JP2007019900A - Broadcast receiving apparatus and broadcast receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of suppressing reduction in a signal level at a reception desired frequency by effectively attenuating a disturbing station signal level unattended with a cost increase in the product of a broadcast receiving apparatus, impediments to downsizing and weight reduction, and an increase in power consumption. <P>SOLUTION: The broadcast receiving apparatus includes: a high frequency amplifying circuit 1 for amplifying a high frequency signal of a received television broadcast; a mixer circuit 2 that mixes a variable oscillation frequency signal corresponding to a channel selection signal with the high frequency signal amplified by the high frequency amplifying circuit 1 to output a low frequency signal; a gain control circuit 11 that generates an AGC signal with an amplitude in response to the electric field strength of the low frequency signal outputted from the mixer circuit 2 to input the AGC signal to the high frequency amplifying circuit 1; and a limiter circuit 5 that monitors the amplitude of the high frequency signal received by the mixer circuit 2 and controls the gain control circuit 11 to maintain the amplitude of the AGC signal just before the amplitude exceeds a prescribed value and to input the amplitude to the high frequency amplifying circuit 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a broadcast receiving apparatus and a broadcast receiving method, and more particularly to a broadcast receiving apparatus and a broadcast receiving method for controlling the amplitude of a received signal.

  In addition to BS broadcasting using broadcasting satellites and CS broadcasting using communication satellites that have already been broadcast, digital terrestrial broadcasting has been started in some areas since December 2003. FIG. 8 is a diagram illustrating a receiving circuit in a conventional television receiver that receives digital waves. FIG. 9 is a diagram showing the radio wave distribution of 16-channel analog waves and 8-channel digital waves of channel numbers 20 to 27 in the Kanto region. In FIG. 8, an RF-AMP (high frequency amplifier circuit) 21 amplifies a high frequency signal received from the antenna and outputs the amplified signal to a MIXER (mixer circuit) 22. The MIXER 22 mixes a local oscillation signal from a local oscillation circuit (not shown) and a high frequency signal output from the RF-AMP 21, and sends a low frequency signal to an IF-BPF (low frequency bandpass filter circuit) 23. input. The IF-BPF 23 performs filtering processing with a predetermined bandwidth on the low-frequency signal input from the MIXER 22 and inputs the filtered signal to an IF-AMP (low-frequency amplifier circuit) 24. The IF-AMP 24 is controlled in amplification factor by a feedback signal from a demodulation circuit (not shown). An RSSI • Filter (field strength filter circuit) 25 inputs a feedback signal corresponding to the electric field strength of the low frequency signal input from the MIXER 22 to the high frequency amplifier circuit 21 to control the amplification factor.

  In the receiving circuit shown in FIG. 8, the RF-AMP 21 receives an analog wave in addition to a plurality of digital waves, so that the electric field strength of all the received radio waves is included from the RSSI • Filter 25. As shown in FIG. 9, when a digital wave of one channel number is received in a frequency band in which eight channels of channel numbers 20 to 27 can be received, other adjacent digital waves and analog waves are received. May be mixed. For this reason, even if a digital wave having a desired channel number corresponding to the user's channel selection is received, other digital waves and analog waves may become interference signals.

As a countermeasure, for example, a patent document proposes a receiver and a reception method. According to this patent document, in order to effectively attenuate the IM (intermodulation) interfering station signal level and suppress the decrease in the receiving station signal level, the main tuner and the sub-tuner are provided. While receiving and demodulating, the sub-tuner detects the state of the broadcast radio wave, and controls the reception state of the main tuner based on the detection result. In other words, the tuning frequency control unit uses the sub-tuner to detect two stations that are intermodulation jamming stations with respect to the receiving station, and among the two stations, the frequency of the jamming station close to the receiving station and the receiving station frequency If the difference is less than or equal to the first set value, the tuning frequency of the tuning circuit is separated from the disturbing station frequency, and if the difference is greater than or equal to the second set value greater than the first set value, Bring the frequency closer to the jamming station frequency. (See Patent Document 1)
JP 2004-229170 A

However, the provision of the sub-tuner in addition to the main tuner as in Patent Document 1 causes new problems such as an increase in product cost, an obstacle to reduction in size and weight, and an increase in power consumption. As for terrestrial digital broadcasting, since broadcasting to mobile communication terminals such as mobile phones is scheduled, obstacles to miniaturization and weight reduction and increase in power consumption are issues that must be solved. It is not preferable that such a problem occurs because the wave is attenuated.
The present invention is to solve such a conventional problem, and effectively attenuates the signal level of the jamming station without increasing the cost of the product, obstructing the reduction in size and weight, and increasing the power consumption. An object is to suppress a decrease in the signal level of the desired reception frequency.

  The broadcast receiving apparatus according to claim 1 is a signal amplifying means (in the embodiment, corresponding to the high frequency amplifier circuit 1 of FIG. 1) for amplifying a received broadcast high frequency signal, and a variable oscillation corresponding to the channel selection signal. A signal mixing means (corresponding to the mixer circuit 2 in FIG. 1 in the embodiment) that outputs a low-frequency signal by mixing the frequency signal and the high-frequency signal amplified by the signal amplification means, and output by the signal mixing means A signal feedback means (corresponding to the gain control circuit 11 in FIG. 1 in the embodiment) that generates a negative feedback signal having an amplitude corresponding to the electric field strength of the low frequency signal and inputs it to the signal amplification means; When the amplitude of the high frequency signal input to the means exceeds a predetermined value and the amplitude exceeds the predetermined value, the amplitude of the negative feedback signal immediately before exceeding the predetermined value is held and input to the signal amplifying means. Signal monitoring means for controlling the signal feedback means as (in the embodiment corresponds to the limiter circuit 5 of FIG. 1) has a configuration which includes a, a.

In the broadcast receiving apparatus according to claim 1, as described in claim 2, the signal monitoring means sets the upper limit value of the high-frequency signal that does not cause distortion in the low-frequency signal output from the signal mixing means to a predetermined value. It may be configured.
Alternatively, in the broadcast receiving apparatus according to claim 1, as described in claim 3, the signal monitoring means has a linear relationship between the high frequency signal input to the signal mixing means and the low frequency signal output from the signal mixing means. Alternatively, the amplitude may be set to a predetermined value that is smaller than the amplitude of the high-frequency signal when it changes non-linearly by a value set in advance (corresponding to 1 dB in the embodiment).

  According to a fourth aspect of the present invention, there is provided a broadcast receiving method comprising: a step A for amplifying a received broadcast high frequency signal by a predetermined signal amplifying means (corresponding to the high frequency amplifier circuit 1 in FIG. 1 in the embodiment); and a channel selection signal. Step B for outputting a low frequency signal by mixing the variable oscillation frequency signal corresponding to the above and the high frequency signal amplified by the signal amplifying means, and an amplitude corresponding to the electric field strength of the low frequency signal output by Step B Step C for generating a negative feedback signal and inputting it to the signal amplifying means, and monitoring the amplitude of the high-frequency signal output by the signal amplifying means, and when the amplitude exceeds a predetermined value, immediately before exceeding the predetermined value Step D is performed in which the amplitude of the negative feedback signal is held and input to the signal amplification means.

5. The broadcast receiving method according to claim 4, wherein, as described in claim 5, step D is configured such that the upper limit value of the high frequency signal that does not cause distortion in the low frequency signal output by step B is set to a predetermined value. May be.
Alternatively, in the broadcast receiving method of claim 4, as described in claim 6, in step D, the relationship between the high-frequency signal before being processed in step B and the low-frequency signal after being processed is linear to nonlinear. The amplitude may be set to a predetermined value that is smaller by a preset value (corresponding to 1 dB in the embodiment) than the amplitude of the high-frequency signal at the time of change.

  According to the broadcast receiving apparatus and the broadcast receiving method of the present invention, it is possible to effectively attenuate the jamming station signal level without increasing the product cost, obstructing the reduction in size and weight, and increasing the power consumption. An effect of suppressing a decrease in signal level is obtained.

Hereinafter, embodiments of a broadcast receiving apparatus according to the present invention will be described with reference to FIGS.
FIG. 1 is a schematic block diagram illustrating a partial configuration of a broadcast receiving apparatus according to the embodiment. As shown in FIG. 1, a broadcast receiving apparatus includes an RF-AMP (high frequency amplifier circuit) 1, a MIXER (mixer circuit) 2, an IF-BPF (low frequency bandpass filter circuit) 3, and an IF-AMP (low frequency amplifier circuit). ) 4, LIMIT (limiter circuit) 5, RSSI • Filter (field strength filter circuit) 6, RSSI • Filter 7, SW (switch circuit) 8, subtractor 9, SW10, RF-AGC (gain control circuit) 11, CPU 12, And it is comprised by the demodulation circuit etc. which are not shown in a figure.

  The RF-AMP 1 receives the high frequency signal a from the antenna and inputs the amplified high frequency signal b to the MIXER 2. The MIXER 2 generates a low frequency signal c by mixing the variable oscillation frequency signal input from the local oscillation circuit (not shown) and the high frequency signal b, and inputs the low frequency signal c to the IF-BPF 3. The IF-BPF 3 performs a filtering process on the low-frequency signal bandwidth of the terrestrial digital broadcasting from the low-frequency signal c input from the MIXER 2, and inputs the low-frequency signal d after the filtering process to the IF-AMP 4. To do. The IF-AMP 4 amplifies the low frequency signal d and inputs the low frequency signal e to the demodulation circuit, and controls the output level according to the feedback signal f from the demodulation circuit.

  A high frequency signal b output from the RF-AMP 1 is input to the LIMIT 5. FIG. 2 is a diagram illustrating an input / output operation of LIMIT5. As shown in FIG. 2A, the high frequency signal b is supplied to the minus side of the input of LIMIT 5 and the reference P1 dB threshold signal th is supplied to the plus side. LIMIT 5 compares these two analog signals and outputs a binary digital signal p as LIMIT Data. That is, as shown in FIG. 2B, when the high frequency signal b on the negative side is less than the threshold value P1 dB, H (a high level signal p is output, and when the high frequency signal b on the negative side is equal to or higher than the threshold value P1 dB, L In general, the input allowable range of MIXER2 is an extremely small value determined by the value of P1 dB as shown in Fig. 2C, which is a limit that causes distortion in the output of MIXER2. P1dB is defined as a point of output b2 that is 1 dB lower than output b1 when the IN-Out characteristic of MIXER2 is in an ideal linear relationship.If the input of RF-AMP1 is less than P1 dB The distortion of the output of RF-AMP1 does not occur and the C / N becomes a good value.When the input of RF-AMP1 exceeds P1 dB, the output of RF-AMP1 is distorted little by little. Therefore, when the output of RF-AMP1 becomes b3 or more, C / N becomes very small and the reception performance is greatly deteriorated, and therefore the input until RF-AMP1 is P1dB or more and the output reaches b3 is limited. It is set as a point range.

  In FIG. 1, a low-frequency signal c output from an analog MIXER 2 is input to an RSSI • Filter 6 and an RSSI • Filter 7 and subjected to filtering processing with different bandwidths. FIG. 3 is a diagram illustrating an example of a bandpass characteristic Fa of the RSSI • Filter 6 having a wide band and a bandpass characteristic Fb of the RSSI • Filter 7 having a narrow band. As shown in FIG. 1, the two signals g1 and g2 filtered in the RSSI • Filter 6 and the RSSI • Filter 7 are input to the SW8, and the RSSI from any one RSSI • Filter is received by the selection signal i from the CPU 12. Signal g is selected.

  FIG. 4 is a diagram illustrating a selection result of SW8 when the selection signal i of the CPU 12 is H (high level) or L (low level). The CPU 12 sets the selection signal i to H when there are many digital waves to be received, selects the signal g1 from the RSSI • Filter 6 having a wide band, and sets the selection signal i to L when there are few digital waves. The signal g2 from the RSSI filter 7 having a narrow band is selected. As shown in FIG. 1, the signal g selected by SW8 is input to the subtractor 9 and SW10. The subtracter 9 subtracts the signal d output from the IF-BPF 3 from the signal g selected by the SW 8 and inputs the difference signal h to the SW 10 and the CPU 12. The CPU 12 compares the difference signal h with a specific threshold value and controls the selection signal j of the SW 10. A signal k selected by the selection signal j is input from the SW 10 to the RF-AGC 11. The control of SW8 and SW10 by the CPU 12 will be further described later.

  FIG. 5 is a diagram illustrating an internal circuit of the RF-AGC 11. In addition to the signal k, the RF-AGC 11 receives the signal p from the LIMIT 5 and the signal m from the CPU 12. The signal k is input to the buffer 112 when the FET switch 111 is on, and the AGC signal q is input to the RF-AMP1. The signal p is input to the gate of the FET switch 111 when the FET switch 113 is on, turns on the FET 111 when it is high, and turns off when it is low. The signal m turns on the FET 113 at a high level and turns it off at a low level. The capacitor 114 holds the signal k immediately before the change because the FET switch 111 changes from on to off when the signal p changes from the high level to the low level while the signal m is at the high level. When the signal p changes from high level to low level and the FET switch 111 changes from on to off, the buffer 112 outputs a fixed level signal k held in the capacitor 114 as an AGC signal. Although not shown in FIG. 5, the gate of the FET switch 111 is set to a high level by a pull-up resistor, and the FET switch 111 operates even when the FET switch 113 is turned off. .

  As described above, when the output b of the RF-AMP 1 is less than P1 dB, that is, when the signal p from the LIMIT 5 is at a high level, the signal k from the SW 10 is supplied to the RF-AMP 1 as an AGC signal, and the output b is equal to or more than P1 dB. Then, the immediately preceding signal k is held, and the held signal is supplied to the RF-AMP 1 as an AGC signal.

Next, the operation of the broadcast receiving apparatus of FIG. 1 will be described based on the flowchart of the CPU 12 shown in FIGS.
In FIG. 6, after predetermined initialization (step S1), it is determined whether or not channel reception is selected by an operation of a remote controller or the like (step S2). When channel reception is selected, a desired reception frequency is detected (step S3). The desired reception frequency is automatically set according to the selected channel to be received. Then, filter coefficients of RSSI • Filter6 and RSSI • Filter7 are set (step S4). For example, as shown in FIG. 3, the filter coefficients of the bandpass characteristic Fa of RSSI • Filter6 and the bandpass characteristic Fb of RSSI • Filter7 are set so that the detected reception desired frequency is located at the center thereof.

  After the desired reception frequency is detected in step S3 and the filter coefficient is set in step S4, or when channel reception selection is not performed in step S2, that is, when the processing in steps S3 and S4 has already been completed. Based on the selected reception channel and the current reception area, the number of receivable channels around the reception channel, that is, the number of digital waves that can be received is checked. In other words, it is detected at which position the desired reception frequency is in the channel frequency band that can be received in the area (step S5). Then, it is determined whether or not the desired reception frequency is located at the center of the frequency band and the number of digital waves in the periphery is large (step S6). When there are few digital waves in the periphery, that is, when the desired reception frequency is located at the end of the receivable frequency band, the output i of the CPU 12 is set to L, and the SW8 has a narrow band from the RSSI • Filter 7. The signal g2 is selected (step S7). Conversely, when there are many digital waves in the vicinity, that is, when the desired reception frequency is located in the center of the receivable frequency band, the output i of the CPU 12 is set to H, and the RSSI • Filter 6 having a wide band in SW8. Is selected (step S8).

  Next, the signal h that is the output of the subtracter 9 is captured (step S9). And it is discriminate | determined whether the signal h is larger than a specific level or below a specific level (step S10). When the signal h is below a specific level, the selection signal j for SW10 is set to L, the signal g of RSSI • Filter6 or RSSI • Filter7 selected by SW8 is selected as the signal k to RF-AGC11, and RF -AGC signal to AMP1 (step S11). When the signal h is larger than a specific level, the selection signal j for the SW 10 is set to H, the signal h that is the output of the subtracter 9 is selected as the signal k to the RF-AGC 11, and the AGC signal to the RF-AMP 1 (Step S12).

After the selection signal j is output in step S11 or step S12, or if no reception channel is selected in step S2 of FIG. 6, it is determined whether or not the Limit switch is turned on by operating the remote controller or the like (step S13) When this switch is turned on, the control signal m given to the RF-AGC 11 is inverted (step S14). When the selection signal m is H, the FET switch 113 is in the ON state in the RF-AGC 11 circuit shown in FIG. 5, and the signal p from the LIMIT 5 becomes valid. Therefore, when the signal p is H, the FET switch 111 is in an ON state, and therefore the signal k from the SW 10 is output as an AGC signal to the RF-AMP 1. On the other hand, when the signal p changes to L, the FET switch 111 is turned off, the immediately preceding signal k is held in the capacitor 114, and a fixed level signal is output as an AGC signal to the RF-AMP1. When the selection signal m is L, the FET switch 113 is in an OFF state, so that the signal p from the LIMIT 5 is invalid. In this case, since the FET switch 111 is kept on by the gate pull-up resistor, the signal k from the SW 10 is always output as an AGC signal to the RF-AMP 1.
After the control signal m is inverted in step S14, or when the Limit switch is not turned on in step S13, the process proceeds to step S2 in FIG.

As described above, the broadcast receiving apparatus of this embodiment includes the high-frequency amplifier circuit 1 that amplifies the received broadcast high-frequency signal, the variable oscillation frequency signal corresponding to the channel selection signal, and the high-frequency signal amplified by the high-frequency amplifier circuit 1. And a gain control circuit 11 that generates an AGC signal having an amplitude corresponding to the electric field strength of the low-frequency signal output by the mixer circuit 2 and inputs the AGC signal to the high-frequency amplifier circuit 1. The amplitude of the high-frequency signal input to the mixer circuit 2 is monitored, and when the amplitude exceeds a predetermined value, the amplitude of the AGC signal immediately before exceeding the predetermined value is held, and the high-frequency amplifier circuit 1 A limiter circuit 5 is provided for controlling the gain control circuit 11 to input.
Therefore, it is possible to effectively attenuate the jamming station signal level and suppress a decrease in the signal level of the desired reception frequency without increasing the cost of the product, obstructing the reduction in size and weight, and increasing the power consumption.
In the above embodiment, the limiter circuit 5 sets the upper limit value of the high frequency signal that does not cause distortion in the low frequency signal output from the mixer circuit 2 as a predetermined value.
Alternatively, the limiter circuit 5 has an amplitude that is 1 dB smaller than the amplitude of the high-frequency signal when the relationship between the high-frequency signal input to the mixer circuit 2 and the low-frequency signal output from the mixer circuit 2 changes from linear to non-linear. Is a predetermined value.
Therefore, it is possible to reproduce high-quality images and sound without distortion.

In the above embodiment, the invention of the broadcast receiving apparatus, that is, the invention of the product has been described. However, the invention of the broadcast receiving method can be realized by the operation of the CPU 12 shown in FIGS.
That is, the broadcast receiving method of the present invention includes a step A for amplifying a received broadcast high frequency signal by a predetermined signal amplifying means, a variable oscillation frequency signal corresponding to a channel selection signal, and a high frequency signal amplified by the signal amplifying means. Step B for outputting a low-frequency signal by mixing and a step C for generating a negative feedback signal having an amplitude corresponding to the electric field strength of the low-frequency signal output by Step B and inputting it to the signal amplification means When the amplitude of the high-frequency signal output by the signal amplifying means is monitored and the amplitude exceeds a predetermined value, the amplitude of the negative feedback signal immediately before exceeding the predetermined value is held and the signal amplifying means is retained. Step D is input.

In the step D, an upper limit value of a high frequency signal that does not cause distortion in the low frequency signal output in the step B is set as the predetermined value.
Alternatively, the step D is set in advance from the amplitude of the high-frequency signal when the relationship between the high-frequency signal before being processed by the step B and the low-frequency signal after the processing changes from linear to non-linear. An amplitude that is smaller by a value is set as the predetermined value.

The block diagram which shows the structure of the broadcast receiver of this invention. The figure explaining operation | movement of the limit circuit in FIG. The figure which shows the characteristic of the two RSSI filter circuits in FIG. The figure which shows the function of the switch circuit of FIG. The figure which shows the internal structure of the RF-AGC circuit in FIG. 2 is a CPU flowchart showing the operation of the broadcast receiving apparatus of FIG. 1. The flowchart of CPU following FIG. The block diagram which shows the structure of the conventional television receiver. The figure which shows the electromagnetic wave distribution of an analog wave and a digital wave in the Kanto area.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High frequency amplifier circuit 2 Mixer circuit 3 Low frequency band pass filter circuit 4 Low frequency amplifier circuit 5 Limiter circuit 6 Electric field strength filter circuit 7 Electric field strength filter circuit 8 Switch circuit 9 Subtractor 10 Switch circuit 11 Gain control circuit 12 CPU

Claims (6)

Signal amplifying means for amplifying the received broadcast high-frequency signal;
Signal mixing means for outputting a low frequency signal by mixing a variable oscillation frequency signal corresponding to a channel selection signal and a high frequency signal amplified by the signal amplification means;
A signal feedback means for generating a negative feedback signal having an amplitude corresponding to the electric field strength of the low-frequency signal output by the signal mixing means and inputting the negative feedback signal to the signal amplifying means;
When the amplitude of the high-frequency signal input to the signal mixing unit exceeds a predetermined value, the amplitude of the negative feedback signal immediately before exceeding the predetermined value is held and input to the signal amplification unit Signal monitoring means for controlling the signal feedback means,
A broadcast receiving apparatus.   The broadcast receiving apparatus according to claim 1, wherein the signal monitoring unit sets the upper limit value of a high-frequency signal that does not cause distortion in the low-frequency signal output from the signal mixing unit as the predetermined value.   The signal monitoring means is set in advance from the amplitude of the high frequency signal when the relationship between the high frequency signal input to the signal mixing means and the low frequency signal output from the signal mixing means changes from linear to nonlinear. The broadcast receiving apparatus according to claim 1, wherein an amplitude smaller by a predetermined value is set as the predetermined value. Amplifying the received broadcast high-frequency signal by a predetermined signal amplifying means;
Step B of outputting a low frequency signal by mixing the variable oscillation frequency signal corresponding to the channel selection signal and the high frequency signal amplified by the signal amplification means;
Generating a negative feedback signal having an amplitude corresponding to the electric field strength of the low-frequency signal output by the step B and inputting the negative feedback signal to the signal amplification means; and
When the amplitude of the high-frequency signal output by the signal amplification means exceeds a predetermined value, the amplitude of the negative feedback signal immediately before exceeding the predetermined value is held and input to the signal amplification means Step D,
Broadcast receiving method to execute.   5. The broadcast receiving method according to claim 4, wherein in step D, an upper limit value of a high-frequency signal that does not cause distortion in the low-frequency signal output in step B is set as the predetermined value.   The step D is a value set in advance from the amplitude of the high-frequency signal when the relationship between the high-frequency signal before being processed by the step B and the low-frequency signal after being processed changes from linear to non-linear. The broadcast receiving method according to claim 4, wherein a small amplitude is set as the predetermined value.

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