JP2005109550A - Digital broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital broadcast receiver capable of improving both a 1/2 IF interference removal capability and an image interference removal capability in a balanced manner. <P>SOLUTION: The above problem can be solved by a digital broadcast receiver (100) provided with a filter means for limiting the band of a radio frequency signal and outputting the radio frequency signal having the limited band. The digital broadcast receiver is provided with a plurality of the filter means (3, 4) having different pass bands, and a switch means (2) for selecting and switching the plurality of filter means by a switch. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to interference removal of a digital broadcast receiver, and more particularly to a digital broadcast receiver that is superior to interference in the BPF band.

  In recent years, digital audio broadcasting has been realized, and digital broadcast receivers that receive digital audio broadcasts that are broadcast in accordance with the European Digital Audio Broadcasting (DAB) standard have been commercialized. A digital broadcast receiver based on the DAB system (hereinafter referred to as a DAB receiver) has characteristics such as being unaffected by noise caused by multipath in mobile reception, and provides audio and data equivalent to a CD. It is possible.

  FIG. 3 is a block diagram showing a configuration of a conventional DAB receiver. In this figure, the DAB receiver 200 includes a variable ATT (attenuator) 11 such as a pin diode, an L-Band BPF (Band Pass Filter) a12 having a pass band of 1452 MHz to 1491 MHz, an L-Band BPFb 13, a gain. L-Band LNA (Low Noise Amp) 14 for securing NF, L-Band MIX (mixer) 15 for converting the RF frequency (1452.96 MHz-1490.624 MHz) to the VHF band, L-Band OSC (local part) Oscillator) 16, VHF band filter 17, PLL (Phase Lock Loop) 18, REF CLOCK (reference clock oscillator) 19, 1st OSC 20 for down-converting the VHF band frequency to 38.912 MHz (1st IF), 1st MIX21, 38. 912 MHz filter (BPF) 2 , 2nd OSC23, 2nd MIX24, 2.048MHz filter 25 that down-converts 38.912MHz to 2nd IF of 2.048MHz or 3.072MHz, and IF signal is output from this 2.048MHz filter 25 ing.

Further, in the above-described DAB receiver 200 and the like, the interference removal characteristic is an important factor. Normally, when there is an adjacent channel in the vicinity of the desired channel, means for suppressing the adjacent channel by a filter is taken, but there are cases where it cannot be sufficiently suppressed depending on the signal level of the interference wave. Therefore, a technique for solving such a problem by reducing the gain of the automatic gain control circuit has been proposed (see, for example, Patent Document 1).
JP 2001-127732 A

  In the conventional DAB receiver 200 as described above, there is a problem of 1/2 IF interference generated in the band (1452-1491 MHz) of the L-Band BPF (L-Band BPFa12, L-Band BPFb13). Hereinafter, this 1/2 IF interference will be described.

  Since the RF frequency of L-Band is as high as 1452.96 MHz to 1490.624 MHz, the configuration of the tracking filter is difficult. Therefore, a dielectric filter, a surface acoustic wave filter (SAW filter), a laminated filter, or the like is used as the L-Band BPF.

  Here, the 1/2 IF interference frequency is defined by the following equation.

1/2 IF interference frequency = RF frequency + 38.912 MHz / 2 (1)
For example, when 1/2 IF interference is considered when receiving L-band channel 1 (L1ch), the 1/2 IF interference frequency is
1452.96 MHz + 19.456 MHz = 1472.416 MHz, and interference occurs in the band of the L-band BPF. In this case, since the signal level of the 1/2 IF interference and the signal level of the desired wave appear at the same level and appear at the center frequency of 2.048 MHz, there is a problem that it is difficult to remove the interference wave.

  The table shown in FIG. 4 shows the result of calculating the 1/2 IF interference frequency in each channel from channel numbers 1 to 23 of the L-band signal based on the above equation (1). As shown in the table, the 1/2 IF interference frequency in the range from L1ch to L12ch (the shaded portion in (a)) is within the band (1452-1491MHz) of L-Band BPFa12 and L-Band BPFb13. become.

  In addition to the 1/2 IF interference, there is image interference. This image disturbance is expressed by the following equation.

Image disturbance = RF frequency + 2 × 38.912 MHz (2)
Similar to the above, for example, when considering image disturbance when channel 1 (L1ch) of L band is received, the image disturbance is expressed by the equation (2):
1452.96 MHz + 77.824 MHz = 1530.784 MHz, and there is an image interference frequency at a location that is only about 40 MHz above the L-Band BPFa12 and L-Band BPFb13 bands. In this case, as shown in FIG. 3, the L-band BPF has a two-stage configuration (L-Band BPFa12, L-Band BPFb13) to improve the image disturbance removal capability.

  In this way, it is possible to obtain an interference removal capability by using an L-band BPF in a multi-stage configuration for image interference removal, but it eliminates 1/2 IF interference that occurs within the L-band BPF band. Difficult to do. Therefore, at present, the influence of the interference wave is reduced by setting RF AGC (automatic gain control in the RF stage) or the like, but the setting of RF AGC is as shown in FIG. When the AGC start is made earlier, the adjacent interference ratio becomes worse, and characteristics such as IM (intermodulation distortion) and 1/2 IF interference are improved. On the other hand, when the AGC start is delayed, the adjacent channel interference signal and the desired signal are in a trade-off relationship, and it is very difficult to set an appropriate trade-off balance (see FIG. 5B).

  Normally, if the AGC start is slow, the signal level of the 1st IF output increases, so that AGC is applied due to adjacent interference, and demodulation is possible even if the IF output level decreases. However, if the AGC start is early, the signal level of the 1st IF output is low, and if the AGC is applied due to adjacent interference, the signal level will drop below the threshold that can be demodulated immediately, so the adjacent interference removal capability is Deteriorate.

  In the case of the above-mentioned 1/2 IF interference, the interference appears at 38.912 MHz. Therefore, when the RF AGC start is slow, the interference level becomes high and the 1/2 IF interference removal capability also deteriorates.

  The present invention has been made in view of the above-described problems, and the object of the present invention is to receive digital broadcast that can improve both the 1/2 IF interference removal capability and the image interference removal capability in a balanced manner. Is to provide a machine.

  In order to solve the above problems, the present invention provides a digital broadcast receiver comprising filter means for band-limiting a radio frequency signal and outputting the band-limited radio frequency signal. And a plurality of filter means having different pass bands, and a switch means for selecting and switching the plurality of filter means with a switch.

  According to a second aspect of the present invention, the digital broadcast receiver is characterized in that two or more of the plurality of filter means are arranged to be connected in parallel.

  According to claim 3 of the present invention, in the digital broadcast receiver, the switch means includes a control terminal to which a control signal for performing switching control of the plurality of filter means is input, The switching means is switched by the control signal, and the switching means is provided with filter switching control means for passing the radio frequency signal through the switched filter means.

  According to a fourth aspect of the present invention, in the digital broadcast receiver, the filter switching control unit includes a corresponding one of the plurality of filter units based on a radio frequency of the radio frequency signal. A switching control signal generating unit configured to select a filter unit and generate a control signal for switching to the selected filtering unit; and supplying the control signal generated by the switching control signal generating unit to the switching unit It is characterized by.

  According to a fifth aspect of the present invention, in the digital broadcast receiver, the filter means is a band pass filter (hereinafter abbreviated as BPF).

  According to the present invention, by switching BPFs of a plurality of L-Bands having different bands according to the L-Band channel, both 1/2 IF interference removal capability and image interference removal capability can be improved in a balanced manner. Can do.

  According to the present invention, by switching BPFs of a plurality of L-Bands having different bands in accordance with L-Band channels, it is possible to improve both the 1/2 IF interference removal capability and the image interference removal capability in a balanced manner. it can.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG.

  FIG. 1 shows a block diagram of a DAB receiver according to the present invention, and the configuration after L-Band MIX (mixer) is the same as the block diagram shown in FIG. Therefore, here, the difference will be described in detail.

  In the DAB receiver 100 according to the present embodiment, L-Band BPFa3 and L-Band BPFb4 having different pass bands are arranged in parallel, and these L-Band BPFa3 and L-Band BPFb4 are connected to the ATT ( Attenuator) 1 is connected. The RF switch 2 is, for example, a PIN diode switch, and is an on / off switch for switching the connection to the L-Band BPFa3 or the L-Band BPFb4.

  Next, the operation of the RF switch 2 will be described. Here, the L-Band BPFa3 band is 1452 to 1472 MHz, and the L-Band BPFb4 band is 1472 to 1491 MHz.

  In the present embodiment, the state of the RF switch 2 is controlled by the CPU 40. FIG. 2 is a flowchart showing a processing procedure of BPF switching control performed by the CPU 40.

  In FIG. 2, when the CPU 40 recognizes the detection of the desired reception channel a by channel search (step S1), the CPU 40 refers to the table managing L1ch to L12ch as group A and L13ch to L23ch as group B, and recognizes the received reception. It is determined whether channel a belongs to group A or group B (step S2). If it is determined in this determination that the reception channel a belongs to group A (group A in step S2), a control signal for switching to L-Band BPFa3 is generated (step S3) and the RF switch 2 is switched to. Supply. On the other hand, if it is determined in the above determination that the reception channel a belongs to group B (group B in step S2), a control signal for switching to L-Band BPFb4 is generated (step S4) and the RF switch 2 is supplied.

When the control signal representing the group A are supplied to the RF switch 2 from CPU 40, is connected to the switch terminals a2 _1, L-Band BPFa3 is turned ON. Conversely, when the control signal representing the group B is supplied to the RF switch 2 from CPU 40, the switch terminal b2 ₂ connection, L-Band BPFb4 is turned ON.

As described above, in this embodiment, L-Band BPFa3 is set to 1452 to 1472 MHz, L-Band BPFb4 is set to 1472 to 1491 MHz, and switching is performed by the RF switch 2 with L12ch and L13ch as a boundary. Here, when 1/2 IF interference is considered, the interference frequency is theoretically out of the band of L-Band BPFa3 and L-Band BPFb4 in all channels from the table shown in FIG. Interference removal capability is improved compared to the conventional one. Actually, the lower channel is close to the BPF band, but the upper side of the channel is farther from the BPF band, so the interference removal capability for 1/2 IF interference is far superior to the conventional one. Further, in this embodiment, for example, when L1ch image interference is considered, the L1ch image interference frequency is 1452.96 + 77.824 MHz = 1530.784 MHz, and in the conventional case, 1530784-1491 = 39. 784 MHz, that is, about 40 MHz away from the upper side of about BPF, and in the case of this embodiment, 1530.784-1472 = 58.784 MHz, that is, about 59 MHz away from the upper side of BPF. improves.

By the way, in the case of the DAB receiver 100 in the present embodiment, it is conceivable that the RF portion is made into an IC. Some current DAB receivers have a function to start AGC for each channel by setting data, and such types of DAB receivers are equipped with the RF switch shown in this embodiment. If the function of switching the BPF is used together, as a result, it is possible to increase the number of channels that can delay the start of AGC. Therefore, in the above case, the characteristics can be improved not only for 1/2 IF interference but also for adjacent interference.
In the present embodiment, the case where the present invention is applied to a DAB receiver has been described. However, the present invention can of course be applied to other digital systems (eg, broadcast receiving apparatuses) using a BPF in the GHz band. It is.

1 is a block diagram of a DAB digital broadcast receiver according to the present invention. FIG. It is a flowchart which shows the switching control process procedure of BPF performed by CPU. It is a block diagram of a conventional DAB digital broadcast receiver. It is a table | surface which shows the 1/2 IF interference frequency for every channel. It is a figure for demonstrating the influence of the adjacent channel interference by the speed of AGC start.

Explanation of symbols

100, 200 DAB receiver 1,11 ATT
2 RF switch 3, 12 L-Band BPF (Band Pass Filter) a
4, 13 L-Band BPFb
5, 14 L-Band LNA (Low Noise
Amp)
6, 15 L-Band MIX (mixer)
7, 16 L-Band OSC (local oscillator)
17 VHF band filter 18 PLL (Phase Lock Loop)
19 REF CLOCK (reference clock transmitter)
20 1st OSC
21 1st MIX
22 38.912 MHz filter (BPF)
23 2nd OSC
24 2nd MIX
25 2.048MHz filter 40 CPU

Claims (5)

A digital broadcast receiver comprising a filter means for band-limiting a radio frequency signal and outputting a band-limited radio frequency signal,
A plurality of filter means having different passbands;
Switch means for selecting and switching the plurality of filter means by a switch;
A digital broadcast receiver comprising: The digital broadcast receiver according to claim 1,
2. A digital broadcast receiver characterized in that two or more of the plurality of filter means are arranged in parallel. The digital broadcast receiver according to claim 1 or 2,
The switch means includes a control terminal to which a control signal for performing switching control of the plurality of filter means is input,
A digital broadcast receiver comprising: a switch switching control unit that switches the switch unit according to the control signal and passes the radio frequency signal through the switched filter unit. The digital broadcast receiver according to claim 3, wherein
The filter switching control unit selects a corresponding filter unit from the plurality of filter units based on a radio frequency of the radio frequency signal, and generates a control signal for switching to the selected filter unit. Comprising a switching control signal generating means,
A digital broadcast receiver characterized in that the control signal generated by the switching control signal generating means is supplied to the switch means. The digital broadcast receiver according to any one of claims 1 to 4,
The digital broadcast receiver characterized in that the filter means is a band-pass filter (hereinafter abbreviated as BPF).

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