JPS59105792A - Processing circuit of luminance signal - Google Patents

Abstract

PURPOSE:To improve both image resolution and sharpness by putting an LPF on an Y-shaped filter to delete the chrominance signal and therefore to secure satisfactorily the band of the luminance signal and at the same time using addition/subtraction type amplifiers which can be easily converted into ICs to constitute the circuits around a comb-shaped filter. CONSTITUTION:The signals supplied through an input terminal 21 are applied to a negative phase input terminal and a positive phase input terminal of a subtraction amplifier 22 via resistances R1 and R2 having approximately equal values to each other. A trap having a series connection of L1 and C1 is connected to the positive phase input terminal side. Then a signal equivalent to the output of an LPF15 is obtained at the positive phase input terminal of the amplifier 22; while a signal equivalent to the output of a BPF16 is obtained at the output terminal of the amplifier 22 since the input signal is applied directly to the negative phase input terminal of the amplifier 22 respectively. The signal is applied to the negative phase input terminal of a subtraction amplifier 25 through a 1H delay line 23, a Y-shaped/comb-shaped filter consisting of an addition amplifier 24 and a pass capacitor C2. Here the DC voltage equal to the terminal 21 is applied is applied via a voltage source E1 and a resistance R3. While the signal of the positive phase input terminal of the amplifier 22 is applied to the positive phase input terminal of the amplifier 25.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a comb-shaped filter circuit for separating a video luminance signal in a luminance signal recording circuit 1% of a VTR.

[Prior art]

As is well known, in home VTRs, completely different signal processing power methods are used for luminance signals and chromaticity signals among video signals to be recorded and reproduced. Therefore, the luminance signal recording circuit requires a filter to remove one chromaticity signal from the input video signal. However, since this filter also attenuates the high-frequency components of the luminance signal, there is a problem in that resolution and sharpness are lowered, especially in the case of the NTSC power type. These matters will be explained using FIGS. 1 and 2.

FIG. 1 is a block diagram of a conventional luminance signal recording circuit. A video signal inputted from an input terminal 1 is level-controlled by an AGC circuit 2 so that it has a certain predetermined magnitude. Furthermore, this level system a'f! r: To do this, this output is AGC
It is fed back via the detection circuit 5. The output of the AGC circuit 2 is passed through a low pass filter (hereinafter referred to as LPP) 41C to remove its chromaticity signal component, and then sent to an emphasis circuit 5, an FMi adjuster 6. The data is recorded onto a magnetic tape 9 via a recording amplifier 7 and a video head 8.

The frequency characteristics of the rabbit LPF'4 will be explained using FIG. 2. In the same figure, (a) is for the TSCS force type, and Φ) is for the PAL force type. Generally, in this type of LPF, the degree of attenuation at the chromaticity subcarrier frequency fsc is 60
It is desirable to have about 4 obB. This frequency is N
The frequency is approximately 3.58 MHz for the TSC method, and approximately 4.45 MHz for the PAL power method.

Therefore, it is common to use an inductive M-type LC filter (or a combination of M-type LC filters) having a trap at this frequency. In this case the cutoff frequency (
-5dB frequency) is approximately 2.8MHz in NTSC,
Select approximately 3.5MHz for PAL. Of course, it is possible to lower the cutoff frequency while leaving the trap frequency as is, but this would result in a high-order and complex filter and increase the delay time, which is not desirable.

By the way, the resolution of Mari's picture on a home VTR is 250.
It is hoped that there will be more than a TV book.

To achieve this, a signal band of 5.1 MHz or more is required.

In the above example, the LPF band is 3.5 MHz for PAL power type, so there is no problem, but for NTSC power type, it is 2.5 MHz.
．． One problem is that it is not possible to obtain sufficient resolution and sharpness because it does not have 8MHz L.

[Purpose of the invention]

The purpose of the present invention is to provide a one-shot means for solving the above-mentioned lack of resolution and sharpness in the NTSC output system, and in particular, it is easy to integrate into an integrated circuit (hereinafter referred to as an IC), and its characteristics can be set and The present invention is intended to provide a luminance signal processing circuit that is easy to change and can be easily changed using external components.

[Summary of the invention]

In the present invention, the above purpose! In order to achieve this, by removing the chromaticity signal using an LPF, a Y-shaped comb filter, and yal'm, a sufficient band for the luminance signal can be secured, and the circuit around the comb filter can be easily integrated into an IC. It is constructed using an addition/subtraction type amplifier, and extraction of signal components that pass through a comb-shaped filter is performed by setting a simple circuit outside the IC, such as a Layer stone array (LC) wrap.

[Embodiments of the invention]

Next, a detailed explanation of the present invention will be given. First, the necessary conditions for implementing the present invention will be described using the drawings.

First, we need a Y-shaped filter.

Only when recording signals based on NTSC power type, PA
Since it is not necessary in cases such as the L method, it is possible to remove this comb-shaped filter characteristic and make it a through characteristic by a simple change such as removing an external element from the IC.
,j.

Second, a comb-shaped filter! Configuring IH (horizontal synchronization period)
The bandwidth of the delay line must also be considered. As you know,
The Y-shaped filter has the configuration shown in FIG. 6, and receives an input signal from an input terminal 10 and a signal delayed by a January delay line 11.

The adder 12 adds the sum and outputs the result to the output terminal 13. However, this figure is a principle circuit diagram when the frequency characteristic of the 1H delay line 11 is flat. The delay line actually used is V
In the case of TR, it is a glass delay line and has a frequency of 2.5 to 6.5 MHz.
BPF with a passing band nearby (Band Pa5s F
ter)no characteristics omotsu. Therefore, if the configuration shown in FIG. 5 is used as it is, the luminance signal component in this passband will be relatively large compared to the signal component at a lower frequency, which is disadvantageous. Therefore, the configuration shown in FIG. 4 is necessary.

In the figure, the signal input from the input terminal 14 is LP
F15 and HPF with approximately the same cutoff frequency
Or join BPF16. The output of 16 is this YIB
The signal delayed by the delay line 17 is added by the adder 18, and the luminance signal component of this band is extracted. and adder 19
This signal is added to the output of the previous LPF 15 and outputted to the output terminal 20 as a desired signal. If this is done, the above-mentioned inconvenience will not occur. The cutoff frequency of the L P F15 is approximately the lower limit of the passband of the 1H delay line 17, and the chromaticity signal band (fsc±500KHz)
You should choose one that is outside of the . Also.

Since the 1H delay line 17 has a bandpass characteristic, the HPF or BPF 16 seems unnecessary, but K is still necessary in order to have a complementary relationship with the shunt signal on the LPF 15 side.

Thirdly, the filter 15 shown in FIG. I hope that i6 can be done with something simple. Generally, this kind of thing is an IC filter, and since it is a part other than an IC, I want it to be simple.

Fourthly, it is desirable that the circuits surrounding the comb filter be integrated into ICs, such as simple addition-subtraction circuits.

An embodiment of the present invention which satisfies the above-mentioned requirements is shown in FIG. In the figure, 21 is an input terminal, 22-25 is a subtracting amplifier, 25 is a 1H delay line, 24 is a summing amplifier, 26 is an output terminal, L is a resistor, L is an inductor, 't-Ct
is a capacitor and E is a voltage source. The signal inputted from the input terminal 21 is applied to the negative phase input terminal and the positive phase input terminal of the subtracting amplifier 22, respectively, through y equal resistors and wires. A trap formed by series connection of beams C and C is connected to the positive phase input terminal side. The trap frequency is set to the chromaticity subcarrier frequency fsc or 1H delay line 2.
Passing center frequency of 6 or BPF16 of Fig. 4 of the rabbit
Select around the center frequency of the pass. For this reason, the subtraction amplifier 22
A signal corresponding to the output of the LPF 15 in FIG. 4 is obtained at the positive phase input terminal of the LPF 15 in FIG.

(The frequency components higher than the trap frequency of L, ,C, are
Especially in the case of the NTSC system, there are almost no such cases. )-force, the input signal is directly applied to the negative phase input terminal of the subtracting amplifier 22, so that a signal corresponding to the output of the BPF 16 in FIG. 4 is obtained at its output terminal.

This signal passes through a January delay line 26, a Y-shaped filter consisting of a summing amplifier 24, a bypass capacitor C2, and is applied to an anti-phase input terminal of a subtracting amplifier 25. Here, voltage source E7,
A DC voltage equal to that of the input terminal 21 is applied via the resistive island. On the other hand, the signal from the positive phase input terminal of the rabbit subtracting amplifier 22 is applied to the positive phase input terminal of the subtracting amplifier 25 . Therefore, a signal corresponding to the output terminal 20 in FIG. 4 is obtained at the output terminal 26, and the desired purpose can be achieved.

Next, it will be explained that the embodiment of FIG. 5 satisfies the above-mentioned structural requirements. First of all, when a comb-shaped filter is not required, as in the case of PAL power type recording, it can be easily removed to obtain a through characteristic. For that purpose, at least.

It is sufficient to remove the trap consisting of C3. In this way, the output of the subtracting amplifier 22 becomes zero, and the output of the subtracting amplifier 22 becomes zero.
Since the input on the negative phase input terminal side of No. 5 also becomes zero, the input terminal 21
The signal appears at the output terminal 26 as it is. Of course, in this case, the comb-shaped filter consisting of the 1H delay line 26 and summing amplifier 24 may be removed and one end of the bypass capacitor C2 may be connected to the output of the subtracting amplifier 22, and this bypass capacitor C1 may also be removed and the subtracting amplifier The output of 22 may be used as an oven.

Second, LPF'15 and BPF16 shown in Figure 4 earlier
It is shared by a combination of the series traps R, , C, and the subtracting amplifier 22.degree. 25, and can be realized with an extremely simple configuration. Furthermore, the complementarity between the LPF 15 and the BPF 16 can be completely compensated for. If it is an IC, the external parts will be parts.
, C, are just two elements.

Third, the circuit is composed of addition/subtraction amplifiers, and is extremely easy to integrate into an IC.

From the above, it can be seen that the embodiment shown in FIG. 5 satisfies all of the above-mentioned requirements.

Furthermore, the advantage of the configuration shown in FIG. be able to.

In a VTR, there is an FM modulator at the subsequent stage, and since the magnitude of the luminance signal is directly related to the FM frequency deviation, it is important to keep it at a constant value.

Of course, its size does not change even if the trap consisting of L, and C is removed. Second, by switching between the 1H delay line 26 and the m-arithmetic amplifier 24 during recording and reproduction, it is possible to configure a C-shaped comb filter for passing the main chromaticity signal.

Therefore, the 1H delay line and the like can be effectively shared between the luminance system and the chromaticity system.

By the way, as a circuit connected to the positive phase input terminal of the subtraction amplifier 22, a series trap consisting of L, , C, was adopted.

In principle, a general LPF may be used, but another reason for using a series trap will be described here.

As mentioned above, the frequency characteristics of the circuit connected here are 1H
It should be determined based on the correlation with the bandpass characteristics of the delay line 25. Therefore, it is desirable that this characteristic be easy to adjust. If we use a series trap consisting of ,C, as shown in Figure 5, we can change the sharpness Q by shaking the combination of false values of L1 or by changing the value of resistor R2 (and R,).

Characteristics can be easily changed. For this adjustment, as shown in Fig. 6, in series traps C,
Furthermore, a resistor R4 may be included, which is within the scope of the present invention.

As another means, only a capacitor or a series circuit of a capacitor and a resistor may be used.

Also, the January delay line 26 is generally within the passband as well.

There are considerable losses. In FIGS. 5 and 6, the configuration is such that this is compensated for by the summing amplifier 24.

As shown in FIG. 7, a preamplifier 27 may be further provided before the 1H delay line 26.

In an ideal Y-shaped filter, the chromaticity subcarrier frequency fsc and its nfy (n: integer, fH
:The degree of attenuation at frequencies separated by the horizontal synchronization frequency is infinite. However, in reality, the degree of attenuation is only about 20 dB due to coupling between the input and output of the 1H delay line. Therefore, an LPF with an attenuation of about 10 to 20 dB at fsc is connected in series with the comb filter circuit shown in Figs.
It is necessary to enter An example of the characteristics of this LPF is shown in FIG. fsc in NTSC system (5,58MHz)
By setting the attenuation degree to 20 dB, the cut-off frequency is set to 3
~3.1 MHz, and the cutoff frequency can be made higher than that of the conventional example shown in FIG. 2(a).

FIG. 9 shows the overall frequency characteristics of this LPF and the comb filter circuit. In other words, the attenuation degree at fsc is 40
dB and have sufficient attenuation even for chromaticity signal components that exist at a distance of nfH from the chromaticity signal component, the cutoff frequency for the luminance signal component can be increased to sMHz or higher. It can be seen that the band can be made wider than in the case of the example, which contributes to improving the resolution and sharpness of the VTR.

〔Effect of the invention〕

As described above, the present invention provides a new configuration of a Y-shaped filter used in a brightness recording system of a VTR.

This improvement in resolution and sharpness can be realized with a circuit that can be easily integrated into an IC, and the necessary external components can be as simple as a single LC@column toshitrap. Furthermore, this external connection, which must be changed depending on the delay line, allows easy adjustment of filter characteristics. Furthermore, when the comb-shaped filter characteristic is not required, such as when recording PAL power type signals, this external attachment has the effect of changing to the through characteristic by an extremely simple operation such as removing the filter.

Furthermore, the output level of the comb-shaped filter circuit is held at an arbitrary constant value, and this value does not change even if the filter is removed, so that the frequency shift of the recorded FM signal can be kept constant. Another advantage is that the 1H delay line and the like can be easily used in common with the C-shaped and square-shaped filters used in Umasuya.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional VTR luminance recording system, Figure 2 is a conventional filter characteristic diagram, Figure 6 is a circuit diagram of the principle of a comb filter, and Figure 4 is a diagram of a comb filter used in the present invention. Block diagram, Figures 5 to 7 are circuit diagrams showing embodiments of the present invention,
FIG. 8 is a characteristic diagram of the filter used in the present invention, and FIG. 9 is a characteristic diagram including the comb-shaped filter according to the present invention. 22・25...Subtraction amplifier 24...Summing amplifier 25...January delay line 1st? Figure 2 (Q,)
(b) f (+Tsukuda Z)
f, M, -
12) 3rd (¥) 1 Figure 4 Figure 5 Figure 7 Figure 9 (!1

Claims (1)

[Claims] The input video signal is applied to the in-phase and anti-phase input terminals of the first differential amplifier through first and second resistors of approximately equal size, and the in-phase input terminal is connected to a trap circuit or a trap circuit consisting of an LC@column circuit. It is grounded through a circuit such as a capacitor that removes signals near the video chromaticity frequency band, and is simultaneously connected to the common-mode input terminal of the second differential amplifier, and the output of the first differential amplifier is is connected to the anti-phase input terminal of the second differential amplifier via a Y-shaped filter consisting of at least a one-month delay line and a summing amplifier, and the output of the second differential amplifier is connected to the negative phase input terminal of the second differential amplifier. A brightness signal processing circuit for a device such as a magnetic recording/playback device, characterized in that it is configured to output a video signal.