JPH11177546A - Frame synchronization symbol recovery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably recover a frame synchronization symbol even when a response speed of an automatic gain controller is increased in the case of receiving a signal whose frame synchronization symbol denotes a non-signal period. SOLUTION: In interlocking with a change in an output signal of a frame synchronization symbol detector 21 at the arrival of a frame synchronization symbol, a band width of a variable band low-pass filter 14 is varied by a filter control means 24 to set a response speed of an automatic gain controller 11 lower. Thus, it is prevented that the operation is conducted with a maximum gain for automatic gain control for the frame synchronization symbol period and the frame synchronization symbol of the received signal is stably recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital audio broadcasting (hereinafter referred to as "digital audio broadcasting").
Simply referred to as DAB. The present invention relates to an apparatus and a method for reproducing a frame synchronization symbol in a receiver for receiving a signal in which the frame synchronization symbol is a non-signal section employed in (1), and a DAB receiver using the same.

[0002]

2. Description of the Related Art In a transmission frame of a DAB system developed by the Eureka Project in Europe, a null symbol having a length of about 1/74 of one frame length (length varies depending on a transmission mode) in one frame. There is a frame synchronization symbol called, and the frame synchronization symbol is a non-signal section. The DAB receiver detects the frame synchronization by detecting the frame synchronization symbol. Therefore, the DAB receiver converts the received signal to an intermediate frequency (Intermediate Frequency).
cy; Hereinafter, simply referred to as IF. After the frequency conversion into the band, the frame-synchronous symbol is detected by performing envelope detection on the frequency-converted signal.

FIG. 7 shows an example of a frame synchronization symbol reproducing apparatus used in a general DAB receiver. As an input of the automatic gain control device 81, an IF signal as shown in FIG. 8A in which a received signal is frequency-converted into an IF band is input. The automatic gain control device 81 includes a variable gain amplifying means 82 for amplifying with a variable gain, a detecting means 83 connected to an output of the variable gain amplifying means 82 for detecting an output signal of the variable gain amplifying means 82, and a detecting means 83 And a low-pass filter 84 for removing unnecessary harmonic components from the output of the variable gain amplifier 82. The output of the low-pass filter 84 is connected to the gain control terminal of the variable gain amplifying means 82. Automatic gain control device 8
1 is determined by the bandwidth of the low-pass filter 84. When the bandwidth of the low-pass filter 84 is set to be narrow, the response speed of the automatic gain control device 81 becomes low, and the low-pass filter 84 Is set wider, the response speed of the automatic gain controller 81 increases. Normally, the automatic gain controller 81 is used to prevent fading.
Is required to have a high response speed, the bandwidth of the low-pass filter 84 is set wide.

[0004] A frame synchronization symbol detecting device 91 performs envelope detection of an IF output signal of the variable gain amplifying unit 82, and performs waveform shaping of an output signal of the envelope detection unit 92 to obtain a frame synchronization symbol. And waveform shaping means 93 for generating The output of the waveform shaping means 93 is configured to be, for example, 0 V only during the frame synchronization symbol section, and to be 5 V otherwise.

[0005]

However, in the conventional DAB receiver as shown in FIG. 7, if the bandwidth of the low-pass filter 84 is set to be wide in consideration of fading, the variable gain amplifying means 82 sets the frame synchronization. In the symbol section,
Since the gain before the arrival of the frame synchronization symbol cannot be maintained, the operation is performed so that the maximum gain is quickly obtained. Therefore, an IF signal whose noise has been amplified in the frame synchronization symbol section is output to the output of the variable gain amplifying means 82 as shown in FIG. 8B. Since the output signal obtained from the IF signal as shown in FIG. 8B through the envelope detection means 92 is as shown in FIG. 8C, the threshold value of the waveform shaping means 93 is set as shown in FIG.
When the setting is made as shown in FIG. 8C, the output after waveform shaping is as shown in FIG. 8D. When compared with the originally reproduced frame synchronization symbol shown in FIG. Is not accurately reproduced, frame synchronization cannot be detected accurately, and the receiving operation becomes unstable.
There is a problem that the receiving operation becomes impossible if forced. Therefore, there is a limitation that the response speed of the automatic gain control device 81 must be determined at least within a range where the frame synchronization symbol can be reproduced.

The DAB system developed by the European Eureka Project has four different transmission modes. Different transmission modes have different frame lengths and different frame synchronization symbol lengths. Therefore, in the development of a receiver corresponding to a plurality of transmission modes, it is possible to optimize the response speed of the automatic gain control device 81 for each transmission mode in accordance with the transmission mode setting data set by the demodulation unit of the receiver. could not.

The present invention solves such a conventional problem. Even when the response speed of the automatic gain control device is increased, the frame synchronization symbol is reproduced stably to stabilize the reception operation. It is another object of the present invention to provide a frame synchronization symbol reproducing apparatus and method capable of optimizing a response speed of an automatic gain control apparatus for each transmission mode, and a DAB receiver using the same.

[0008]

According to the frame synchronization symbol reproducing apparatus of the present invention, when detecting the frame synchronization symbol of the signal output from the automatic gain control device, the output signal of the frame synchronization symbol detecting apparatus is converted to the frame synchronization symbol. The response speed of the automatic gain control device is set to be low in the frame synchronization symbol period by utilizing the change at the time of arrival, whereby the automatic gain control device has the maximum gain in the frame synchronization symbol period. Such operation can be prevented, and the frame synchronization symbol included in the received signal can be stably reproduced. Also, the response speed of the automatic gain control device outside the frame synchronization symbol section can be optimized for each transmission mode by the transmission mode setting data from the demodulation unit of the receiver.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention provides a variable gain amplifying means for receiving a signal in which a frame synchronization symbol is a non-signal section and amplifying the signal with a variable gain; An automatic gain control device including: a detection unit that detects an output signal; and a variable band low-pass filter that receives an output signal of the detection unit as an input and outputs a control signal for setting a gain of the variable gain amplifying unit. A signal output from the variable gain amplifying means as an input, an envelope detecting means for detecting a frame synchronization symbol included in the signal, a waveform shaping means for shaping the waveform of the output signal of the envelope detecting means, Frame synchronization symbol detection comprising: filter control means for outputting a control signal for varying the bandwidth of the variable band low-pass filter according to output fluctuations of the waveform shaping means. A frame synchronization symbol reproducing apparatus is composed of a location by the response speed of the automatic gain control to the low speed in the frame synchronization symbol section,
It is possible to prevent the automatic gain control device from operating to have the maximum gain in the frame synchronization symbol section, and to stably reproduce the frame synchronization symbol included in the received signal.

According to a second aspect of the present invention, there is provided a variable gain amplifying means for receiving a signal in which a frame synchronization symbol is a non-signal section and amplifying the signal with a variable gain, and detecting an output signal of the variable gain amplifying means. A wideband low-pass filter having one or a plurality of different bandwidths for receiving an output signal of the detection unit as an input and outputting a control signal for setting a gain of the variable gain amplifying unit; A narrow-band low-pass filter that receives an output signal of the unit as an input and outputs a control signal for setting a gain of the variable gain amplifying unit; and a wide-band low-pass filter having the one or more different bandwidths. An output signal and an output signal of a narrow band low-pass filter are input, and one of the signals from the wide band low-pass filter having one or more different bandwidths and the narrow band An automatic gain control device comprising: a filter switching unit that selects one of the output signals of the low-pass filter and outputs a control signal for setting a gain of the variable gain amplifying unit to the variable gain amplifying unit; ,
A signal output from the variable gain amplifying means is used as an input,
Envelope detecting means for detecting a frame synchronization symbol included in the signal, waveform shaping means for shaping the waveform of an output signal of the envelope detecting means, and a filter of the filter switching means by an output fluctuation of the waveform shaping means. A frame synchronization symbol reproducing device comprising a filter control means for outputting a control signal for selection, and a frame synchronization symbol reproducing device, wherein the response speed of the automatic gain control device is reduced in a frame synchronization symbol section. Thereby, it is possible to prevent the automatic gain control device from operating to have the maximum gain in the frame synchronization symbol section,
The frame synchronization symbol included in the received signal can be reproduced stably.

According to a third aspect of the present invention, there is provided a variable gain amplifying means for receiving a signal in which a frame synchronization symbol is a non-signal section and amplifying the signal with a variable gain, and detecting an output signal of the variable gain amplifying means. A wideband low-pass filter having one or a plurality of different bandwidths for receiving an output signal of the detection unit as an input and outputting a control signal for setting a gain of the variable gain amplifying unit; Or a filter switching means for selecting one of signals from a wideband low-pass filter having a plurality of different bandwidths and outputting a control signal for setting a gain to the variable gain amplifying means. A gain control device, an envelope detection means for receiving a signal output from the variable gain amplifying means and detecting a frame synchronization symbol included in the signal, and an envelope detection means Waveform shaping means for shaping the waveform of the output signal of the stage, charging / discharging means for charging / discharging by an external control signal, data conversion means for converting transmission mode setting data from a demodulation unit into a DC voltage, and said charging / discharging means Is connected to an inverting input terminal, and the output of the data conversion means is connected to a non-inverting input terminal, and the output signal from the waveform shaping means and the output signal from the comparator are input, and Signal switching means for selecting and outputting one of the output signal from the waveform shaping means and the output signal from the comparator, and the output signal from the waveform shaping means and the signal from the signal switching means. A logic circuit for receiving an output signal and controlling the charge / discharge means and the signal switching means to generate a frame synchronization symbol A frame synchronization symbol reproducing apparatus composed of a frame synchronization symbol detection device provided with, when the frame synchronization symbol arrives,
The logic circuit controls the charging / discharging means and the signal switching means, so that the frame synchronization symbol included in the received signal can be stably reproduced.

According to a fourth aspect of the present invention, there is provided a variable gain amplifying means for receiving a signal in which a frame synchronization symbol is a non-signal section and amplifying the signal with a variable gain, and detecting an output signal of the variable gain amplifying means. A wideband low-pass filter having one or a plurality of different bandwidths for receiving an output signal of the detection unit as an input and outputting a control signal for setting a gain of the variable gain amplifying unit; Or a filter switching means for selecting one of signals from a wideband low-pass filter having a plurality of different bandwidths and outputting a control signal for setting a gain to the variable gain amplifying means. A gain control device, an envelope detection means for receiving a signal output from the variable gain amplifying means and detecting a frame synchronization symbol included in the signal, and an envelope detection means A waveform shaping means for shaping the waveform of the output signal of the stage, a counter means which is given an initial value from the transmission mode setting data 12 from the demodulation unit and starts a counter operation by an external control signal, and an operation clock of the counter means. A clock generation unit, an output signal from the waveform shaping unit, and an output signal from the counter unit, and an output signal from the waveform shaping unit and a most significant bit from the counter unit according to an external control signal; A signal switching unit for selecting and outputting one of the output signals, and an output signal from the waveform shaping unit and an output signal from the signal switching unit, and controlling the counter unit and the signal switching unit. And a frame synchronization symbol detection device having a logic circuit for generating a frame synchronization symbol. Is a frame synchronizing symbol reproducing apparatus, when the frame synchronization symbol arrives, by the logic circuit for controlling the counter means and the signal switching means, a frame synchronization symbol included in the received signal can be stably reproduced.

The invention according to claim 5 of the present invention is characterized in that the filter control means changes its output in accordance with the transmission mode setting data from the demodulation section. Device, the response speed of the automatic gain control device outside the frame synchronization symbol interval,
It can be optimized for each transmission mode.

The invention according to claim 6 of the present invention is characterized in that the filter control means changes its output in accordance with the transmission mode setting data from the demodulation section. Device, the response speed of the automatic gain control device outside the frame synchronization symbol interval,
It can be optimized for each transmission mode.

According to a seventh aspect of the present invention, the filter switching means selects one of one or a plurality of wide band low-pass filters according to transmission mode setting data from a demodulation unit. 4. The frame synchronization symbol reproducing device according to claim 3, wherein the response speed of the automatic gain control device outside the frame synchronization symbol section can be optimized for each transmission mode.

According to an eighth aspect of the present invention, the filter switching means selects one of one or a plurality of wideband low-pass filters according to transmission mode setting data from a demodulation unit. 5. The frame synchronization symbol reproducing device according to claim 4, wherein the response speed of the automatic gain control device outside the frame synchronization symbol section can be optimized for each transmission mode.

According to a ninth aspect of the present invention, in the frame synchronization symbol reproducing apparatus according to the first or fifth aspect, the filter is operated in conjunction with the output signal of the waveform shaping means changing when the frame synchronization symbol arrives. A frame synchronization symbol reproducing method, wherein the control means varies the bandwidth of the variable band low-pass filter and changes the response speed of the automatic gain control device to a low speed in the frame synchronization symbol period. By reducing the response speed of the automatic gain control device, it is possible to prevent the automatic gain control device from operating so as to have the maximum gain in the frame synchronization symbol period, and to stabilize the frame synchronization symbol included in the received signal. And can be played.

According to a tenth aspect of the present invention, in the frame synchronization symbol reproducing apparatus according to the second or sixth aspect, the filter is operated in conjunction with the output signal of the waveform shaping means changing when the frame synchronization symbol arrives. A method for reproducing a frame synchronization symbol, wherein the control means controls the filter switching means to change the response speed of the automatic gain control device to a low speed in the frame synchronization symbol period. , It is possible to prevent the automatic gain control device from operating at the maximum gain in the frame synchronization symbol section, and to stably reproduce the frame synchronization symbol included in the received signal. Can be.

According to an eleventh aspect of the present invention, there is provided the frame synchronization symbol reproducing apparatus according to the third or seventh aspect, wherein the output signal of the logic circuit changes in response to the arrival of the frame synchronization symbol. Controlling the charge / discharge means and the signal switching means to generate a frame synchronization symbol, wherein the logic circuit controls the charge / discharge means and the signal switching means when the frame synchronization symbol arrives By doing so, it is possible to stably reproduce the frame synchronization symbols included in the received signal.

According to a twelfth aspect of the present invention, there is provided the frame synchronization symbol reproducing apparatus according to the fourth or eighth aspect, wherein the logic circuit outputs an output signal of the logic circuit in synchronization with the arrival of the frame synchronization symbol. Controlling a counter means and a signal switching means to generate a frame synchronization symbol, wherein a logic circuit controls the counter means and the signal switching means when a frame synchronization symbol arrives. Accordingly, the frame synchronization symbol included in the received signal can be reproduced stably.

According to a thirteenth aspect of the present invention, there is provided a digital audio broadcast receiver using the frame synchronization symbol reproducing apparatus according to the first or fifth aspect, which can realize a high-performance digital audio receiver. it can.

According to a fourteenth aspect of the present invention, there is provided a digital audio broadcast receiver using the frame synchronization symbol reproducing device according to the second or sixth aspect, which can realize a high-performance digital audio receiver. it can.

According to a fifteenth aspect of the present invention, there is provided a digital audio broadcast receiver using the frame synchronization symbol reproducing apparatus according to the third or seventh aspect, which realizes a high-performance digital audio receiver. it can.

According to a sixteenth aspect of the present invention, there is provided a digital audio broadcast receiver using the frame synchronization symbol reproducing apparatus according to the fourth or eighth aspect, which realizes a high-performance digital audio receiver. it can.

(Embodiment 1) FIG. 1 shows a frame synchronization symbol reproducing apparatus according to Embodiment 1 of the present invention. In FIG. 1, the input of the automatic gain control device 11 has a received signal frequency-converted into an IF band as shown in FIG.
Is input. The automatic gain control device 11 includes a variable gain amplifying means 12 for amplifying with a variable gain, a detecting means 13 for detecting an output signal of the variable gain amplifying means 12, and an output signal of the detecting means 13 as inputs. And a variable band low-pass filter 14 that outputs a control signal to the variable gain amplifier 12. The output of the variable band low-pass filter 14 is connected to a gain control terminal of the variable gain amplifier 12.

The response speed of the automatic gain control device 11 is determined by the bandwidth of the variable band low-pass filter 14. When the bandwidth of the variable band low-pass filter 14 is set narrow, the response speed of the automatic gain control device 11 is reduced. Slows down,
When the bandwidth of the variable band low-pass filter 14 is set to be wide, the response speed of the automatic gain control device 11 increases. Normally, the response speed of the automatic gain control device 11 needs to be high in order to prevent fading, so that the bandwidth of the variable band low-pass filter 14 is set wide. The bandwidth of the variable band low-pass filter 14 is configured so as to be widest when the control signal is 5V and narrowest when the control signal is 0V.

The frame synchronization symbol detection device 21 performs an envelope detection of an IF output signal from the variable gain amplifying unit 12 and an output signal of the envelope detection unit 22 to perform waveform shaping. It comprises a waveform shaping means 23 for generating a symbol, and a filter control means 24 for controlling the bandwidth of the variable band low-pass filter 14 by the output of the waveform shaping means 23 according to the transmission mode setting data from the demodulation unit. .

The output of the waveform shaping means 23 becomes, for example, 0 V only during the frame synchronization symbol section, and otherwise becomes 5 V.
V. The filter control means 24 outputs 5 V when the output of the waveform shaping means 23 is 5 V so as to set the bandwidth of the variable band low-pass filter 14 to be the widest, and outputs 0 V when the output is 0 V. Thus, the bandwidth of the variable band low-pass filter 14 is set to be the narrowest. Further, the output when the output of the waveform shaping means 23 is 5 V is configured to be changeable according to the transmission mode setting data from the demodulation unit. For example, it is configured to output 5 V when the data from the demodulation unit is “1” and output 4 V when the data is “0”. With this configuration, the bandwidth of the variable band low-pass filter can be changed for each transmission mode according to the transmission mode setting data, and the response of the automatic gain control device 11 outside the frame synchronization symbol section can be changed. The speed can be optimized for each transmission mode.

Next, the operation of the apparatus shown in FIG. 1 will be described. Here, the case where the transmission mode setting data from the demodulation unit is “1” will be described, but the same operation is performed when the transmission mode setting data is “0”. First, when the IF input signal of the variable gain amplifying means 12 enters the frame synchronization symbol as shown at point a in FIG. 5A, the output signal of the variable gain amplifying means 12 is also shown at point a in FIG. In order to enter the frame synchronization symbol as described above, the signal output through the envelope detection means 22 and the waveform shaping means 23 connected to the output of the variable gain amplifying means 12 is shown at a point a in FIG. As shown in FIG. Therefore, the filter control means 24 sets the bandwidth of the variable band low-pass filter 14 to be the narrowest, and changes the response speed of the automatic gain control device 11 to a low speed.

Then, since the gain of the variable gain amplifying means 12 operates at the gain immediately before entering the frame synchronization symbol, it is possible to prevent the variable gain amplifying means 12 from operating at the maximum gain in the frame synchronization symbol section. In this case, it is possible to prevent noise from being amplified in the frame synchronization symbol section from point a to point b in FIG. That is, the signal output through the envelope detection means 22 and the waveform shaping means 23 connected to the output of the variable gain amplifying means 12 is between point a and point b as shown in FIG. Keep 0V. This state is continued while the IF input signal of the variable gain amplifying means 12 reaches the point a and the point b in FIG. 5A, that is, during the frame synchronization symbol section, and the response speed of the automatic gain control device 11 is reduced. To keep.

Next, when the IF input signal of the variable gain amplifying means 12 escapes from the frame synchronization symbol as shown at point a in FIG. 5A, the output signal of the variable gain amplifying means 12 is also changed to the state shown in FIG. As shown at point b, the signal output from the envelope detecting means 22 and the waveform shaping means 23 connected to the output of the variable gain amplifying means 12 and exiting from the frame synchronization symbol is the signal shown in FIG. 5 as shown at point b
V. For this reason, the filter control means 24 sets the bandwidth of the variable band low-pass filter 14 to be the widest, and changes the response speed of the automatic gain control device 11 at high speed to cope with fading. This state continues until the IF input signal of the variable gain amplifying means 12 enters the frame synchronization symbol again, and the response speed of the automatic gain control device 11 is kept high.

As described above, according to the first embodiment, the filter control unit 24 controls the variable band low-pass filter 14
, The response speed of the automatic gain control device 11 is reduced in the frame synchronization symbol period, and the variable gain amplifying unit 12 is prevented from operating at the maximum gain in the frame synchronization symbol period. Noise can be prevented from being amplified in the synchronization symbol section,
The frame synchronization symbol can be reproduced stably. Furthermore, the response speed of the automatic gain control device 11 outside the frame synchronization symbol section can be optimized for each transmission mode according to the transmission mode setting data from the demodulation unit.

(Embodiment 2) FIG. 2 shows a frame synchronization symbol reproducing apparatus according to Embodiment 2 of the present invention. In FIG. 2, the inputs of the automatic gain control device 31 include:
An IF signal as shown in FIG. 5A in which a received signal is frequency-converted into an IF band is input. The automatic gain control device 31 includes a variable gain amplifying unit 12 for amplifying with a variable gain.
A detecting means 13 for detecting an output signal of the variable gain amplifying means 12; a variable band low-pass filter 32 which receives the output signal of the detecting means 13 and outputs a control signal to the variable gain amplifying means 12; , And outputs a control signal for setting the gain of the variable gain amplifying means 12. The second wideband low-pass filter 33 having a bandwidth different from that of the first wide-band low-pass filter 32. When,
A narrow-band low-pass filter 34 that receives an output signal of the detection unit 13 as an input and outputs a control signal for setting the gain of the variable gain amplifying unit 12, an output signal of the first wide-band low-pass filter 32, 2 broadband low-pass filter 3
3 and the output signal of the narrow-band low-pass filter 34 are input, and one of the output signal from the first wide-band low-pass filter 32 and the output signal from the second wide-band low-pass filter 33 is input. Selecting one of the output signal and the output signal of the narrowband low-pass filter 34,
A filter switching means for outputting a control signal to the variable gain amplifying means; and an output of the filter switching means is connected to a gain control terminal of the variable gain controlling means. The variable gain control means 12 and the detection means 13 are the same as those used in FIG.

The filter switching means 35 selects a signal from the first broadband low-pass filter 32 when the control signal is 5V, and selects a signal from the second wideband low-pass filter 33 when the control signal is 4V. When the voltage is 0 V, the signal of the narrow-band low-pass filter 34 is selected.

The response speed of the automatic gain controller 31 is determined by the output of the filter switching means 35. When the output of the filter switching means 35 selects and outputs the output signal of the narrow band low-pass filter 34. Is that the response speed of the automatic gain control device 31 becomes low, and the output of the filter switching means 35 selects the output signal of the first broadband low-pass filter 32 or the output signal of the second wideband low-pass filter 33. In this case, the response speed of the automatic gain control device 31 becomes high. Normally, the response speed of the automatic gain control device 31 needs to be high in order to prevent fading, so the output of the filter switching means 35 outputs the output signal of the first broadband low-pass filter 32 or the second signal. The output signal of the wideband low-pass filter 33 is output.

The frame synchronization symbol detector 41 includes an envelope detector 22 for performing envelope detection of the IF output signal from the variable gain amplifying unit 12, and a waveform shaping unit for performing waveform shaping of the output signal of the envelope detector 22. 23, and a filter control means 24 for controlling the signal switching means 34 based on the output of the waveform shaping means 23. Envelope detection means 2
2. The waveform shaping means 23 and the filter control means 24 are the same as those used in FIG.

The filter control means 24 includes the waveform shaping means 2
3 outputs 5 V when the output of 3 is 5 V, so that the filter switching means 35 selects the signal from the first broadband low-pass filter 32. 35 sets the bandwidth of the narrow-band low-pass filter 34 to be the narrowest. Further, the output when the output of the waveform shaping means 23 is 5 V is configured to be changeable according to the transmission mode setting data from the demodulation unit. For example, when the data from the demodulation unit is 1, 5
It outputs V and outputs 4 V when it is 0.
With this configuration, the bandwidth of the wideband low-pass filter can be changed for each transmission mode according to the transmission mode setting data, and the response speed of the automatic gain control device 31 outside the frame synchronization symbol section can be changed. Can be optimized for each transmission mode.

Next, the operation of the apparatus shown in FIG. 2 will be described. Here, the case where the transmission mode setting data from the demodulation unit is “1” will be described, but the same operation is performed when the transmission mode setting data is “0”. First, when the IF input signal of the variable gain amplifying means 12 enters the frame synchronization symbol as shown at point a of FIG. 5A, the output signal of the variable gain amplifying means 12 also becomes at the point a of FIG. As shown in the figure, the signal output through the envelope detection means 22 and the waveform shaping means 23 connected to the output of the variable gain amplifying means 12 to enter the frame synchronization symbol is at a point a in FIG. It changes to 0V as shown. Therefore, the output signal of the filter switching means 35 is output, and the response speed of the automatic gain control device 31 is changed to a low speed.

Then, since the gain of the variable gain amplifying means 12 operates at the gain immediately before entering the frame synchronization symbol, the output of the variable gain amplifying means 12 is as shown in FIG.
It is possible to prevent operation at the maximum gain in the frame synchronization symbol section during the period from point a to point b, and to prevent noise from being amplified in the frame synchronization symbol section. This state is continued while the input signal of the variable gain amplifying means 12 goes from the point a to the point b in FIG. 5A, that is, in the frame synchronization symbol section, and the response speed of the automatic gain control device 31 is reduced. To keep.

Next, when the IF input signal of the variable gain amplifying means 12 escapes from the frame synchronization symbol, the output signal of the variable gain amplifying means 12 also escapes from the frame synchronization symbol and is connected to the output of the variable gain amplifying means 12. The signal output via the envelope detection means 22 and the waveform shaping means 23 changes to 5V. For this reason, the output signal of the first broadband low-pass filter 32 is output from the output of the filter switching means 35, and the automatic gain control device 3
The response speed of No. 1 is changed at high speed to cope with fading. This state is continued until the IF input signal of the variable gain amplifying means 12 enters the frame synchronization symbol again, and the response speed of the automatic gain control device 31 is kept high.

As described above, according to the second embodiment, the filter control means 24 controls the filter switching means 35 so that the first broadband low-pass filters 32 and 33 or the narrow-band low-pass filter 34 By switching the bandwidth by selecting any one of the above, the response speed of the automatic gain control device 31 is reduced in the frame synchronization symbol period, and the variable gain amplifying means 12 operates at the maximum gain in the frame synchronization symbol period. By preventing the noise, amplification of noise in the frame synchronization symbol section can be prevented, and the frame synchronization symbol can be stably reproduced.
Furthermore, according to the transmission mode setting data from the demodulation unit,
Automatic gain control device 31 outside frame synchronization symbol section
Can be optimized for each transmission mode.

(Embodiment 3) FIG. 3 shows a frame synchronization symbol reproducing apparatus according to a third embodiment of the present invention. In FIG. 3, the input of the automatic gain control device 51 has the received signal frequency-converted into the IF band in FIG.
Is input. The automatic gain control device 51 includes a variable gain amplifying means 12 for amplifying with a variable gain, a detecting means 13 for detecting an output signal of the variable gain amplifying means 12, and an output signal of the detecting means 13 as inputs. A first broadband low-pass filter 32 for outputting a control signal to the control signal 12 and an output signal of the detection means 13 are input, and a control signal for setting the gain of the variable gain amplifying means 12 is output. Low-pass filter 3
2, a second wideband low-pass filter 33 having a bandwidth different from the second, a first broadband low-pass filter 32 and an output signal of the second wide-band low-pass filter 33 as inputs. Filter switching means 52 for selecting one of the output signal from wideband low-pass filter 32 and the output signal from second wide-band low-pass filter 33 and outputting a control signal to variable gain amplifying means 12
The output of the filter switching means 52 is connected to the gain control terminal of the variable gain control means 12. The variable gain control means 12 and the detection means 13 are the same as those used in FIG. 1, and the first wide band low pass filter 32, the second wide band low pass filter 33 and the filter switching means 35 are the same as those shown in FIG. It is the same as that used in.

The filter switching means 52 selects the signal from the first broadband low-pass filter 32 when the transmission mode setting data from the control signal is "1", and selects the signal from the second broadband when the transmission mode setting data is "0". The signal from the low-pass filter 33 is selected.

The response speed of the automatic gain control device 51 is determined by the bandwidth of the first broadband low-pass filter 32 or the second wideband low-pass filter 33, and the response speed of the automatic gain control device 51 becomes high. .

The frame synchronization symbol detector 61 includes an envelope detector 22 for performing envelope detection of the IF output signal from the variable gain amplifying unit 12, and a waveform shaping unit for performing waveform shaping of the output signal of the envelope detector 22. 23, a charging / discharging means 62 for performing charging / discharging by an external control signal, a data converting means 63 for converting data from the demodulation section into a DC voltage, and an output of the charging / discharging means 62 connected to an inverting input terminal, The output of the means 63 is connected to the non-inverting input terminal of the comparator 64, the output signal of the waveform shaping means 23 and the output signal of the comparator 64, and the control signal from the outside is used to input the signal from the waveform shaping means 23. A signal switching unit 65 for selecting and outputting one of the output signal and the output signal from the comparator 64, and an output signal from the waveform shaping unit 23. And signal includes a logic circuit 66 for inputting the output signal from the switching means 65, the output of the logic circuit 66 is connected to the control terminal of the control terminal and the signal switching means 65 of the charging and discharging means 62. The envelope detecting means 22 and the waveform shaping means 23 are the same as those used in FIG.

The charging / discharging means 62 is set to charge when the signal applied to the control terminal is 5 V, for example, and to discharge when the signal applied to the control terminal is 0 V. The data conversion unit 63 generates a different DC voltage for each transmission mode according to data based on the transmission mode from the demodulation unit. For example, it is configured to output 2.5 V when the data from the demodulation unit is “1” and output 1.5 V when the data is “0”.
The charging / discharging means 62 and the data converting means 63 determine the time from when the charging / discharging circuit means 62 starts discharging, when the output of the charging / discharging means 62 starts dropping from 5 V and falls below the output voltage from the data converting means 63. The time constant of the charging / discharging circuit means 62 and the output voltage from the data converting means 63 are set so that the time becomes equal to the frame synchronization symbol length corresponding to the transmission mode.

The signal switching means 65 selects and outputs the output signal from the waveform shaping means 23 when the signal supplied to the control terminal is, for example, 5 V. When the signal supplied to the control terminal is, for example, 0 V, The output signal from the comparator 64 is set to be selected and output. Logic circuit 6
Reference numeral 6 denotes, for example, a two-input AND circuit.

Next, the operation of the apparatus shown in FIG. 3 will be described. Here, the case where the transmission mode setting data from the demodulation unit is “1” will be described, but the same operation is performed when the transmission mode setting data is “0”. When the power is turned on, 5 V is set to the output of the logic circuit 66, 5 V is applied to the control voltage of the signal switching unit 65, the charging / discharging unit 62 is charged, and the output of the charging / discharging unit is set to 5 V. It shall be. Since the output from the first broadband low-pass filter 32 is selected by the filter switching means 52, the response speed of the automatic gain control device 51 is high,
The operation is the same as that of the conventional example shown in FIG. For this reason, the envelope detecting means 2 connected to the output of the variable gain amplifying means 12
2 and the signal output via the waveform shaping means 23 are shown in FIG.
The result is as shown in FIG.

As shown in FIG. 8D, the waveform shaping means 2
Since the setting is made so as to select and output the output signal from 3, 0 V is applied to both inputs of the logic circuit 66, and the output of the logic circuit 66 is indicated by a point a in FIG. As shown in FIG. At this time, the charging / discharging circuit means 62
Since the control terminal is supplied with 0 V, the charging / discharging circuit means 62 starts discharging from the point a in FIG. 6B, but since the DC voltage outputted from the data converting means 63 is 2.5 V While the output of the charging / discharging circuit means 62 is a voltage higher than 2.5 V (up to the point b in FIG. 6B), the output of the comparator 64 maintains 0 V as shown in FIG. 6C. Further, 0 V is applied to the control terminal of the signal switching means 65, and the signal switching means 65 selects an output signal from the comparator 64.

While the output of the comparator 64 indicates 0 V, the response speed of the automatic gain control device 51 is set to high speed, so that the gain of the variable gain amplifying means 12 quickly reaches the maximum gain in the frame synchronization symbol section. Works like that. Therefore, the output of the variable gain amplifying means 12 includes:
As shown in FIG. 8B, an IF signal in which noise has been amplified in the frame synchronization symbol section is output. The output signal obtained from the IF signal as shown in FIG. 8B through the envelope detection means 22 is as shown in FIG. 8D. However, since the output of the signal switching means 65 which selects and outputs the output of the comparator 64 remains at 0 V, the logic circuit 6
The output of 6 keeps 0V.

The output of the charging / discharging circuit means 62 gradually decreases, and the output of the charging / discharging circuit means 62
When the voltage falls below 2.5 V, which is the output from 3 (point b in FIG. 6B), the output of the comparator 64 becomes 5 V as shown at point b in FIG. It becomes 5V. At this time, since the output of the waveform shaping unit 23 is already 5 V, the output of the logic circuit 66 becomes 5 V as shown at point b in FIG. Therefore, 5 V is applied to the control terminal of the signal switching means 65, and the waveform shaping means 2
3 is selected and output. Then, since 5 V is applied to both inputs of the logic circuit 66, the output of the logic circuit 66 maintains 5 V. At the same time, the charging / discharging circuit means 62 starts charging, and the output of the charging / discharging circuit means 62 immediately exceeds the output of 2.5 V from the data converting means 63 (point c in FIG. 6B). The output becomes 0 V as shown at point c in FIG.

The charge / discharge circuit means 62 and the data conversion means 63 start charging the charge / discharge circuit means 62, the output of the charge / discharge circuit means 62 starts to decrease from 5V, and falls below the output voltage from the data conversion means 63. The time constant of the charging / discharging circuit means 62 and the output voltage from the data converting means 63 are set so that the time until the time becomes equal to the frame synchronization symbol length corresponding to the transmission mode. The output at 62 has reached 5 V by the next frame synchronization symbol.

As described above, according to the third embodiment, the charge / discharge circuit means 62 starts discharging, and the charge / discharge circuit means 62
The output of the frame synchronization symbol detection device 61 keeps 0 V until the output of the frame synchronization symbol detection device 61 starts to decrease from 5 V and falls below the output voltage from the data conversion means 63. The keeping time matches the frame synchronization symbol length, and the frame synchronization symbol can be stably reproduced. Further, according to the transmission mode setting data from the demodulation unit, the response speed of the automatic gain control device 31 outside the frame synchronization symbol section can be optimized for each transmission mode.

(Embodiment 4) FIG. 4 shows a frame synchronization symbol reproducing apparatus according to a fourth embodiment of the present invention. In FIG. 4, the input of the automatic gain control device 51 has a received signal frequency-converted into an IF band as shown in FIG.
Is input. The automatic gain control device 51 is the same as that used in FIG.

The frame synchronization symbol detecting device 71 comprises an envelope detecting means 22 for performing an envelope detection of the IF output signal from the variable gain amplifying means 12, and a waveform shaping means for performing a waveform shaping of the output signal of the envelope detecting means 22. 23 and a counter means 7 which is given an initial value by transmission mode setting data from the demodulation unit and starts a counter operation by an external control signal.
2, a clock generating means 73 for providing an operation clock of the counter means 72, and an output signal from the waveform shaping means 23 and a most significant bit output signal from the counter means 72. The waveform shaping is performed by an external control signal. Means 2
Signal switching means 65 for selecting and outputting one of the output signal from the counter 3 and the output signal from the counter means 72.
And a logic circuit 66 for inputting the output signal from the waveform shaping means 23 and the output signal from the signal switching means 65, and the output of the logic circuit 66 is
And the control terminal of the signal switching means 65. Envelope detection means 22 and waveform shaping means 23
Are the same as those used in FIG. 1, and the signal switching means 65 and the logic circuit 66 are the same as those used in FIG.

When the signal supplied to the control terminal changes from, for example, 5 V to 0 V (negative edge), the counter 72 sets an initial value that differs for each transmission mode in accordance with the transmission mode setting data from the demodulation unit. Set to start counting operation.

The clock generating means 73 includes the counter means 7
2 is supplied with an operation clock. The counter 72 and the clock generator 73 start counting when the counter 72 starts counting, for example, when the most significant bit is “1” (5
The initial value of the counter 72 and the clock frequency of the clock generator 73 are set so that the time until V) becomes equal to the frame synchronization symbol length according to the transmission mode. For example, when the reciprocal of the time that becomes the greatest common divisor of the frame synchronization symbol length of the corresponding transmission mode is set as the clock frequency of the clock generation unit 73, the count number until the clock frequency and the time equal to the frame synchronization symbol length become minimum Can be.

The signal switching means 65 selects and outputs the output signal from the waveform shaping means 23 when the signal applied to the control terminal is, for example, 5 V. When the signal applied to the control terminal is, for example, 0 V, A setting is made so that the output signal of the most significant bit of the counter means 72 is selected and output.

Next, the operation of the apparatus shown in FIG. 4 will be described. Here, the case where the transmission mode setting data from the demodulation unit is “1” will be described, but the same operation is performed when the transmission mode setting data is “0”. When the power is turned on, it is assumed that the output of the logic circuit 66 is set to 5 V, and the control voltage of the signal switching means 65 is 5 V. Since the output from the first broadband low-pass filter 32 is selected by the filter switching means 52, the response speed of the automatic gain control device 51 is high, and the operation is equivalent to that of the conventional example of FIG. Therefore, the variable gain amplifying means 12
The signal output via the envelope detection means 22 and the waveform shaping means 23 connected to the output of FIG. 8 is as shown in FIG.

As shown in FIG. 8D, the waveform shaping means 2
Since the signal switching means 65 is set so as to select and output the output signal from the waveform shaping means 23 when the output from 3 changes to 0 V, 0 V is applied to both inputs of the logic circuit 66. Therefore, the output of the logic circuit 66 becomes 0 V as shown at point a in FIG. At this time, since the control terminal of the counter 72 changes from 5 V to 0 V, the counter 72 starts the counting operation from an initial value corresponding to the data based on the transmission mode from the demodulator. 0 (0 V) is output from the most significant bit of. Also, 0 V is applied to the control terminal of the signal switching means 65, and the signal switching means 65 selects an output signal from the most significant bit of the counter means 72.

While the output of the most significant bit of the counter means 72 indicates 0 V, the response speed of the automatic gain control device 51 is set to a high speed, so that the gain of the variable gain amplifying means 12 is increased in the frame synchronization symbol section. Operate quickly to maximum gain. Therefore, the variable gain amplifying means 1
As an output of 2, an IF signal in which noise is amplified in a frame synchronization symbol section is output as shown in FIG. The IF signal as shown in FIG.
The output signal obtained through the waveform shaping unit 23 is as shown in FIG.
(D). However, since the output of the signal switching means 65 which selects and outputs the output of the most significant bit of the counter means 72 remains at 0 V, the logic circuit 66
Keeps 0V.

When the output of the most significant bit of the counter means 72 becomes "1" (5V), the output of the signal switching means 65 also becomes 5V. At this time, since the output of the waveform shaping means 23 is already 5 V, the output of the logic circuit 66 is shown in FIG.
It becomes 5V as shown at point b. Therefore, 5 V is applied to the control terminal of the signal switching means 65, and the output signal from the waveform shaping means 23 is selected and output. Then, since 5 V is applied to both inputs of the logic circuit 66, the output of the logic circuit 66 maintains 5 V.

As described above, according to the fourth embodiment, the counter 72 starts the counting operation, and the most significant bit of the counter 72 changes from “0” (0 V) to “1” (5
V), the output of the frame synchronization symbol detection device 71 maintains 0 V. Therefore, the time during which the output of the frame synchronization symbol detection device 71 maintains 0 V matches the frame synchronization symbol length, and Can be reproduced stably. Further, according to the transmission mode setting data from the demodulation unit, the response speed of the automatic gain control device 31 outside the frame synchronization symbol section can be optimized for each transmission mode.

[0064]

As is apparent from the above description, according to the first aspect of the present invention, the variable band low band is linked to the fact that the output signal of the frame synchronization symbol detecting device changes when a frame synchronization symbol arrives. By varying the bandwidth of the pass filter and reducing the response speed of the automatic gain control device, it is possible to prevent the automatic gain control device from operating to the maximum gain in the frame synchronization symbol section, and to reduce the frame synchronization. Symbols can be reproduced stably. Further, according to the transmission mode setting data from the demodulation unit, the response speed of the automatic gain control device outside the frame synchronization symbol section can be optimized for each transmission mode.

According to the second aspect of the present invention, the output signal of the narrow-band low-pass filter is selected in conjunction with the fact that the output signal of the frame synchronization symbol detector changes when the frame synchronization symbol arrives. By lowering the response speed of the automatic gain control device, the same effect as that of the first aspect can be obtained. Further, since the variable band low-pass filter used in the first invention is not used, cost reduction can be achieved.

According to the third aspect of the present invention, the frame synchronization symbol is stably reproduced by the charging / discharging means in conjunction with the change of the output signal of the frame synchronization symbol detection device when the frame synchronization symbol arrives. be able to. Also, unlike the first and second inventions,
Since the frame synchronization symbol is generated independently for the automatic gain control device, the frame synchronization symbol can be reproduced without affecting the automatic gain control device.

According to the fourth aspect of the present invention, the frame synchronization symbol can be generated by the counter means in conjunction with the change of the output signal of the frame synchronization symbol detection device when the frame synchronization symbol arrives, The frame synchronization symbol can be reproduced stably. Also, unlike the first and second inventions, since the frame synchronization symbol is generated independently for the automatic gain control device, the frame synchronization symbol is reproduced without affecting the automatic gain control device. can do. Further, unlike the third invention, the charge / discharge circuit is not used,
Since the frame synchronization symbol is generated only by digital processing, the frame synchronization symbol length can be easily set as compared with the case where the frame synchronization symbol length is set by the time constant of the charge / discharge circuit.

In the description of the third invention and the fourth invention, two wideband low-pass filters are used.
If there is no need to support a plurality of transmission modes, only one wideband low-pass filter is required, and in that case, a filter switching unit is not required.

The DAB system developed by the Eureka Project in Europe has been described above as an example. However, the received signal includes a frame synchronization symbol, and there is an amplitude difference between the frame synchronization symbol and other symbols. The present invention can be similarly applied to various communication systems.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a frame synchronization symbol reproducing apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram showing a frame synchronization symbol reproducing device according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a frame synchronization symbol reproducing device according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a frame synchronization symbol reproducing device according to a fourth embodiment of the present invention.

5A is a waveform diagram of an IF signal input to the variable gain amplifying means of the present invention. FIG. 5B is a diagram of an IF signal output from the variable gain amplifying means according to the first to third embodiments of the present invention. Waveform diagram (C) Waveform diagram of the output signal from the waveform shaping means in the first and second embodiments of the present invention

FIG. 6A is a waveform diagram of an output signal from a logic circuit according to the third and fourth embodiments of the present invention. FIG. 6B is a diagram of an output signal from the charging / discharging means according to the third embodiment of the present invention. Waveform diagram (C) Waveform diagram of the output signal from the comparator according to the third embodiment of the present invention

FIG. 7 is a block diagram showing a frame synchronization symbol reproducing device in a conventional example.

8A is a waveform diagram of an IF signal input to a variable gain amplifying unit in a conventional example. FIG. 8B is a waveform diagram of an IF signal output from a variable gain amplifying unit in a conventional example. (D) Waveform diagram of output signal from waveform shaping device in conventional example (E) Waveform diagram of frame synchronization symbol to be originally detected in conventional example

[Explanation of symbols]

11, 31, 51 Automatic gain control device 21, 41, 61, 71 Frame synchronization symbol detection device 12 Variable gain amplification means 13 Detection means 14 Variable band low-pass filter 22 Envelope detection means 23 Waveform shaping means 24 Filter control means 32 First broadband low-pass filter 33 Second broadband low-pass filter 34 Narrow-band low-pass filter 35, 52 Filter switching means 62 Charge / discharge means 63 Data conversion means 64 Comparator 65 Signal switching means 66 Logic circuit 72 Counter means 73 Clock generation means

Claims (16)

[Claims] 1. A variable gain amplifying means for receiving a signal in which a frame synchronization symbol is a non-signal section and amplifying the signal with a variable gain, a detecting means for detecting an output signal of the variable gain amplifying means, and an output signal of the detecting means And an automatic gain control device including a variable band low-pass filter that outputs a control signal for setting the gain of the variable gain amplifying means, and a signal output from the variable gain amplifying means as an input. ,
An envelope detection means for detecting a frame synchronization symbol included in the signal; a waveform shaping means for shaping a waveform of an output signal of the envelope detection means; and an output fluctuation of the waveform shaping means, the variable band low-pass filter A frame synchronization symbol reproducing device comprising: a frame synchronization symbol detection device including: a filter control unit that outputs a control signal for varying a bandwidth of the frame synchronization symbol. 2. A variable gain amplifying means for receiving a signal in which a frame synchronization symbol is a no-signal section and amplifying the signal with a variable gain, a detecting means for detecting an output signal of the variable gain amplifying means, and an output signal of the detecting means. And outputs a control signal for setting the gain of the variable gain amplifying means.
Or a wideband low-pass filter having a plurality of different bandwidths, and a narrow-band low-pass filter that receives an output signal of the detection unit as an input and outputs a control signal for setting a gain of the variable gain amplifying unit. Inputting the output signal of the wideband low-pass filter and the output signal of the narrow-band low-pass filter having the one or more different bandwidths,
One of the signals from the wideband low-pass filter having the one or more different bandwidths and one of the output signals of the narrow-band low-pass filter are selected, and the variable gain amplifying means selects the variable gain amplifying means. An automatic gain control device including a filter switching unit that outputs a control signal for setting the gain of the unit, and a signal output from the variable gain amplifying unit as an input,
Envelope detecting means for detecting a frame synchronization symbol included in the signal, waveform shaping means for shaping the waveform of an output signal of the envelope detecting means, and a filter of the filter switching means by an output fluctuation of the waveform shaping means. A frame synchronization symbol reproducing device comprising: a frame synchronization symbol detection device including a filter control unit that outputs a control signal for selection. 3. A variable gain amplifying means for receiving a signal in which a frame synchronization symbol is a no-signal section and amplifying the signal with a variable gain, a detecting means for detecting an output signal of the variable gain amplifying means, and an output signal of the detecting means. And outputs a control signal for setting the gain of the variable gain amplifying means.
Alternatively, a wideband low-pass filter having a plurality of different bandwidths, and one of the signals from the one or more wideband low-pass filters having the different bandwidths are selected, and a gain is supplied to the variable gain amplifying means. An automatic gain control device including a filter switching unit that outputs a control signal for setting a, and a signal output from the variable gain amplifying unit as an input,
Envelope detection means for detecting a frame synchronization symbol included in a signal, waveform shaping means for shaping a waveform of an output signal of the envelope detection means, charge / discharge means for charging / discharging by an external control signal, and a demodulation unit A data conversion means for converting the transmission mode setting data from a DC voltage to a DC voltage, a comparator having an output of the charge / discharge means connected to an inverting input terminal, and an output of the data conversion means connected to a non-inverting input terminal, An output signal from the waveform shaping unit and an output signal from the comparator are input, and one of an output signal from the waveform shaping unit and an output signal from the comparator is selected and output by an external control signal. Signal switching means, and an output signal from the waveform shaping means and an output signal from the signal switching means. And said signal switching means to control, frame synchronization symbol detection device and the frame consists of synchronization symbol reproducing apparatus that includes a logic circuit for generating a frame synchronization symbol. 4. A variable gain amplifying means for receiving a signal in which a frame synchronization symbol is a non-signal section and amplifying the signal with a variable gain, a detecting means for detecting an output signal of the variable gain amplifying means, and an output signal of the detecting means. And outputs a control signal for setting the gain of the variable gain amplifying means.
Alternatively, a wideband low-pass filter having a plurality of different bandwidths, and one of the signals from the one or more wideband low-pass filters having the different bandwidths are selected, and a gain is supplied to the variable gain amplifying means. An automatic gain control device including a filter switching unit that outputs a control signal for setting a, and a signal output from the variable gain amplifying unit as an input,
Envelope detection means for detecting a frame synchronization symbol included in the signal, waveform shaping means for shaping the waveform of the output signal of the envelope detection means, and an initial value given by transmission mode setting data from the demodulation unit, Counter means for starting a counter operation by an external control signal, clock generating means for providing an operation clock of the counter means, and an output signal from the waveform shaping means and an output signal from the counter means as inputs, and control from the outside. Signal switching means for selecting and outputting one of an output signal from the waveform shaping means and a most significant bit output signal from the counter means, and an output signal from the waveform shaping means and the signal switching means And an output signal from the control unit, and controls the counter unit and the signal switching unit to output a frame signal. Frame synchronization symbol reproducing apparatus composed of a frame synchronization symbol detection device and a logic circuit for generating a period symbol. 5. The frame synchronization symbol reproducing apparatus according to claim 1, wherein the filter control means changes its output in accordance with the transmission mode setting data from the demodulation section. 6. The frame synchronization symbol reproducing device according to claim 2, wherein the filter control means changes its output in accordance with the transmission mode setting data from the demodulation section. 7. The filter switching means according to claim 3, wherein the output of the filter is selected from one or a plurality of wideband low-pass filters according to transmission mode setting data from a demodulation unit. Frame synchronization symbol playback device. 8. The filter switching means according to claim 4, wherein an output of the filter switching means selects one of one or a plurality of wideband low-pass filters according to transmission mode setting data from a demodulation unit. Frame synchronization symbol playback device. 9. The frame synchronization symbol reproducing apparatus according to claim 1, wherein the output signal of the waveform shaping means changes when the frame synchronization symbol arrives.
A frame synchronization symbol reproducing method, wherein the filter control means varies the bandwidth of the variable band low-pass filter and changes the response speed of the automatic gain control device to a low speed in the frame synchronization symbol section. 10. The frame synchronization symbol reproducing apparatus according to claim 2, wherein the filter control means controls the filter switching means in conjunction with the output signal of the waveform shaping means changing when the frame synchronization symbol arrives. And changing the response speed of the automatic gain control device to a low speed in the frame synchronization symbol section. 11. The frame synchronization symbol reproducing apparatus according to claim 3, wherein the logic circuit controls the charging / discharging means and the signal switching means in conjunction with the change of the output signal of the logic circuit when the frame synchronization symbol arrives. And generating a frame synchronization symbol. 12. The frame synchronization symbol reproducing device according to claim 4, wherein the logic circuit controls the counter means and the signal switching means in conjunction with the change of the output signal of the logic circuit when the frame synchronization symbol arrives. And generating a frame synchronization symbol. 13. A digital audio broadcast receiver using the frame synchronization symbol reproducing device according to claim 1. 14. A digital audio broadcast receiver using the frame synchronization symbol reproducing device according to claim 2. 15. A digital audio broadcast receiver using the frame synchronization symbol reproducing device according to claim 3. 16. A digital audio broadcast receiver using the frame synchronization symbol reproducing device according to claim 4.