JP2009182781A - Diversity reception device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a diversity reception device for digital broadcasting can be improved in reception sensitivity in a weak electric field environment, but large in power consumption since two systems of receiving circuits need to be placed in operation as compared with an ordinary reception device for digital broadcasting and the problem that characteristic improvement effect by diversity operation can not be obtained in the strong electric field environment and distortion in a channel selecting circuit is generated to cause deterioration in receiving operation. <P>SOLUTION: A diversity reception device 100 performs diversity operation only in the weak electric field environment, and stops the diversity operation when the electric field intensity of a reception signal is larger than a predetermined value, and a gain varying circuit 2 is disposed in front of the channel selecting circuit and a gain in the circuit 2 is made small in gain when the electric field intensity of the reception signal is larger than the predetermined value, so that the channel selecting circuit generates no distortion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for receiving a digital broadcast such as a terrestrial digital broadcast, and more particularly to a digital broadcast receiving apparatus that includes a plurality of channel selection circuits and a digital demodulation circuit and performs diversity reception.

  Digital terrestrial broadcasting in Japan started in 2003 and is currently in a situation where the number of viewers is increasing while expanding the broadcasting area. Terrestrial digital broadcasting employs an OFDM (Orthogonal Frequency Division Multiplexing) modulation system as a digital modulation system. The OFDM modulation system is excellent in mobile reception, and can be broadcast for mobiles called one-segment broadcasting that is transmitted using only a part of the channel band and can reduce power consumption of the receiver. This one-segment broadcasting service was started in 2006, and not only a home television receiver but also a market for mobile receivers for in-vehicle use and mobile phone use is expected.

When receiving digital terrestrial broadcasting, especially in mobile receivers, multiple systems of antennas, channel selection circuits, and digital demodulation circuits are provided, and maximum ratio combining technology is applied to the received signals of each system to improve reception sensitivity. Products that use the diversity reception technology designed for this purpose are shipped as products.
An example of a receiving apparatus using diversity reception technology is described in Patent Document 1.

JP 2007-43609 A

Terrestrial digital broadcasting is a broadcasting system suitable for reception on a mobile body, and diversity receivers incorporating diversity reception technology for in-vehicle use, mobile phone use, etc. are shipped as products.
As a feature of a mobile receiver (hereinafter referred to as a mobile receiver), unlike a stationary receiver (hereinafter referred to as a fixed receiver), the mobile body is located away from a broadcasting station. Since it can move in a wide range from areas where the electric field strength of broadcast radio waves is weak (weak electric field environment) to areas where the electric field strength is very close to the broadcasting station (strong electric field environment), the dynamic range of the received electric field strength is wide. It is necessary.
Note that the need for such a wide dynamic range of the received electric field strength does not need to be considered in a fixed receiver, for example, a television receiver installed in a home or a recording device with a built-in tuner.

Diversity reception techniques such as a combined diversity reception technique are effective techniques for improving reception characteristics in a weak electric field environment, but are ineffective in improving reception characteristics in a strong electric field environment. For this reason, a signal input in a strong electric field environment may cause distortion in the channel selection circuit and degrade reception characteristics, which may cause generation of block noise in video or noise in audio.
In order to prevent such a situation, there is a demand for a receiving apparatus having diversity reception technology suitable for a weak electric field environment and a receiving apparatus that realizes a suitable receiving characteristic even in a strong electric field environment.

In addition, since a digital broadcast receiver for a mobile body is mounted on a mobile terminal, there are demands for downsizing and a demand for low power consumption for driving the battery for a long time.
Therefore, the high-frequency block from the high-frequency signal input terminal to the demodulator and diversity combiner is smaller in mobile receivers than the same high-frequency block used in stationary receivers such as stationary television receivers. And lower power consumption.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a digital broadcast receiving apparatus that performs diversity reception that realizes a suitable receiving operation in which reception characteristics do not deteriorate even if the received signal electric field strength is large, that is, diversity in a mobile unit. To provide a receiving apparatus.

  In order to achieve the above object, a diversity receiver of the present invention performs a channel selection process for a signal input to a first signal input terminal, a second signal input terminal, and the first signal input terminal. A first channel selection circuit to perform, a second channel selection circuit to perform channel selection processing of a signal input to the second signal input terminal, and a demodulation process to a signal output from the first channel selection circuit And a second demodulation circuit that performs demodulation processing on a signal output from the second channel selection circuit, and outputs signals output from the first demodulation circuit and the second demodulation circuit. A digital circuit including at least a synthesis circuit that outputs a digital data signal that has been digitally compressed by diversity synthesis, a signal processing circuit that performs digital expansion processing on the digital data signal, a video / audio processing circuit, and a central processing circuit Broadcast diversity In the receiver, the central processing circuit performs diversity combining by controlling the combining circuit when the level of the signal input to the first demodulating circuit is equal to or higher than a first threshold value. Without outputting the digital data signal based on the signal supplied from the first demodulation circuit, the operation of the second channel selection circuit and the second demodulation circuit is stopped.

Also preferably, in the diversity receiver of the present invention, the central processing circuit is configured such that when the level of the signal input to the first demodulation circuit is less than a first threshold value, the combining circuit is The control unit performs diversity combining and outputs a digital data signal based on the signal supplied from the first demodulating circuit.
Preferably, the diversity receiver of the present invention receives a gain control signal input from the first demodulation circuit between the first signal input terminal and the first channel selection circuit, and A gain control circuit configured to switch and output a gain of a signal input to the first signal input terminal to either a first gain or a second gain smaller than the first gain; When the level of a signal input to the first demodulating circuit is equal to or higher than a second threshold value, the circuit outputs a signal input from the first signal input terminal to the second signal input terminal. The gain is controlled so as to be output to the first receiving circuit according to the gain.
Also preferably, in the diversity receiver according to the present invention, the gain control is performed when the level of a signal input to the first demodulation circuit is less than a second threshold value. The circuit outputs a signal input from the first signal input terminal to the first receiving circuit with the gain of 1.
Preferably, the central processing unit of the diversity receiver of the present invention switches from the state where the diversity operation is not performed and the operations of the second channel selection circuit and the second demodulation circuit are stopped to the diversity operation. In this case, when the level of the signal input to the first demodulation circuit is less than the third threshold value which is smaller than the first threshold value, the synthesis circuit is controlled to perform diversity synthesis. A digital data signal is output based on the signal supplied from the first demodulation circuit.
Further preferably, in the first demodulating circuit of the diversity receiver of the present invention, the first control circuit receives the signal input from the first signal input terminal by the gain control circuit according to the first gain. In the case where the level of the signal input to the first demodulating circuit is lower than the fourth threshold value, which is lower than the fourth threshold value. The gain control circuit is controlled to control the gain so that a signal input from the first signal input terminal is output to the first receiving circuit by the second gain.
Preferably, in the diversity receiver according to the present invention, the second gain is variable in accordance with a level of a signal input from the first signal input terminal.

  ADVANTAGE OF THE INVENTION According to this invention, in the mobile receiver which receives a digital broadcast by diversity, even if the received signal electric field strength is large, it is possible to realize a suitable receiving operation that does not deteriorate the reception characteristics.

In one embodiment of the present invention, of the first and second channel selection circuits and the demodulation circuit provided for the diversity reception function, the second channel selection circuit and the second demodulation circuit can stop the operation. It has a function. The combining circuit that performs diversity combining has a function of combining the signals output from the first and second demodulating circuits and outputting them as digital data, and the signal output from the first demodulating circuit without performing a diversity operation. And a function of selectively executing only the function of outputting only digital data as digital data. The first and second demodulation circuits have a determination function for this purpose.
In addition, a variable gain circuit is disposed in front of the first channel selection circuit, and the gain of the variable gain circuit is higher when the electric field strength of the received signal is larger than a certain value as compared with a normal operation state. It becomes the minimum state. The first channel selection circuit has a determination function for this purpose.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each figure, components having common functions are denoted by the same reference numerals, and description thereof will be omitted to avoid duplication as much as possible.

  With reference to FIG. 1, the operation of an embodiment of the diversity receiver of the present invention will be described. FIG. 1 is a block diagram showing a configuration of a first embodiment of a diversity receiver for digital broadcasting according to the present invention. 100 is a diversity receiver for digital broadcasting, 1a is a first high-frequency signal input terminal, 1b is a second high-frequency signal input terminal, 2 is a gain variable circuit, 3a is a first channel selection circuit (channel selection 1), 3b Is a second channel selection circuit (channel selection 2), 3c is a determination circuit in the first channel selection circuit 3a, 4a is a first demodulation circuit (demodulation 1), and 4b is a second demodulation circuit (demodulation 2). 5 is a diversity combining circuit, 6 is a signal processing circuit (B / E), 7 is a video / audio signal processing circuit (A / V), 8 is a central processing unit (CPU), and 9a is a first processing unit. A receiving circuit composed of a channel selecting circuit 3a and a first demodulating circuit 4a, and a receiving circuit 9b composed of a second selecting circuit 3b and a second demodulating circuit 4b.

In FIG. 1, first, an operation during normal television viewing will be described.
A broadcast signal transmitted from the broadcast station is received by an antenna (not shown), input to the digital broadcast receiving device 100 via the first high-frequency signal input terminal 1a, and the first selection via the gain variable circuit 2. Supplied to the station circuit.
A digital broadcast system has a plurality of frequency-divided broadcast channels, and an antenna usually receives all broadcast channel signals.

Digital terrestrial broadcasting in Japan uses signals from 470 [MHz] to 770 [MHz] in the UHF (Ultra High Frequency) band, and one channel has a band of 6 [MHz], for a total of 50 frequencies. A channel exists.
The first channel selection circuit 3a is operated by a user operating an operating device (not shown) from signals including a plurality of frequency channels supplied via the first high-frequency signal input terminal 1a and the gain variable circuit 2. The channel selection operation is performed to convert only the frequency channel desired by the user into a predetermined frequency signal suitable for the operation of the first demodulation circuit 4a in the subsequent stage, and the signal of the frequency channel desired by the user (reception desired) Frequency channel signal) is output to the first demodulation circuit 4a. Similarly, the second channel selection circuit 3b also outputs to the second demodulation circuit 4b a signal of the frequency channel that the user desires to watch (the same reception desired frequency channel signal as the first channel selection circuit 3a).
Since signals other than the frequency channel that the user desires to view may interfere with television viewing, they are removed by the filter circuit (not shown) in the channel selection circuit 3a together with the frequency conversion operation.
The first demodulating circuit 4 a digitally demodulates the received reception desired frequency channel signal and outputs it to the diversity combining circuit 5.

In general, a digital broadcast signal received by an antenna (not shown) varies greatly in received power (received signal electric field strength) depending on conditions such as the position of the antenna, the surrounding environment, and the distance from the broadcasting station.
For stable reception operation, it is necessary to keep the signal power level input to the demodulation circuit constant. Therefore, the first receiving circuit 9a composed of the first channel selecting circuit 3a and the first demodulating circuit 4a includes the first demodulating circuit even if the power of the broadcast signal input to the antenna (not shown) is different. An automatic gain control (AGC) function is provided so that the signal power level input to 4a becomes a constant value, and the signal power level input to the first demodulation circuit 4a is within a predetermined range. Value is kept.

  The broadcast signal transmitted from the broadcast station is received by the first high-frequency signal input terminal 1a and also input to the second high-frequency signal input terminal 1b by another antenna (not shown). The second high-frequency signal input terminal 1b outputs to the second receiving circuit (second tuning circuit 3b and second demodulating circuit 4b) 9b. The second receiving circuit 9b The received reception desired frequency channel signal is digitally demodulated by the same processing as the processing performed by the first receiving circuit 9 a and output to the diversity combining circuit 5.

The diversity combining circuit 5 performs diversity combining processing such as maximum ratio combining on the signals output from the input first demodulation circuit 4a and second demodulation circuit 4b, and further performs processing such as error correction (not shown). And output to the signal processing circuit 6 as digital data called a transport stream signal.
The signal processing circuit 6 demultiplexes the multiplexed stream in the input transport stream signal, performs decompression processing on the digitally compressed video signal and audio signal, and performs video / audio processing on the decompressed signal Output to the circuit 7. The video / audio processing circuit 7 outputs an audio signal from an unillustrated speaker or the like for an input signal, and outputs an image signal from an unillustrated monitor or the like.

Analog broadcasting has a feature that video and audio gradually deteriorate as the quality of the received signal deteriorates.
On the other hand, digital signals are characterized in that if the quality of the received signal is equal to or higher than a certain value, it is possible to provide the user with video and audio without noise without being deteriorated in signal quality. However, the digital signal has a feature that video and audio are suddenly not reproduced when the quality of the received signal falls below a certain value.
The channel selection circuit and the demodulation circuit are not problematic for normal video / audio reproduction even with only one system, but the quality of the received signal when viewing digital broadcasts while moving like in-vehicle digital broadcast receivers. May not be stable, and video and audio may be interrupted during viewing.
Diversity processing such as the above-described maximum ratio combining processing has the effect of improving the signal quality after processing over the signal quality before processing. For example, the diversity combining circuit 5 uses the first receiving circuit 9a and the second receiving circuit 9b. By synthesizing these signals, it is possible to improve the reception characteristics as compared with the case of operating with only one system of reception circuit.

Receiving circuits 9a and 9b composed of a tuning circuit and a demodulating circuit are connected to the CPU 8 provided in the digital broadcast receiving apparatus 100 via a control bus, respectively, and initialization settings and operational state stabilization after power-on. Etc. are undergoing processing.
When a user changes a program to be viewed, the user operates a remote controller or the like, and a signal corresponding to the user's operation is input to the CPU 8 of the digital broadcast receiving apparatus 100. Upon receiving this operation signal, the CPU 8 controls the operations of the first channel selection circuit 3a and the second channel selection circuit 3b in the first reception circuit 9a and the second reception circuit 9b. In response to this control, each of the first channel selection circuit 3a and the second channel selection circuit 3b selects the same frequency channel including the desired program, and outputs the same to each demodulation circuit 4a or 4b. Then, the respective demodulation circuits 4 a and 4 b output demodulated signals to the diversity combining circuit 5.

Since the first channel selection circuit 3a and the second channel selection circuit 3b each include a high frequency circuit, it is necessary to avoid noise caused by the control bus. For this reason, the channel selection circuits 3a and 3b are not directly connected to the control bus but are connected to the control bus via the demodulation circuit 4a or 4b.
In each of the first receiving circuit 9a and the second receiving circuit 9b, the first demodulating circuit 4a and the second demodulating circuit 4b are controlled by switching the control bus only when it is necessary to perform a channel selection operation. The bus is connected to the corresponding first channel selection circuit 3a and second channel selection circuit 3b, and when the channel selection operation is completed, the control bus is disconnected from each channel selection circuit.

Since there is a disadvantage that the control at the time of channel selection becomes complicated, if the noise due to the control bus is not taken into consideration, the first channel selection circuit 3a and the second channel selection circuit 3b are not configured as shown in FIG. You may connect directly with the control bus from CPU8.
In the case of direct connection, it is not necessary to perform control via the first demodulation circuit 4a and the second demodulation circuit 4b, so that control at the time of channel selection can be simplified.

Diversity operation (diversity processing operation) is a function that is effective in improving the receiver's weak electric field reception sensitivity, etc., and stable reception even when the signal power level of a terrestrial digital broadcast signal input to an antenna (not shown) is small. This function is necessary to realize the operation. However, in order to perform diversity operation by synthesizing two systems of signals obtained from two systems of receiving circuits (channel selection circuit and demodulation circuit), the two systems of channel selection circuit and demodulation circuit are always operated. There is a need.
The mobile receiver needs to suppress its power consumption as much as possible in consideration of the battery operation, and the diversity operation is contrary to this power consumption reduction request.

For this reason, in one embodiment of the present invention, when the signal power level of a digital terrestrial broadcast signal input to an antenna (not shown) is high enough to maintain a stable reception operation with one channel selection circuit and demodulation circuit. The transport stream signal is generated using only signals obtained from the first channel selection circuit 3a and the first demodulation circuit 4a without performing the diversity operation. At this time, the second channel selection circuit 3b and the second channel selection circuit 3 The demodulation circuit 4b is stopped.
Since the reception power level is small and sufficient reception operation cannot be performed with one system, if the transport stream contains many errors, the diversity operation is performed by operating the two channel selection circuits and the demodulation circuit. Improve electric field sensitivity.

  By executing the above operation, the channel selection circuit and the demodulation circuit can be operated by only one system except when the signal power level of the received signal is so small that a normal reception operation cannot be obtained unless the diversity operation is performed. The reception operation is performed, and the power consumption can be reduced as compared with the case where the two channel selection circuits and the demodulation circuit are always operated.

As already mentioned, since the mobile receiver is movable, the reception area is not constant, and if it is in the vicinity of a broadcast station or relay station that outputs broadcast waves of digital terrestrial broadcasting, the digital broadcast receiver The signal power input to can be very strong.
When the signal power level of the received signal is high, distortion is likely to occur in the channel selection circuit, which causes an error in the transport stream. For this reason, a configuration in which distortion does not occur in the channel selection circuit even when the power level of the received signal is large is necessary. As a countermeasure against this, the present invention includes a variable gain circuit 2 as shown in FIG.
Hereinafter, the operation of the variable gain circuit 2 which is a feature of the present invention will be described.

The variable gain circuit 2 has two operation states for adjusting the gain of the input signal, and one of the operation states is an operation state with a large gain. The other is an operating state with a small gain. The variable gain circuit 2 switches between these two operating states by a control signal input from the outside, and either one of the operating states is selected and executed.
For example, in an operation state with a large gain, an operation with a gain of 1 is performed. That is, the reception signal input to the variable gain circuit 2 is output to the first channel selection circuit 3a at the same power level.
Also, for example, in an operation state with a small gain, the received signal input to the variable gain circuit 2 is attenuated within the variable gain circuit 2 and output to the first channel selection circuit 3a. That is, when the gain variable circuit 2 outputs to the first channel selection circuit 3a while operating in a large gain state, the power level of the received signal is such that distortion occurs in the first channel selection circuit 3a with this signal power. Is large, the variable gain circuit 2 operates in a small gain operating state to suppress the occurrence of distortion.

That is, when the power level of the reception signal input from the first high-frequency signal input terminal 1a is small, the gain variable circuit 2 operates in an operating state with a large gain. In this state, a high-frequency signal with sufficient power is supplied to the first channel selection circuit 3a, and a stable reception operation is maintained.
When the power level of the reception signal input from the first high-frequency signal input terminal 1a is high, the variable gain circuit 2 operates in an operation state with a small gain. That is, the gain variable circuit 2 attenuates the high frequency signal input to the first high frequency signal input terminal 1a and supplies the attenuated high frequency signal to the first channel selection circuit 3a.
With this switching operation, even when the power level of the received signal is so high that distortion occurs in the first channel selection circuit 3a, the variable gain circuit 2 operates in a low gain state under the control of the outside. As a result, the first channel selection circuit 3a can maintain a stable reception operation without causing distortion.

A gain control signal for controlling the operating state of the variable gain circuit 2 is supplied from the first channel selection circuit 3a. The first channel selection circuit 3a includes a function (for example, a determination circuit 3c) that detects and evaluates the power level of the input signal. As this function, the operation state of the AGC operation already described can be used.
The first channel selection circuit 3a evaluates whether or not the power level of the high-frequency signal input to the first channel selection circuit 3a has reached a signal power level that causes signal distortion internally. The determination is made by the function (determination circuit 3c).
When the power level of the high frequency signal received by the first high frequency signal input terminal 1a is strong enough to cause distortion in the first channel selection circuit 3a, the first channel selection circuit 3a A control signal for controlling the state of the variable gain circuit 2 is generated so as to reduce the gain of the operation state, and is supplied to the variable gain circuit 2. The low gain level may be a predetermined value such as 0.5 times, or may be variable according to the detected level.
Further, the first channel selection circuit 3a has a variable gain circuit 2 if the power level of the high frequency signal received by the first high frequency signal input terminal 1a is a level that does not cause distortion in the first channel selection circuit 3a. The first channel selection circuit 3 a generates a control signal for controlling the state of the variable gain circuit 2 and supplies the control signal to the variable gain circuit 2 so as to increase the gain of the operation state.

  Preferably, in this determination, when the operating state of the variable gain circuit 2 is the same between the condition for switching from large to small and the condition for switching from small to large, the state is not stable and the two states are always changed. Therefore, it is necessary to provide hysteresis characteristics.

  The series of operations described above will be described below using the flowchart shown in FIG. 2 and the hysteresis diagram shown in FIG. FIG. 2 is a flowchart for explaining an embodiment of the receiving operation of the diversity receiver of the present invention. FIG. 3 is a diagram for explaining an embodiment of the hysteresis characteristic of the diversity receiver of the present invention. For execution of the following flowchart, the CPU 8 controls each component of the receiving device 100.

  In step S202, the CPU 8 performs processing such as channel selection, synchronization operation processing, and the like for the first receiving circuit 9a and the second receiving circuit 9b as initial settings. In addition, the operation state is diversity operation and the gain of the variable gain circuit is large.

  In step S203, the first channel selection circuit 3a of the first reception circuit 9a determines whether or not the power level of the input reception signal is low enough to require diversity reception (L <t1?). The determination result is output to the CPU 8. Here, the power level of the received signal is L, and the threshold of the power level of the received signal that cannot be maintained unless the diversity operation is performed is t1. That is, when the power level L of the received signal is less than the threshold value t1, the process proceeds to step S204b, and when it is equal to or greater than the threshold value t1, the process proceeds to step S204a.

In step S204b, the diversity operation is performed as it is, and the process proceeds to step S203 again. By repeating the above processing, it is always determined whether or not the power level L of the received signal does not exceed the threshold value t1.
In step S204a, since it is not necessary to perform the diversity operation in the processing operation when the power level L of the received signal exceeds the threshold value t1, the operation state of the receiving apparatus is switched to the non-diversity operation. Transition to processing. At this time, the second receiving circuit 9b composed of the second channel selection circuit 3b and the second demodulation circuit 4b stops operating under the control of the CPU 8 to reduce power consumption.

Next, in step S205, the first channel selection circuit 3a of the first reception circuit 9a determines whether the power level L of the reception signal exceeds the threshold value t2 from the signal input from the gain variable circuit 2. (L <t2?) And outputs the determination result to the CPU 8 and the variable gain circuit 2. Note that the minimum value of the signal strength that causes distortion in the first channel selection circuit 3a is determined as the threshold value t2.
If the power level L of the received signal is less than the threshold value t2, the process proceeds to step S206b. If the power level L of the received signal is equal to or greater than the threshold value t2, the process proceeds to step S206a.

In step S206b, the operation state of the variable gain circuit 2 is maintained in an operation state with a large gain (gain = 1), and the process proceeds to step S207b.
In step S207b, it is determined whether or not the power level L of the received signal exceeds the threshold value t1 ′ (L <t1 ′?), And the determination result is output to the CPU 8 and the gain variable circuit 2.
When the power level L of the received signal is less than the threshold value t1 ′, the process proceeds to step S202. When the power level L of the received signal is equal to or higher than the threshold value t1 ′, the process returns to step S205. .

  In step S206a, control is performed from the first channel selection circuit 3a so as to reduce the operating state of the variable gain circuit 2 and the variable gain circuit 2 functions in an operating state with a small gain. That is, the gain variable circuit 2 attenuates the power level of the received high-frequency signal and outputs the attenuated power level to the first channel selection circuit 3a to suppress the occurrence of distortion in the first channel selection circuit 3a. Thereafter, the process proceeds to step S207a.

In step S207a, it is determined whether or not the power level L of the received signal exceeds the threshold value t2 ′ (L <t2 ′?), And the determination result is output to the CPU 8 and the gain variable circuit 2.
When the power level L of the received signal is less than the threshold value t2 ′, the process proceeds to step S208. When the power level L of the received signal is equal to or higher than the threshold value t2 ′, the process of step S207a is repeated. .
In step S208, it is determined whether or not the power level L of the received signal exceeds the threshold value t1 ′ (L <t1 ′?), And the determination result is output to the CPU 8 and the gain variable circuit 2.
In step 208, as in step S207b, it is determined whether or not the power level L of the received signal exceeds the threshold value t1 ′ (L <t1 ′?), And the determination result is output to the CPU 8 and the gain variable circuit 2. To do.
When the power level L of the received signal is less than the threshold value t1 ′, the process proceeds to step S203. When the power level L of the received signal is equal to or higher than the threshold value t1 ′, the process returns to step S205. .

The switching of the operation state of the variable gain circuit 2 has a hysteresis characteristic so as not to cause a chattering operation. That is, a threshold value t2 for determination in step S205 and a threshold value t2 'that is a determination condition in step S207a are provided. As shown in FIG. 3, the minimum threshold value has a relationship of t2'<t2. Is given.
Similarly, a hysteresis characteristic is provided for the diversity operation and the non-diversity operation so that the chattering operation does not occur. That is, the threshold value t1 for determination in step S203 and the threshold value t1 ′ that is the determination condition in steps S207b and S208 are provided. As shown in FIG. 3, the minimum threshold value includes t1 ′ < The relationship of t1 is given.
In FIG. 3, the horizontal axis represents the detection level of the signal power detected by the first channel selection circuit 3a to determine the power level of the reception signal, and the vertical axis represents the operating state of the reception apparatus. The state (1) is a state in which the receiving apparatus is in a non-diversity operation and the detected signal power level is large and the gain of the variable gain circuit 2 is small. This state (1) is the state of step S206a in FIG. State (2) is a state in which the receiving apparatus is in a non-diversity operation and the detected signal power level is small and the gain of the variable gain circuit 2 is large (gain = 1). This state (2) is the state of step S206b in FIG. Furthermore, the state (3) is a state in which the receiving apparatus is in a diversity operation, and the detected signal power level is small and the gain of the variable gain circuit 2 is large (gain = 1). This state (3) is a state after the initial setting in step S202 in FIG.
In the description of the present embodiment, the case where the state (3) is set in the initial setting (step S202) of FIG. 2 has been described. However, the effect set by the present invention can be obtained regardless of the state (1) or (2) set as the initial setting.

Through the series of operations described above, the digital broadcast diversity receiver can be adaptively operated according to the power level of the received signal to reduce power consumption. Furthermore, even when the power level is high, it is possible to prevent reception characteristics from being deteriorated due to the occurrence of distortion, and it is possible to provide a digital broadcast receiver having a wide dynamic range of received signals.
Also preferably, the diversity receiver of the present invention is a diversity receiver for digital broadcasting provided with two channels of a channel selection circuit, a demodulation circuit, and the like for diversity operation, and gain control is performed before the first channel selection circuit. Arrange the circuit. The gain of the gain control circuit is configured such that the gain is changed by a control signal input from the outside.
Preferably, the first demodulation circuit is provided with a circuit for determining the signal strength of the input signal, and a control signal for controlling the gain of the gain control circuit is generated and output based on the determination result of the determination circuit. It is.
In the above-described embodiment, the strength of the received signal is determined based on the detected power level by detecting the power level. However, it may be determined based on other items such as voltage instead of the power level.

According to the above-described embodiment, when the determination circuit in the first demodulation circuit determines that the signal strength input to the high-frequency signal input terminal is greater than a certain value, the gain of the gain control circuit is A control signal is output so as to decrease, and the gain of the gain control circuit decreases.
As a result, the signal strength input to the first channel selection circuit is minimized, the signal is not distorted in the channel selection circuit, and the reception characteristics are not deteriorated even if the reception signal electric field strength is large. Receive operation is realized.

  The present invention can be applied to a digital broadcast receiver having a diversity reception function and a vehicle-mounted digital broadcast receiver, a home digital broadcast receiver, a portable terminal digital broadcast receiver, and the like.

The block diagram which shows the structure of one Example of the diversity receiver of this invention. The flowchart for demonstrating one Example of operation | movement of the channel search function of the diversity receiver of this invention. The figure for demonstrating one Example of the hysteresis characteristic of the diversity receiver of this invention.

Explanation of symbols

  1a, 1b: high-frequency signal input terminal, 2: gain variable circuit, 3a, 3b: channel selection circuit, 3c: determination circuit, 4a, 4b: demodulation circuit, 5: diversity combining circuit, 6: signal processing circuit, 7: video Audio signal processing circuit, 8: CPU, 9a, 9b: receiving circuit, 100: diversity receiver.

Claims (7)

A first signal input terminal; a second signal input terminal; a first channel selection circuit for performing a channel selection process of a signal input to the first signal input terminal; and the second signal input terminal. A second channel selection circuit for performing a channel selection process on an input signal; a first demodulation circuit for performing a demodulation process on a signal output from the first channel selection circuit; and an output from the second channel selection circuit. A second demodulating circuit that performs demodulation processing on the signal to be processed, and a combining circuit that outputs a digital data signal that is digitally compressed by diversity combining the signals output from the first demodulating circuit and the second demodulating circuit; In the diversity receiver for digital broadcasting comprising at least a signal processing circuit for performing digital expansion processing on the digital data signal, a video / audio processing circuit, and a central processing circuit,
The central processing circuit controls the combining circuit when the level of a signal input to the first demodulating circuit is equal to or higher than a first threshold value, and performs the first combining without performing diversity combining. A diversity receiving apparatus that outputs a digital data signal based on the signal supplied from the demodulator circuit and stops the operation of the second channel selection circuit and the second demodulation circuit.   2. The diversity receiver according to claim 1, wherein the central processing circuit controls the combining circuit when a level of a signal input to the first demodulating circuit is less than a first threshold value. 3. And a diversity receiver that performs diversity combining and outputs a digital data signal based on the signal supplied from the first demodulation circuit. In the diversity receiver according to claim 1 or 2,
Gain of a signal input to the first signal input terminal upon receiving a gain control signal input from the first demodulator circuit between the first signal input terminal and the first channel selection circuit Including a gain control circuit that outputs a first gain and a second gain smaller than the first gain.
In the first demodulation circuit, the gain control circuit is input from the first signal input terminal when the level of the signal input to the first demodulation circuit is equal to or higher than a second threshold value. A diversity receiving apparatus, wherein gain control is performed so that a signal is output to the first receiving circuit by the second gain. The diversity receiver according to claim 1, wherein:
When the level of the signal input to the first demodulation circuit is less than the second threshold value, the gain control circuit is input from the first signal input terminal to the first demodulation circuit. A diversity receiving apparatus, wherein the signal is output to the first receiving circuit by the first gain. The diversity receiver according to claim 1, wherein:
The central processing unit inputs an input to the first demodulation circuit when performing a diversity operation without performing a diversity operation and stopping the operations of the second channel selection circuit and the second demodulation circuit. When the level of the signal to be processed is less than the third threshold value, which is smaller than the first threshold value, the combining circuit is controlled to perform diversity combining, and the signal supplied from the first demodulating circuit is A diversity receiver characterized in that it outputs a digital data signal. The diversity receiver according to any one of claims 1 to 5,
The first demodulating circuit changes from the state in which the gain control circuit outputs the signal input from the first signal input terminal to the first receiving circuit by the first gain, to the second gain. In the case of switching, when the level of the signal input to the first demodulation circuit is less than a fourth threshold value which is smaller than the second threshold value, the gain control circuit is controlled to control the first control circuit. The diversity receiving apparatus is characterized in that gain control is performed so that a signal input from a signal input terminal is output to the first receiving circuit by the second gain.   7. The diversity receiver according to claim 2, wherein the second gain is varied according to a level of a signal input from the first signal input terminal.

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