JPS60214695A - Processing circuit of luminance signal - Google Patents

Abstract

PURPOSE:To amplify the input level of a comb-shaped filter, to attenuate an output level, to suppress the crosstalk of a chromaticity signal and to remove sufficiently said signal by utilizing an LPF and a Y-shaped/comb-shaped filter in series. CONSTITUTION:A video signal from an input terminal 1 is adjusted in level by a feedback signal from an AGC detector circuit 4 in an AGC circuit 2, and inputted to an LPF10. An output from the LPF10 is added to a comb-shaped filter 13 through a switch 12 of a comb-shaped filter circuit 100. The filter 13 is constituted of 1hr delay line 35, subtractor amplifiers 50 and 54, an amplifier 51, adder amplifier 52 and an attenuator 53. The input signal from an input terminal 11 is amplified, and its output is attenuated by the attenuator 53, then its band is limited by the LPF10 and the filter 13. The output of the filter 13 is fed back to the circuit 2 from an output terminal 15, processed by an emphasis circuit 5, frequency modulator 6, etc., and the output is made constant and recorded on a magnetic tape 9 together with signals of a chromaticity signal recording system.

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 of a VTR, and a feedback path of an AGC circuit for stabilizing video processing. Regarding.

[Background of the invention]

As is well known, home VTRs are capable of recording and reproducing
Of the generated video signals, completely different signal processing methods are used for luminance signals and chromaticity signals. However, the luminance signal recording circuit requires a filter to remove the chromaticity signal from the input video signal. However, this filter only works for luminance signals.

Especially the NTSC system because it also attenuates high frequency components.

1. The resolution and sharpness may decrease when ;There was a problem. These matters will be explained using FIGS. 1 and 2.

Figure 1 is a block diagram of a conventional luminance signal recording circuit.

It is a diagram. Video signal input from input terminal 1.

is level-controlled by the AGC circuit 2 so that it reaches a certain specified level by 1°. The output of AGC circuit 2 is low.

Pass-pass filter (hereinafter referred to as I, P'F) 3 detects color.

The degree component is removed. Note that this output is AGC times.

In order to control the level of the signal, the signal is fed back through the AGC detection circuit 4°. The output of LPF5 is sent to emphasis circuit 5.
The signal is recorded onto a magnetic tape 9 via a 7M modulator 6, a recording amplifier 7, and a video head 8.

FIG. 2 shows the recording signal frequency distribution of 8 mm video.

The recording band of luminance signals is approximately 0.6MHz compared to conventional VTRs.
Since the width is increased, the bands of I and PF shown in FIG. 1 can be widened. However, if the width is made as wide as it is, the removal of the chromaticity signal will be insufficient, and this will appear as dot interference in the luminance signal and as moiré in the chromaticity signal. Therefore, we expanded the band of the luminance signal and removed the chromaticity signal.
゜In order to remove this interference, a comb filter (
(hereinafter referred to as a Y-shaped comb filter) is required.

It is. Frequency when using a Y-shaped comb filter.

The numerical characteristics are shown in Figure 3.

The conditions for the Y-shaped comb filter are as follows: 1°. These are (1) sufficiently removing the chromaticity signal, and (2) using a comb filter for chromaticity reproduction.

(3) There is no waveform deterioration of the luminance signal, (4) It is easy to integrate into an IC, (5) The chromaticity signal, .

This can be easily removed when using the PAL system, which has a high carrier frequency.

There has never been a Y-shaped comb filter that satisfies the above requirements.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a Y-shaped comb filter that satisfies the above-mentioned conditions in order to secure a recording band for luminance signals and achieve the best image quality.

[Summary of the invention]

The present invention suppresses the crosstalk of chromaticity signals by using an LPF and a Y-shaped comb filter lf1 stacked, and also amplifies the input level of the Y-shaped comb filter and attenuates its output level. Ensure the degree of signal attenuation. Also,
Easy to integrate into IC.

Constructed using addition and subtraction type amplifiers, comb-shaped 1°7f
The extraction of signal components that pass through the router is performed by setting up a simple circuit such as a series LC (LC) wrap outside the IC.

[Embodiments of the invention]

Examples of the luminance signal processing circuit of the present invention will be described below.

・　3　・ I will clarify.

FIG. 4 is a block diagram of the video signal system of the present invention. The recording switches 12 and 24 are arranged as shown in the figure.

First, the luminance signal recording system will be explained. In the figure, a video signal input to an input terminal 1 is level-controlled by an AGC circuit 2 and input to PLFj[]. The signal from which the chromaticity signal component has been removed by the LPFiQ and the comb filter 16 is fed back to the AGC circuit 2 from the terminal 15 via the AGC detection circuit 4.

level control is performed. Therefore, even if the level of the multi-terminal 15 fluctuates due to variations in the gain of the comb-shaped 1 filter 13, the AGC circuit operates to keep this signal at a constant level. The video signal processing in the emphasis circuit 5, frequency modulator 6, etc. is kept constant.

can be converted into The output of frequency modulator 6 is:

A magnetic tape is transmitted through a recording amplifier 7 and a video head 8.

- Recorded in step 9.

Next, the chromaticity signal recording system will be explained. The video signal input to input terminal 1° is passed through switch 24 to 14. .

It is input to a band pass filter (BPF) 25.

Chromaticity subcarrier frequency f,. The chromaticity signal with a band of ±500KHz is extracted by BPF'25 and sent to the ACC circuit 26.
is controlled to a certain level. The chromaticity signal whose level has been controlled to a constant value is passed through a recording chromaticity signal processing circuit 275 and converted to a low range chromaticity subcarrier frequency f by a converter 28 during recording. ±
After being converted to a low frequency of 500KHz, it is input to the LPF29. The output of the LPF 29 is added to the luminance signal in an adder 16, and recorded on a magnetic tape 9 via a recording amplifier 7° and a video head 8.

Next, the chromaticity signal reproduction system will be explained. Switch 12 during playback
, 24 are connected to the opposite side shown. BPF25
and the ACC circuit 26 during recording and playback.

Also, the comb-shaped filter 11st,
.

When recording, it is used as a Y-shaped comb filter (when playing back, V
c is used as a c-shaped comb filter.

In this way, the J-comb filter 3 is constructed.

The 1H delay line is also used.

Low-range chromaticity signals input through the input terminal 21 during playback.

The signal is converted into a high frequency band by the converter 23 during playback and then converted to BPF.
25, the ACC circuit 26, the comb filter 13, and the reproduced chromaticity signal processing circuit 32, and are output to the output terminal 33. Note that 34 is f. This is a carrier generator that generates ±'IJC carriers. - In the configuration described above, the comb filter circuit 1 of the present invention including the comb filter 13
00 will be explained.

As is well known, the basic circuit of a comb filter has the configuration shown in FIG. The same parts as in Figure 4 are the same.

- Signed. In FIG. 5, the switch 12 is in the position shown in the figure during recording, and is reversed during playback.

First, the time of playback will be explained. Input terminal 30 has playback.

A chromaticity signal is input, and this signal is delayed by 1H - line 3
The signal delayed by 5 is subtracted by a subtracter 6B, resulting in a C-shaped filter characteristic, which is output to an output terminal 31.

Next, the Y-shaped filter during recording will be explained. The luminance signal input from the input terminal 11 is added to a signal delayed by the 1H delay line 55 at an adder 37°, and the result is output to the output terminal 15. However, the figure shows the case where the frequency characteristics of the 1H delay line 65 are flat, and the delay line actually used is a glass delay line in the case of a VTR! l12.5-6.
There is also a pass band near 5MHz -) BPF' (Ba
nd Pa5s Filter) characteristics.

Motsu. Therefore, there is no problem when operating as a C-shaped comb filter, but when operating as a Y-shaped comb filter, the configuration shown in FIG. 5 passes through.

A cine capital in which the luminance component in the band is relatively large compared to the signal component at a lower frequency of 1°.

This is the case. Therefore, the configuration shown in FIG. 6 is necessary.

Ru. The same parts as in FIG. 5 are given the same reference numerals and explained.

Part of is omitted. In Fig. 6, the signal input from the input terminal 11° is passed through the LPF 39 and the HPF' (High Pa5sF
ilter) or joins BPF40. BPIl'
The output of 40 is added to a signal delayed by a 1H delay line 65 in an adder 41, and the luminance component of this band is extracted. Then, in the adder 42, it is added to the output of the previous LPF 39.7, and the signal is outputted to the output terminal 15 as a desired signal. If this is done, the above-mentioned inconvenience will not occur. The cutoff frequency of the LPF 39 should be selected so that it is approximately at the lower limit of the passband of the 1H delay line 35 and outside the chromaticity signal band (fSC ± 500KHz.Also, since the 1H delay line 35 has band characteristics, , HP
F or BPF4Q seems unnecessary, but it is a shunt signal on the LPF39 side.

In order to have a complementary relationship, it is necessary.

A certain 0 river Also, in an ideal Y-shaped filter.

is the chromaticity subcarrier frequency f8C and these nfh(n
; integer, fh; horizontal synchronization frequency).

The degree of attenuation in frequency is infinite. but.

In reality, the coupling l between the input and output of the 1H delay line.

For this reason, only about 20 dB of attenuation can be achieved.

Therefore, LPIFlQ in Fig. 4 has an attenuation degree of % f8C.

The characteristic is about 20 dB.

In the configuration shown in FIG. 6, at least the switch circuit 12 is built into the chromaticity signal processing circuit C. Therefore, when operating as a Y-shaped comb filter, the chromaticity signal being recorded is, for example, transferred to the switch circuit.・Crosstalk from roads, etc. is unavoidable.・Accordingly, in order to eliminate the influence of this crosstalk, an amplifier is provided at the output of the BPF 40 in FIG.
Attenuator before 2.

By providing , the crosstalk of chromaticity signals is increased.

It can be attenuated by the amplification variation of the width transducer.

An example of a filter that satisfies the above requirements is shown in FIG. 7. The same parts as in FIG. 6 are marked with the same "-" signal, and a part of the explanation of lf1 is omitted. In the figure, B+-Rs is a resistor, L+ is an inductor, C+ and Cz are capacitors, and B+ is a DC voltage source. During recording, the switch 12 is connected as shown.

The luminance signals inputted through the input terminal 11 are applied to the negative phase input terminal and the positive phase input terminal of the subtraction amplifier 50 through both the resistors R+ and R*, respectively, with values approximately equal to each other by 1°. A trap consisting of an inductor L+ and a capacitor C1 connected in series is connected to the positive phase input terminal side. The trap frequency is set to the chromaticity subcarrier frequency fsc and the 1H delay line 3
The transmission center frequency of 5 or BPF4 in Figure 6 above
Select a frequency near the passing center frequency of 0'. For this reason, the decrease and increase
A signal corresponding to the output of the LPF 39 shown in FIG. 6 is obtained at the positive phase input terminal of the width converter 54. (L+, Cr) There are almost no frequency components higher than the lamp frequency in the case of the NTS, C system. ) On the other hand, subtracting amplifier.

Since the input signal is directly applied to the negative phase input terminal 50, a signal corresponding to the output of the BPF 40 shown in FIG. 6 is obtained at its output terminal. After this signal is amplified by the amplifier circuit 51 for suppressing the crosstalk of the chromaticity signal mentioned above, it is passed through the 1H delay line 35 and the summing amplifier 52 to obtain a Y-shaped comb characteristic. By attenuating this signal with an attenuator 56, crosstalk is suppressed. This output is applied to the negative phase input terminal of the subtraction amplifier 54 via the capacitor C21°.

Here, a voltage source Ff+ is connected to an input terminal 11 via a resistor R5.
A DC voltage equal to is applied. On the other hand, the same signal as the signal at the positive phase input terminal of the subtracting amplifier 50 is applied to the positive phase input terminal. Therefore, at 1°, the output terminal 15 corresponds to the output terminal 15 in FIG.

You can obtain the desired signal and achieve the desired purpose.

By the way, when the circuit connected to the positive phase input terminal of the subtracting amplifier 50 is integrated into an IC, it is desired to have a simple configuration since the external components are elements. Therefore, L+, Cr.

A series trap consisting of In principle, 5 general LPs? However, the frequency characteristics of the circuit connected here should be determined in correlation with the bandpass characteristics of the 1H delay line 32. Therefore, it is desirable that this characteristic be easily adjustable. Inductor L+ as shown in Figure 1117
, if we use a series trap consisting of capacitor C+, we get
Inductor 'L+.

Change the value of capacitor C1 or resistor R2 (.

and R+) to change the sharpness Q.

The characteristics can be easily changed. Naoto l.

For the adjustment of the inductor as shown in Figure 8.

L+, further into the series trap of capacitor C1.

You may also insert a resistor R4 in .

Furthermore, the 1H delay line 32 generally has considerable loss even within the passband. In Figures 8 and 9, this! .

11・ The configuration is such that the summing amplifier 52 compensates for the difference.

is the front stage of the 1H delay line 32, as shown in FIG.

In addition, a preamplifier 55 may be further provided. .

In addition, as shown in FIG. By inserting it into the input side, the attenuator 53 in FIG. 7 may be removed and its attenuation may be supplemented by the subtracting amplifier 54.

Of the configurations described above, the specific circuit diagram of the present invention is shown in the eleventh section.
As shown in the figure. This is the amplifier 50 that subtracts the amplifier 51 in FIG.
The structure is supplemented by

The same parts as in FIG. 7 are given the same reference numerals, and some explanations are omitted. R1 to Ri and Ra-R9 are resistors, 'L1 is an inductor, Cr-Cs is a capacitor, Q+ to Qs are transistors, (1) to (S) are current sources, and (1) is a DC voltage source. The amplification degree of the level input to the comb filter is
The resistance of the resistor Rs and the transistors Ql, Q, and 2 is determined by the resistance, and in this embodiment, the resistance is about 20 dB. resistance R4,
The attenuator 53 shown in FIG. 7 is configured with R7. The DC fluctuation caused by the mode switching of the switch 12 is amplified by a subtraction amplifier consisting of transistors Q@, Qa, etc., and becomes a control signal for the output terminals 15, 5, and AG (: circuit).Therefore, the Y-shaped comb filter After securing the band of
The capacitor CI and the resistance R= are made small. In addition, the above factors and the transistor Q! Considering the Miller effect of , reduce the impedance of the transistor QS.

Therefore, capacitor C2 also needs to be made smaller. ,1
In addition, when the chromaticity subcarrier frequency is high and a comb filter is unnecessary, as in the case of the PAL system, the number of chromaticity subcarriers is small.

At least the trap consisting of inductor L+ and capacitor C1 should be removed. Do it like this.

For example, the input signal of the input terminal 11 is transmitted through the resistor R2 to 1.
.

The signal is amplified by a subtracting amplifier consisting of transistors Qa, Qs, etc., and is output to the output terminal 15. At this time, the output of the subtracting amplifier consisting of transistors Q, +, Qt, etc. becomes zero, so the input signal of transistor Q6 becomes zero.

Therefore, the 1.1 signal input from the input terminal 11 is
The signal is amplified and output to the output terminal 15, thereby achieving the intended purpose.

Furthermore, in FIGS. 7 to 11 showing embodiments of the present invention, the signals that are added to and subtracted from the signals that have passed through the 1H delay line that constitutes the comb-shaped filter are...the signals that have passed through the switch 12. ◇ [Effects of the Invention] As described above, the present invention provides a new structure of the Y-shaped filter circuit used in the luminance recording system of a VTR.

It is intended to provide 1ci The chromaticity signal is improved by amplifying the signal input to the comb filter and attenuating the output.

Lostalk can be suppressed and chromaticity signals can be sufficiently removed.

Moreover, it is a 1H delay line that constitutes a C-shaped comb filter.

Can be used for both. 1-1 In addition, processing of the main signal is increased with an external LC) wrap.

Waveform deterioration can be minimized because only a width transducer is required, making it possible to use PAL.

Since this method can be handled by removing at least this trap, there is an effect that it can be performed with a simple operation when integrated into an IC. ,.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional VTR luminance recording system. Figure 2 is a frequency characteristic diagram of an 8 mm video recording signal. Figure 6 is a characteristic diagram of a comb-shaped filter. Figure 4 is a recording signal processing according to the present invention. Block diagram of the circuit, no. Figure 5 is the principle circuit diagram of the comb-shaped Fu [Ruta], and Figure 6 is the circuit diagram. A block diagram of a comb-shaped filter. Figures 7 to 11 are circuit diagrams showing embodiments of the filter of the present invention. be. 2...AGC circuit 4...AGC detection detection circuit 10...LP? 100...Comb filter circuit diagram 50, 54...Subtraction amplifier 51...Amplifier. 35...1H delay line 52...Summing amplification I. Figure 6 Figure 7 Figure 1O diagram 1 I diagram

Claims (1)

[Scope of Claims] An AGC circuit and an AGC detection circuit that control the level of an input video signal to a constant level, an LPF that limits the band of this video signal, and a band limit. An empha that performs nonlinear processing on the video signal. In a luminance signal processing circuit consisting of a cis circuit and a frequency modulator, from a jl'I delay line and a summing amplifier. A comb-shaped filter circuit is provided that amplifies the input signal of the comb-shaped filter and attenuates its output by 1 degree, and the outputs band-limited by the 8LPF and this comb-shaped filter circuit are A, G.
It is returned to the AGC circuit VCR via the C detection circuit. Shine, which is characterized by level control. degree signal processing circuit. 1゜