Patent Application
20100311382
The present invention relates to a reception device capable of selectively receiving an analog broadcast signal and a digital broadcast signal and to an electronic device using the same.
The following describes a conventional reception device that is disclosed in Patent Document 1 with reference to
Moreover, reception device 1 is provided with I signal output terminal 11 connected between first frequency conversion unit 7 and phase synthesis unit 9 and Q signal output terminal 12 connected between second frequency conversion unit 8 and phase synthesis unit 9. Furthermore, reception device 1 is provided with control unit 13 that controls a frequency of the first local signal and the second local signal outputted from oscillation unit 6. When receiving the digital broadcast signal, control unit 13 controls the frequency of the first local signal and the second local signal to be a central frequency of a reception frequency band. With this, control unit 13 causes I signal output terminal 11 to output an I signal as a baseband signal and Q signal output terminal 12 to output a Q signal as a baseband signal. On the other hand, when receiving the analog broadcast signal, reception device 1 controls the frequency of the first local signal and the second local signal to be a frequency that is (central frequency of the reception frequency band±IF frequency), and causes IF signal output terminal 10 to output the IF signal.
With such a configuration, it is possible to remove an image disturbing signal for reception device 1 that selectively receives the analog broadcast signal and the digital broadcast signal.
However, when receiving the analog broadcast signal, conventional reception device 1 illustrated in
Moreover, when receiving the digital broadcast signal, conventional reception device 1 uses an I signal low-pass filter (not shown) connected to a subsequent stage of I signal output terminal 11 and a Q signal low-pass filter (not shown) connected to a subsequent stage of Q signal output terminal 12 in order to remove an adjacent disturbing signal.
However, when receiving the analog broadcast signal, it is necessary to make attenuation properties of the IF bandpass filter connected to the subsequent stage of IF signal output terminal 10 steep in order to remove an adjacent disturbing signal. However, a problem has been noted that, as the attenuation properties of the IF bandpass filter become steeper, ripple characteristics or group delay characteristics, for example, of the IF bandpass filter are deteriorated. This consequently poses a problem of deterioration in reception quality of the reception device.
Patent Document 1: Unexamined Japanese Patent Publication No. H08-130690
DISCLOSURE OF THE INVENTION
The present invention aims to improve reception quality of a reception device that selectively receives an analog broadcast signal and a digital broadcast signal when receiving the analog broadcast signal.
A reception device according to the present invention is a reception device that selectively receives an analog broadcast signal and a digital broadcast signal. A reception device according to the present invention includes: an oscillation unit operable to output an oscillator signal; a frequency conversion unit operable to output an IF signal group based on the oscillator signal outputted from the oscillation unit and a reception signal; a filter unit connected to an output side of the frequency conversion unit; and a control unit operable to control a frequency of the oscillator signal outputted from the oscillation unit. Further, according to the reception device according to the present invention, the control unit controls: the frequency of the oscillator signal to be within a reception frequency band when receiving the digital broadcast signal; and the frequency of the oscillator signal to be outside the reception frequency band when receiving the analog broadcast signal.
With such a configuration, the present invention can improve the reception quality when receiving the analog broadcast signal.
The following describes a high-frequency reception device according to Embodiment 1 of the present invention with reference to the drawings.
Referring to
Moreover, reception device 14 is provided with phase synthesis unit 22 that phase-shifts and synthesizes one or both of a signal outputted from first filter 19 and a signal outputted from second filter 21. Furthermore, reception device 14 is provided with output terminal 23 connected to an output side of phase synthesis unit 22. Reception device 14 may be provided with third frequency conversion unit (not shown) that is connected between phase synthesis unit 22 and output terminal 23, and that up-converts an output signal from the phase synthesis unit. With this, reception device 14 removes a disturbing signal using an IF filter (not shown) that is configured by such as a SAW (Surface Acoustic Wave) filter connected to an output side of the third frequency conversion unit.
Further, reception device 14 may be provided with other frequency conversion units (not shown) that are connected to previous or subsequent stages of first frequency converter 18 and second frequency converter 20 and convert a frequency of the input signal, and another filter (not shown) configured by such as an SAW filter that removes a disturbing signal.
Moreover, in order to compensate characteristics of first filter 19 and second filter 21 and to reduce a size and a current of the circuit, first frequency converter 18 and second frequency converter 20 may be configured by a frequency converter circuit having filter properties. Furthermore, the filter properties may be variable between digital broadcasting reception and analog broadcasting reception.
Further, according to this embodiment, first filter 19 and second filter 21 are described to have low-pass properties as an example, but first filter 19 and second filter 21 may have bandpass properties when receiving the analog broadcast signal. In this case, it is possible to control only the high-pass cutoff frequency to be kept high. Alternatively, it is possible to control both the low-pass and the high-pass cutoff frequencies to be kept high.
Further, reception device 14 is provided with control unit 24 that controls a frequency of the first local signal and the second local signal outputted from phase shifter 17. When reception device 14 receives the digital broadcast signal, control unit 24 controls the frequency of the first local signal and the second local signal to be kept within a reception frequency band. In other words, when the reception frequency band is 6 MHz, control unit 24 controls oscillation unit 16 so that an absolute value |RF−Lo| of a difference between frequency RF of the reception signal inputted into input terminal 15 and frequency Lo of the first local signal and the second local signal is kept within 6 MHz. Specifically, control unit 24 can controls frequency Lo of the first local signal and the second local signal by setting a dividing ratio to a phase synchronizing circuit (hereinafter referred to as the PLL (Phase Locked Loop)) that is included in oscillation unit 16. With this, control unit 24 causes first frequency converter 18 to output the first IF signal as the baseband signal and second frequency converter 20 to output the second IF signal as the baseband signal, and causes phase synthesis unit 22 to synthesize these signals. On the other hand, when reception device 14 receives the analog broadcast signal, the frequency of the first local signal and the second local signal are controlled to be kept outside the reception frequency band (that is, within an adjacent frequency band excluding a border between the reception frequency band and the adjacent frequency band). With this, control unit 24 causes first frequency converter 18 and second frequency converter 20 to output the signals with the frequency of the difference between the reception frequency band and the local signals, and causes phase synthesis unit 22 to synthesize these signal. Thus, with reception device 14 that selectively receives the analog broadcast signal and the digital broadcast signal, it is possible to remove an image disturbing signal both when receiving a digital broadcasting and when receiving an analog broadcasting.
The following describes a control by control unit 24 in detail with reference to the drawings. First, a case in which reception device 14 receives a digital broadcast signal is described with reference to
Further, when the frequency of the first local signal and the second local signal is a central frequency of reception frequency band 27, it is possible to further lower the cutoff frequency of first filter 19 and second filter 21. As a result, it is possible to further improve attenuation of adjacent signal 26 for first filter 19 and second filter 21. Further, as the digital broadcast signal has higher tolerability to a DC offset spurious in first frequency converter 18 and second frequency converter 20 than the analog broadcast signal, it is possible to set frequency Lo of the first local signal and the second local signal to be within reception frequency band 27.
Next, a case in which reception device 14 receives an analog broadcast signal is described with reference to
The analog broadcast signal has lower tolerability to the DC offset spurious in first frequency converter 18 and second frequency converter 20 than the digital broadcast signal. Therefore, it is possible to improve reception quality by control unit 24 setting frequency Lo of the first local signal and the second local signal to be outside reception frequency band 31 when receiving the analog broadcast signal.
Specifically, as the analog broadcast signal has lower tolerability to the spurious within the reception signal band frequency than the digital broadcast signal, such a spurious is detected as disturbance in a playback video if present. In contrast, in the case of the digital broadcast signal, a bit error rate can be improved by error correction and the like even when there is any spurious present, and accordingly, a spurious that is smaller than a predetermined level may not be easily detected as disturbance in a playback video.
Further, when receiving the analog broadcasting, control unit 24 controls the first local signal and the second local signal so that their frequency departs from the reception frequency band by a width of the frequency of adjacent frequency band 32 at maximum. With this, the frequency of the signals inputted to first filter 19 and second filter 21 is kept low. Specifically, it is possible to reduce the cutoff frequency of first filter 19 and second filter 21 in the analog reception. As a result, attenuation properties required for an IF bandpass filter (not shown) connected to a subsequent stage of output terminal 23 of the IF signal can be reduced. Alternatively, without using the IF bandpass filter, it is possible to obtain sufficient adjacent disturbance removal properties when receiving the analog broadcasting, using first filter 19 and second filter 21. With this, it is possible to improve reception quality of the reception device that selectively receives the analog broadcast signal and the digital broadcast signal.
As described above, reception device 14 according to this embodiment uses first filter 19 and second filter 21 that are used when receiving the digital broadcasting in order to remove the disturbing signal when receiving the analog broadcasting, thereby improving reception quality.
Further, control unit 24 may control the cutoff frequency of first filter 19 and second filter 21 to be a first frequency when receiving the digital broadcast signal, and may control the cutoff frequency of first filter 19 and second filter 21 to be a second frequency that is higher than the first frequency when receiving the analog broadcast signal. With this, it is possible to remove adjacent disturbance appropriately depending on whether the reception is of the digital broadcast signal or of the analog broadcasting.
It is desirable that, when reception device 14 receives the analog broadcast signal as shown in
The reason of this is described below. In general, the analog broadcast signal includes video carrier frequency Fv, color subcarrier frequency Fc, and sound carrier frequency Fs in ascending order of the frequency. Further, such as ripple characteristics and group delay characteristics of a sound signal required for first filter 19 and second filter 21 are low, as compared to a video signal. Therefore, control unit 24 can set the cutoff frequency of first filter 19 and second filter 21 low by controlling frequency Lo of the first local signal and the second local signal to be below reception frequency band 31. Specifically, it is possible to improve the adjacent disturbance removal properties of first filter 19 and second filter 21. Further, when the analog broadcast signal includes sound carrier frequency Fs, color subcarrier frequency Fc, and video carrier frequency Fv in ascending order of the frequency, it is desirable by contrast that control unit 24 controls frequency Lo of the first local signal and the second local signal to be above reception frequency band 31. Specifically, when reception device 14 receives the analog broadcast signal, control unit 24 controls the first local signal and the second local signal to be outside reception frequency band 31 on a side closer to the video carrier frequency of reception frequency band 31.
Further, reception device 14 may be provided with first signal output terminal 23I connected between first filter 19 and phase synthesis unit 22, and second signal output terminal 23Q connected between second filter 21 and phase synthesis unit 22. In this case, when receiving the digital broadcasting, the first IF signal as the output signal of first filter 19 is outputted from first signal output terminal 23I, and the second IF signal as the output signal of second filter 21 is outputted from second signal output terminal 23Q. With this, when receiving the digital broadcasting, phase synthesis unit 22 may be eliminated, thereby reducing power consumption of reception device 14.
Furthermore, first filter 19 and second filter 21 may be a digital filter. In this case, as shown in
Next, the following describes a high-frequency reception device using a phase synchronizing circuit according to Embodiment 2 of the present invention with reference to the drawings.
Referring to
With such a configuration, even when a configuration in which first mixer 138 and second mixer 140 are connected in two stages is employed, it is not necessary to provide large-sized oscillation unit 116A for each mixer. Specifically, by providing frequency divider/multiplier 144, the oscillator signal and the other oscillator signal can be generated using common oscillation unit 116A, thereby reducing the size of the circuit to a large extent.
First mixer 138 is provided with phase shifter 117a that outputs first local signal and a second local signal respectively having phases substantially perpendicular to each other at a phase difference of 90 degrees based on the oscillator signal outputted from PLL 116. Further, first mixer 138 is provided with first frequency converter 118 that down-converts, using the first local signal outputted from phase shifter 117, a reception signal inputted to input terminal 115 into a first IF signal. Moreover, first mixer 138 is provided with second frequency converter 120 that down-converts, using the second local signal outputted from phase shifter 117, the reception signal inputted to input terminal 115 into a second IF signal. The first IF signal and the second IF signal have phases substantially perpendicular to each other. As described above, first mixer 138 outputs the IF signal group configured by the first IF signal and the second IF signal.
Filter unit 139 is provided with first filter 119 connected to an output side of first frequency converter 118 and second filter 121 connected to an output side of second frequency converter 120. An example of first filter 119 and second filter 121 is a low-pass filter whose cutoff frequency is variable.
Second mixer 140 is provided with third frequency converter 142 that up-converts a signal outputted from PLL 116 into a third IF signal of a frequency that is higher than that of the first IF signal. Further, second mixer 140 is provided with fourth frequency converter 143 that up-converts, using a fourth local signal outputted from phase shifter 141, a signal outputted from second filter 121 into a fourth IF signal of a frequency that is higher than that of the second IF signal. As described above, second mixer 140 outputs the other IF signal group configured by the third IF signal and the fourth IF signal.
Further, reception device 114 is provided with phase synthesis unit 122 that phase-shifts and synthesizes one or both of the third IF signal outputted from third frequency converter 142 and the fourth IF signal outputted from fourth frequency converter 143, thereby removing an image disturbing signal. Moreover, reception device 114 is provided with output terminal 123 connected to an output side of phase synthesis unit 122. It should be appreciated that reception device 114 may remove the disturbing signal using an IF filter (not shown) configured by such as an SAW filter connected to an output side of output terminal 123.
Further, in order to compensate characteristics of first filter 119 and second filter 121 and to reduce a size and a current of the circuit, first frequency conversion unit 118 and second frequency converter 120 may be configured by a frequency converter circuit having filter properties. Moreover, the filter properties can be variable between the digital broadcasting reception and the analog broadcasting reception. Furthermore, according to this embodiment, filter unit 139 is described to have low-pass properties as an example, but filter unit 139 may have bandpass properties when receiving the analog broadcast signal. In this case, it is possible to control only the high-pass cutoff frequency to be kept high. Alternatively, it is possible to control both the low-pass and the high-pass cutoff frequency to be kept high.
The following describes a control by control unit 124 in detail. First, a case in which reception device 114 receives a digital broadcast signal is described. When reception device 114 receives the digital broadcast signal, control unit 124 controls the frequency of the oscillator signal to be kept within the reception frequency band. Further, control unit 124 causes first frequency converter 118 to output the first IF signal and second frequency converter 120 to output the second IF signal whose phase is delayed by 90 degrees from the first IF signal. Then, control unit 124 causes second mixer 140 to frequency-convert, using the other oscillator signal that has been obtained by dividing or multiplying the first oscillator signal, a signal obtained by filtering the first IF signal by first filter 119 and a signal obtained by filtering the second IF signal by second filter 121 respectively into the third IF signal and the fourth IF signal.
Similarly to the example described according to Embodiment 1, when receiving the digital broadcast signal, control unit 124 controls, as shown in
Further, when frequency Lo of the oscillator signal corresponds to reception signal 25, that is, the central frequency of reception frequency band 27, the cutoff frequency of first filter 119 and second filter 121 can be kept even lower. As a result, it is possible to further improve attenuation of adjacent signal 26 in first filter 119 and second filter 121. Further, the digital broadcast signal has higher tolerability to the DC offset spurious in first frequency converter 118 and second frequency converter 120 than the analog broadcast signal. Therefore, even if a spurious is present in the reception signal, a bit error rate can be improved by error correction and the like, and disturbance in the playback video may not be easily detected. Accordingly, it is possible to set frequency Lo of the oscillator signal to be within reception frequency band 27.
Next, a case in which reception device 114 receives an analog broadcast signal is described. When reception device 114 receives the analog broadcast signal, as in Embodiment 1, control unit 124 controls the frequency of the first oscillator signal to be kept outside reception frequency band 31 (that is, within adjacent frequency band 32 excluding a border between reception frequency band 31 and adjacent frequency band 32). Further, control unit 124 causes first frequency converter 118 and second frequency converter 120 to output the IF signal group (the first IF signal and the second IF signal) of a low frequency which is a difference between reception frequency band 31 and the oscillator signal. Then, control unit 124 causes second mixer 140 to frequency-convert, using the other oscillator signal that has been obtained by dividing or multiplying the oscillator signal, the IF signal group into the other IF signal group (the third IF signal and the fourth IF signal).
As shown in
The analog broadcast signal has lower tolerability to the DC offset spurious in first frequency converter 118 and second frequency converter 120 than the digital broadcast signal. Therefore, it is possible to improve reception quality by control unit 124 setting frequency Lo of the oscillator signal to be outside reception frequency band 31 when receiving the analog broadcast signal.
Specifically, as the analog broadcast signal has lower tolerability to the spurious within the reception signal band frequency than the digital broadcast signal, such a spurious is detected as disturbance in a playback video if present. In contrast, in the case of the digital broadcast signal, a bit error rate can be improved by error correction and the like even when there is any spurious present, and accordingly, a spurious that is smaller than a predetermined level may not be easily detected as disturbance in a playback video.
Further, when receiving the analog broadcasting, control unit 124 causes frequency Lo of the oscillator signal to depart from the reception frequency band by the width of the frequency of adjacent frequency band 32 at maximum. With this, the frequency of the signals inputted to first filter 119 and second filter 121 is kept low. Specifically, it is possible to reduce the cutoff frequency of first filter 119 and second filter 121 when receiving the analog broadcasting. As a result, attenuation properties required for an IF bandpass filter (not shown) connected to a subsequent stage of output terminal 123 of the IF signal can be reduced. Alternatively, it is possible to obtain sufficient adjacent disturbance removal properties without using the IF bandpass filter, by using first filter 119 and second filter 121, when receiving the analog broadcasting. With this, it is possible to improve reception quality of reception device 114 that selectively receives the analog broadcast signal and the digital broadcast signal.
As described above, reception device 114 according to this embodiment uses first filter 119 and second filter 121 that are used when receiving the digital broadcasting in order to remove the disturbing signal when receiving the analog broadcasting. Therefore, it is possible to improve reception quality when receiving the analog broadcasting.
Further, control unit 124 may control the cutoff frequency of first filter 119 and second filter 121 to be a first frequency when receiving the digital broadcast signal, and may control the cutoff frequency of first filter 119 and second filter 121 to be a second frequency that is higher than the first frequency when receiving the analog broadcast signal. With this, it is possible to remove adjacent disturbance appropriately depending on whether the reception is of the digital broadcast signal or of the analog broadcasting.
It is desirable that, when reception device 114 receives the analog broadcast signal as shown in
Further, reception device 114 may be provided with third signal output terminal 123I connected between third frequency converter 142 and phase synthesis unit 122, and fourth signal output terminal 123Q connected between fourth frequency converter 143 and phase synthesis unit 22. In this case, when receiving the digital broadcasting, the third IF signal is outputted from third signal output terminal 123I and fourth IF signal is outputted from fourth signal output terminal 123Q. Further, reception device 114 may be connected with a digital demodulator (not shown) to which the third IF signal and the fourth IF signal are inputted. With this, when receiving the digital broadcasting, phase synthesis unit 22 may be eliminated, thereby reducing power consumption of reception device 14.
Further, reception device 114 carry out the frequency conversion using the signals outputted from a single PLL 116 without using two mixers. With this, it is possible to downsize the reception device.
First filter 119 and second filter 121 according to this embodiment can be a digital filter. In this case, as shown in
Next, a configuration of PLL 116 is described with reference to
In this configuration, where a frequency of the reference signal is fREF, a frequency of the oscillator signal is fLO1, and a frequency of the other oscillator signal is fLO2, comparator 146 outputs a pulse signal that is in proportion to a phase difference between two frequencies of inputted fREF and fLO1/M. Loop filter 147 outputs a voltage signal obtained by lowpass filtering a pulse signal outputted from comparator 146. In a situation in which the voltage signal is converged to a certain voltage, oscillator 148 outputs stable frequency fLO1 as the first oscillator signal. With such a loop configuration, fLO1 and fLO2 are respectively expressed by formula 1 and formula 2.
fLO1=fREF×M Formula 1
fLO2=fLO1/P=fREF×M/P Formula 2
Now, a specific example of operation is shown by numbers when reference signal fREF is taken as 4 MHz in
On the other hand, when receiving the analog broadcast signal, assuming that the reception frequency band is from 506 MHz to 512 MHz (19 channels in terrestrial broadcasting within Japan), the IF signal group is 3.5 MHz, and the other IF signal group is 10 MHz, oscillator signal fLO1 is 505.5 MHz (=lower 0.5 MHz of the reception frequency band), and the other oscillator signal fLO2 is 13.5 MHz. Therefore, dividing ratio M controlled by control unit 124 is 126.375 (=505.5 MHz/4 MHz), and dividing/multiplying ratio P is 37.444 (≈505.5 MHz/13.5 MHz).
For frequency divider 150A and frequency divider/multiplier 144A, a fractional-N method, a delta-sigma method or the like is employed for fractional frequency division. By using such a method, it is possible to dramatically decrease resolution set for fLO1 and fLO2.
With such a configuration, the other oscillator signal according to this embodiment is generated by dividing and multiplying the oscillator signal generated by single PLL 116. Therefore, a VCO (Voltage Controlled Oscillator) included in PLL 116 may not be additionally provided in order to generate the other oscillator signal. Specifically, it is possible to use dividing/multiplying circuit (logic circuit) realizing size reduction to a large extent as semiconductor fabrication becomes finer, thereby downsizing the reception device.
fLO1=fREF×M′×P′ Formula 3
fLO2=fLO1/P′=fREF×M′ Formula 4
Now, a specific example of operation is shown by numbers when reference signal fREF is taken as 4 MHz in
When reception device 114 receives the digital broadcast signal (the reception frequency band: 500 MHz to 506 MHz, the IF signal group: 0 MHz, and the other IF signal group: 10 MHz), dividing ratio M′ is 2.5 (=10 MHz/4 MHz), and dividing/multiplying ratio P′ is 50.3 (=503 MHz/10 MHz).
On the other hand, when receiving the analog broadcast signal (the reception frequency band: 506 MHz to 512 MHz, the IF signal group: 3.5 MHz, and the other IF signal group: 10 MHz), dividing ratio M′ is 3.375 (=13.5 MHz/4 MHz), and dividing/multiplying ratio P′ is 37.444 (≈505.5 MHz/13.5 MHz).
Synthesize dividing ratio (=M′×P′) when serially connecting dividing ratio M′ and dividing/multiplying ratio P′ set respectively for frequency divider 150B and frequency divider/multiplier 144B of the configuration shown in
Specifically, with the configuration shown in
In the examples of operation as described with reference to
Next,
According to the configuration shown in
Specifically, by mounting reception device 14, 114 that selectively receives the analog broadcast signal and the digital broadcast signal described in each embodiment to electronic device 201, it is possible to improve image quality of display unit 204, and to downsize electronic device 201.
According to the present invention, it is possible to improve reception quality of the reception device that selectively receives the analog broadcast signal and the digital broadcast signal when receiving an analog broadcast signal, and therefore, the present invention can be utilized in electronic devices, for example, such as televisions, car navigation systems for automobile use, and mobile terminals.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-107656 | Apr 2008 | JP | national |
| 2008-245822 | Sep 2008 | JP | national |
This application is a U.S. National Phase Application of PCT international application PCT/JP2009/001748.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/001748 | 4/16/2009 | WO | 00 | 8/11/2010 |
