JPS647551B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an interpolation multiplex signal separation circuit, and particularly
This invention relates to a separation circuit that separates a video signal into a luminance signal and a color signal in the NTSC color television system.

In the NTSC color television system, the color signal is interpolated and multiplexed in the form of a carrier signal onto the high frequency portion of the luminance signal. For this reason, unless the luminance signal and color signal are completely separated using a bandpass filter or the like, they will interfere with each other and degrade the image quality.

Normally, if the color signal is simply extracted from the video signal using a bandpass filter centered around the carrier frequency of the color signal, the high frequency components of the luminance signal contained in this signal will become color noise and cause cross color interference. cause. Furthermore, if the carrier color signal remains in the high frequency component of the luminance signal, dot interference will occur.

Conventionally, in order to reduce these interferences, the transmitting side lowers the high-frequency components of luminance, and the receiver's luminance signal amplification system lowers the high-frequency amplification, but both of these methods result in a decrease in resolution. cannot be said to be the optimal method.

Recently, research has been conducted to remove these interferences using comb filters that utilize ultrasonic delay lines.
As shown in Fig. 1, a C-type filter delays the video signal input from the input terminal 1 by one horizontal scanning time by a 1H delay line 2, combines it with the direct signals from the bypass circuits 3 and 4, and obtains a difference signal between the two. A circuit has been developed that extracts a color signal from the output of Y-type filter 5 and extracts a luminance signal from the output of Y-type filter 6, which obtains a sum signal of both.

According to this circuit, a video signal is converted into a color signal and a luminance signal by a combination of a C-type filter with the characteristics shown in FIG. 2 and a Y-type filter with the characteristics shown in FIG. 3 (comb filter). can be separated into

On the other hand, in order for a glass delay line to operate well, it is generally necessary to insert an anti-resonant coil in parallel to the input/output transducer, which cuts out the low and high frequencies of the glass delay line. Shows bandpass characteristics. Therefore, if the passband of the glass delay line is centered around the frequency band of the chrominance signal, the low-frequency components of the luminance signal will be blocked in the circuit shown in Figure 1 above, so a separate low-pass filter is provided. It is necessary to mix it into the luminance signal output shown in FIG.

However, in such a mixing circuit, it is difficult to accurately phase match the signals, and because the frequency characteristics are not flat, ghost-like ringing appears on the screen, especially due to the transient response of the ultrasonic delay line.
Preventing this ringing requires a more complicated circuit, which increases costs and has not yet been put to practical use.

In addition, as shown in FIG. 3 of Utility Model Application Publication No. 50-157839 and its explanation, the input converter of delay element DL ₂
A comb filter is also known in which an input signal is applied to _T11 through a variable resistor _R26 , and the tap voltage of this variable resistor _R26 is input to an inductance _L22 of an adder.

However, in the above-mentioned known example, since the input transducer T ₁₁ is connected in parallel with the inductance L ₂₁ and the resistor R ₂₅ , the delayed output and the direct signal are not complementary, and therefore the output of the combining circuit is It won't be flat.

An object of the present invention is to provide a separation circuit that can effectively separate the interpolation multiplexed signal as described above.

As shown in the block diagram of FIG. 4, the present invention separates the interpolated multiplexed signal from the signal power source 11 into a direct signal and a delayed signal input to the ultrasonic solid-state delay line 12, and the delay line signal that has passed through the delay line. and the direct signal in a synthesis circuit to obtain a sum signal and a difference signal, an anti-resonant coil 16 is connected in parallel to the input transducer 13 of the delay line to form a resonant circuit, and this resonant circuit A voltage divider load 14 is connected in series with the voltage divider load 14 and an interpolation multiplex signal is applied to both ends of the voltage divider load 14, and an interpolation multiplex signal is applied to both ends of the voltage divider. In the interpolation multiplex signal separation circuit which gives a complementary relationship to the delayed signal that has passed through the output transducer 12, the signal at both ends of the voltage dividing load 14 is sent to the middle tap of the anti-resonant coil of the output transducer 15. This is characterized in that the voltage is applied through an emitter follower type level adjustment circuit as shown in the figure.

Next, specific examples of the present invention will be described.

Figure 5 shows color television video signal input 21.
In this embodiment of the circuit of the present invention, which separates the signal into a color signal output CC and a luminance signal output YY, a capacitor 28 connects the midpoint 27 of an anti-resonator coil 26 inserted in parallel to the input transducer 23 of the delay line. It is grounded and constitutes an inductive M type circuit, with a partial voltage load of 2
The voltage applied to 4 is conducted through a level adjustment circuit 20 to a midpoint 30 of an antiresonant coil 29 of an output transducer 25. This output side is also provided with an inductive M type circuit similar to the input side.

Here, since an emitter follower circuit is used for the level adjustment circuit 20, the input circuit and the output circuit are less likely to interfere with each other, and furthermore, since the output functions as a current source, it has the advantage that adjustment by volume is easy. Note that this level adjustment circuit has a ninth
Using a circuit like the one shown in the figure has the following advantages.

In the above embodiment, the equivalent circuit in the frequency range (approximately 0 to 2.5 MHz) below the operating band of the glass delay line is as shown in FIG. In Figure 6
C ₀ is the constraint capacitance of the input/output transducer, L is the inductance of each half of the anti-resonant coil, and M is the mutual inductance.

If we take L almost equal to M in this circuit, then
Its input and output impedance is Therefore, the frequency band used by this circuit is 1>
If selected within the range of 4ω ² LC ₀ , this circuit will have no reactance component and no phase shift will occur between the signal voltage applied across the voltage divider load and the input voltage.

Moreover, in the range of 1≫4ω ² LC ₀ , the input/output impedance becomes 2L/C, and the frequency dependence becomes extremely small. Here, it goes without saying that the value of C is determined so that z ₀ =R.

Next is the frequency range in which the glass delay line operates (approximately
2.5MHz to 4.5MHz), the equivalent circuit is as shown in FIG. Here, R ₀ and C ₂ are the equivalent resonant resistance and equivalent resonant capacitance of the delay line, respectively. In Fig. 7, when the glass delay line starts operating, the above-mentioned equivalent resonant capacitance C ₂ and the anti-resonant coil 26 resonate in parallel, and if the Q is made large, it can be seen as an equivalent circuit as shown in Fig. 8. I can do it.

At this time, the glass delay line will operate most efficiently if the inductance of the anti-resonate coil is set to 4L and 2R = R ₀ .

That is, in the circuit of FIG. 8, the glass delay line 2
2 and the signal applied to the partial voltage load 24 are combined on the output transducer side to form a sum signal or a difference signal, forming the above-mentioned comb filter.

Note that if the level adjustment circuit 20 is configured as shown in FIG. 9, a phase shift circuit 31 is inserted on the input side when one stage of transistor circuit is used, and its
This has the advantage that when the current phase is changed by changing the ratio of , the null point can be changed without changing the frequency characteristics of the comb filter.

According to the circuit of the embodiment shown in FIG. 5, there is no phase shift between the output of the low-frequency signal that does not pass through the glass delay line and the output of the high-frequency signal that passes through the glass delay line. The frequency characteristics of the signal without the ultrasonic delay line are as shown in Figure 10, the frequency characteristics of the signal that has passed through the ultrasonic delay line are as shown in Figure 11, and the final comb-shaped characteristic when both are added is shown in Figure 12. In short, since the voltage dividing resistors perform complementary operations, the overall pulse response is good and extremely flat output characteristics can be obtained.

According to the circuit of the present invention described above, a band sufficient to pass a color television video signal can be obtained with a flat output characteristic using a relatively simple circuit configuration, and a color signal and a luminance signal can be can be well separated using the comb filter characteristics of the delay line, making it possible to construct a high-resolution color television circuit at low cost.

It should be noted that even if the partial voltage load in the embodiment shown in FIG. 5 is changed to a tapped resistor or inductance, or a capacitor connected between the anti-resonant coil or the like is omitted when carrying out the present invention, if necessary, The phase characteristics of the circuit are different from those of the conventional method.
Depending on the selection of the value, it can be used for practical purposes.

[Brief explanation of the drawing]

Figures 1 to 3 are block diagrams of conventional comb filters and their passband characteristics;
The figure is a basic block diagram of the present invention, Figures 5 to 8 are wiring diagrams of specific embodiments of the present invention and equivalent circuit diagrams at the frequency used, and Figure 9 is an implementation of the level adjustment circuit of the present invention. The example connection diagrams, FIGS. 10 to 12, are frequency characteristic diagrams in the circuit of the present invention. 12...Glass delay line, 13...Input transducer, 15...Output transducer, 14
...Divided voltage load, 16...Anti-resonant coil of input transducer.

Claims (1)

[Claims] 1. An interpolated multiplexed signal is separated into a direct signal and a delayed signal input to an ultrasonic solid-state delay line, and the delayed signal that has passed through the delay line and the direct signal are combined by a synthesis circuit to produce a sum signal. and a difference signal, an anti-resonant coil is connected in parallel to the input transducer of the delay line to form a resonant circuit, and a voltage dividing resistor is connected in series to this resonant circuit to connect both ends of these. Adding an interpolation multiplexed signal so that all the interpolation multiplexed signal current flows through the resonant circuit to provide a complementary relationship between the direct signal obtained through the voltage dividing resistor and the delayed signal passed through the delay line, An interpolation multiplex signal separation circuit, characterized in that the direct signal is input to the synthesis circuit through a level adjustment circuit comprising an emitter follower circuit. 2. The interpolation multiplex signal separation circuit according to claim 1, wherein a phase shift circuit for null point adjustment is inserted in the level adjustment circuit.