alternating appearance of.

FIG. 2 shows the field detector (10) used in this embodiment.
It is a figure showing an example of. In the figure, the extraction unit (11) is a unit for extracting a vertical synchronization signal from the composite synchronization signal, and extracts the vertical synchronization signal delayed by the output pulse width of the retrievable monostable multivibrator (12) from the input signal. Output. The pulse width of the multivibrator (12) must be longer than the sum of the width of the equivalent pulse and the width of the serration, and shorter than the half of the period of the horizontal sync signal minus the width of the serration. Don't The delay unit (13) delays the extracted vertical synchronizing signal until the end of the back porch of the vertical synchronizing signal, and the detecting unit (14) uses the trailing edge of the delayed vertical synchronizing signal as a reference to determine the next horizontal synchronizing signal. Is a part that determines the length of time until is input and detects whether the field following the vertical synchronization signal is an odd field or an even field. The pulse width of the monostable multivibrator (15) included in the detector (14) is 2 times the period of the horizontal sync signal.
It must be longer than one-half and shorter than the period of the horizontal synchronizing signal.

With this configuration, even if an error sometimes occurs in the field signal detected each time the vertical synchronizing signal is input due to noise included in the received signal, the field discrimination circuit is referred to by referring to the field detection signals of a plurality of fields. Since the output of is determined, the correct field discrimination output can be expected. Also, since there is no part that depends on the number of scanning lines,
It is possible to cope with video signals with different numbers of scanning lines without changing the field estimation unit.

When the field detection timing is different from the above case, the field detection signal may be used without being inverted so that the gate circuit 1 (23) can correctly estimate the field. Also, the storage unit 2 (22)
In the above, the number of fields of the field detection signal to be stored depends on the probability of erroneous field detection and is preferably determined by experiment.

EFFECTS OF THE INVENTION The present invention can expect a correct field discrimination output even when a received signal contains noise, and since there is no portion depending on the number of scanning lines, an image with a different number of scanning lines can be obtained. The signal can also be dealt with without any change in the field estimation unit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a view showing details of a field detecting section used in the present invention. (10) …… Field detection unit (20) …… Field estimation unit

Claims (1)

(57) [Claims] 1. A field discriminating circuit of a television receiver which performs 2: 1 interlacing, wherein the field discriminating circuit separates a vertical synchronizing signal from a composite synchronizing signal input and generates an even and odd field detecting signal. And a field estimation unit that estimates a field from the field detection signal, wherein the field estimation unit captures field detection signals for a plurality of fields output from the field detection unit at a timing of the vertical synchronization signal. One storage unit, a gate circuit for comparing the field detection signal with the signal incorporated in the first storage unit, a second storage unit for storing the output of the gate circuit and outputting the output at the timing of the vertical synchronization signal. A storage unit, and an output signal of the second storage unit is input to the gate circuit. , The gate circuit outputs the field detection signal to the second storage unit only when the even and odd field detection signals are alternately taken into the first storage unit a plurality of times in succession to detect even and odd fields. A field discriminating circuit for a television receiver, which inverts the output of the second storage unit and outputs the inverted signal to the second storage unit when signals are not alternately captured.