JPH01174187A - Band pass filter - Google Patents

Abstract

PURPOSE:To eliminate the blur of color and an S/N of a color signal by lowering a level near the center frequency in the pass band characteristic of a band pass filter passing the color signal. CONSTITUTION:The band pass filter 4 transmitting the color signal consists of a band pass filter 2 whose center frequency is 3.58MHz and a variable circuit 5 varying the level near the center frequency. The variable circuit 5 has a 3.58MHz trap and the inverse trap and either of them is active in response to the switching signal given from the terminal 8 and the trap quantity is controlled by a control signal from a color signal level detector 9 in response to the level of color signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a bandpass filter used in a circuit for processing color signals in video tape recorders (VTRs), color television receivers, and the like.

In VTRs and color television receivers, a comb-shaped filter (1) or the like is used to separate the luminance signal (Y) and color signal (C) from the video signal, as shown in Figure 4. However, since this separated color signal contains a luminance signal component that cannot be separated by the comb filter (1), it is sent to a subsequent stage to ensure completeness of color signal extraction. A band-pass filter (2) is provided in the band-pass filter (2), and after passing the color signal through the band-pass filter (2), a color signal processing circuit (3) is provided.
). Furthermore, during reproduction of the VTR, the reproduced color signal that has been subjected to high frequency conversion is passed through and supplied to the subsequent synthesis circuit. This band pass filter (2) includes, for example, a low pass filter consisting of a coil (Ll) and a capacitor (C+) as shown in the fifth leapfrog, a parallel peaking circuit consisting of the capacitor (C3) and a coil (L2), and a capacitor ( C3), a series peaking circuit consisting of a coil (L3), and a bypass filter consisting of the coil (L2) and a capacitor (C2), and as a whole exhibits a passband characteristic as shown in FIG. Here, the center frequency of the bandpass filter is 3.
It is 58MHz.

By the way, in recent years, technology for improving the image quality of VTRs has made significant progress.For example, the brightness signal band has been expanded to increase the horizontal resolution, and the SN ratio of the brightness signal has been increased. In addition, with regard to color signals, recording current characteristics have been improved and a circuit called side hand emphasis has been installed to improve high-frequency color signal components.As mentioned above, Of these, horizontal resolution is particularly attracting attention, but conversely, as the image quality of the luminance signal has improved, the SN ratio of the color signal and color blurring have become more noticeable.However, the conventional bandpass filters mentioned above , has not helped in any way to solve such problems.

The present invention has been made to solve the above-mentioned problems, and the present invention has been made to solve the above-mentioned problems.
An object of the present invention is to provide a bandpass filter that can improve the ratio.

Means for Solving the Problems In order to achieve the above object, the present invention has a configuration in which a bandpass filter that passes color signals is provided with means for lowering the level near the center frequency in the passband characteristic.

With this configuration, the passband characteristics of the bandpass filter appear to be upward, with both sides raised, and the high-frequency components of the color signal are emphasized, resulting in color blurring. It disappears. Furthermore, the SN ratio of color signals is also improved. still,
As for the characteristics of a bandpass filter, only the center frequency decreases, and the levels on both sides remain the same, so it may be difficult to think that the levels on both sides have increased, but the color signal processing circuit that follows is generally an ACC (automatic color filter). It is normal to have a level control) circuit, and this ACC
Since the circuit controls the level based on the color bust signal, the frequency is 3°58M)lz, which corresponds to the center frequency.
The fact that the level of the color bust signal is suppressed by the bandpass filter means that the level of the entire color signal is increased by that amount by the ACC circuit.

Example Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, (2) is the same band-pass filter part as the conventional one, and the band-pass filter (4) of this embodiment further has a variable circuit (5) that varies the level near the center frequency.
) has been established. This variable circuit (5) is 3.58MHz
It has a trap (6) and an anti-trap (7), one of which operates in response to a switching signal applied from a terminal (8), and a color signal level detector (9). ) The trap amount is controlled according to the color signal level using the control signal detected by the color signal.

FIG. 2 shows a specific example of the configuration of the variable circuit (5).
An operational amplifier (10), a second operational amplifier (11) forming an anti-trap (7), and those operational amplifiers (10)
Feedback circuit (12) that provides common feedback for (11)
1. Second operational amplifier (10)
It has a power supply changeover switch (13), a feedback changeover switch (14), and an output changeover switch (15) for changing over the operation of (11). These switches (13), (14), and (15) are controlled simultaneously by a switching signal (S-). In the illustrated state, the changeover switches (13) (14
) (15) are both set on the first operational amplifier (10) side.

Therefore, in this state, a trap of 3.58M1lz (6
) will work. These switches (13) (1
4) When (15) is switched to the opposite state, it is set on the second operational amplifier (11) side, and the anti-trap (7) of 3.85M) Iz will work. Control signal (Sc)
Controlling the feedback amount (β) by changing the trap amount or anti-trap amount around 3.58 Mtlz. The control mode is such that when the color signal level is high, the trap amount (or anti-trap amount) is decreased, and when the color signal level is low, the trap amount (or anti-trap amount) is increased. be exposed. However, the amount shall be selected to a value that does not cause oscillation due to positive feedback at most.

When using the band pass filter (4) of this embodiment in a VTR, the 3.58 MHz trap (6
) is operated, and during playback, the anti-trap (7) of 3.58 Mtlz is operated. At this time, the switching signal (S) is a switching signal between recording mode and playback mode. When used in a television receiver, only the 3.58 Mtlz playing card (6) should be operated. Good.Furthermore, since the 3.58 MHz anti-trap (7) is not necessary as a bandpass filter exclusively for television receivers, it may be deleted.In that case, the second operational amplifier (II ) and switches (13), (14), and (15) are no longer required, so the configuration becomes extremely simple.

In Fig. 3, the solid line (16) shows the passband characteristic of the bandpass filter (4) when the trap (6) is operated, and the dotted line (17) shows the passband characteristic when the anti-tramp (7) is operated. It shows the passband characteristics. And (E)
indicates the trap amount, and this trump amount corresponds to the emphasis amount when viewed from both side portions (A,) (A2). Similarly, the anti-trap amount in the case of the dotted line (17) corresponds to the Dayen 2 assist amount.

As described above, according to the present invention, the SN ratio and color fringing of color signals can be suitably improved by incorporating an emphasis characteristic into a bandpass filter.

Further, it is possible to eliminate the need for a special sideband emphasis circuit, which has been conventionally used in color signal processing circuits.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a bandpass filter embodying the present invention, FIG. 2 is a circuit diagram of its main parts, and FIG. 3 is a passband characteristic diagram thereof. FIG. 4 is a block diagram showing a partial configuration of a general color signal processing system used in VTRs and the like. FIG. 5 is a block diagram of a conventional bandpass filter, and FIG. 6 is a passband characteristic diagram thereof. (4) - Bandpass filter, (5) - Possible i circuit. (6) −3,581′ lHz trap.

Claims (1)

[Claims] (1) A bandpass filter that passes a color signal, characterized in that a bandpass filter is provided with means for lowering a level near a center frequency in a passband characteristic.