JP2007067879A - Transmission signal attenuating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmission signal attenuating device for attenuating a transmission signal according to tilt characteristics contrary to attenuation characteristics in a transmission line of a CATV system, and capable of adjusting a reference frequency and a slope used as an origin of a slope of tilt characteristics and moreover shutting off a high frequency noise component. <P>SOLUTION: An attenuation circuit 2 comprises tilt circuits 10 and 20 having different reference frequencies, and switches the circuits 10 and 20 to which, a transmission signal inputted and passed via a change-over switch 40. Slope characteristics can be adjusted for each of the tilt circuits 10, 20 by conductive current to a diode D. When one tilt circuit is selected via the change-over switch 40, current flowing to a diode of the selected tilt circuit can be adjusted through variable resistor VR. In addition, a low pass filter for shutting off a high frequency noise component is arranged at a transmission line for the tilt circuit 10 of a low reference frequency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a transmission signal attenuating apparatus for attenuating a transmission signal with a tilt characteristic that is an attenuation characteristic opposite to the attenuation characteristic of the transmission line in order to compensate the attenuation characteristic of the transmission signal in the transmission line of a CATV system or the like. .

Conventionally, this type of device is known as a so-called tilt circuit, and is usually used by being incorporated in an amplification device for amplifying a transmission signal.
Since the tilt circuit attenuates the transmission signal with an attenuation characteristic (tilt characteristic) opposite to the attenuation characteristic of the transmission signal generated in the transmission line, it corresponds to the maximum frequency of the transmission signal in the CATV system used. Thus, the attenuation characteristic is set.

  Specifically, when the maximum frequency of a transmission signal flowing through a transmission line (such as a coaxial cable) is 770 MHz, which is the maximum frequency of a terrestrial television broadcast signal, the tilt circuit uses this reference frequency as the reference frequency. The attenuation characteristic (tilt characteristic) is set so that the attenuation amount is the smallest and the attenuation amount increases as the frequency becomes lower than the reference frequency, and the maximum frequency of the transmission signal flowing through the transmission line is from the broadcasting satellite (BS). When the maximum frequency of the received signal of the broadcast signal is 1336 MHz, the tilt circuit uses 1336 MHz as a reference frequency, and the attenuation amount is the smallest at this reference frequency, and the attenuation amount increases as the frequency becomes lower than the reference frequency. Thus, the attenuation characteristic (tilt characteristic) is set.

  For this reason, when the number of broadcast signal channels distributed to the terminal side in the CATV system increases and the maximum frequency of the transmission signal is changed, the tilt circuit also needs to be replaced with one corresponding to the frequency. It was.

  Therefore, conventionally, even if the number of transmission signal channels is changed in the CATV system, the maximum frequency of the transmission signal attenuated by the tilt circuit is switched by using a switch in order to eliminate such replacement work. It has been proposed that the tilt circuit can be used as it is (see, for example, Patent Document 1).

In other words, the proposed tilt circuit has a diode connected in parallel to a part of the resonance circuit that determines the reference frequency described above, and whether or not to short-circuit both ends of the element by energizing the diode is determined by a manual switch. By switching (in other words, changing the circuit constant), the resonance point of the resonance circuit (that is, the reference frequency of the tilt characteristic) can be changed.
JP-A-10-70428

  However, although the proposed tilt circuit can switch the maximum frequency at which the transmission signal can be attenuated, the attenuation amount of the transmission signal itself is constant and cannot be adjusted, so it matches the attenuation characteristics of the transmission line. Therefore, the slope of the attenuation with respect to the frequency (slope) could not be adjusted.

  On the other hand, a tilt circuit is known that uses a diode whose impedance changes depending on the energization current so that the slope of the attenuation with respect to the frequency can be adjusted. For this reason, it is conceivable to provide a slope adjusting diode in the proposed tilt circuit so that the slope can be adjusted.

  However, in the proposed tilt circuit, a diode is provided to change the resonance point of the resonance circuit, and the diode is energized. Therefore, a separate adjustment diode is provided for slope adjustment, and the adjustment is performed. It was not possible to supply a current for slope adjustment only to the diode for use. In addition, even if it can be done, there is a problem that the circuit configuration becomes complicated and problems such as wraparound of the transmission signal are likely to occur.

  Furthermore, the proposed tilt circuit changes the maximum frequency of the transmission signal to be attenuated (the reference frequency of the tilt characteristic) by changing the resonance point of the resonance circuit. When switched to the low frequency side, the signal from that frequency to the maximum frequency on the high frequency side passes without loss.

  As a result, when the proposed tilt circuit is incorporated in an amplifying apparatus or the like and the reference frequency of the tilt characteristic is set to the low frequency side, not only the transmission signal whose level is adjusted by the tilt circuit but also the transmission signal. A noise component having a high frequency will also be amplified, and distortion may occur in the regular transmission signal.

  The present invention has been made in view of such problems, and in a transmission signal attenuating apparatus for attenuating a transmission signal with a tilt characteristic that is opposite to the attenuation characteristic of a transmission signal generated in a transmission line of a CATV system or the like, It is an object of the present invention to not only change the reference frequency that becomes the starting point of the characteristic slope, but also to adjust the slope and to easily block a noise component having a frequency higher than that of the transmission signal.

The invention according to claim 1, which has been made to achieve the object,
A transmission signal attenuating device for attenuating the transmission signal with a tilt characteristic which is an attenuation characteristic opposite to the attenuation characteristic of the transmission line in order to compensate the attenuation characteristic of the transmission signal in the transmission line,
A transmission signal having a frequency lower than the first frequency is attenuated by the tilt characteristic with reference to the first frequency, and the slope of the tilt characteristic can be adjusted by a DC voltage or current supplied from the outside. A tilt circuit;
With the second frequency higher than the first frequency as a reference, a transmission signal having a frequency lower than the second frequency is attenuated by the tilt characteristic, and the tilt characteristic is reduced by a DC voltage or current supplied from the outside. A second tilt circuit capable of adjusting the slope;
A signal path switch for switching whether the transmission signal is input to the first tilt circuit and passed or input to the second tilt circuit by an external operation;
The DC voltage or current for adjusting the attenuation amount is configured to be adjustable by an external operation, and the adjusted DC voltage or current is selected by the signal path switching switch via the signal path switching switch. Or a slope correction circuit to be supplied to the second tilt circuit;
It is provided with.

The invention according to claim 2 is the transmission signal attenuating device according to claim 2,
A low-pass filter for blocking a transmission signal having a frequency higher than the first frequency is provided on the signal path on the first tilt circuit side switched via the signal path switch. To do.

  The transmission signal attenuating apparatus according to claim 1, further comprising a first tilt circuit and a second tilt circuit having different reference frequencies as starting points of the slope of the tilt characteristic, and these tilts are provided via a signal path switch. It is possible to switch between which of the circuits the transmission signal is input and passed. Each tilt circuit is configured so that the slope of the tilt characteristic can be adjusted by a DC voltage or current supplied from the outside. When any tilt circuit is selected via the signal path switch, slope correction is performed. The circuit supplies a DC voltage or current for attenuation adjustment to the selected tilt circuit via the signal path selector switch.

  For this reason, according to the transmission signal attenuating apparatus of the present invention, by switching the tilt circuit through which the transmission signal passes, not only can the reference frequency that becomes the starting point of the slope of the tilt characteristic be changed, but also the slope correction circuit that is common to each tilt circuit. Through this, the slope of the tilt characteristic can be adjusted.

  Therefore, if the transmission signal attenuation device of the present invention is used, even if the frequency of the transmission signal requiring level adjustment or the attenuation characteristic of the transmission signal on the transmission line changes due to an increase in the number of broadcast channels in the CATV system, The tilt characteristic can be optimally adjusted in accordance with the change.

  In the present invention, the tilt circuit requires at least two tilt circuits. However, the number of the tilt circuits is increased by increasing the number of tilt circuits having different reference frequencies, which are the starting points of the slope of the tilt characteristic, to three or more. If the signal path selector switch can be used to select which transmission signal is passed, the reference frequency that is the starting point of the slope of the tilt characteristic can be switched in more stages.

  Further, as described above, the transmission signal attenuating apparatus of the present invention is provided with a plurality of tilt circuits having different reference frequencies in order to switch the reference frequency of the tilt characteristic, so that a signal such as a filter is provided at the front stage or the rear stage of each tilt circuit. A processing circuit can be provided.

  According to a second aspect of the present invention, a low-pass filter that prevents passage of a transmission signal having a frequency higher than the first frequency is provided on the signal path on the first tilt circuit side switched via the signal path selector switch. In this way, when the second tilt circuit is selected, the transmission signal having a frequency higher than the first frequency is not cut off, and when the first tilt circuit is selected, the frequency is higher than the first frequency. High unnecessary signal components can be blocked.

  Therefore, according to the transmission signal attenuating apparatus of the present invention, an unnecessary signal component having a frequency higher than that of the transmission signal to be amplified is input to the amplifying apparatus (circuit) provided at a later stage than the apparatus, and after amplification. It is possible to easily and reliably prevent distortion of the transmission signal.

Embodiments of the present invention will be described below.
FIG. 1 is an electric circuit diagram showing a configuration of an attenuation circuit 2 according to an embodiment to which the present invention is applied.
The attenuation circuit 2 of the present embodiment is incorporated in an amplifying apparatus that is provided in series with a transmission line (coaxial cable or the like) of a CATV system and amplifies a transmission signal that flows through the transmission line. In this amplifying apparatus, the attenuating circuit 2 attenuates the transmission signal amplified by the amplifying circuit 4 in the preceding stage with a tilt characteristic that is opposite to the attenuating characteristic of the transmission line, and then in the next stage. Used to input to the amplifier circuit 6.

  As shown in FIG. 1, the attenuation circuit 2 of the present embodiment has passed through the first tilt circuit 10 and the first tilt circuit 10 and the second tilt circuit 20 having different reference frequencies that are the starting points of the slope of the tilt characteristic. Of the transmission signals, a low-pass filter (LPF) 30 for blocking the passage of signal components higher than the reference frequency of the first tilt circuit 10, and the transmission signal input from the amplifier circuit 4 are converted into two tilt circuits 10, 20. A signal path changeover switch (hereinafter simply referred to as a changeover switch) 40 is provided for manually switching which of the input signals is to be passed to the amplifier circuit 6 side of the next stage.

  Here, the attenuation characteristic (tilt characteristic) of the first tilt circuit 10 is such that, as shown in FIG. 2 (a), the reference frequency f1 as the starting point of the slope distributes broadcast radio waves with right and left circular polarizations. Among the reception signals of the broadcast signal from the incoming communication satellite (CS), the maximum frequency of the reception signal of the broadcast signal distributed with right-handed polarization is set to 2150 MHz.

  The first tilt circuit 10 attenuates the transmission signal having a frequency lower than the set reference frequency f1 with the slope characteristic set so that the attenuation amount increases as the frequency decreases.

Note that the attenuation characteristic of the LPF 30 is set so as to prevent passage of a signal component higher than the reference frequency f1 of the first tilt circuit 10, as shown in FIG.
On the other hand, as shown in FIG. 2 (b), the attenuation characteristic (tilt characteristic) of the second tilt circuit 20 is such that the reference frequency f2 that is the starting point of the slope is the received signal of the broadcast signal from the communication satellite (CS). Among them, it is set to 2655 MHz (that is, f2> f1), which is the maximum frequency of the reception signal of the broadcast signal distributed with left-handed polarization.

  Then, the second tilt circuit 20 attenuates the transmission signal having a frequency lower than the set reference frequency f2 with a slope characteristic set so that the attenuation amount increases as the frequency decreases.

  Further, as shown in FIG. 1, each of these tilt circuits 10 and 20 is a well-known circuit composed of a series resonance circuit and a parallel resonance circuit made up of a resistor, a capacitor, a coil and the like. The part uses a diode D whose impedance changes depending on the energization current. By changing the current flowing through the diode D, the circuit constants, and thus the slopes shown in FIGS. The characteristics can be adjusted.

  Therefore, in the attenuation circuit 2 of the present embodiment, the power supply voltage (DC positive voltage) + B is applied to the transmission line connected to the input side of the first tilt circuit 10 or the second tilt circuit 20 via the changeover switch 40. Is connected to the output side of the first tilt circuit 10 or the second tilt circuit 20 via the changeover switch 40 (however, the output side of the first tilt circuit 10 is connected via the LPF 30). The coil L2 for applying a divided voltage obtained by dividing the power supply voltage + B by the resistor R1 and the variable resistor VR is connected to the transmission line.

  For this reason, in the attenuation circuit 2 of the present embodiment, if the variable resistor VR is manually operated to change the resistance value, the divided voltage divided by the resistor R1 and the variable resistor VR is changed. Thus, the voltage applied to the output side of the first tilt circuit 10 or the second tilt circuit 20 selected via the changeover switch 40 can be adjusted.

  If the voltage on the output side of the first tilt circuit 10 or the second tilt circuit 20 selected via the changeover switch 40 is adjusted in this way, the diode D from the input side in the tilt circuit 10 or 20 is adjusted. Therefore, the slope characteristics of the tilt circuits 10 and 20 can be adjusted by operating the variable resistor VR.

  The coils L1 and L2 are for blocking high-frequency signal components such as transmission signals and allowing only DC signal components to pass therethrough, and connection points on the transmission line to which these coils L1 and L2 are connected, Between each of the amplifier circuits 4 and 6, there is provided a capacitor that blocks a DC signal component and passes only a high-frequency signal component such as a transmission signal.

In the present embodiment, the functions as the slope correction circuit of the present invention are realized by the coils L1 and L2 and the resistors R1 and VR that generate the divided voltage.
As described above, the attenuation circuit 2 of the present embodiment includes the two tilt circuits 10 and 20 in which the reference frequencies that are the starting points of the slopes of the tilt characteristics are set to the different frequencies f1 and f2. Via the changeover switch 40, it is possible to switch between which of the tilt circuits 10 and 20 the transmission signal is input and passed.

  The tilt circuits 10 and 20 are configured such that the slope characteristics can be adjusted by the current flowing through the diode D, and when any of the tilt circuits 10 or 20 is selected via the changeover switch 40, the slope correction circuit. The current flowing through the diode D is set by the divided voltage set by the variable resistor VR.

  Therefore, according to the attenuation circuit 2 of the present embodiment, the tilt characteristic is changed by switching the tilt circuit that passes the transmission signal via the changeover switch 40 to either the first tilt circuit 10 or the second tilt circuit 20. The slope of the tilt characteristic can also be adjusted via the variable resistor VR common to the tilt circuits 10 and 20.

  Therefore, if the attenuation circuit 2 of the present embodiment is used, even if the frequency of the transmission signal that requires level adjustment or the attenuation characteristic of the transmission signal on the transmission line changes due to an increase in the number of broadcast channels in the CATV system, The tilt characteristic can be optimally adjusted in accordance with the change.

  Further, an LPF 30 is provided at the subsequent stage of the first tilt circuit 10, and the LPF 30 prevents passage of signal components higher than the reference frequency f 1 of the first tilt circuit 10. When the first tilt circuit 10 is selected, an unnecessary signal component having a frequency higher than the reference frequency f1 is not input to the amplifier circuit 6, and the amplified transmission signal is not distorted. .

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, A various aspect can be taken in the range which does not deviate from the summary of this invention.
For example, in the embodiment described above, the attenuation circuit 2 is described as being provided with the two tilt circuits 10 and 20, but the number of tilt circuits having different reference frequencies is further increased, and a transmission signal is transmitted to any of the plurality of tilt circuits. If the changeover switch 40 can be used to select whether or not to pass, the tilt characteristic can be switched in more stages, and the variable resistor VR is also provided for the slope characteristic in each selected tilt circuit. To be able to adjust.

  Further, for example, in the above embodiment, in order to adjust the slope characteristics of the tilt circuits 10 and 20, the DC voltage applied to the output side of the tilt circuit 10 or 20 selected by the changeover switch 40 is changed to the variable resistor VR. However, instead of the variable resistor VR for adjusting the applied voltage, a current control circuit for controlling the current flowing into the tilt circuit 10 or 20 selected by the changeover switch 40 may be provided. Good.

It is an electric circuit diagram showing the structure of the attenuation circuit of embodiment. It is explanatory drawing showing the attenuation characteristic of the 1st tilt circuit which comprises the attenuation circuit of embodiment, a 2nd tilt circuit, and LPF.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... Attenuation circuit 4, 6 ... Amplification circuit, 10 ... 1st tilt circuit, 20 ... 2nd tilt circuit, 30 ... Low pass filter (LPF), 40 ... Changeover switch, D ... Diode, L1, L2 ... Coil, R1 ... resistance, VR ... variable resistance.

Claims (2)

A transmission signal attenuating device for attenuating the transmission signal with a tilt characteristic which is an attenuation characteristic opposite to the attenuation characteristic of the transmission line in order to compensate the attenuation characteristic of the transmission signal in the transmission line,
A transmission signal having a frequency lower than the first frequency is attenuated by the tilt characteristic with reference to the first frequency, and the slope of the tilt characteristic can be adjusted by a DC voltage or current supplied from the outside. A tilt circuit;
With the second frequency higher than the first frequency as a reference, a transmission signal having a frequency lower than the second frequency is attenuated by the tilt characteristic, and the tilt characteristic is reduced by a DC voltage or current supplied from the outside. A second tilt circuit capable of adjusting the slope;
A signal path switch for switching whether the transmission signal is input to the first tilt circuit and passed or input to the second tilt circuit by an external operation;
The DC voltage or current for adjusting the attenuation amount is configured to be adjustable by an external operation, and the adjusted DC voltage or current is selected by the signal path switching switch via the signal path switching switch. Or a slope correction circuit to be supplied to the second tilt circuit;
A transmission signal attenuating device comprising:   A low-pass filter for blocking a transmission signal having a frequency higher than the first frequency is provided on the signal path on the first tilt circuit side switched via the signal path switch. The transmission signal attenuation device according to claim 1.

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