JPS5824071B2 - Comb filter for extracting chromaticity signals from video tape recorders - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a comb filter for extracting chromaticity signals from a video tape recorder (hereinafter referred to as VTR).

The above-mentioned VTR magnetically records a video signal for one field of a television signal on a single magnetization locus inclined with respect to the running direction of the magnetic tape on a magnetic tape.
A helical scan type that reproduces this is also common.

Conventionally, in VTRs and the like having the above-mentioned configuration, 1
A horizontal period (hereinafter referred to as IH) delay line is used. In the recording system, this IH delay line is used as a comb-shaped filter to extract the chromaticity signal except for the luminance signal, and is also used in the playback system. In the system, it is used for demodulating color signals of a VTR using a line sequential method.

Furthermore, in VTRs other than the above-mentioned line-sequential type, it is also used to improve the S/N ratio of chromaticity signals or to prevent crosstalk between adjacent tracks.

Using an IH delay line in both the recording system and the reproducing system has disadvantages in the case of a portable VTR in that it is disadvantageous in terms of space and increases in cost.

In order to eliminate such drawbacks, it is conceivable to switch the IH delay line between recording and reproduction.

In this way, as a VTR that shares a delay line,
Taking the case of the line sequential method as an example, its outline will be explained with reference to FIG.

In the figure, ■ is the luminance signal recording system, ■ is the chromaticity signal recording system, ■ is the luminance signal reproduction system, ■ is the chromaticity signal reproduction system, ■ is the IH delay line, ■ is the E-E system, and H is the video head. be.

Note that 81 to S3 are changeover switches that are electronically switched according to recording and reproducing operations.

During recording, selector switches 81, S2, S3
Both are switched to the solid line side, and among the input signals from the input terminal TIN, the luminance signal is passed through the luminance signal recording system ■, and the chromaticity signal is separated by the comb-shaped fino and evening signals using the IH delay line ■. The signal is mixed with the luminance signal through the luminance signal recording system (2), applied to the video head H, and recorded on the magnetic tape.

During this recording, monitoring is possible through the E-E system (2) directly connected to the input and output ends.

During playback, selector switch S1. Both S2 and S3 are switched to the dashed line side, and among the signals taken out by the video head H, the luminance signal is passed through the luminance signal reproduction system (■).
Further, the chromaticity signal passes through the chromaticity signal reproduction system (2), is processed by the IH delay line (2), is mixed with the luminance signal, and is taken out from the output terminal T out.

As described above, the IH delay line is configured to be switched and shared between the recording system and the reproducing system.

Next, referring to FIG. 2, the overall configuration of the device shown in FIG. 1 will be explained.

First, during recording, the changeover switches S1, S2, and S3, which are electronically switched as described above, are all switched to the solid line side, and S4 is also switched to the solid line side, and E
- Monitoring during recording is possible through the E system 32.

The video human input signal from the input terminal TIN is transmitted to the E-E system 32 via the changeover switch S4, and is also applied to the low-pass filter 1, where only the luminance signal component is separated. taken out.

Although not shown in the drawings, an AGC circuit is added to the luminance signal so that its output remains approximately constant even with changes in the level of the human input signal.

Above low frequency fill. The luminance signal separated by the filter 1 has its high-frequency signal component enhanced by the pre-emphasis circuit 2, is further frequency-modulated by the frequency modulation circuit 3, and then is filtered by the high-pass filter 4 to convert the FM signal generated by the frequency modulation. Of these, the chromaticity signal is described later.

The portion overlapping with the low frequency converted signal is cut and added to the mixing circuit 15.

On the other hand, the above-mentioned video input signal is applied to a bandpass filter 5 and a synchronization signal separation circuit 8.

Although not shown, it corresponds to the above AGC circuit.
An ACC circuit is added.

The video human input signal includes luminance and chromaticity signal components, and first, the chromaticity signal component is separated by a relatively wide band filter 5, and then the changeover switch S1 (
The signal is passed through a comb filter using an IH Taylor line 6 to remove unnecessary components, and its output is applied to a ring modulator 7 via a changeover switch S2 (solid line side).

The output of the bandpass filter 5 has a color subcarrier (3,58M
A chromaticity signal including Hz) is extracted, and this signal is applied to the burst gate circuit 9, and the above-mentioned horizontal synchronization signal separated by the above-mentioned synchronization signal separation circuit 8 drives the above-mentioned burst gate circuit 9, and the above-mentioned color 3,58 in degree signal
Only the burst signal consisting of ME(z) is taken out.

The burst signal is applied to an APC (automatic phase control) circuit 10 to perform continuous wave phase control.

The above-mentioned 3, 58 ME from this APC circuit 10 (
The continuous wave signal of z is applied to the switch circuit 12 and also to the 90° phase shift circuit 11, and the switch circuit 12 switches the signal having a phase difference of 00.90° for each IH to the ring modulator. Added to 7.

The above-mentioned signal having a different phase for each IH from the switch circuit 12 is applied to the ring modulator 7, and the above-mentioned IH signal is
It is mixed with a chromaticity signal applied through a comb filter using an H delay line 6, and the difference is taken, and the chromaticity signal is converted to a low frequency band and line-sequentialized.

The chromaticity signal converted to a low frequency band is frequency-modulated by a frequency modulation circuit 13, and then extracted by a low-pass filter 14 and applied to a mixing circuit 15, where it is mixed with the luminance signal component, It is amplified by the recording amplifier 16 and sent to the video head H via the selector switch S3 (solid line side).
and recorded on magnetic tape.

Next, to explain the operation during playback, selector switch S
1, S2, S3 and S4 are respectively switched to the dashed line side, and the signal taken out by the video head H is first amplified by the reproduction amplifier 17.

The luminance signal component of the output signal of the regenerative amplifier 17 is extracted by a high-pass filter 18, the amplitude is made constant by a limiter circuit 19, and then demodulated by a demodulator 20 to return it to the original signal. Unnecessary carrier wave components are removed by the filter 21 and added to the mixing circuit 31.

On the other hand, the chromaticity signal is extracted by a low-pass filter 22, applied to a demodulator 24 via a limiter circuit 23, and further passed through a low-pass filter 25 to a ring modulator 24 as described above.
Added to 6.

The output signal of the low-pass filter 25 includes a marking pulse as a line color-specific signal created based on the burst signal, and this signal is sent to the marking pulse extraction circuit 2.
7, the indicator pulse extracted by the indicator pulse extraction circuit 27 is applied to the switch circuit 30 for switching control.

A signal from the 3.58 MHz oscillator 28 and a signal that passes through the 90° phase shift circuit 29 are applied to the switch circuit 30, and the indicator pulse causes the switch circuit 30 to shift to 00 phase. , 58 ME (z signal is 90
Switching is performed by switching one of the 0-phase 3.58 MHz signals.

The operation of the reproduction system switch circuit 30 is exactly the same as the operation of the recording system switch circuit 12 described above.

That is, the reproduction system is configured to add a 0° phase signal to the horizontal period modulated by the 00 phase signal in the recording system using the above indicator pulse.

The same is true when switching to a 90° phase signal; in this case, in a horizontal period modulated by a 90° phase signal in the recording system, a 90° phase signal is also added to the reproducing system.

The signal from the switch circuit 30, which switches the signal having a phase of Oo and 90° as described above using the indicator pulse, is applied to the ring modulator 26, where the chromaticity signal is frequency converted and the signal is switched. switch S1
(dotted line side) to the IH delay line 6, and its output is applied to the mixing circuit 31 via the changeover switch S2 (dotted line side), where it is mixed with the luminance signal described above and output to the output terminal. It is taken out from T out.

The present invention provides a comb filter for extracting chromaticity signals of a video tape recorder, which is suitable as the above-mentioned comb filter.

An embodiment of the present invention will be described below with reference to FIG.

FIG. 3 shows an actual circuit of a comb filter using an IH delay line.

In this figure, the level of the chromaticity signal is suitably adjusted by a level adjuster VR from an input terminal IN, and then applied to a transistor Q1 whose emitter is grounded.

The chromaticity signal amplified and inverted by the transistor Q1 is further applied via an IH delay line DL to the emitter of a transistor Q2 whose base is grounded by a capacitor C2.

On the other hand, without passing through the IH delay line DL, the resistor R3
The chromaticity signal is applied to the emitter of the transistor Q2 via a series circuit of the capacitor C1 and the capacitor C1.

Since the human input impedance of the base-grounded transistor Q2 becomes low, the chromaticity signal via the IH delay line DL and the IH delay line DL
The chromaticity signal before IH delay, which is added without going through the IH delay, is added to the emitter of transistor Q2 at the synthesis point O without affecting each signal.

Therefore, the problem that the chromaticity signal via the IH delay line DL is returned to the input terminal via the capacitor C1 and the resistor R3 does not occur.

Further, the input end and output end of the IH delay line DL are matched by a resistor R1 and a resistor R2, respectively, and inductances L1, L2 and I
The frequency characteristics are compensated for by the internal capacitance of the H delay line DL.

In the matched state as described above, the IH-delayed chromaticity signal and the pre-IH-delayed chromaticity signal are combined, amplified by the transistor Q2, and taken out from the output terminal OUT.

Even if the above chromaticity signal contains high-frequency components of the luminance signal, the human-powered chromaticity signal is inverted and IH-delayed, and the human-powered chromaticity signal is added as is, so the high-frequency component of the luminance signal is added. The components are canceled and only the chromaticity signal can be extracted.

As described above, the present invention includes a first transistor Q1 with a common emitter to which a chromaticity signal is supplied, a delay line DL that delays an output signal from the transistor by one horizontal period, and the transistor Q1 and the delay line D.
The above chromaticity signal via L and the resistor R without passing through these first transistors Q1 and delay line DL.
a second transistor Q2 with a common base to which the chromaticity signal via another impedance element such as 3 and a capacitor 01 is input; and a delay line DL that compensates for the frequency characteristics of the signal passing through the delay line. 1, in which the high-frequency component of the luminance signal included in the chromaticity signal is phase-inverted by the first transistor Q1 and delayed by the delay line DL. Since it is configured to be mixed and canceled with that of the previous horizontal period, the second
Since both the chromaticity signal that has passed through the delay line DL and the chromaticity signal that has not passed through the delay line DL are input to the transistor Q2,
These chromaticity signals are input to the second transistor Q2 without affecting each other, thus eliminating problems such as the signal passing through the delay line DL returning to the input terminal of the first transistor Q1 via the impedance element. can.

[Brief explanation of the drawing]

Fig. 1 is a schematic block diagram for explaining the present invention, Fig. 2 is a schematic block diagram for explaining the present invention;
The figure is a block diagram for explaining the present invention, and FIG. 3 is a circuit diagram showing one embodiment of the present invention. Q: the first transistor; Q2: the second transistor;
DL: delay line, R3: resistor, C1: capacitor, Ll, R2: inductance.

Claims (1)

[Claims] 1. A first transistor with a common emitter to which a chromaticity signal is supplied, a delay line that delays an output signal from the transistor by one horizontal period, and a chromaticity signal that is transmitted through the first transistor and the delay line. and a chromaticity signal that passes through another impedance element without going through these first transistors and the delay line, and a second transistor whose base is grounded, and frequency characteristic compensation of the signal that passes through the delay line. means, wherein the high frequency component of the luminance signal included in the chromaticity signal is
A comb filter for extracting a chromaticity signal of a video tape recorder, characterized in that the comb filter is inverted by the first transistor and is mixed with and canceled out by one horizontal period before that which is delayed by the delay line.