JPS6312616Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image quality correction circuit in a television receiver.

Generally, in order to increase the sharpness of an image, a preshoot or an overshoot is applied to parts where the level of the video signal suddenly changes to emphasize the outline parts. In this case, there are two methods: one that provides only overshoot, and one that provides both preshoot and overshoot, but I feel that the latter provides better sharpness in terms of visual characteristics. Overshoot can be easily added using emitter peaking in a video amplification circuit, but the following methods are available for adding preshoot. The first method is a second-order differential method, which includes a low-pass circuit that passes the video signal and a high-pass circuit that emphasizes contours that performs second-order differentiation of the video signal, and combines the outputs of both circuits and converts the output into a video signal. and overshoot. The second method is to use a video intermediate frequency amplification circuit to correct the group delay time and add a preshoot, and a video amplification circuit to add an overshoot. The first method requires a low-pass circuit, an edge-enhancing high-pass circuit, and a synthesis circuit, and the circuit is complex and has a large number of parts. In the second method, the group delay time is changed using the video intermediate frequency amplification circuit, so
Care must be taken not to affect the phase of the CHROMA circuit. Furthermore, when a peak AGC circuit is used, the design becomes complicated as the influence on the AGC voltage and the synchronization signal also have pre-cuts, which must be taken into consideration.

Thirdly, there is the use of delay circuits. FIG. 1 shows the frequency characteristics of three types of delay circuits A, B, and C, FIG. 2 shows the rectangular wave characteristics, and FIG. 3 shows the group delay characteristics. Delay circuit A provides sufficient attenuation to the carrier color signal component (3.58MHz) as shown in Figure 1a, but the group delay time characteristic becomes wavy as shown in Figure 3a. This results in linking. Delay circuits B and C have no or only slight linking, as shown in Figure 2b and c.
Since 3.58MHz is not attenuated as shown in Fig. 1b and c, it is necessary to provide a separate trap circuit. Fourth
The figure shows a delay circuit that can attenuate a specific frequency like delay circuit A, where D ₁ is a delay element and R ₀ is a matching resistor. c is resistance R ₁ , R ₂ , coil L ₁ , capacitor
A trap circuit consisting of C ₁ is connected in parallel, d is a resistor R ₃ ,
A trap circuit consisting of R ₄ , coil L ₂ and capacitor C ₂ is connected in series. However, as described above, it is difficult to satisfy both the preshoot and overshoot characteristics with such a configuration, so a second-order differentiator circuit is provided separately. Therefore, there is a drawback that the circuit configuration becomes complicated.

In view of the above-mentioned points, the present invention provides an image correction circuit that applies a preshoot using a delay circuit with a trap that attenuates a specific frequency, and applies an overshoot using emitter peaking or the like using a video amplification circuit connected to the delay circuit. It is.

FIG. 5 is a connection diagram showing an embodiment of the present invention. 1 is a video signal input terminal, R ₅ and R ₆ are matching resistors, 2 is a delay circuit with a trap for the carrier color signal component (3.58MHz), 3 is a video amplification circuit, 4 is an emitter peaking circuit, and 5 is an emitter peaking circuit. It is an output terminal. The video signal input to input terminal 1 is sent to delay circuit 2 with trap.
A precipitate is added at the emitter peaking circuit 4, and an overshoot is added at the emitter peaking circuit 4, and the signal is output to the output terminal 5. FIG. 6 shows an embodiment of the delay circuit 2 with a trap, which includes a coil L ₃ and a capacitor.
_C3 constitutes a trap circuit, and coils _L4 to _L7 and capacitors _C4 to _L7 constitute a delay circuit. Also the 7th
The figure shows an example of an emitter peaking circuit, where TR is a transistor, VR is a variable resistor, and resistor R ₈ , coil L ₈ , and capacitor C ₈ constitute the peaking circuit.

FIGS. 8, 9, and 10 are characteristic diagrams showing the frequency characteristics, rectangular wave characteristics, and group delay characteristics of the trap-equipped delay circuit 2, respectively. Figures 8e and f show cases with different trap characteristics, and Figures 10g and h,
i indicates the case where the frequency at which the maximum group delay occurs is different. The width of the pre-cut can be changed by changing the ratio of frequency components in which the group delay time advances, and the size of the pre-cut can be changed by changing the advance time. Also, the frequency at which the group delay time begins to advance is set to be higher than 0.5MHz so that the delay time is appropriate in relation to the chroma signal. As for the group delay characteristics, the maximum group delay time and the frequency that provides it are appropriately selected as shown in Fig. 10g, h, and i according to the overall frequency characteristics and the characteristics of the emitter peaking circuit shown in Fig. 7. .

As described above, according to the present invention, a preshoot is provided by a delay circuit that attenuates a specific frequency, and an overshoot is provided by a video amplification circuit cascaded to the delay circuit. Therefore, the configuration of each circuit is simple, and at the same time, design is facilitated because other circuits are not affected. That is, the width and magnitude of the precut are determined by selecting the frequency of the lead phase of the group delay time of the trapped delay circuit and setting the lead time. The width and size of the overshoot is adjusted using an emitter peaking circuit. Furthermore, since an element having such a function can be constituted by an IC, and a trap circuit, a delay circuit, and an image correction circuit can be integrated into one, it is useful for integration such as reducing the number of pins of the IC. In addition, according to the present invention, the carrier color signal component is attenuated by the delay circuit, so a signal that does not include the carrier color signal component is input to the video amplification circuit, and the corrected video signal is sharp and has no color interference. will be removed.

[Brief explanation of the drawing]

FIG. 1 is a frequency characteristic diagram of the delay circuit, FIG. 2 is a rectangular wave characteristic diagram thereof, and FIG. 3 is a group delay characteristic diagram thereof.
Figure 4 shows the conventional trap circuit and delay circuit.
5 is a connection diagram of one embodiment of the present invention; FIG. 6 is a connection diagram showing an example of the configuration of a delay circuit with a trap; FIG. 7 is a connection diagram of an emitter peaking circuit; 8, 9, and 10 are characteristic diagrams showing the frequency characteristics, rectangular wave response, and group delay characteristics of the trap-equipped delay circuit according to the present invention, respectively. 2...delay circuit with trap, 3...video amplification circuit, 4...emitter peaking circuit.

Claims (1)

[Claims for Utility Model Registration] The frequency component of 3.58MHz, which is the carrier color signal component, is particularly attenuated, and its group delay time is approximately
The phase lead starts from 0.5MHz, the phase lead increases monotonically as the frequency increases, reaches the maximum phase lead at 1.5 to 3MHz, and then the phase lead decreases monotonically.A video signal is supplied as input, and the output is An image quality correction circuit comprising: a delay circuit that obtains a pre-shot video signal; and a video amplification circuit that is cascade-connected to the delay circuit and applies an overshoot to the output video signal of the delay circuit. .