JPH02222308A - Signal processor - Google Patents

Abstract

PURPOSE:To obtain a band limiting system after an amplitude modulation being low in its cost and high in performance by setting a group delay characteristic of a wave to be modulated to the direction for offsetting a group delay characteristic of a band pass filter by a group delay variable circuit. CONSTITUTION:A first and a second waves to be modulated given to input terminals 1, 2 are inputted to group delay correcting circuits 5, 6 having a characteristic respectively, varied as to its group delay, multiplied by carrier waves supplied by input terminals 3, 4 by a multiplier 7 and a multiplier 8, respectively and added by an adder 9. An added signal is inputted to a band pass filter 10 having a prescribed characteristic and brought to band limit, and an output 11 is obtained. In this case, the group delay variable quantity in the group delay correcting circuits 5, 6 is varied by a characteristic of the band pass filter 10. In such a way, a and limiting system after an amplitude modulation having scarcely a ripple in both an amplitude characteristic and a group delay characteristic and having a high performance can be obtained by an inexpensive band pass filter 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a signal processing device that amplitude modulates a signal and passes it through a bandpass filter.

BACKGROUND OF THE INVENTION In recent years, there has been a demand for improved performance in video signal processing devices and the like, and very high performance bandpass filters are also required.

Generally, when the modulated wave has a wide band, a band-pass filter after amplitude modulation requires a correspondingly wide band-pass filter. A wideband bandpass filter is designed by combining a lowpass filter and a bypass filter. The group delay characteristic of such a wideband bandpass filter exhibits a downwardly convex characteristic near the center frequency of the bandpass filter. Conventionally, a bandpass filter after amplitude modulation has been configured using several stages of phase compensation circuits in order to correct the above-mentioned downwardly convex group delay characteristic.

FIG. 5 shows a configuration diagram of a conventional bandpass filter. 5
1 is a modulated wave input terminal after amplitude modulation, 52 is a modulated wave output terminal after passing through a bandpass filter, 53 is a bypass filter (abbreviated as H, P, F), 54, 55, 56 are shown in FIG. In the group delay M compensation circuit having the configuration shown in , 57 is a low-pass filter (abbreviated as L, P, F).

As mentioned above, take the band pass filters H, P, F,
When configured with P and F, the amplitude characteristic becomes flat, and the group delay characteristic exhibits a downwardly convex characteristic (see Fig. 2).

In order to compensate for this downwardly convex characteristic, a group delay compensation circuit as shown in FIG. 6 is required, and in the case of a wide band pass filter, about three stages are required as shown in FIG. In FIG. 6, LSI is a coil whose peak frequency of group delay amount is variable, and the characteristic diagram of the group delay compensation circuit when the peak frequency is WC is as shown in FIG.

Problems to be Solved by the Invention However, in this type of bandpass filter, for example, as shown in FIG. 8, which shows a characteristic diagram of the bandpass filter in FIG. Ripples occur in both characteristics. Further, in the group delay compensation circuit shown in FIG. 6, it is difficult to adjust the number of turns of the coil L81. In this way, the ripple within the band due to the phase compensation circuit,
Further, there is a problem in that adjustment is required to correct variations in the constants of the phase compensation circuit, making it expensive. Furthermore, in proportion to the number of stages using phase compensation circuits,
Since the delay time of the bandpass filter itself becomes long, there is a problem in that when time-aligning with signals of other systems, it is necessary to use a delay circuit having the same delay time for the other systems.

The present invention solves these conventional problems and provides an inexpensive and high-performance band limiting system after amplitude modulation.

Means for Solving the Problems The present invention provides a system in which a signal is amplitude-modulated and the modulated wave is passed through a band-pass filter, and includes a group delay correction circuit that receives a modulated wave and corrects its phase; an amplitude modulator that amplitude modulates the output of the modulated wave;
a bandpass filter to which the modulated output of the amplitude modulator is applied and has characteristics that are line symmetrical about the carrier frequency;
The group delay correction circuit is characterized in that it changes the phase of the modulated wave so as to cancel out the group delay characteristic of the bandpass filter.

By setting the group delay characteristic of the active modulated wave in a direction that cancels out the group delay characteristic of the bandpass filter using the variable group delay circuit (negative direction with respect to the frequency), the group delay characteristic of the modulated wave can be changed at the carrier frequency. Since it has an upwardly convex shape, the convex group delay characteristic can be corrected around the carrier frequency of the bandpass filter, and a good band-limiting system after amplitude modulation can be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a quadrature two-phase amplitude modulation system, which is an embodiment of the present invention. In Figure 1, 1
, 2 are the first . The input terminals 3 and 4 of the second modulated wave are the input terminals of the first modulated wave which are orthogonal in phase. This is an input terminal for the second carrier wave. 5.6 is a group delay correction circuit that corrects the phase of the first and second modulated waves, 7 is a multiplier, 8 is a multiplier, 9 is an adder that adds the outputs of multipliers 7 and 8, and 10 is a bandpass filter, and 11 is an output terminal.

The operation of the amplitude modulation system configured as described above will be described below.

The first . The second modulated waves are group delay correction circuits 5 and 6, each having the characteristics shown in FIG.
The signals are inputted to the carrier waves, the group delay of which is varied, multiplied by the carrier waves provided by the input terminals 3 and 4 in a multiplier 79 and multiplier 8, respectively, and added in an adder 9. The added signal is input to a band pass filter 10 having the characteristics shown in FIG. 2, where the band is limited and an output 10 is obtained. Here, group delay correction circuits 5 and 6
The variable amount of group delay in is made to vary depending on the characteristics of the bandpass filter 10. For example, if the delay amount of the frequency (Wc + Wo) in a band pass filter is behind the Wc frequency, the group delay correction circuit will adjust the delay amount at the Wo frequency to be faster than the delay amount at the DC (direct current component). It is sufficient to design the group delay correction circuits 5 and 8 (see FIGS. 2 and 3).

FIG. 4 shows an embodiment of the group delay correction circuit. 40 is a modulated wave input terminal, 41 is a modulated wave output terminal, Q42 is a variable group delay transistor, C44 and R45 are a variable group delay capacitor and resistor, C46 is a capacitor for compensating amplitude characteristics, and C43 is an emitter follower. be. In this circuit, since the impedance of C44 in transistor Q42 changes depending on the frequency, a modulated wave having the frequency characteristics shown in FIG. 3 can be obtained from output terminal 41.

In this way, the group delay correction circuit can be constructed with a relatively simple circuit, and the amount of variable group delay can be determined by C44 and R45. The ripples seen in the amplitude and frequency characteristics of the conventional example can also be reduced, and problems such as the number of turns of the coil do not occur.

As described above, in this embodiment, it is possible to construct a band limiting system after amplitude modulation that is easier and has higher performance than the conventional system.

Effects of the Invention As described above, the present invention includes a group delay correction circuit that varies the group delay characteristic of a modulated wave according to a group delay characteristic of a bandpass filter, an amplitude modulator, and a band limit of the output of the amplitude modulator. By providing a band-pass filter that is symmetrical about the carrier frequency, it is a relatively simple and inexpensive band-pass filter that does not require a phase compensation circuit, and has high-performance amplitude with low ripple in both amplitude and group delay characteristics. This makes it possible to realize a band-limiting system after modulation.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an amplitude modulation system according to an embodiment of the present invention, Fig. 2 is a frequency characteristic diagram of a bandpass filter required in the present invention, Fig. 3 is a block diagram of the bandpass filter in the book, and Fig. 6 is a block diagram of an amplitude modulation system according to an embodiment of the present invention. The figure is a conventional numerical characteristic diagram, and FIG. 8 is a frequency characteristic diagram of a conventional bandpass filter. DESCRIPTION OF SYMBOLS 1... Modulated wave input terminal, 2... Modulated wave input terminal, 3... Carrier wave input terminal, 4... Carrier wave input terminal, 5... Group delay correction circuit, 6...
・Group delay correction circuit, 7... Multiplier, 8...
Multiplier 1.9...Adder, 10...Band pass filter, 11...Output terminal. Name of agent: Patent attorney Shigetaka Awano, etc. Name of engineer: Figure 1 Figure Figure Q

Claims (1)

[Claims] In a system in which a signal is amplitude-modulated and the modulated wave is passed through a band-pass filter, there is a group delay correction circuit that receives a modulated wave and corrects its phase, and the output of the group delay correction circuit is amplitude-modulated as the modulated wave. The group delay correction circuit includes an amplitude modulator and a bandpass filter to which a modulated output of the amplitude modulator is applied and has characteristics that are line symmetrical about a carrier frequency, and the group delay correction circuit adjusts the phase of the modulated wave to the bandpass filter. A signal processing device characterized in that the signal processing device changes the group delay characteristics of