JPS6047775B2 - envelope delay compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an envelope delay compensator that compensates for an envelope delay in the phase of an amplitude modulated wave such as a vestigial sideband television broadcast wave.

In general, television radio waves use the vestigial sideband method, and the amplitude modulated waves of this vestigial sideband method have a narrower occupied frequency bandwidth, making it an excellent method for increasing the efficiency of using the frequency band of radio waves. However, this method has the drawback that transmission distortion peculiar to this method occurs due to the restriction of the transmission frequency band.

The transmission distortion peculiar to such a residual sideband method is due to orthogonal components generated based on the asymmetry of the sidebands, and
Waveform distortion occurs because the phase characteristics of the video signal reproduced by demodulation are not linear with respect to frequency.

Among these transmission distortions, distortion due to orthogonal components has less influence on image quality when the degree of amplitude modulation is shallow. On the other hand, the latter phase distortion causes waveform distortion such as so-called smear and leading white, and is a cause of significant image quality deterioration. In particular, in recent years, as satellite relay broadcasting stations have been added and broadcasting networks based on satellite relay have expanded, such satellite relay has come to be carried out in multiple stages, such as five or six stages. Since the phase distortions generated in each of the broadcasting devices are accumulated sequentially, a significant deterioration in image quality occurs in the received and reproduced image by television radio waves from the end broadcasting station. Therefore, in order to prevent image quality deterioration due to phase distortion in such satellite multi-stage relaying, there is a strong need for the development of a small, low-cost phase compensator. In order to meet the demand for the development of such a phase compensator, conventionally, a phase compensator as shown in Fig. 1 was inserted into the intermediate frequency band of a satellite relay broadcaster to compensate for the above-mentioned phase distortion. However, a phase compensator consisting of a lumped constant LC circuit configured as shown in Figure 1J has the phase envelope delay frequency characteristic and amplitude frequency characteristic as shown in Figure 2. , the center frequency f of the frequency band.

to the maximum delay time in. When set to the required value, the band characteristics of the phase delay, such as the half-width, are determined as shown in the figure. Therefore, in a satellite broadcaster for television radio waves, a trapezoidal wide band as shown by the solid line in Figure 3 is used. When delay frequency characteristics are required, multiple phase compensators having the configuration shown in Figure 1 are connected in cascade and their respective frequency bands are sequentially shifted as shown by dotted lines in Figure 3. The characteristics were integrated to obtain the required trapezoidal characteristics. Furthermore, if the circuit elements used in the phase compensator configured as shown in Figure 1 have a low resistance rather than a pure reactance, as shown in Figure 2, near the frequency that indicates the maximum delay time, Since transmission loss occurs and the amplitude frequency characteristics become uneven, resulting in characteristic deterioration, normally an amplitude equalizer is connected in tandem with the phase compensator configured as shown in Figure 1, and the combined amplitude frequency is In order to flatten the characteristic and, as mentioned above, to obtain a broadband trapezoidal characteristic by cascading a plurality of phase compensators with such a configuration, for example, the practical phase compensator shown in FIG. As shown in the compensator circuit configuration example, between each cascaded section,
Furthermore, an attenuator was inserted to prevent the effects of mutual impedance characteristics from occurring.

On the other hand, a narrowband phase compensator constructed by using a bridge circuit or a circulator and connecting a reflection element consisting of a series or parallel five-resonance circuit to one terminal of the bridge circuit or a circulator is disclosed in, for example, Japanese Patent Laid-Open No. 49-87257. Although it is known from a publication, widening the band has not yet been considered.
For this purpose, conventional television broadcasting satellites. The only phase compensator with wideband characteristics, that is, the wideband envelope delay compensator used in broadcast relay broadcasting equipment, uses the former lumped constant type LC circuit, and therefore has a complicated circuit configuration. As they grew older, they became larger and more expensive.

However, with the expansion of television broadcasting networks, the construction of low-power satellite relay broadcasting stations is expected to increase in the future. There is an extremely strong demand for lower prices, and there is a strong need for its development. The object of the present invention is to meet such demands by using a bridge circuit or a circulator to provide a compensator that is extremely compact and simple in structure compared to a conventional compensator using a lumped constant LC circuit. Another object of the present invention is to provide a wideband envelope delay compensator suitable for use in phase compensation for a low-power modulation stage in a low-power satellite relay broadcaster or a large-scale broadcaster. In other words, the envelope delay compensator of the present invention achieves wideband performance by connecting a plurality of series or parallel resonant circuits in parallel or series to one terminal of the bridge circuit or circulator, excluding the input/output terminals. The present invention is characterized in that it is configured to perform envelope delay compensation.

The present invention will be described in detail below with reference to the drawings. Masu,
In order to facilitate explanation of the configuration and operation of the envelope delay compensator of the present invention, a phase compensator using a conventionally known bridge circuit or circulator will be described.

In the bridge circuit shown in Figure 5, terminals 1 and 2
It is assumed that a four-terminal pair circuit is constructed in which terminals 3 and 4 are common terminals. Here, terminal 1 is used as an input terminal, terminal 2 is used as an output terminal, and terminal 3 is provided with a terminating resistor R equal to the characteristic impedance of the circuit. , when connecting arbitrary impedance Z to terminal 4, terminal 1 to terminal 2
The transfer function T of the handrail is calculated by setting the input and output voltages to V1 and V2, respectively, where z=storage
(2) becomes.

Therefore, if Z=RO, then T=0, no voltage is generated at the output terminal 2, and V2=0. However, terminal 4
However, when a pure reactance Jx is connected to
? (4) Therefore, the amplitude characteristic 1T] and the phase characteristic θ are as follows. In the circuit configuration shown in Fig. 5, the amplitude is constant and the phase is a function of X, so an ideal phase compensation circuit is realized. This means that the conditions for doing so are met.

Now, as shown in Fig. 6, a series resonant circuit consisting of an inductance L and a capacitance C is used as the above-mentioned pure reactance base, and the delay time γ is, however, ω1゛1119W0bLJ(-1) Therefore,
This characteristic is based on the lumped constant type L
The characteristics are the same as those of a phase compensator using a C circuit.

That is, the circuit configuration shown in FIG. 1 and the circuit configuration shown in FIG. 6 have the same delay time characteristics. The above is the reason for constructing a phase compensation circuit in which a series or parallel resonant circuit is connected to one terminal of a bridge circuit or a circulator.

Incidentally, the frequency characteristics of the delay time in the circuit configuration shown in FIG. 6 are as shown in FIG. 7. Here, the bandwidth of ∆
Since there is a relationship with FO, the maximum delay time τ.

Increasing the value gives a narrow band characteristic. Further, the bandwidth ΔFO in the above equation is a function of the inductance L and does not depend on the capacitance C. Therefore, the method of adjusting the delay characteristic of the phase compensator as shown in Figure 6 is to keep the inductance L at the same value and change only the value of the capacitance C, as shown in Figure 8a. Keep the shape of the characteristic as it is and keep the center frequency F.

The center frequency F at that time is changed by changing the value of the inductance L. By correcting the deviation as described above by changing the value of capacitance C, the shape of the delay band characteristic changes as shown in Fig. 8C by the circuit configuration shown in Fig. 8B. can be done. On the other hand, in the phase compensator shown in FIG.
Each circuit element has a center frequency F.

and the maximum delay time R. and the center frequency F. movement or maximum delay time R. When adjusting, the values of these five circuit elements must be changed, and if the values of each circuit element vary,
The input and output impedances are each constant resistance R. , the overall delay band characteristics deteriorate. As is clear from the above, the phase delay compensator using the conventionally known bridge circuit shown in FIG. It is extremely superior in terms of both the simplicity of the circuit configuration and the ease of circuit adjustment, as well as the ease of design. Next, we will discuss the present invention, which realizes trapezoidal broadband envelope delay time characteristics like the phase envelope delay compensator in a satellite relay broadcaster for television broadcasting, starting from the phase compensator using the bridge circuit shown in Figure 6 above. The configuration according to the invention will be explained.

First, FIG. 9 shows an example of the configuration of an envelope delay compensator with a wide band according to the present invention. In the illustrated configuration, only by connecting a plurality of (1) series resonant circuits in parallel to the terminal 4 in the conventional circuit configuration illustrated in FIG.
As shown in the lower part of the figure, it is possible to obtain broadband trapezoidal characteristics that are completely similar to the characteristics of the conventional phase compensator shown in FIG. 8, and the conventional circuit using the lumped constant type LC circuit shown in FIG. In comparison with the structure, the delay compensator 7 of the present invention shown in FIG. 9 differs from the phase compensator using the conventional bridge circuit shown in FIG. Since there is no need to cascade the compensators, the number of circuit elements is much smaller, and therefore the circuit adjustment is extremely simple, which proves to be extremely superior. However, if it is necessary to obtain a large delay time even for a phase compensator configured using a bridge circuit or a circulator, the Q factor will increase from the relationship in equation (9).
Center frequency F.

As shown in FIG. 10c, a concave portion appears in the amplitude frequency characteristic near . In the phase compensator using the lumped constant LC circuit shown in Figure 1, an amplitude equalizer as shown in Figure 4 is used to flatten the amplitude frequency characteristics in order to prevent the occurrence of depressions in the amplitude characteristics. However, the circuit configuration became more complex. Therefore, for a phase compensator using a bridge circuit or a circulator, it is also possible to use an amplitude equalizer to compensate for the concavity, but using a separate amplitude equalizer would require a very large configuration. It becomes complicated. On the other hand, in the phase delay compensator according to the present invention, if the loss resistance r1 due to the resistance of the resonant circuit connected to the terminal 4 cannot be ignored in the circuit configuration shown in FIG. As shown in the figure, amplitude equalization can be performed within a range that does not impair the frequency characteristics of the delay time simply by connecting a resistor R2 having a specific resistance value in parallel with the resonant circuit.

Therefore, the admittance Y of the circuit element connected to the terminal 4 in the circuit configuration shown in FIG. 11 is as follows.

Therefore, a terminating resistor R is used to connect the value of this admittance Y to terminals 2 and 3. In other words, when normalized by the value of the characteristic impedance of the line connected to terminal 1, the transfer function T of the circuit configuration shown in FIG. If it is small, r1 times R2,
If the value of the parallel resistor R2 is set so that
7) In the circuit configuration shown in FIG. 11, the amplitude is constant and the phase characteristic is the same as the phase characteristic of equation (6) in the circuit configuration shown in FIG.

Therefore, even when connecting LC resonant circuits in multiple stages to obtain trapezoidal broadband delay time characteristics necessary for compensating the phase delay characteristics of television satellite relay broadcasters, etc., as shown in FIG. A flat amplitude frequency characteristic can be obtained by simply connecting a single resistor R2 to a multi-stage LC resonant circuit. In the above explanation, only an example in which a bridge circuit is used as an envelope delay compensator according to the present invention has been described, but the envelope delay compensator according to the present invention is not limited to a bridge circuit. As shown in , a wideband configuration can be similarly achieved by using a circulator.

Next, the operating principle of the amplitude characteristic equalization described above can also be explained as follows.

For example, if the reflective element connected to the terminal 4 in the circuit configuration shown in FIG. 12 is configured as shown in FIG. 14a, the center frequency F.

The amplitude characteristic at is shown in b in the same figure, and the center frequency F
.

The amplitude characteristic at a frequency sufficiently far away from is as shown in c in the same figure, so if these amplitude characteristics are equal, then RO2 = Rlr2, as described above (15)
It has the same form as the expression.

Similarly to the above, when the LC parallel resonant circuit is connected as a reflective element as shown in FIG. 15a, the center frequency F.

The amplitude characteristic at a frequency sufficiently far from the center is as shown in b in the same figure, and the amplitude characteristic at a frequency sufficiently far from the center is as shown in c in the same figure.
RO=RO-R2 Here,,,+RORO+R2 Therefore, the following relationship is obtained: RO2=Rlr2 (18) Therefore, by inserting a series resistor having the value of the above relationship, the amplitude characteristics can be compensated. .

Note that at high frequencies, the resistance value of the resistance component r1 of the inductance L increases to some extent, and Rlr2=RO
From the relationship of 2, the above-mentioned parallel or series insertion resistance R2
Since the value of becomes small, in such a case, the resistance element R2
By inserting a capacitor in series with the resistor R2, the series circuit consisting of the capacitor and the resistor R2 is equivalently converted into parallel, and the value of the resistor R2 described above can be obtained.

As is clear from the above description, according to the present invention, an envelope delay compensator is constructed by combining a bridge circuit or a circulator and a reactive reflective element, and a trapezoidal broadband phase delay compensation characteristic is obtained. Because you can
Compared to conventional phase compensators, the circuit configuration is extremely simple, and an envelope delay compensator that is easy to adjust, small in size, and inexpensive can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of one section of a phase compensator using a conventional lumped constant LC circuit, and FIG. 2 is a characteristic curve diagram showing the frequency characteristics of delay time and amplitude.
Figure 3 is a characteristic curve diagram showing an example of the delay time frequency characteristics of a conventional multi-stage phase compensator, Figure 4 is a circuit diagram showing an example of the configuration, and Figure 5 is a conventional envelope diagram using a bridge. Block diagram showing an example of the principle configuration of a delay compensator, No. 6
The figure is also a block diagram showing a configuration example using (1) a series resonant circuit as a reflective element, Figure 7 is a characteristic curve diagram showing the delay time frequency characteristics, and Figure 8 A, b, and c are the same. A characteristic curve diagram and a block diagram for explaining the characteristic adjustment method, and FIG. 9 shows an example of the configuration of the envelope delay compensator of the present invention which has a wide band using a plurality of d°C series resonant circuits, and the delay time frequency characteristics. A block diagram and a characteristic curve diagram showing examples, respectively, and Figures 10A, b, and c are the circuit configuration, delay time, and amplitude frequency characteristics when the reflective element has a loss resistance in the configuration example of the phase compensator shown in Figure 5. 11 is a block diagram showing an example of amplitude equalization, and FIG. 12 is a block diagram showing an example of amplitude equalization in the case of a multi-stage configuration. Figure 13 is a block diagram showing an example of a phase compensator configured using a circulator and subjected to amplitude equalization.
Figures 14A, b, and c are equivalent circuit diagrams for explaining the principle of amplitude equalization when using a series resonant reflection element, and Figures 15A, b, and c are equivalent circuit diagrams for explaining the principle of amplitude equalization when a series resonant reflection element is used. This is an equivalent circuit diagram for explaining the principle of amplitude equalization.

Claims (1)

[Claims] 1 Constructed to perform broadband envelope delay compensation by connecting multiple series or parallel resonant circuits in parallel or series to one terminal other than the input/output terminal of the bridge circuit or circulator. An envelope delay compensator characterized by: