JP2006203530A - Digital broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital broadcast receiver which removes an adjacent interference signal with a simple system configuration. <P>SOLUTION: An intermediate frequency filter 15 has three kinds of frequency characteristics which are changed over by the control signal of a control unit 18. The control unit 18 has an interference signal detection mode and an optimum frequency characteristic holding mode. The control unit 18 receives a hope signal, and immediately after that, successively sets the frequency characteristics of the intermediate frequency filter 15 to three states, based on the interference signal detection mode. The control unit 18 selects the state of the intermediate frequency filter 15 at the lowest level, based on the output of a level detector 16 which detects a peak level of each state in the intermediate frequency signal including the hope signal and the interference signal. The output of a gain control amplifier 8 is detected by a level detector 17, so as to confirm existence/absence of the hope signal. The control unit 18 changes its mode into the holding mode, so as to control the intermediate frequency filter 15 concerning the selected frequency characteristic. Consequently, the interference signal is largely attenuated and an excellent reception characteristic is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a digital broadcast receiver having a function of detecting and removing an interference signal adjacent to a reception desired signal.

  In a conventional broadcast and communication receiver, a filter that passes a desired frequency converted to an intermediate frequency or a filter for removing an unnecessary frequency is used (for example, see Patent Document 1). As such a receiver, a digital broadcast receiver will be described as an example with reference to FIGS.

  As shown in FIG. 6, the conventional digital receiver includes a front-stage tuning filter 1 that removes unnecessary frequency components, a front-stage amplifier 2 that amplifies a desired signal connected to the front-stage tuning filter 1, and an output of the front-stage amplifier 2. The interstage tuning filter 3 connected, the mixer 4 that converts a desired signal connected to the output of the interstage tuning filter 3 into an intermediate frequency signal, and the local oscillation signal to the mixer 4 connected to the input of the mixer 4 Voltage control oscillator 100 to be supplied, intermediate frequency filter 5 connected to the output of mixer 4, intermediate frequency amplifier 6 for amplifying a desired signal connected to the output of intermediate frequency filter 5, and output of intermediate frequency amplifier 6 And a gain control amplifier 8 connected to the output of the surface acoustic wave filter 7, and a demodulator 9 connected to the output of the gain control amplifier 8. It is. The integrated circuit 10 includes a mixer 4, a voltage control oscillator 100, an intermediate frequency filter 5, an intermediate frequency amplifier 6, and a gain control amplifier 8.

  In the conventional digital broadcasting receiver, as shown in FIG. 6, the received signal received by the antenna is removed from the signal of unnecessary frequency components by the pre-stage tuning filter 1, the pre-stage amplifier 2, and the inter-stage tuning filter 3 to obtain a desired signal. After the signal is amplified, it is converted into a desired intermediate frequency signal by the mixer 4.

The intermediate frequency filter 5 has frequency characteristics indicated by solid lines in FIGS. 7A to 7D, and the desired signal and the interference signal indicated by diagonal lines are obtained from the amplitude before passing through the filter shown in FIG. The amplitude after passing through the filter shown in (b) is changed. Therefore, the interference signal is attenuated by the intermediate frequency filter 5 and amplified by the intermediate frequency amplifier 6, and the intermediate frequency signal is further input to the demodulator 9 through the surface acoustic wave filter 7 and the gain control amplifier 8. The demodulator 9 demodulates the input intermediate frequency signal into a video or audio digital signal.
JP 2003-218713 A

  However, in such a conventional configuration, the intermediate frequency filter has a wide pass band of several tens of MHz, and when the frequency of the disturbing signal is very close to the frequency of the desired signal as shown in FIG. Since the interference signal exists in the band of the intermediate frequency filter and the interference signal is hardly attenuated as shown in FIG. 7D, there is a problem that the reception characteristic is deteriorated.

  Such an interference signal is called an adjacent interference signal. Especially when digital broadcasting and conventional analog broadcasting are mixed, there may be an analog signal with a higher level than the digital signal adjacent to the digital signal. When receiving a digital signal, an analog signal unnecessary for the intermediate frequency filter Therefore, an analog signal having a higher level than the digital signal that is a desired signal is input to the intermediate frequency amplifier, so that the distortion characteristic of the intermediate frequency amplifier is greatly deteriorated and the reception characteristic is deteriorated. The same applies when the adjacent interfering signal is on the lower frequency side than the desired signal.

  To solve this problem, the broadcasting station that transmits the signal slightly offsets the transmission frequency of the signal from the adjacent interfering signal so that the desired signal and the adjacent interfering signal are separated from each other. However, there was a problem that sufficient effects were not obtained.

  The present invention is directed to solving the above-described problems of the prior art, and it is possible to eliminate adjacent disturbance signals with a simple system configuration against the removal of adjacent disturbance signals that is impossible with a conventional digital broadcast receiver. An object of the present invention is to provide a digital broadcast receiver that can be removed.

  In order to achieve the above object, a digital broadcast receiver according to the present invention includes a mixer that converts an RF signal received by digital broadcast into an intermediate frequency signal, a variable intermediate frequency filter connected to the output of the mixer, and a variable intermediate An intermediate frequency amplifier connected to the output of the frequency filter, a level detector connected to the output of the intermediate frequency amplifier, and a controller connected to the output of the level detector and the control input of the variable intermediate frequency filter to The frequency characteristic of the variable intermediate frequency filter is controlled by the controller with respect to the output of the corresponding level detector.

  In addition, the variable intermediate frequency filter is configured by an inductor, a plurality of capacitors, and a plurality of switches, or is configured by connecting a plurality of filters in parallel.

  According to the above configuration, when there is an interference signal adjacent to the desired signal to be received, the controller switches the frequency characteristics of the intermediate frequency filter by the controller when the desired signal is received, and the output level of the intermediate frequency amplifier is detected by the level detector. By doing so, it is possible to select the frequency characteristic of the intermediate frequency filter that minimizes the output level of the intermediate frequency amplifier.

  According to the present invention, even if an interference signal is present adjacent to a desired reception signal, the frequency characteristic of the intermediate frequency filter is selected so that the interference signal is minimized, and the interference signal input to the intermediate frequency amplifier is selected. By reducing the level, there is an effect that good reception characteristics can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a digital broadcast receiver according to Embodiment 1 of the present invention. Here, components corresponding to the components described in FIG. 6 showing the conventional example and having substantially the same functions are denoted by the same reference numerals, and description of the components is omitted.

  In addition to the conventional digital broadcast receiver shown in FIG. 6 as shown in FIG. 1, the digital broadcast receiver according to the first embodiment has an intermediate frequency filter 15 capable of varying frequency characteristics and an output level of the intermediate frequency amplifier 6. Is comprised of a level detector 16 for detecting the output level, a level detector 17 for detecting the output level of the gain control amplifier 8, and a controller 18 for controlling the intermediate frequency filter 15 from the output signals of the level detectors 16 and 17. . The integrated circuit 20 includes a mixer 4, a voltage controlled oscillator 100, an intermediate frequency filter 15, an intermediate frequency amplifier 6, level detectors 16 and 17, and a controller 18.

  The operations of the intermediate frequency filter 15, the controller 18, and the level detectors 16 and 17 in the first embodiment will be described with reference to FIGS. 1 and 2A to 2F. First, the intermediate frequency filter 15 has three types of frequency characteristics indicated by solid lines in FIGS. 2 (a), 2 (b), and 2 (c). The switching of these three types of frequency characteristics is performed by a control signal from the controller 18.

  There are two types of operation of the controller 18, a jamming signal detection mode for detecting a jamming signal and a holding mode for holding the optimum frequency characteristic of the intermediate frequency filter 15 from the signal level of the detected jamming signal. The controller 18 operates in the interference signal detection mode immediately after receiving the desired signal. The controller 18 sequentially sets the frequency characteristics of the intermediate frequency filter 15 in the three states of FIGS. 2 (a), (b), and (c).

  Here, the case where the frequency of the adjacent interfering signal is higher than the frequency of the desired signal as shown in FIGS. When the intermediate frequency filter 15 is set to the frequency characteristics shown in FIG. 2A, the desired signal and the disturbing signal indicated by hatching are slightly attenuated as shown in FIG. 2D. When the frequency characteristic of the intermediate frequency filter 15 is shown in FIG. 2B, the interference signal is greatly attenuated as shown in FIG. Further, when the frequency characteristic of the intermediate frequency filter 15 is as shown in FIG. 2C, the interference signal is not attenuated at all as shown in FIG.

  The peak level of each state is detected by the level detector 16 in the intermediate frequency signal including the desired signal and the interference signal shown in FIGS. 2 (d), 2 (e) and 2 (f). The controller 18 selects the state of the intermediate frequency filter 15 having the lowest level shown in FIG. 2E from the output of the level detector 16. Further, it is confirmed that the desired signal exists by detecting the output level of the gain control amplifier 8 by the level detector 17.

  Next, the controller 18 changes to the holding mode, and controls the intermediate frequency filter 15 so that the frequency characteristics shown in FIG. 2E selected in the interference signal detection mode are obtained. If the interference signal is present at a lower frequency than the desired signal, the controller 18 controls the intermediate frequency filter 15 so that the frequency characteristic shown in FIG.

  Further, when there is no interference signal at a frequency close to the desired signal, the output level of the level detector 16 does not change in the frequency characteristics shown in FIGS. 2 (a), 2 (b) and 2 (c). The controller 18 controls the intermediate frequency filter 15 so as to have the frequency characteristics shown in FIG. As a result, the interference signal input to the intermediate frequency amplifier 6 can be greatly attenuated, so that deterioration of distortion characteristics can be prevented and good reception characteristics can be obtained.

  Further, since the intermediate frequency filter 15 for removing the interference signal is used for the detection of the interference signal, a new filter for detecting the interference signal is not required, and the system can be simplified.

  Next, examples of the intermediate frequency filter according to the first embodiment will be described with reference to FIGS. 2 (a) to 2 (f) and FIGS. 3 (a) and 3 (b). As shown in FIG. 3A, the intermediate frequency filter includes an inductor 21, capacitors 22, 23 and 24, and switches 25 and 26. The frequency characteristics of the intermediate frequency filter are changed by changing the capacitance value connected between the terminals of the intermediate frequency filter by turning the switches 25 and 26 on and off.

  Now, since the capacitance value is the smallest when both the switches 25 and 26 are OFF, the frequency characteristic of the intermediate frequency filter is in the state where the center frequency is the highest as shown in FIG. Further, since the capacitance value is the largest when both the switches 25 and 26 are on, the frequency characteristic of the intermediate frequency filter has the lowest center frequency as shown in FIG. Further, since the capacitance value is an intermediate value between the two conditions when the switch 25 is turned on and the switch 26 is turned off, the frequency characteristic of the intermediate frequency filter is the center of the intermediate frequency filter as shown in FIG. The frequency and the frequency of the desired signal are almost the same.

  As an example of actually configuring the switches 25 and 26, a switch using MOS switches 27 and 28 made of MOS transistors as shown in FIG. The frequency characteristics of the intermediate frequency filter are controlled by switching the gate voltages of the MOS switches 27 and 28 to “H” / “L” by the controller 18 shown in FIG.

  FIG. 4 is a circuit diagram showing an example of the intermediate frequency filter according to Embodiment 2 of the present invention. Further, the configuration of the digital broadcast receiver in the second embodiment is the same as that of the first embodiment, and the description thereof is omitted. In the intermediate frequency filter according to the second embodiment shown in FIG. 4, a filter 30 constituted by an inductor 31, capacitors 32, 33 and a switch 34 and a filter 35 constituted by an inductor 36, capacitors 37, 38 and a switch 39 are connected in parallel. It is composed in the form.

  The operation of the intermediate frequency filter according to the second embodiment will be described with reference to FIGS. 4 and 5A to 5H. First, the frequency characteristics of the intermediate frequency filter are such that the frequency characteristics of the filter 30 and the filter 35 overlap as shown by the solid line and the alternate long and short dash line in FIG. The frequency characteristics of the filter 30 and the filter 35 are controlled by turning on and off the switch 34 and the switch 39, respectively. The controller 18 shown in FIG. 1 adjusts the frequency characteristics of the intermediate frequency filter 15 to the four types of frequency characteristics shown in FIGS. 5A, 5B, 5C, and 5D in the interference signal detection mode. Control sequentially.

  5A shows a state where the switch 34 is turned on and the switch 39 is turned off, FIG. 5B shows a state where both the switches 34 and 39 are turned off, and FIG. 5C shows a state where both the switches 34 and 39 are turned on. FIG. 5D shows a state in which the switch 34 is turned off and the switch 39 is turned on. Now, as shown by hatching in FIGS. 5 (a) to 5 (h), when the frequency of the disturbing signal is higher than the frequency of the desired signal, the middle of FIGS. 5 (e), (f), (g) and (h). From the signal level in each state after passing through the frequency filter, the controller 18 controls to maintain the frequency characteristics of the intermediate frequency filter so that the peak level of the intermediate frequency signal is the lowest in FIG. To do.

  The intermediate frequency filter according to the second embodiment has two interference signals in the adjacent frequency band higher and lower than the frequency of the desired signal by allowing the frequency characteristics of the filters 30 and 35 to be individually varied. Even in this case, the level of the interference signal can be reduced by setting the intermediate frequency filter to the frequency characteristics shown in FIG.

  When there is no interfering signal in the adjacent frequency band of the desired signal, the frequency characteristics of the intermediate frequency filter are the levels shown in FIG. 1 in the states of FIGS. 5 (a), (b), (c), and (d). Since the signal level input to the detection circuit 16 is constant, the controller 18 controls the intermediate frequency filter 15 to the state shown in FIG. Since the state of FIG. 5A is the state in which the bandwidth of the intermediate frequency filter 15 is the widest, the frequency characteristics of the intermediate frequency filter 15 are almost constant within the band of the desired signal, and a part of the desired signal is attenuated. Nothing will happen.

  In digital broadcasting, particularly, attenuation of a part of a desired signal leads to deterioration in reception sensitivity. Therefore, widening the frequency characteristics in the intermediate frequency filter 15 can obtain better reception characteristics as a digital broadcasting receiver.

  The digital broadcast receiver according to the present invention selects the frequency characteristic of the intermediate frequency filter so that the interference signal is minimized even if there is an interference signal adjacent to the desired reception signal, and inputs it to the intermediate frequency amplifier. By reducing the level of the interference signal, good reception characteristics can be obtained, which is useful as a digital broadcast receiver having a function of detecting and removing the interference signal adjacent to the reception desired signal.

1 is a block diagram showing a schematic configuration of a digital broadcast receiver in Embodiment 1 of the present invention. Schematic diagram for explaining the operation of the intermediate frequency filter according to the first embodiment. Circuit diagram showing an intermediate frequency filter in the first embodiment The circuit diagram which shows the intermediate frequency filter in Embodiment 2 of this invention Schematic diagram for explaining the operation of the intermediate frequency filter according to the second embodiment. A block diagram showing a schematic configuration of a conventional digital broadcast receiver Schematic diagram explaining the operation of a conventional intermediate frequency filter

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Prestage tuning filter 2 Prestage amplifier 3 Interstage tuning filter 4 Mixers 5, 15 Intermediate frequency filter 6 Intermediate frequency amplifier 7 Surface acoustic wave filter 8 Gain control amplifier 9 Demodulator 10, 20 Integrated circuit 16, 17 Level detector 18 Controller 21, 31, 36 Inductors 22, 23, 24, 32, 33, 37, 38 Capacitors 25, 26, 34, 39 Switch 27, 28 MOS switch 30, 35 Filter 100 Voltage controlled oscillator

Claims (3)

A mixer for converting an RF signal received in digital broadcasting into an intermediate frequency signal; a variable intermediate frequency filter connected to the output of the mixer; an intermediate frequency amplifier connected to the output of the variable intermediate frequency filter; A level detector connected to an output; and a controller connected to an output of the level detector and a control input of the variable intermediate frequency filter;
A digital broadcast receiver, wherein the controller controls frequency characteristics of the variable intermediate frequency filter with respect to an output of the level detector corresponding to an interference signal.   2. The digital broadcast receiver according to claim 1, wherein the variable intermediate frequency filter includes an inductor, a plurality of capacitors, and a plurality of switches.   The digital broadcast receiver according to claim 1, wherein the variable intermediate frequency filter is configured by connecting a plurality of filters in parallel.

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