JP2009272689A - Receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver of high performance, which performs gain control considering signal levels of signals even when signals near to an intermediate frequency exist or even when signals separated by several-tens MHz from a center frequency exist, and which prevents deterioration in receiving performance due to channels other than a receiving channel. <P>SOLUTION: The receiver includes an AGC detection circuit 16 for generating a second gain control signal corresponding to an intermediate frequency signal from an output of a mixer circuit 6, an AGC detection circuit 17 for generating a third gain control signal corresponding to an output signal of a band-pass filter 8 from an output of an IF amplifier circuit 9, and an averaging circuit 20 for generating a first gain control signal based on the second gain control signal and the third gain control signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a receiver that selects and receives one channel from a multi-channel signal, and more particularly to a terrestrial television receiver having a large number of channels and nonuniform signal levels.

  A block diagram of a terrestrial digital broadcast receiver 101 as a conventional receiver is shown in FIG. In the terrestrial digital broadcast receiver 101, a plurality of digitally modulated RF signals are input from the receiver input terminal 102, and are input to the mixer circuit 106 via the bandpass filter 103, the RF AGC amplifier circuit 104, and the bandpass filter 105. Entered.

  The signal input to the mixer circuit 106 is mixed with the local oscillation signal output from the local oscillation circuit 107 in accordance with the reception frequency, and the frequency is converted into an IF signal. The frequency-converted IF signal is input to the A / D converter 112 through the band-pass filter 108, the IF amplifier circuit 109, the band-pass filter 110 including the SAW filter, and the IF AGC amplifier circuit 111, and converted into a digital signal. After that, the demodulation circuit 113 performs digital demodulation to demodulate the original digital data.

  Here, the input signal level of the A / D converter 112 must always be a constant level even when the input level of the receiver changes, and a level detection circuit 114 and an AGC control signal generation circuit 115 are provided in the digital demodulation unit. Yes. Based on the information input from the level detection circuit 114, the AGC control signal generation circuit 115 increases the gains of the RF AGC amplification circuit 104 and the IF AGC amplification circuit 111 so that the input signal level of the A / D converter 112 becomes constant. Control.

  FIG. 13 shows a block diagram of a digital broadcast receiver 116 as a second example of a conventional receiver. Similarly to the terrestrial digital broadcast receiver 101, when the digital broadcast receiver 116 receives a plurality of digitally modulated RF signals from the receiver input terminal 102, the bandpass filter 103, the RF AGC amplifier circuit 104, Processing by the bandpass filter 105, the mixer circuit 106, the local oscillation circuit 107, the bandpass filter 108, the IF amplifier circuit 109, the bandpass filter 110, the IF AGC amplifier circuit 111, the A / D converter 112, and the demodulation circuit 113 is performed. Demodulated to original digital data.

  Also in the digital broadcast receiver 116, a level detection circuit 114 and an AGC control signal generation circuit 115 are provided in the digital demodulation unit. The AGC control signal generation circuit 115 controls the gain of the IF AGC amplification circuit 111 so that the input signal level of the A / D converter 112 becomes constant based on the information input from the level detection circuit 114.

  The output signal of the IF amplifier circuit 109 is input to the band pass filter 110 and also input to the AGC detection circuit 117. The AGC detection circuit 117 generates an output voltage corresponding to the level of the input signal and outputs it to the DC amplifier circuit 118. The gain k of the DC amplifier circuit 118 is fixed. The gain of the RF AGC amplifier circuit 104 is controlled by the output voltage of the DC amplifier circuit 118.

  13, the AGC control signal generation circuit 115 controls the gain of the IF AGC amplification circuit 111, and the AGC detection circuit 117 controls the gain of the RF AGC amplification circuit 104.

  Next, the AGC control operation will be described. For example, in the terrestrial digital broadcast receiver 101 of FIG. 12, the characteristics of the level detection circuit 114 are such that when the output signal level of the A / D converter 112, that is, the input signal level of the level detection circuit 114 is large, a small DC voltage is generated. Conversely, when the input signal level of the level detection circuit 114 is small, a large DC voltage is generated. The input signal level of the A / D converter 112 is an analog amplitude level, but the output signal level of the A / D converter 112 is a digital value.

  The characteristics of the RF AGC amplifier circuit 104 and the IF AGC amplifier circuit 111 are such that the attenuation is small when the AGC control voltage input to each circuit is large, and conversely, the attenuation is large when the AGC control voltage is small. To be.

  Here, when the level of the RF signal input to the terrestrial digital broadcast receiver 101 is large, the input signal level of the level detection circuit 114 also increases, but the output voltage of the level detection circuit 114 decreases, so that IF AGC The gain of the IF AGC amplifier circuit 111 is controlled so that the attenuation amount of the amplifier circuit 111 is increased and the input signal level of the A / D converter 112 is lowered.

  Further, when the level of the RF signal input to the terrestrial digital broadcast receiver 101 is small, the input signal level of the level detection circuit 114 also decreases, but the output voltage of the level detection circuit 114 increases, so that IF AGC The gain of the IF AGC amplifier circuit 111 is controlled so that the attenuation amount of the amplifier circuit 111 is reduced and the input signal level of the A / D converter 112 is increased.

  Thus, even if the input signal level of the receiver fluctuates, the input signal level of the A / D converter 112 that is always a constant level can be obtained.

  Next, the function of each filter will be described. A plurality of RF signals are input to the receiver input terminal 102. At the time of reception, a local oscillation signal having a frequency corresponding to the reception frequency is generated, so that the frequency of the desired signal, that is, the frequency of the signal to be received is converted to the IF frequency. At this time, the center frequency of the band-pass filters 103 and 105 is varied so that the center frequency substantially coincides with the reception frequency, and the desired signal is allowed to pass therethrough, and a signal far from the desired signal is roughly filtered.

  The center frequency of the band-pass filter 108 is set to the IF frequency, and a frequency that is several tens of MHz or more away from the IF frequency is roughly filtered, but the frequency of the adjacent signal and the adjacent signal cannot be reduced so much. The band-pass filter 110 has a steep characteristic that allows only the IF frequency to pass and removes adjacent signals and adjacent signals, and a SAW filter is generally used.

Similar to the terrestrial digital broadcast receiver 101 in FIG. 12 and the digital broadcast receiver 116 in FIG. 13, in Patent Document 1, an AGC control signal is extracted from before and after the intermediate frequency band filter, assuming that the gain is controlled by AGC. An AGC circuit is disclosed that is added to two variable gain amplifiers to reduce distortion and prevent NF degradation. Patent Document 2 discloses an AGC system capable of adjusting an appropriate RF-AGC without performing an RF-AGC search from a preset RF-AGC set value at an AGC turnover point. Yes.
JP 2000-244353 A (published September 8, 2000) JP 2006-109335 A (published April 20, 2006)

  In the terrestrial digital broadcast receiver 101 of FIG. 12, the level detection circuit 114 detects the signal level of the subsequent stage of the steep band pass filter 110 constituted by the SAW filter, and generates an AGC control signal. In this case, the gain of the RF AGC amplifier circuit 104 can be controlled in accordance with the desired received signal level, but the adjacent signal, adjacent signal and other signals are removed by the SAW filter, so that the levels of the other signals When the other channel signal whose level is higher than the desired signal is input to the receiver regardless of the gain of the RF AGC amplifier circuit 104, the other channel signal having the higher level is input to the RF AGC amplifier circuit. 104 and the mixer circuit 106, there is a problem that amplitude distortion is generated and the reception performance is deteriorated.

  Further, in order to improve the above problem, as shown in the digital broadcast receiver 116 of FIG. 13, an AGC detection circuit 117 is disposed after the band pass filter 108 so that the adjacent signal and the adjacent signal are not removed much. In some cases, the AGC control signal may be generated at the same time.

  In this case, the gain of the RF AGC amplifier circuit 104 is controlled in accordance with the level of the adjacent signal or the adjacent signal. If the adjacent signal or the adjacent signal level is high, the RF AGC amplifier circuit 104 is controlled. The amplitude distortion can be improved by lowering the gain. However, in this case, the frequency that is several tens of MHz or more away from the IF frequency is largely removed by the filter, so if the signal in a band that is several tens of MHz or more away from the IF frequency is large, the signal becomes an interference signal, The problem of deteriorating reception performance is not improved.

  The present invention has been made in view of the above-described conventional problems, and the purpose thereof is to determine whether there is a signal in the vicinity of an intermediate frequency or a signal that is several tens of MHz away from the center frequency. It is an object of the present invention to provide a high-performance receiver capable of gain control in consideration of the signal level of this signal and preventing deterioration in reception performance due to other channels other than the reception channel.

  In order to solve the above-described problems, the receiver of the present invention increases the gain by an RF signal input terminal for inputting a multi-channel RF signal and a first gain control signal arranged at a subsequent stage of the RF signal input terminal. An intermediate frequency signal that is frequency-converted to an intermediate frequency by mixing the RF signal and the local oscillation signal by mixing the RF signal and the local oscillation signal, the RF gain control means that is fixed or controlled, the local oscillation means that generates a local oscillation signal according to the reception frequency A frequency conversion means for generating a first intermediate frequency bandpass filter that is arranged downstream of the frequency conversion means and that allows the intermediate frequency signal to be selected and passed in a wider band, and the first intermediate frequency bandpass filter. And a second intermediate frequency bandpass filter that is arranged in a subsequent stage and allows the intermediate frequency signal to be selected in a narrower band and pass therethrough. A first automatic gain control detecting means for generating a second gain control signal corresponding to the intermediate frequency signal; and a third gain control signal corresponding to the output signal of the first intermediate frequency bandpass filter Second automatic gain control detecting means for performing, and gain control signal generating means for generating the first gain control signal based on the second gain control signal and the third gain control signal. Features.

  According to the above invention, the first automatic gain control detection means detects a signal in a band separated from the intermediate frequency by several tens of MHz or more to generate the second gain control signal, and the second automatic gain control signal is generated. Gain control detection means detects the proximity signal having the intermediate frequency to generate the third gain control signal, and the gain control signal generation means includes the second gain control signal and the third gain control signal. Is used to generate the first gain control signal.

  According to such a configuration, the signal level of a signal in the vicinity of an intermediate frequency, such as an adjacent signal separated by one channel from the desired signal or an adjacent signal separated by two channels from the desired signal, and several tens of minutes from the intermediate frequency. Since the gain control signal generating means generates the first gain control signal according to the signal level of the signal in the band separated by MHz or more, it is possible to control the gain of the RF gain control means. It becomes. Therefore, even if a large adjacent signal or a large adjacent signal exists, or a large signal exists in a band that is several tens of MHz or more away from the intermediate frequency, the RF gain control is performed according to the signal level. It is possible to reduce the gain of the means, and it is possible to improve amplitude distortion caused by signals other than the desired signal.

  In addition, even when there is a signal in the vicinity of an intermediate frequency, such as an adjacent signal or adjacent signal, even when there is a signal that is several tens of MHz away from the center frequency, gain control considering the signal level of those signals Therefore, it is possible to realize a high-performance receiver that prevents deterioration of reception performance due to other channels other than the reception channel.

  In the receiver, an intermediate frequency band elimination filter may be provided upstream of the first automatic gain control detection means.

  This makes it possible to perform gain control that places more importance on signals that are several tens of MHz away from the center frequency. The output of the frequency converting means can be impedance matched over a wide range, reflection in the band stop band of the intermediate frequency band elimination filter is reduced, and distortion in the frequency converting means is reduced.

  In the receiver, the gain control signal generation means may select one of the second gain control signal and the third gain control signal and output the selected one as the first gain control signal. Good.

  Thereby, emphasis is placed on control that emphasizes a signal that is several tens of MHz away from the center frequency in the first intermediate frequency bandpass filter, and emphasis on adjacent signals and adjacent signals in the second intermediate frequency bandpass filter. Control can be selectively switched to enable control more suitable for reception conditions.

  In the receiver, the gain control signal generation means may combine the second gain control signal and the third gain control signal and output the resultant as the first gain control signal.

  In the receiver, the combining is averaging, and the gain control signal generating means averages the second gain control signal and the third gain control signal, and the first gain control signal May be output as

  With these configurations, even if the level of the signal input to the RF signal input terminal varies, it is possible to perform control so that the signal level of the intermediate frequency signal is constant.

  The receiver may include signal-to-noise ratio detecting means for detecting a signal-to-noise ratio at a subsequent stage of the second intermediate frequency bandpass filter.

  Further, in the receiver, the signal-to-noise ratio detecting means is a first signal-to-noise ratio when the gain control signal generating means outputs the second gain control signal as the first gain control signal. And a second signal-to-noise ratio when the gain control signal generating means outputs the third gain control signal as the first gain control signal, and the first signal-to-noise ratio is When the second signal-to-noise ratio is greater than the second signal-to-noise ratio, the gain control signal generating means outputs the second gain control signal as the first gain control signal, and the second signal-to-noise ratio is When the signal-to-noise ratio is greater than 1, the gain control signal generation means may output the third gain control signal as the first gain control signal.

  Further, the receiver further includes a storage unit and a switching determination unit, and the switching determination unit determines whether the first signal-to-noise ratio and the second signal-to-noise ratio are large or small. When the channel is set, the storage means stores the determination result, and when receiving the corresponding channel, the gain control signal generation means outputs the first gain control signal based on the determination result stored in the storage means. May be.

  Further, in the receiver, the switching determination means may perform the determination of the size at a time other than the time of channel setting of the receiver or a preset viewing time.

  With these configurations, control that places importance on signals that are tens of MHz away from the center frequency in the first intermediate frequency bandpass filter, and adjacent signals and adjacent signals in the second intermediate frequency bandpass filter It is possible to selectively switch the control to be emphasized and to perform control more suitable for the reception condition.

  As described above, the receiver of the present invention generates the first gain control signal corresponding to the intermediate frequency signal between the subsequent stage of the frequency conversion means and the previous stage of the first intermediate frequency bandpass filter. The automatic gain control detection means is provided between the subsequent stage of the first intermediate frequency bandpass filter and the front stage of the second intermediate frequency bandpass filter, and is used as an output signal of the first intermediate frequency bandpass filter. A second automatic gain control detecting means for generating a corresponding third gain control signal, and a gain for generating the first gain control signal based on the second gain control signal and the third gain control signal Control signal generating means.

  Therefore, even when there is a signal near the intermediate frequency, or even when there is a signal that is several tens of MHz away from the center frequency, gain control can be performed in consideration of the signal level of those signals, and other than the receiving channel. There is an effect of providing a high-performance receiver that prevents deterioration of reception performance due to a channel.

  One embodiment of the present invention will be described below with reference to Examples 1 to 3 and FIGS. 1 to 11.

[Example 1]
FIG. 1 is a block diagram of a digital broadcast receiver 1 according to the first embodiment. The digital broadcast receiver 1 includes a receiver input 2, a bandpass filter 3, an RF (radio frequency) AGC (automatic gain control) amplifier circuit 4, a bandpass filter 5, a mixer circuit 6, and a local oscillation. Circuit 7, band pass filter 8, IF (intermediate frequency) amplifier circuit 9, band pass filter 10, IF AGC amplifier circuit 11, A / D converter 12, demodulator circuit 13, level detector circuit 14, AGC control signal generation The circuit 15 includes an AGC detection circuit 16, an AGC detection circuit 17, a DC (direct current) amplification circuit 18, a DC amplification circuit 19, and an averaging circuit 20.

  A plurality of digitally modulated RF signals are input from the receiver input terminal 2 and input to the mixer circuit 6 via the bandpass filter 3, the RF AGC amplifier circuit 4, and the bandpass filter 5.

  The signal input to the mixer circuit 6 is mixed with the local oscillation signal output from the local oscillation circuit 7 in accordance with the frequency of the reception signal, and the frequency is converted into an IF signal. The center frequency of the bandpass filter 3 and the bandpass filter 5 varies so as to substantially match the reception frequency, that is, the frequency of the signal to be received. As a result, a desired signal, that is, a signal to be received is passed, and a signal away from the desired signal is roughly filtered.

  The received signal frequency-converted to the IF frequency by the mixer circuit 6 is roughly filtered at a frequency separated from the IF frequency by several tens of MHz by the band-pass filter 8, and is passed through the IF amplifier circuit 9 to the band-pass filter 10. Entered.

  The band-pass filter 10 has a steep characteristic that allows only a band signal of one channel to pass, and a SAW (Surface Acoustic Wave) filter is generally used. The signal from which signals other than the desired signal are removed by the bandpass filter 10 is input to the IF AGC amplifier circuit 11, converted into a digital signal by the A / D converter 12, and then digitally demodulated by the demodulation circuit 13. The original digital data is demodulated.

  Further, the reception signal frequency-converted to the IF frequency by the mixer circuit 6 is input to the AGC detection circuit 16. The AGC detection circuit 16 generates an output signal that is a direct-current voltage corresponding to the magnitude of the input signal level, and outputs the output signal to the DC amplification circuit 18. The gain k1 of the DC amplifier circuit 18 is fixed.

  Further, the received signal frequency-converted to the IF frequency by the mixer circuit 6 is roughly filtered by a band pass filter 8 at a frequency separated from the IF frequency by several tens of MHz, and after passing through the IF amplifier circuit 9, the AGC is performed. The signal is input to the detection circuit 17. The AGC detection circuit 17 generates an output signal that is a DC voltage corresponding to the magnitude of the input signal level, and outputs the output signal to the DC amplifier circuit 19. The gain k2 of the DC amplifier circuit 19 is fixed.

  Since signals output from the AGC detection circuit 16 and the AGC detection circuit 17 generally have a low signal level, the RF AGC amplification circuit 4 cannot be directly controlled. Therefore, a DC amplifier circuit 18 and a DC amplifier circuit 19 are provided.

  An output signal, which is a DC voltage, generated according to the input signal level by the AGC detection circuit 16 is amplified by the DC amplification circuit 18 and output to the averaging circuit 20. The output signal, which is a DC voltage, generated according to the input signal level by the AGC detection circuit 17 is amplified by the DC amplification circuit 19 and output to the averaging circuit 20.

  The averaging circuit 20 averages the two input DC voltage signals according to the following equation (1). The signal averaged by the averaging circuit 20 is fed back to the RF AGC amplifier circuit 4 as a gain control signal of the RF AGC amplifier circuit 4, and even if the signal level input to the receiver input terminal 2 fluctuates, The RF AGC loop operates so that the signal level of the IF signal is constant.

The gain k1 of the DC amplifier circuit 18 and the gain k2 of the DC amplifier circuit 19 are determined based on the level of the signal output from each AGC detection circuit and the level of the gain control signal of the RF AGC amplifier circuit 4.
Averaged signal = (output of DC amplification circuit 18 + output of DC amplification circuit 19) / 2 (1)
Next, frequency response characteristics in each block will be described. At the input end of the AGC detection circuit 16, signals separated from the desired signal frequency are roughly filtered by the band pass filter 3 and the band pass filter 5. A graph showing an example of the frequency response characteristic at this time is shown in FIG. In the graph below, the frequency normalized with the center frequency of the desired signal is on the x axis, and the level displayed in dB with the amplitude level at the center frequency of the desired signal as the reference level is on the y axis.

  As shown in FIG. 2, a signal with a frequency of 80 MHz or more away from the center frequency is attenuated by 40 dB or more, but a signal with a frequency away from 20 MHz to 50 MHz with respect to the center frequency is attenuated by several dB to 20 dB. ing.

  In addition to the bandpass filter 3 and the bandpass filter 5, the input end of the AGC detection circuit 17 is filtered by the bandpass filter 8. A graph showing an example of the frequency response characteristic at this time is shown in FIG.

  As shown in FIG. 3, a signal with a frequency 30 MHz or more away from the center frequency is attenuated by 30 dB or more, but a signal with a frequency within ± 15 MHz with respect to the center frequency is attenuated by about 7 dB.

  FIG. 4 is a graph showing an example of the frequency response characteristic at the output of the bandpass filter 10, that is, the frequency response characteristic at the input of the IF AGC amplifier circuit 11. In this embodiment, the bandwidth of one channel is 6 MHz. Further, a signal that is ± 6 MHz away from the desired signal is an adjacent signal, and a signal that is ± 12 MHz away from the desired signal is the adjacent signal.

  As shown in FIG. 4, the band pass filter 10 passes only the desired signal. Actually, for example, within the range of the center frequency ± 2.65 MHz, that is, the bandwidth of 5.3 MHz, the attenuation is approximately 0 dB, and the attenuation is −10 dB at the center frequency ± 3 MHz. Generally, the amount of attenuation is large.

  Next, an example in which a plurality of digitally modulated RF signals are input to the receiver will be described. For example, as shown in FIG. 5, a total of 6 signals of −90 MHz, −36 MHz, −12 MHz, +6 MHz, +48 MHz, and +60 MHz are input at a level 20 dB larger than the desired signal with respect to the desired signal (a signal of 0 Hz at a normalized frequency). Suppose that

  As shown in FIG. 6, the signals input to the AGC detection circuit 17 are hardly attenuated at −12 MHz, 0 MHz, and +6 MHz, but the other signals are greatly attenuated. Therefore, the AGC detection circuit 17 detects a desired signal, an adjacent signal, and an adjacent signal, and generates an output signal that is a DC voltage used for gain control. Further, the −36 MHz and +48 MHz signals are not detected by the AGC detection circuit 17 and are not involved in the generation of an output signal that is a DC voltage used for gain control.

  As shown in FIG. 7, the signals input to the AGC detection circuit 16 also have -36 MHz and +48 MHz signals as relatively large levels, and these signals are used for gain control.

  Therefore, the AGC detection circuit 17 can be responsible for gain control that emphasizes the size of adjacent signals and adjacent signals, and the AGC detection circuit 16 can be responsible for gain control including signals that are several tens of MHz away from the center frequency. . The averaging circuit 20 averages the signal output from the AGC detection circuit 16 and amplified by the DC amplification circuit 18 and the signal output from the AGC detection circuit 17 and amplified by the DC amplification circuit 19. Even in the presence of signals such as signals and adjacent signals, or in the presence of signals that are several tens of MHz away from the center frequency, gain control can be performed in consideration of the levels of these signals.

  By changing the setting of the gain k1 of the DC amplifier circuit 18 and the gain k2 of the DC amplifier circuit 19, importance is placed on adjacent signals and adjacent signals, or on the contrary, signals that are several tens of MHz away from the center frequency. This allows flexible design.

[Example 2]
FIG. 8 is a block diagram of the digital broadcast receiver 21 according to the second embodiment. The digital broadcast receiver 21 is obtained by adding a band elimination filter 22 for removing a desired signal as a center on the input side of the AGC detection circuit 16 in the digital broadcast receiver 1 shown in FIG.

  The frequency response characteristics up to the input end of the AGC detection circuit 16 are as shown in FIG. 9 due to the bandpass filter 3, the bandpass filter 5 and the band elimination filter 22. 5 is input to the digital broadcast receiver 21, the signal level of each signal is as shown in FIG.

  Compared with FIG. 10 and FIG. 7 showing the signal input to the AGC detection circuit 16 of the digital broadcast receiver 1, the digital broadcast receiver 21 performs gain control that places more importance on a signal that is several tens of MHz away from the center frequency. Is possible. Further, since the signal output from the mixer circuit 6 is input to the bandpass filter 8 and the band elimination filter 22, the output of the mixer circuit 6 can be impedance-matched over a wide range, and the band rejection band of the band elimination filter 22 can be obtained. Further, there is an advantage that reflection at the center is reduced and distortion in the mixer circuit 6 is reduced.

  Since the frequency response characteristic up to the input end of the AGC detection circuit 16 is as shown in FIG. 9, the signal shown in FIG. 10 does not have an amplitude at the center frequency of 0 dB.

Example 3
FIG. 11 is a block diagram of the digital broadcast receiver 23 according to the third embodiment. The digital broadcast receiver 23 replaces the averaging circuit 20 with the changeover switch 24 in the digital broadcast receiver 1 shown in FIG. 1 and controls the AGC detection circuit 16 to place importance on a signal that is several tens of MHz away from the center frequency. Control that places importance on adjacent signals and adjacent signals in the detection circuit 17 is selectively switched, and control that is more suitable for reception conditions becomes possible.

  Further, the demodulation circuit 13 is provided with an S / N detection circuit 25 for detecting a signal-to-noise ratio (S / N). The S / N detection circuit 25 includes an S / N (first S / N) when the DC amplifier circuit 18 and the RF AGC amplifier circuit 4 are connected by the changeover switch 24, a DC amplifier circuit 19, and an RF AGC amplifier circuit. 4 is detected by the changeover switch 24 and the two S / Ns are temporarily stored in the changeover determination circuit 28. Then, the switching determination circuit 28 determines a better S / N, that is, a larger S / N, and stores the better S / N in the memory 26. When selecting a channel, the microcomputer 27 optimizes the S / N from the memory 26. The switching control circuit 29 sets the changeover switch 24.

  In the determination by the switching determination circuit 28, when the first S / N is larger than the second S / N, the first S / N is stored in the memory 26. At the time of channel selection, the microcomputer 27 reads the optimum switching setting from the memory 26, and the switching control circuit 29 switches the changeover switch 24 to connect the DC amplifier circuit 18 and the RF AGC amplifier circuit 4. Thereby, the digital broadcast receiver 23 performs control that places importance on a signal that is several tens of MHz away from the center frequency.

  In the determination by the switching determination circuit 28, when the second S / N is larger than the first S / N, the second S / N is stored in the memory 26. At the time of channel selection, the microcomputer 27 reads the optimum switching setting from the memory 26, and the switching control circuit 29 switches the changeover switch 24 to connect the DC amplifier circuit 19 and the RF AGC amplifier circuit 4. Thus, the digital broadcast receiver 23 performs control that places importance on adjacent signals and adjacent signals.

  In this case, since it takes time to measure the optimal setting value of each channel, it is inappropriate to perform the viewing at the time of viewing, and is performed at the time of initial channel setting or at a time other than the preset viewing time.

[Summary of Embodiment]
The receivers 1, 2, and 23 according to the embodiment of the present invention are configured by a receiver input terminal 2 that inputs a multi-channel RF signal and a first gain control signal that is arranged at a stage subsequent to the receiver input terminal 2. RF AGC amplifier circuit 4 that fixes or controls gain, local oscillation circuit 7 that generates a local oscillation signal according to the reception frequency, and frequency conversion to an intermediate frequency by mixing the RF signal and the local oscillation signal A mixer circuit 6 for generating the intermediate frequency signal, and a band pass filter 8 that is disposed in a subsequent stage of the mixer circuit 6 and selects and passes the intermediate frequency signal in a wider band, and is disposed in a subsequent stage of the band pass filter 8. A receiver including a band-pass filter for selecting and passing the intermediate frequency signal in a narrower band, and a second gain control signal corresponding to the intermediate frequency signal. AGC detection circuit 16 for generating a signal, AGC detection circuit 17 for generating a third gain control signal corresponding to the output signal of the bandpass filter 8, the second gain control signal and the third gain control signal And gain control signal generating means for generating the first gain control signal based on the above.

  According to the above configuration, the AGC detection circuit 16 detects the signal in a band separated from the intermediate frequency by several tens of MHz or more to generate the second gain control signal, and the AGC detection circuit 17 A proximity signal is detected to generate the third gain control signal, and the gain control signal generation means uses the second gain control signal and the third gain control signal to generate the first gain control signal. Is generated.

  According to such a configuration, the signal level of a signal in the vicinity of an intermediate frequency, such as an adjacent signal separated by one channel from the desired signal or an adjacent signal separated by two channels from the desired signal, and several tens of minutes from the intermediate frequency. Since the gain control signal generating means generates the first gain control signal according to the signal level of the signal in the band separated by more than MHz, the gain of the RF AGC amplifier circuit 4 can be controlled. It becomes. Therefore, even if a large adjacent signal or a large adjacent signal exists, or a large signal exists in a band that is several tens of MHz or more away from the intermediate frequency, an RF AGC amplifier circuit is provided according to the signal level. 4 can be reduced, and amplitude distortion caused by signals other than the desired signal can be improved.

  In addition, even when there is a signal in the vicinity of an intermediate frequency, such as an adjacent signal or adjacent signal, even when there is a signal that is several tens of MHz away from the center frequency, gain control considering the signal level of those signals Therefore, it is possible to realize a high-performance receiver that prevents deterioration of reception performance due to other channels other than the reception channel.

  The receiver may include a band elimination filter 22 before the AGC detection circuit 16.

  This makes it possible to perform gain control that places more importance on signals that are several tens of MHz away from the center frequency. Moreover, impedance matching is possible over a wide range of the output of the mixer circuit 6, reflection in the band stop band of the band elimination filter 22 is reduced, and distortion in the mixer circuit 6 is reduced.

  In the receiver 23, the changeover switch 24 and the changeover control circuit 29 select one of the second gain control signal and the third gain control signal and output the selected one as the first gain control signal. May be.

  As a result, the control that places importance on the signal that is several tens of MHz away from the center frequency in the bandpass filter 8 and the control that places importance on the adjacent signal and the adjacent signal in the bandpass filter 10 are selectively switched, and the reception condition is further improved. It is possible to perform control suitable for the above.

  In the receivers 1 and 21, the averaging circuit 20 may synthesize the second gain control signal and the third gain control signal and output them as the first gain control signal.

  In the receiver 21, the synthesis is averaging, and the averaging circuit 20 averages the second gain control signal and the third gain control signal, and outputs the averaged gain control signal as the first gain control signal. May be.

  With these configurations, even if the level of the signal input to the receiver input terminal 2 fluctuates, it is possible to perform control so that the signal level of the intermediate frequency signal is constant.

  The receiver 23 may include an S / N detection circuit 25 that detects a signal-to-noise ratio at the subsequent stage of the bandpass filter 10.

  In the receiver 23, the S / N detection circuit 25 includes a first signal to noise when the changeover switch 24 and the changeover control circuit 29 output the second gain control signal as the first gain control signal. And the second signal-to-noise ratio when the changeover switch 24 and the changeover control circuit 29 output the third gain control signal as the first gain control signal, and detect the first signal pair When the noise ratio is larger than the second signal-to-noise ratio, the changeover switch 24 and the changeover control circuit 29 output the second gain control signal as the first gain control signal, and the second signal pair. When the noise ratio is larger than the first signal-to-noise ratio, the changeover switch 24 and the changeover control circuit 29 may output the third gain control signal as the first gain control signal.

  Further, the receiver 23 further includes a memory 26 and a switching determination circuit 28. The switching determination circuit 28 determines whether the first signal-to-noise ratio and the second signal-to-noise ratio are large or small. 23. When the channel is set, the memory 26 stores the determination result. When receiving the corresponding channel, the changeover switch 24 and the switching control circuit 29 are configured to output the first gain control signal based on the determination result stored in the memory 26. May be output.

  Further, in the receiver 23, the switching determination circuit 28 may perform the size determination at a time other than the time of channel setting of the receiver or the preset viewing time.

  With these configurations, the control for emphasizing the signal that is several tens of MHz away from the center frequency in the bandpass filter 8 and the control for emphasizing the adjacent signal and the adjacent signal in the bandpass filter 10 are selectively switched. Control suitable for reception conditions is possible.

  The receiver of the present invention can perform gain control in consideration of the signal level of signals even when there are signals in the vicinity of the intermediate frequency or signals that are several tens of MHz away from the center frequency. It is suitable for use in a terrestrial digital broadcast receiver because it prevents deterioration in reception performance due to other channels other than the channel.

1 is a block diagram of a digital broadcast receiver according to an embodiment of the present invention. It is a graph which shows the frequency response characteristic to the input terminal of the AGC detection circuit of the digital broadcast receiver which concerns on the Example of this invention. It is a graph which shows the frequency response characteristic to the input end of the other AGC detection circuit of the digital broadcast receiver which concerns on the Example of this invention. It is a graph which shows the frequency response characteristic in the input of IF AGC amplifier circuit of the digital broadcast receiver which concerns on the Example of this invention. It is a figure showing each signal level of a plurality of digitally modulated RF signals. FIG. 6 is a diagram showing signal levels at the input end of another AGC detection circuit of the digital broadcast receiver according to the embodiment of the present invention when a plurality of RF signals shown in FIG. 5 are input. FIG. 6 is a diagram showing signal levels at an input end of an AGC detection circuit of a digital broadcast receiver according to an embodiment of the present invention when a plurality of RF signals shown in FIG. 5 are input. It is a block diagram of a digital broadcast receiver according to another embodiment of the present invention. It is a graph which shows the frequency response characteristic to the input terminal of the AGC detection circuit of the digital broadcast receiver which concerns on the other Example of this invention. FIG. 6 is a diagram illustrating signal levels at an input end of an AGC detection circuit of a digital broadcast receiver according to another embodiment of the present invention when a plurality of RF signals shown in FIG. 5 are input. It is a block diagram of the digital broadcast receiver which concerns on another Example of this invention. It is a block diagram of a conventional terrestrial digital broadcast receiver. It is a block diagram of another conventional terrestrial digital broadcast receiver.

Explanation of symbols

1, 2, 23 Digital broadcast receiver 2 Receiver input terminal (RF signal input terminal)
3, 5 Band pass filter 4 RF AGC amplifier circuit (RF gain control means)
6 Mixer circuit (frequency conversion means)
7 Local oscillator circuit (local oscillator means)
8 Bandpass filter (first intermediate frequency bandpass filter)
9 IF amplifier circuit 10 Band pass filter (second intermediate frequency band pass filter)
DESCRIPTION OF SYMBOLS 11 IF AGC amplifier circuit 12 A / D converter 13 Demodulation circuit 14 Level detection circuit 15 AGC control signal generation circuit 16 AGC detection circuit (1st automatic gain control detection means)
17 AGC detection circuit (second automatic gain control detection means)
18, 19 DC amplifier circuit 20 Averaging circuit (gain control signal generating means)
22 Band elimination filter (intermediate frequency band elimination filter)
24 changeover switch (gain control signal generating means)
25 S / N detection circuit (signal-to-noise ratio detection means)
26 Memory (storage means)
27 microcomputer 28 switching determination circuit (switching determination means)
29 switching control circuit (gain control signal generating means)
k1, k2 gain

Claims (9)

An RF signal input terminal for inputting multi-channel RF signals;
RF gain control means arranged at a subsequent stage of the RF signal input terminal for fixing or controlling the gain by a first gain control signal;
Local oscillation means for generating a local oscillation signal according to the reception frequency;
A frequency conversion unit that generates an intermediate frequency signal that is frequency-converted to an intermediate frequency by mixing the RF signal and the local oscillation signal;
A first intermediate frequency bandpass filter that is arranged at a subsequent stage of the frequency converting means and allows the intermediate frequency signal to be selected and passed in a wider band;
A receiver comprising a second intermediate frequency bandpass filter disposed downstream of the first intermediate frequency bandpass filter and allowing the intermediate frequency signal to be selected and passed through a narrower band;
First automatic gain control detection means for generating a second gain control signal according to the intermediate frequency signal;
Second automatic gain control detection means for generating a third gain control signal according to the output signal of the first intermediate frequency bandpass filter;
A receiver comprising: gain control signal generating means for generating the first gain control signal based on the second gain control signal and the third gain control signal.   The receiver according to claim 1, further comprising an intermediate frequency band elimination filter in a stage preceding the first automatic gain control detection unit.   The gain control signal generation means selects one of the second gain control signal and the third gain control signal and outputs the selected signal as the first gain control signal. The receiver according to 1 or 2.   3. The gain control signal generation unit synthesizes the second gain control signal and the third gain control signal, and outputs the resultant signal as the first gain control signal. 4. Receiver. The synthesis is averaging;
5. The reception according to claim 4, wherein the gain control signal generation means averages the second gain control signal and the third gain control signal, and outputs the averaged gain control signal as the first gain control signal. Machine.   The receiver according to claim 3, further comprising a signal-to-noise ratio detection unit that detects a signal-to-noise ratio at a subsequent stage of the second intermediate frequency bandpass filter. The signal-to-noise ratio detection means includes a first signal-to-noise ratio when the gain control signal generation means outputs the second gain control signal as the first gain control signal, and the gain control signal generation. Detecting a second signal-to-noise ratio when the means outputs the third gain control signal as the first gain control signal;
If the first signal to noise ratio is greater than the second signal to noise ratio, the gain control signal generating means outputs the second gain control signal as the first gain control signal;
When the second signal-to-noise ratio is larger than the first signal-to-noise ratio, the gain control signal generating means outputs the third gain control signal as the first gain control signal. The receiver according to claim 6. A storage unit and a switching determination unit;
The switching determination means performs the determination of the magnitude of the first signal-to-noise ratio and the second signal-to-noise ratio at the time of channel setting of the receiver,
The storage means stores the determination result,
The receiver according to claim 7, wherein the gain control signal generation unit outputs the first gain control signal based on the determination result stored in the storage unit when receiving the channel.   9. The receiver according to claim 8, wherein the switching determination unit performs the size determination at a time other than the time of channel setting of the receiver or a preset viewing time.

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