JPH067650Y2 - Non-standard signal discrimination circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a non-standard signal discriminating circuit used in an IDTV receiver or the like.

(B) Conventional technology In an IDTV receiver, since image quality improvement processing such as scanning conversion is performed by using adjacent two-frame or two-field television signals, the input television signal looks like a broadcast signal. Standard signal according to NTSC signal standard,
It is necessary to determine whether it is a non-standard signal that does not comply with the above standards, such as a reproduction signal of a VTR (video tape recorder), and switch the processing mode in the high image quality processing circuit.

For this reason, for example, in the Proceedings P2-297 of the National Convention of the 70th Anniversary of the Institute of Electronics, Information and Communication Engineers in 1987, as an example of the detection method of the detection signal of the nonstandard signal, color A
What detects the fluctuation of the phase detection output voltage when the non-standard signal of the PC circuit is received is introduced. That is, this method uses the fluctuation of the detected output voltage due to the breakage of the accurate phase inversion of the color burst signal between frames in the non-standard signal.

However, in the above detection circuit, when a change in the phase detection output voltage is detected, it is immediately determined that the signal is a non-standard signal, so a signal on the boundary between the standard signal and the non-standard signal or a temporary non-standard signal is detected. Such a signal is judged to be a standard signal or a non-standard signal and its operation is extremely unstable.

(C) Problems to be solved by the present invention The present invention has been made in view of the above points, and it is an object of the present invention to provide a non-standard signal discriminating circuit that can perform a non-standard signal discriminating operation extremely stably. To aim.

(D) Means for solving the problem In the present invention, a plurality of stages of delay circuits for delaying the detection output of the non-standard signal by at least one field period and an OR circuit using the output of each stage as an input are added. Then, when an output corresponding to the above detection output is obtained from this OR circuit, it is determined to be a non-standard signal.

(E) Action According to the above configuration, if a non-standard detection output is obtained even in one of several field periods, it is determined as a non-standard signal, and therefore the standard signal and the non-standard signal are frequently switched. However, the change cycle of detection becomes long and the detection operation becomes stable.

(F) Embodiment The drawing shows an embodiment of the discrimination circuit of the present invention. In the figure, (1) is a color bust signal (BS) and a color subcarrier signal (C) from a voltage controlled oscillator (VCO).
W), a color detection circuit (2) for detecting a phase difference, a low-pass filter (3), and a color AP including the VCO (4).
It is a C circuit. Further, (5) is an amplification circuit (5) for amplifying the output voltage of the phase detection circuit (2), an absolute value conversion circuit (6) for converting the output into an absolute value, and a constant output voltage set in advance. It is a non-standard signal detection circuit including a voltage comparison circuit (7) for comparing the voltage (Eo). Further, (8) is a four-stage D flip-flop circuit in which the output of the comparison circuit (7) is the D input of the first stage and the vertical synchronizing pulse is the clock input of each stage.
A delay circuit composed of (9), (10), (11), and (12), and (13) is an OR circuit that receives the output of each of these flip-flops. The non-standard signal detection circuit (5) is basically the same as that described in the above-mentioned paper, and therefore when the non-standard signal is input, the output voltage of the phase detection circuit (2) fluctuates greatly. A "high" signal is derived from the voltage comparison circuit (7), and when it is a standard signal, it is "low" in reverse.
Will be output. Therefore, if this comparison output becomes "high" even once in four field periods, that is, if a non-standard signal is detected even once, the output of the OR circuit (13) remains "high" until the next four field periods. Indicates that the condition is maintained and the signal is nonstandard. That is, if the standard signal is not input during the four field period, it is not judged as the standard signal [the output of the OR circuit (13) is "low"].

The non-standard signal detection circuit (5) is not limited to the one using the phase detection output of the color APC circuit as in the above embodiment,
It may be configured to detect whether the frequency of the horizontal sync signal or the vertical sync signal and the frequency of the color burst signal have a specified multiple relationship.

(G) Effect of the device According to the discriminating circuit of the present invention, even if the non-standard detection output frequently changes for some reason, a stable discriminating operation can be performed. Therefore, it can be used for an IDTV receiver. In this case, it is possible to eliminate the unnaturalness of the reproduced image due to the operation mode of the scan conversion circuit or the like being frequently switched in response to the determination operation.

[Brief description of drawings]

The drawing is a block diagram showing an embodiment of the discriminating circuit of the present invention. (5) ... non-standard signal detection circuit, (8) ... delay circuit, (13) ...
… Or circuit.

Claims (1)

[Scope of utility model registration request] 1. A detection circuit for producing an output when an input television signal is a non-standard signal, a plurality of stages of delay circuits for delaying the output of the detection circuit by at least one field period, and each stage of the delay circuits. A non-standard signal discriminating circuit configured to determine that the output is a non-standard signal when an output corresponding to the detection output is obtained from the OR circuit.