Radio-frequency receiver and integrated circuit employed for the receiver

This application is a U.S. National Phase Application of PCT International Application PCT/JP2006/315459.

The present invention relates to a mobile radio-frequency receiver formed of two radio-frequency receiver sections for receiving digital broadcasting signals and also relates to an integrated circuit employed for the radio-frequency receiver.

Japanese Patent Unexamined Publication No. H05-191312 discloses a conventional radio-frequency receiver. As shown in FIG. 7 , conventional radio-frequency receiver 201 contains radio-frequency receiving circuits 202 a and 202 b that are identical in construction. Radio-frequency circuit 202 a ( 202 b ) contains input terminal 204 a ( 204 b ) that receives digital broadcasting signals from antenna 203 a ( 203 b ), output terminal 205 a ( 205 b ) that carries output signals and PLL-control terminal 206 a ( 206 b ) that carries PLL-control signals. Radio-frequency receiving circuits 202 a and 202 b are accommodated in a same housing.

Besides, radio-frequency receiving circuit 202 a ( 202 b ) contains mixer 207 a ( 207 b ) and oscillation circuit 209 a ( 209 b ). Mixer 207 a ( 207 b ) receives a signal from input terminal 204 a ( 204 b ) and sends it to output terminal 205 a ( 205 b ). Mixer 207 a ( 207 b ) also receives an oscillation signal from oscillation circuit 209 a ( 209 b ) via selective switching section 208 a ( 208 b ).

Such structured radio-frequency receiver 201 is usually battery-operated, for example, at a low voltage of 3V. It is therefore difficult to supply high tuning voltage to variable capacitance diodes that constitute oscillation circuits 209 a and 209 b in terms of decreasing power consumption and noise.

To address the problem, each of oscillation circuits 209 a and 209 b contains four connected units of an oscillator and a tuning circuit: three units for selectively receiving all channels (hereinafter abbreviated to ch) in the UHF (ultra high frequency) band; and one unit for receiving 7-ch in the VHF (very high frequency) band.

That is, conventional radio-frequency receiver 201 , since having two radio-frequency receiving circuits 202 a and 202 b, needs eight units of the oscillator and the tuning circuit in total.

The tuning circuit is formed of a capacitor and an inductor connected in parallel; the inductor has a large footprint in the circuit. This has been an obstacle to reduction in size of an integrated circuit; accordingly, an obstacle to reduction in size of a radio-frequency receiver.

The radio-frequency receiver of the present invention has two radio-frequency receiver sections for receiving digital broadcasting signals. The two radio-frequency receiver sections contain a first and a second input terminals for receiving digital broadcasting signals; a first mixer whose one input receives the signals from the first input terminal; a second mixers whose one input receives the signals from the second input terminal; a first output terminal for receiving signals fed from the first mixer; a second output terminal for receiving signals fed from the second mixer; a PLL controller; a plurality of low-voltage-driven oscillation circuits that is connected to the PLL controller and oscillates at a frequency higher than the digital broadcasting signals; a first selective switching circuit which is connected to the output of plurality of oscillation circuits and to the PLL controller for controlling, and has a first terminal and a second terminal; a first frequency-divider section connected to the first terminal and another input of the first mixer; and a second frequency-divider section connected to the second terminal and another input of the second mixer. The PLL controller controls the first selective switching circuit so that the plurality of oscillation circuits is selectively connected to each of the first and the second terminals. Besides, the first and the second frequency-divider sections have variable frequency-dividing rate.

In the aforementioned structure of the present invention, an inductor constituting the oscillation circuits, which has been an obstacle to miniaturization, is shared between the first and the second radio-frequency receiver sections. This allows the radio-frequency receiver to be compact.

Besides, the oscillation circuits operate at an oscillation frequency higher than the digital broadcasting signal, allowing the inductor to be more compact. As a result, the radio-frequency receiver can be further downsized.

FIG. 1 is a block diagram illustrating the structure of a radio-frequency receiver in accordance with a first exemplary embodiment of the present invention.

FIG. 2 shows a relationship between channel assignment of all channels in the UHF band and the frequencies of signals fed into another input of a mixer of the radio-frequency receiver in accordance with the first exemplary embodiment.

FIG. 3 is a block diagram illustrating another structure of the radio-frequency receiver in accordance with the first exemplary embodiment.

FIG. 4 is a block diagram illustrating the structure of a radio-frequency receiver in accordance with a second exemplary embodiment of the present invention.

FIG. 5 shows a relationship between channel assignment of all channels in the UHF band plus 7-ch in the VHF band and the frequencies of signals fed into another input of a mixer of the radio-frequency receiver in accordance with the second exemplary embodiment.

FIG. 6 is a block diagram illustrating another structure of the radio-frequency receiver in accordance with the second exemplary embodiment.

FIG. 7 is a block diagram illustrating a conventional structure of a radio-frequency receiver.

12 a, 12 b input terminal

13 a, 13 b output terminal

16 a, 16 b mixer

21 , 29 oscillator section

22 a, 22 b frequency-divider section

24 a, 24 b, 24 c, 24 d, 24 e oscillation circuit

25 , 28 selective switching circuit

35 PLL controller

The exemplary embodiments of the present invention are described hereinafter with reference to the accompanying drawings.

First Exemplary Embodiment

FIG. 1 is a block diagram illustrating the structure of radio-frequency receiver 10 in accordance with the first exemplary embodiment of the present invention. The first exemplary embodiment describes the structure employing a direct-conversion type frequency converter in receiving digital broadcasting signals in the UHF band. Mixer 16 a as a first mixer and mixer 16 b as a second mixer are direct-conversion type frequency converters. Mixer 16 a is so structured that the frequency of the digital broadcasting signals fed into one input of mixer 16 a equals to the frequency for conversion fed into another input of mixer 16 a. Similarly, Mixer 16 b is so structured that the frequency of the digital broadcasting signals fed into one input of mixer 16 b equals to the frequency for conversion fed into another input of mixer 16 b.

Radio-frequency receiver 10 of FIG. 1 contains radio-frequency receiver sections 20 a, 20 b; PLL (phase locked loop)-control terminal 14 that receives PLL-control signals; PLL-controller 35 connected to PLL control terminal 14 ; frequency-divider section 22 a that is a first frequency-divider connected to radio-frequency receiver section 20 a; frequency-divider section 22 b that is a second frequency-divider connected to radio-frequency receiver section 20 b; and oscillator section 21 connected to frequency-divider sections 22 a and 22 b.

Radio-frequency receiver section 20 a contains input terminal 12 a as a first input terminal that receives digital broadcasting signals from antenna 11 a and output terminal 13 a as a first output terminal that receives output signals. Between input terminal 12 a as the first input terminal and output terminal 13 a, the following components are connected in the order named: amplifier 15 a, mixer 16 a, band-pass filter 17 a and amplifier 18 a. That is, the output of amplifier 15 a is fed into one input of mixer 16 a.

Radio-frequency receiver section 20 b contains input terminal 12 b as a second input terminal that receives digital broadcasting signals from antenna 11 b and output terminal 13 b as a second output terminal that receives output signals. Between input terminal 12 b and output terminal 13 b, the following components are connected in the order named: amplifier 15 b, mixer 16 b, band-pass filter 17 b and amplifier 18 b. That is, the output of amplifier 15 b is fed into one input of mixer 16 a.

Another input of mixer 16 a receives oscillation signals from oscillator section 21 via output terminal 23 a of frequency-divider section 22 a. Similarly, another input of mixer 16 b receives oscillation signals from oscillator section 21 via output terminal 23 b of frequency-divider section 22 b.

Oscillator section 21 contains four oscillation circuits 24 a, 24 b, 24 c, 24 d; and selective switching circuit 25 as a first selective switching circuit. Selective switching circuit 25 has terminal 21 a as a first terminal and terminal 21 b as a second terminal. Under the control of PLL controller 35 , selective switching circuit 25 selects two out of the outputs from the four oscillation circuits 24 a through 24 d and send them to terminals 21 a and 21 b. Oscillation circuit 24 a is a series-connected unit of oscillator 26 a and tuning circuit 27 a. Similarly, oscillation circuit 24 b is a series-connected unit of oscillator 26 b and tuning circuit 27 b; Oscillation circuit 24 c is a series-connected unit of oscillator 26 c and tuning circuit 27 c; and oscillation circuit 24 d is a series-connected unit of oscillator 26 d and tuning circuit 27 d. When a variable capacitance diode has a large variable capacitance range in tuning voltage, the range of the oscillation frequency expands. In this case, the number of the oscillation circuits can be reduced.

The oscillation signal from terminal 21 a of selective switching circuit 25 is fed into input terminal 23 c of frequency-divider section 22 a. Between input terminal 23 c and output terminal 23 a of frequency-divider section 22 a, frequency dividers 30 a, 30 b and 30 c are connected in series in the order named. Of three dividers 30 a, 30 b and 30 c, two dividers have a frequency-dividing rate of ½; and the rest one has a frequency-dividing rate of ⅓. The embodiment describes the structure having divider 30 a with a frequency-dividing rate of ⅓ and dividers 30 b, 30 c with a frequency-dividing rate of ½.

Electronic switches 31 a, 31 b and 31 c are connected in parallel to frequency dividers 30 a, 30 b and 30 c, respectively.

On the other hand, the oscillation signal from terminal 21 b of selective switching circuit 25 is fed into input terminal 23 d of frequency-divider section 22 b. Between input terminal 23 d and output terminal 23 b of frequency-divider section 22 b, frequency dividers 32 a, 32 b and 32 c are connected in series in the order named. Of three dividers 32 a, 32 b and 32 c, two dividers have a frequency-dividing rate of ½; and the rest one has a frequency-dividing rate of ⅓. The embodiment describes the structure having divider 32 a with a frequency-dividing rate of ⅓ and dividers 32 b, 32 c with a frequency-dividing rate of ½.

Electronic switches 33 a, 33 b and 33 c are connected in parallel to frequency dividers 32 a, 32 b and 32 c, respectively.

PLL-control terminal 14 for receiving PLL-control data is connected to PLL controller 35 . PLL controller 35 sends control signals to selective switching circuit 25 of oscillator section 21 ; oscillators 26 a, 26 b, 26 c, and 26 d; and frequency-divider sections 22 a and 22 b.

Integrating mixers 16 a, 16 b; frequency-divider sections 22 a, 22 b; oscillator section 21 ; and PLL controller 35 into a package provides a size-reduced integrated circuit. In the integrated circuit used for radio-frequency receiver 10 of the first exemplary embodiment, at least the following components are integrated into the same package: mixer 16 a as a first mixer; mixer 16 b as a second mixer; frequency-divider section 22 a as a first frequency-divider; frequency-divider section 22 b as a second frequency-divider; oscillator section 21 containing a plurality of oscillation circuits ( 24 a, 24 b, 24 c, 24 d ) and selective switching circuit 25 as a first selective switching circuit; and PLL controller 35 .

Hereinafter will be described radio-frequency receiver 10 having the structure above.

Digital broadcasting signals, for example, digital broadcasting signals of 13-ch through 62-ch in the UHF band are captured by antennas 11 a and 11 b and sent to input terminals 12 a and 12 b. The signals fed from terminals 12 a and 12 b are then amplified by gain-controllable amplifiers 15 a and 15 b, respectively.

The output signals from amplifiers 15 a and 15 b are fed into one input of mixers 16 a and 16 b, respectively. Mixers 16 a and 16 b are direct-conversion type frequency converters. Frequency-divider sections 22 a and 22 b feed signals, which have the same frequency as the digital broadcasting signals fed into the aforementioned input terminal of mixers 16 a and 16 b, to another input of mixers 16 a and 16 b.

The output signals from mixers 16 a and 16 b are fed into band-pass filters 17 a and 17 b where an interfering signal is suppressed. The output signals from the band-pass filters 17 a and 17 b enters into amplifiers 18 a and 18 b, and the amplified signals go out of output terminals 13 a and 13 b.

Next will be described the output signals, which are fed into another input of mixers 16 a and 16 b from frequency-divider sections 22 a and 22 b, with reference to FIG. 2 .

FIG. 2 shows a relationship between channel assignment (hereinafter, ch-assignment) of all channels in the UHF band and the frequencies of signals fed into another input of mixers 16 a and 16 b of radio-frequency receiver 10 in the embodiment. The uppermost of FIG. 2 shows ch-assignment 101 in the UHF band. The channels are horizontally shown in the order of increasing their numbers toward the right. The channels of 13-ch, 30-ch, 50-ch, 61-ch and 62-ch are represented as 101 a, 101 b, 101 c, 101 d and 101 e, respectively.

Radio-frequency receiver 10 , since it is designed for a mobile receiver, is usually driven by battery, for example, with a low voltage of 3V. Such a low voltage cannot provide the variable capacitance diode of the tuning circuit of oscillator section 21 with high tuning voltage unless a DC-DC converter is employed.

Oscillator section 21 needs two or more oscillators because a single oscillator cannot cover all the frequencies. The structure of the first exemplary embodiment contains, as shown in FIG. 1 , oscillation circuit 24 a formed of oscillator 26 a and tuning circuit 27 a; oscillation circuit 24 b formed of oscillator 26 b and tuning circuit 27 b; and oscillation circuit 24 c formed of oscillator 26 c and tuning circuit 27 c.

The middle section of FIG. 2 shows frequency 102 of the signal fed into another input of mixer 16 a. Frequency 102 is divided into frequency bands 103 , 104 and 105 in the horizontal direction. The oscillating frequencies from oscillation circuits 24 a, 24 b and 24 c are divided by frequency-divider section 22 a into the signal frequencies of frequency bands 103 , 104 and 105 , respectively.

With the use of two frequency-dividers each of which has a frequency-dividing rate of ½, the frequency-dividing rate of frequency-divider section 22 a is determined to be ¼ under the control of PLL controller 35 . That is, each of oscillating frequencies 2411 (for oscillation circuit 24 a ), 2412 (for oscillation circuit 24 b ), 2413 (for oscillation circuit 24 c ) is given a frequency ranging from 1892 MHz to 3068 MHz, which is four-times higher than the signal frequencies of all the channels in the UHF band. Employing a high oscillation frequency allows the inductors of tuning circuits 27 a, 27 b and 27 c to be reduced in size. This is also true with tuning circuit 27 d of oscillation circuit 24 d, which will be described later.

As described above, frequency 102 ( FIG. 2 ) is fed into another input of mixer 16 a. Frequency band 103 ranges from frequency 101 a (13-ch) as the lowest to frequency 101 b (30-ch) as the highest. That is, oscillation frequency 2411 of oscillation circuit 24 a for receiving frequency band 103 should take oscillation frequency 2411 ranging from 1892 MHz (=473 MHz×4, that is, four-times higher than frequency 101 a (13-ch) as the lowest in band 103 ) to 2300 MHz (=575 MHz×4, that is, four-times higher than frequency 101 b (30-ch) as the highest). In frequency-divider section 22 a, electronic switch 31 a only turns on, whereas switches 31 b and 31 c turn off, so that frequency-divider section 22 a serves as a divider for dividing a frequency into ¼. FIG. 2 shows frequency band 103 as fa×¼; where, fa represents oscillation frequency 2411 .

Similarly, frequency band 104 ranges from frequency 101 b (30-ch) as the lowest to frequency 101 c (50-ch) as the highest. That is, oscillation circuit 24 b should take oscillation frequency 2412 ranging from 2300 MHz (=575 MHz×4, that is, four-times higher than frequency 101 b (30-ch) as the lowest in band 104 ) to 2780 MHz (=695 MHz×4, that is, four-times higher than frequency 101 c (50-ch) as the highest). In frequency-divider section 22 a, the switch selection is the same as that for receiving frequency band 103 , that is, frequency-divider section 22 a divides a frequency into ¼. FIG. 2 shows frequency band 104 as fb×¼; where, fb represents oscillation frequency 2412 .

Similarly, frequency band 105 ranges from frequency 101 c (50-ch) as the lowest to frequency 101 e (62-ch) as the highest. That is, oscillation circuit 24 c should take oscillation frequency 2413 ranging from 2780 MHz (=695 MHz×4, that is, four-times higher than frequency 101 c (50-ch) as the lowest in band 105 ) to 3068 MHz (=767 MHz×4, that is, four-times higher than frequency 101 e (62-ch) as the highest). In frequency-divider section 22 a, the switch selection is the same as that for receiving frequency band 103 , that is, frequency-divider section 22 a divides a frequency into ¼. FIG. 2 shows frequency band 105 as fc×¼; where, fc represents oscillation frequency 2413 .

Receiving a control signal from PLL controller 35 , any one of oscillation circuits 24 a, 24 b and 24 c becomes active. Selective switching circuit 25 selects the oscillation signal from the “turned-on” oscillation circuit and sends the signal to frequency-divider section 22 a. As described earlier, frequency-divider section 22 a has a frequency-dividing rate of ¼ under the control of PLL controller 35 . In this way, mixer 16 a receives, through another input, an output signal in a range of 473 MHz to 767 MHz fed from output terminal 23 a of frequency-divider section 22 a.

With the structure above, a desired signal is selected from the broadcasting signals of all the channels ranging from 13-ch to 62-ch received at radio-frequency receiver section 20 a.

It has demonstrated that oscillation frequency 2411 of oscillation circuit 24 a has a ratio of the lowest frequency to the highest frequency of 1.5 or greater; here in the structure, a conservative ratio of 1.2 is given to oscillation circuit 24 a in consideration of a margin of the oscillation frequency. Oscillation circuits 24 b, 24 c and 24 d have a ratio the same as is determined in oscillation circuit 24 a.

Adding oscillation circuit 24 d to the structure above, as shown in FIG. 1 , allows radio-frequency receiver sections 20 a and 20 b to receive different channels with each other in the broadcasting signals of all the channels in the UHF band. The structure will be described hereinafter.

The bottom section of FIG. 2 shows frequency 107 of the signal fed into another input of mixer 16 b. Frequency 107 is divided into frequency bands 108 , 106 , 109 and 110 in the horizontal direction. Oscillating frequencies 2413 (of oscillation circuit 24 c ), 2414 (of oscillation circuit 24 d ), 2411 (of oscillation circuit 24 a ) and 2412 (of oscillation circuit 24 b ) are divided by frequency-divider section 22 b into the signal frequencies of frequency bands 108 , 106 , 109 and 110 , respectively. Frequency-divider section 22 b serves as a frequency divider with the following frequency dividing ratio: 6/1 for circuit 24 c; ¼ for circuit 24 d; ⅓ for circuit 24 a and circuit 24 b.

Frequency 107 ( FIG. 2 ) is fed into another input of mixer 16 b. Frequency band 108 ranges from frequency 101 a (13-ch) as the lowest to frequency 101 b (30-ch) as the highest. That is, oscillation circuit 24 c should take oscillation frequency 2413 ranging from 2838 MHz (=473 MHz×6, that is, six-times higher than frequency 101 a (13-ch) as the lowest in band 107 ) to 3450 MHz (=575 MHz×6, that is, six-times higher than frequency 101 b (30-ch) as the highest). In frequency-divider section 22 b, electronic switch 33 c only turns on, whereas switches 33 a and 33 b turn off, so that frequency-divider section 22 b serves as a divider for dividing a frequency into ⅙. FIG. 2 shows frequency band 108 as fc×⅙; where, fc represents oscillation frequency 2413 .

Similarly, frequency band 106 ranges from frequency 101 b (30-ch) as the lowest to frequency 101 c (50-ch) as the highest. That is, oscillation circuit 24 d should take oscillation frequency 2414 ranging from 2300 MHz (=575 MHz×4, that is, four-times higher than frequency 101 b (30-ch) as the lowest in band 108 ) to 2780 MHz (=695 MHz×4, that is, four-times higher than frequency 101 c (50-ch) as the highest). The switch selection is the same as that for frequency band 104 , that is, in frequency-divider section 22 b, electronic switch 33 a only turns on, whereas switches 33 b and 33 c turn off, so that frequency-divider section 22 b serves as a divider for dividing a frequency into ¼. FIG. 2 shows frequency band 106 as fd×¼; where, fd represents oscillation frequency 2414 .

Frequency band 109 ranges from frequency 101 c (50-ch) as the lowest to frequency 101 d (61-ch) as the highest. That is, oscillation circuit 24 a should take oscillation frequency 2411 ranging from 2085 MHz (=695 MHz×3, that is, three-times higher than frequency 101 c (50-ch) as the lowest in band 109 ) to 2283 MHz (=761 MHz×3, that is, three-times higher than frequency 101 d (61-ch) as the highest). In frequency-divider section 22 b, electronic switch 33 a only turns off, whereas switches 33 b and 33 c turn on, so that frequency-divider section 22 b serves as a divider for dividing a frequency into ⅓. FIG. 2 shows frequency band 109 as fa×⅓; where, fa represents oscillation frequency 2411 .

Frequency band 110 ranges from frequency 101 d (61-ch) as the lowest to frequency 101 e (62-ch) as the highest. That is, oscillation circuit 24 b should take oscillation frequency 2412 ranging from 2283 MHz (=761 MHz×3, that is, three-times higher than frequency 101 d (61-ch) as the lowest in band 110 ) to 2301 MHz (=767 MHz×3, that is, three-times higher than frequency 101 e (62-ch) as the highest). In frequency-divider section 22 b, electronic switch 33 a only turns off, whereas switches 33 b and 33 c turn on, so that frequency-divider section 22 b serves as a divider for dividing a frequency into ⅓. FIG. 2 shows frequency band 110 as fb×⅓; where, fb represents oscillation frequency 2412 .

To be more specific, when the receiver receives signals in the range from 13-ch to 30-ch, oscillation circuit 24 a, which is the oscillator for frequency band 103 , and oscillation circuit 24 c for frequency band 108 become active. The oscillation signal from oscillation circuit 24 a is fed into frequency-divider section 22 a that serves as a ¼ divider, whereas the signal from oscillation circuit 24 c is fed into frequency-divider section 22 b that serves as a ⅙ divider. The output signals from frequency-divider sections 22 a and 22 b are fed into another input of each of mixers 16 a and 16 b.

When the receiver receives signals in the range from 30-ch to 50-ch, oscillation circuit 24 b, which is the oscillator for frequency band 104 , and oscillation circuit 24 d for frequency band 106 become active. The oscillation signals from oscillation circuits 24 b and 24 d are fed into frequency-divider sections 22 a and 22 b, both of which serve as a ¼ divider. The output signals from frequency-divider sections 22 a and 22 b are fed into another input of each of mixers 16 a and 16 b.

When the receiver receives signals in the range from 50-ch to 61-ch, oscillation circuit 24 c for frequency band 105 and oscillation circuit 24 c for frequency band 109 become active. The oscillation signal from oscillation circuit 24 c is fed into frequency-divider section 22 a that serves as a ¼ divider, whereas the signal from oscillation circuit 24 a is fed into frequency-divider section 22 b that serves as a ⅓ divider. The output signals from frequency-divider sections 22 a and 22 b are fed into another input of each of mixers 16 a and 16 b.

When the receiver receives signals in the range from 61-ch to 62-ch, oscillation circuit 24 c for frequency band 105 and oscillation circuit 24 d for frequency band 110 become active. The oscillation signal from oscillation circuit 24 c is fed into frequency-divider section 22 a that serves as a ¼ divider, whereas the signal from oscillation circuit 24 d is fed into frequency-divider section 22 b that serves as a ⅓ divider. The output signals from frequency-divider sections 22 a and 22 b are fed into another input of each of mixers 16 a and 16 b.

As described above, a control signal from PLL controller 35 allows two oscillation circuits out of the four to become active according to a receiving channel. The oscillation signals fed from the two “turned-on” oscillation circuits are selected by selective switching circuit 25 and fed into frequency-divider sections 22 a and 22 b where the signals undergo frequency dividing. Each of sections 22 a and 22 b is controlled by PLL controller 35 so as to have a frequency-dividing rate of any one of ⅓, ¼ and ⅙. In this way, each signal having a desired frequency is fed into another input of each of mixers 16 a and 16 b.

With the structure above, radio-frequency receiver sections 20 a and 20 b separately receive two channels, which may be different or may be the same, in receiving digital broadcasting signals in the UHF band.

Although the structure has two radio-frequency receiver sections 20 a and 20 b, the required number of oscillation circuits of oscillator section 21 is four (i.e., 24 a, 24 b, 24 c and 24 d ), which is half the number of a conventional structure. That is, the number of inductors required in tuning circuits 27 a, 27 b, 27 c and 27 d constituting oscillation circuits 24 a, 24 b, 24 c and 24 d, respectively, can be reduced to half.

The inductors, because of a large footprint, have inconveniently increased in size the integrated circuit. According to the structure of the embodiment, however, the number of inductors can be reduced to half, compared to a conventional structure. This contributes to a downsized integrated circuit, which accordingly allows radio-frequency receiver 10 to have a compact structure.

Besides, the oscillation circuits 24 a, 24 b, 24 c and 24 d operate at oscillation frequencies four-times higher than the digital broadcasting signals, allowing the inductor to be more compact. As a result, the integrated circuit can be further decreased in size and the radio-frequency receiver 10 can be downsized.

A diversity receiving is obtained as follows: in FIG. 3 , the control signal from PLL controller 35 activates one of the four oscillation circuits. The oscillation signal from the “turned-on” oscillation circuit is fed into frequency-divider sections 22 a and 22 b. After that, the output signals from sections 22 a and 22 b are fed into another input of each of mixers 16 a and 16 b. That is, selective switching circuit 25 receives an oscillation signal from the turned-on oscillation circuit and sends the signal to frequency-divider sections 22 a and 22 b. Diversity receiving is thus obtained.

FIG. 3 is a block diagram illustrating another structure of radio-frequency receiver 10 of the first exemplary embodiment. In addition to the structure shown in FIG. 1 , radio-frequency receiver 10 of FIG. 3 contains additional selective switching circuit 28 between frequency-divider sections 22 a, 22 b and mixers 16 a, 16 b. Selective switching circuit 28 contains, as shown in FIG. 3 , output terminal 28 a connected to another input of mixer 16 a; output terminal 28 b connected to another input of mixer 16 b; input terminal 28 c connected to frequency-divider section 22 a; input terminal 28 d connected to frequency-divider section 22 b; and input terminal 28 e connected to PLL controller 35 . With the structure above, PLL controller 35 of radio-frequency receiver 10 controls oscillation circuits 26 a, 26 b, 26 c and 26 d so that any one of them turns on. At the same time, PLL controller 35 controls frequency-divider sections 22 a and 22 b so that either one of them operates at a frequency-dividing rate of ¼. Selected by selective switching circuits 25 and 28 , the output signal fed from either one of frequency-divider sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b. Diversity receiving of all the channels in the UHF band is thus obtained.

In the receiving above, the receiver needs power supply for only one of oscillation circuits 26 a, 26 b, 26 c and 26 d, and one of frequency-divider sections 22 a and 22 b, contributing to power savings.

Although the first exemplary embodiment describes a direct-conversion type frequency converter, it is not limited thereto; the structure of the present invention is also applicable to a down-conversion type frequency converter. That is, mixer 16 a as a first mixer and mixer 16 b as a second mixer serve as down-conversion type frequency converters. In this case, the frequency for frequency conversion fed into another input of mixer 16 a is higher or lower than the frequency of the digital broadcasting signal fed into one input of mixer 16 a by the intermediate frequency. Similarly, the frequency for frequency conversion fed into another input of mixer 16 b is higher or lower than the frequency of the digital broadcasting signal fed into one input of mixer 16 b by the intermediate frequency. The receiver can receive both of digital and analog broadcasting system by forming the receiver into the following structure: forming the oscillator section with four oscillation circuits 24 a, 24 b, 24 c and 24 d. Three out of the four circuits, each of which is responsible for a three-divided range of a frequency band that has frequency four-times higher than the digital broadcasting signal, generate oscillation signals suitable for each range. The rest one oscillation circuit has an oscillation frequency that contains the oscillation frequency of the oscillation circuit for the second range of the frequency band. Such structured receiver can cope with both the digital and analog broadcasting systems.

In a case where radio-frequency receiver section 20 a receives a channel different from radio-frequency section 20 b, two oscillation circuits turn on. If the operating two circuits generate oscillation frequencies in a close range, C/N (carrier-noise) ratio of both frequencies is degraded. In some cases, the oscillation frequency of one circuit is wrongly received by the mixer for receiving the frequency of the other oscillation circuit, so that interference can occur. To avoid the inconveniencies, each of the four oscillation circuits needs shielding separately in radio-frequency range.

Frequency-divider sections 22 a and 22 b also needs shielding in radio-frequency range because they generate harmonic signals in the frequency dividing process. That is, the following components are separately shielded at radio-frequency: frequency-divider section 22 a as a first frequency-divider; frequency-divider section 22 b as a second frequency-divider; and oscillator section 21 containing a plurality of oscillation circuits ( 24 a, 24 b, 24 c, and 24 d ) and selective switching circuit 25 as a first selective switching circuit.

The harmonic signals fed from frequency-divider sections 22 a and 22 b easily cause interference by radiation. To reduce the ill effect caused by radiation, frequency-divider section 22 a as a first frequency-divider is disposed close to mixer 16 a as a first mixer, and frequency-divider section 22 b as a second frequency-divider is disposed close to mixer 16 b as a second mixer.

Second Exemplary Embodiment

FIG. 4 is a block diagram illustrating the structure of radio-frequency receiver 10 a in accordance with the second exemplary embodiment. Radio-frequency receiver 10 in FIG. 1 of the first embodiment receives all the channels in the UHF band, whereas the radio-frequency receiver of the second embodiment receives all the channels in the UHF band, plus 7-ch in the VHF band. In the structure shown in FIG. 4 , like parts are identified by the same reference marks as in FIG. 1 and detailed explanation thereof will be omitted.

Oscillator section 29 of FIG. 4 is formed of four oscillation circuits 24 a, 24 b, 24 c and 24 e. Oscillation circuit 24 e corresponds to circuit 24 d of the structure of the first embodiment, but differs from circuit 24 d in the highest and the lowest frequencies. Oscillation circuit 24 e is a unit of oscillator 26 e and tuning circuit 27 e connected to oscillator 26 e.

Next will be described the output signals from frequency-divider sections 22 a and 22 b, which are fed into another input of each of mixers 16 a and 16 b, with reference to FIG. 5 .

FIG. 5 shows a relationship between channel assignment of all channels in the UHF band and 7-ch in the VHF band and the frequencies of signals fed into another input of a mixer of the radio-frequency receiver in accordance with the second exemplary embodiment. In the structure shown in FIG. 5 , like parts are identified by the same reference marks as in FIG. 2 and detailed explanation thereof will be omitted.

The uppermost of FIG. 5 shows ch-assignment 131 of 7-ch in the VHF band and all the channels in the UHF band. The channels are horizontally shown in the order of increasing their numbers toward the right. The channels of 7-ch, 13-ch, 29-ch, 30-ch, 49-ch, 50-ch, 61-ch and 62-ch are represented as 151 , 101 a, 101 f, 101 b, 101 g, 101 c, 101 d and 101 e, respectively.

The middle section of FIG. 5 shows frequency 132 of the signal fed into another input of mixer 16 a. Frequency 132 is divided into frequency bands 152 , 103 , 104 and 105 in the horizontal direction. The receiver receives all the channels in the UHF band by determining frequencies 103 , 104 and 105 as is the case with the structure in the first exemplary embodiment. To receive frequency band 152 , i.e., 7-ch in the VHF band, the receiver operates oscillation circuit 24 a, which has an oscillation frequency ranging from 1892 MHz to 2300 MHz, at an oscillation frequency of 2292 MHz. Frequency-divider section 22 a divides the oscillation frequency into ¼, and then further divides it into ⅓. After that, frequency-divider section 22 a outputs a signal with a frequency of 191 MHz (corresponding to 7-ch), which is fed into another input of mixer 16 a. In this way, radio-frequency receiver section 20 a receives 7-ch as a desired channel.

Adding oscillation circuit 24 e to the oscillator section allows radio-frequency receiver sections 20 a and 20 b to separately receive two channels—which may be different or may be the same—in receiving digital broadcasting signals in the UHF band. The method will be described below.

It has demonstrated that oscillation frequency 2415 of oscillation circuit 24 e has a ratio of the lowest frequency to the highest frequency of 1.5 or greater; here in the structure, a conservative ratio of 1.2 is given to oscillation circuit 24 e in consideration of a margin of the oscillation frequency.

The bottom section of FIG. 5 shows frequency 140 of the signal fed into another input of mixer 16 b. Frequency 140 is divided into frequency bands 153 , 121 , 122 , 123 and 110 in the horizontal direction. Oscillating frequencies 2413 (of oscillation circuit 24 c ), 2415 (of oscillation circuit 24 e ), 2411 (of oscillation circuit 24 a ) and 2412 (of oscillation circuit 24 b ) are divided by frequency-divider section 22 b into the signal frequencies of frequency bands 121 , 122 , 123 and 110 , respectively. Frequency-divider section 22 b serves as a frequency divider with the following frequency dividing ratio: 6/1 for circuit 24 c; ¼ for circuit 24 e; ⅓ for circuit 24 a and circuit 24 b.

Frequency band 121 ranges from frequency 101 a (13-ch) as the lowest to frequency 101 f (29-ch) as the highest. That is, oscillation circuit 24 c should take oscillation frequency 2413 ranging from 2838 MHz (=473 MHz×6, that is, six-times higher than frequency 101 a (13-ch) as the lowest in band 121 ) to 3414 MHz (=569 MHz×6, that is, six-times higher than frequency 101 f (29-ch) as the highest). FIG. 5 shows frequency band 121 as fc×⅙; where, fc represents oscillation frequency 2413 .

Similarly, frequency band 122 ranges from frequency 101 f (29-ch) as the lowest to frequency 101 g (49-ch) as the highest. That is, oscillation circuit 24 e should take oscillation frequency 2415 ranging from 2276 MHz (=569 MHz×4, that is, four-times higher than frequency 101 f (29-ch) as the lowest in band 122 ) to 2756 MHz (=689 MHz×4, that is, four-times higher than frequency 101 g (49-ch) as the highest). FIG. 5 shows frequency band 122 as fe×¼; where, fe represents oscillation frequency 2415 .

Frequency band 123 ranges from frequency 101 g (49-ch) as the lowest to frequency 101 d (61-ch) as the highest. That is, oscillation circuit 24 a should take oscillation frequency 2411 ranging from 2067 MHz (=689 MHz×3, that is, three-times higher than frequency 101 g (49-ch) as the lowest in band 123 ) to 2283 MHz (=761 MHz×3, that is, three-times higher than frequency 101 d (61-ch) as the highest). FIG. 5 shows frequency band 123 as fa×⅓; where, fa represents oscillation frequency 2411 .

Frequency band 110 ranges from frequency 101 d (61-ch) as the lowest to frequency 101 e (62-ch) as the highest. That is, oscillation circuit 24 b should take oscillation frequency 2412 ranging from 2283 MHz (=761 MHz×3, that is, three-times higher than frequency 101 d (61-ch) as the lowest in band 110 ) to 2301 MHz (=767 MHz×3, that is, three-times higher than frequency 101 e (62-ch) as the highest). FIG. 5 shows frequency band 110 as fb×⅓; where, fb represents oscillation frequency 2412 .

To be more specific, when the receiver receives signals in the range from 13-ch to 29-ch, oscillation circuit 24 a, which is the oscillator for frequency band 103 , and oscillation circuit 24 c for frequency band 121 become active. The oscillation signal from oscillation circuit 24 a is fed into frequency-divider section 22 a that serves as a ¼ divider, whereas the signal from oscillation circuit 24 c is fed into frequency-divider section 22 b that serves as a ⅙ divider. Each output signal from frequency-divider sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b.

When the receiver receives signals in the range from 29-ch to 30-ch, oscillation circuit 24 a, which is the oscillator for frequency band 103 , and oscillation circuit 24 e for frequency band 122 become active. The oscillation signals from oscillation circuits 24 a and 24 e are fed into frequency-divider sections 22 a and 22 b, both of which serve as a ¼ divider. Each output signal from frequency-divider sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b.

When the receiver receives signals in the range from 30-ch to 49-ch, oscillation circuit 24 b, which is the oscillator for frequency band 104 , and oscillation circuit 24 e for frequency band 122 become active. The oscillation signals from oscillation circuits 24 b and 24 e are fed into frequency-divider sections 22 a and 22 b, both of which serve as a ¼ divider. Each output signal from frequency-divider sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b.

When the receiver receives signals in the range from 49-ch to 50-ch, oscillation circuit 24 b, which is the oscillator for frequency band 104 , and oscillation circuit 24 a for frequency band 123 become active. The oscillation signal from oscillation circuit 24 b is fed into frequency-divider section 22 a that serves as a ¼ divider, whereas the signal from oscillation circuit 24 a is fed into frequency-divider section 22 b that serves as a ⅓ divider. Each output signal from frequency-divider sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b.

When the receiver receives signals in the range from 50-ch to 61-ch, oscillation circuit 24 c, which is the oscillator for frequency band 105 , and oscillation circuit 24 a for frequency band 123 become active. The oscillation signal from oscillation circuit 24 c is fed into frequency-divider section 22 a that serves as a ¼ divider, whereas the signal from oscillation circuit 24 a is fed into frequency-divider section 22 b that serves as a ⅓ divider. Each output signal from frequency-divider sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b.

When the receiver receives signals in the range from 61-ch to 62-ch, oscillation circuit 24 c, which is the oscillator for frequency band 105 , and oscillation circuit 24 b for frequency band 110 become active. The oscillation signal from oscillation circuit 24 c is fed into frequency-divider section 22 a that serves as a ¼ divider, whereas the signal from oscillation circuit 24 b is fed into frequency-divider section 22 b that serves as a ⅓ divider. Each output signal from frequency-divider sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b.

As described above, a control signal from PLL controller 35 allows two oscillation circuits out of the four to become active according to a receiving channel. The oscillation signals fed from the two “turned-on” oscillation circuits are selected by selective switching circuit 25 and fed into frequency-divider sections 22 a and 22 b where the signals undergo frequency dividing. Each of sections 22 a and 22 b is controlled by PLL controller 35 so as to have a frequency-dividing rate of any one of ⅓, ¼ and ⅙. In this way, each signal having a desired frequency is fed into another input of each of mixers 16 a and 16 b.

With the structure above, radio-frequency receiver sections 20 a and 20 b separately receive two channels, which may be different or may be the same, in receiving digital broadcasting signals of the UHF band.

Next will be described a case where radio-frequency receiver sections 20 a and 2 b simultaneously receive 7-ch in the VHF band.

When radio-frequency receiver section 20 a receives 7-ch, the receiver provides oscillation frequency 2411 of oscillation circuit 24 a with 1/12 frequency dividing; oscillation frequency 2411 (=2292 MHz) of oscillation circuit 24 a undergoes ¼ dividing, and then ⅓ dividing (i.e., 2292 MHz×¼×⅓=191 MHz). Frequency 103 a (=573 MHz) is obtained by dividing oscillation frequency 2411 (=2292 MHz) into ¼.

When radio-frequency receiver section 20 b receives 7-ch, the receiver provides oscillation frequency 2415 of oscillation circuit 24 e with 1/12 frequency dividing; oscillation frequency 2415 (=2292 MHz) of oscillation circuit 24 e undergoes ¼ dividing, and then ⅓ dividing (i.e., 2292 MHz×¼×⅓=191 MHz). Frequency 122 a (=573 MHz) is obtained by dividing oscillation frequency 2415 (=2292 MHz) into ¼.

As described above, operating oscillation circuit 24 a (for radio-frequency receiver section 20 a ) and oscillation circuit 24 b (for radio-frequency receiver section 20 b ) allows the receiver to simultaneously receive VHF 7-ch.

According to the receiver of the embodiment, the frequency band of digital broadcasting signals, which is assigned in the UHF band, is divided into three: lower frequency band 103 , intermediate frequency band 104 and higher frequency band 105 . The receiver contains oscillation circuits 24 a, 24 b and 24 c, which are responsible for frequency bands 103 , 104 and 105 , respectively. Lower frequency band 103 , which includes frequency 103 a in a high range, is determined in a manner that the oscillation frequency of oscillation circuit 24 a is divided into ¼. At the same time, the frequency that is obtained by dividing frequency 103 a into ⅓ is not lower than the frequency of VHF 7-ch (=191 MHz). That is, it is necessary that the oscillation frequency of oscillation circuit 24 a is not lower than 2292 MHz (191 MHz×12).

Frequency band 122 , which includes frequency 122 a in a low range, is determined in a manner that the oscillation frequency of oscillation circuit 24 e is divided into ¼, takes a range lower than intermediate frequency band 104 . At the same time, the frequency that is obtained by dividing frequency 122 a into ⅓ is not higher than the frequency of VHF 7-ch (=191 MHz). That is, it is necessary that the oscillation frequency of oscillation circuit 24 e is not higher than 2292 MHz (191 MHz×12).

Operating oscillation circuit 24 a and frequency-divider section 22 a as a 1/12 divider allows radio-frequency receiver section 20 a to receive 7-ch in the VHF band. Similarly, operating oscillation circuit 24 e and frequency-divider section 22 b as a 1/12 divider allows radio-frequency receiver section 20 b to receive 7-ch in the VHF band.

According to radio-frequency receiver 10 a of the second embodiment, as described above, the highest frequency of the oscillation circuit that is responsible for frequency band 103 as the lowest range of three-divided digital-broadcasting-signal band is equal to or higher than the lowest frequency of the remaining oscillation circuit. Frequency-divider section 22 a as a first frequency-divider employs a frequency-dividing rate of ¼, on the other hand, frequency-divider section 22 b as a second frequency-divider employs a frequency-dividing rate of any one of ⅓, ¼, ⅙, and 1/12. With the structure, the receiver of the embodiment receives all the channels in the UHF band plus 7-ch in the VHF band.

When receiving one and the same segment of 7-ch, the receiver may operates either one of two oscillation circuits 24 a, 24 e. In this case, the oscillation signal from the operated oscillation circuit is fed into frequency-divider sections 22 a, 22 b, both of which serve as a 1/12 divider. Each output signal from sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b.

As another possible way to receive one and the same segment of 7-ch, the receiver additionally employs a second selective switching circuit between frequency-divider sections 22 a, 22 b and mixers 16 a, 16 b, and operates either one of two oscillation circuits 24 a, 24 e according to the control signal from PLL controller 35 . The output signal from the operated oscillation circuit, via either one of the frequency-divider sections, is fed into another input of each of mixers 16 a and 16 b.

FIG. 6 is a block diagram illustrating another structure of radio-frequency receiver 10 a of the second exemplary embodiment. In addition to the structure shown in FIG. 3 , the radio-frequency receiver of FIG. 6 contains additional selective switching circuit 28 between frequency-divider sections 22 a, 22 b and mixers 16 a, 16 b. Selective switching circuit 28 contains, as shown in FIG. 6 , output terminal 28 a connected to another input of mixer 16 a; output terminal 28 b connected to another input of mixer 16 b; input terminal 28 c connected to frequency-divider section 22 a; input terminal 28 d connected to frequency-divider section 22 b; and input terminal 28 e connected to PLL controller 35 . With the structure above, PLL controller 35 of radio-frequency receiver 10 controls oscillation circuits 26 a, 26 b, 26 c and 26 d so that any one of them turns on. At the same time, PLL controller 35 controls frequency-divider sections 22 a and 22 b so that either one of them has a frequency-dividing rate of ¼ or 1/12. Selected by selective switching circuits 25 and 28 , an output signal from either one of frequency-divider sections 22 a and 22 b is fed into another input of each of mixers 16 a and 16 b. Diversity receiving of all the channels in the UHF band plus 7-ch in the VHF band is thus obtained.

In the structure above, selective switching circuit 25 selects the turned-on oscillation circuit and sends the signal fed from the selected circuit to the frequency-divider section that serves as a 1/12 divider. Receiving the output signal fed from the frequency-divider section, selective switching circuit 28 selectively feeds the signal to another input of each of mixers 16 a and 16 b. In this way, diversity receiving is obtained. In this case, the structure needs power supply for one of frequency-divider sections 22 a and 22 b, contributing to power savings.

When one and the same segment is received by two radio-frequency receiver sections, the oscillation frequency should be preferably produced by either one of the oscillation circuits. It is because that interference can occur between the similarly arranged oscillating frequencies of oscillation circuits 24 a and 24 e.

Although the structure has two radio-frequency receiver sections 20 a and 20 b, the required number of oscillation circuits of oscillator section 29 is four (i.e., 24 a, 24 b, 24 c, and 24 d ), which is half the number of a conventional structure. That is, the number of inductors required in tuning circuits 27 a, 27 b, 27 c and 27 d constituting oscillation circuits 24 a, 24 b, 24 c and 24 d, respectively, can be reduced to half.

The inductors, because of a large footprint, have inconveniently increased in size the integrated circuit. According to the structure of the embodiment, however, the number of inductors can be reduced to half, compared to a conventional structure. This contributes to a downsized integrated circuit, which accordingly allows radio-frequency receiver 10 a to have a compact structure.

Besides, oscillation circuits 24 a, 24 b, 24 c and 24 e operate at oscillation frequency four-times higher than that of the digital broadcasting signal, allowing the inductor to be more compact. This contributes to a size-reduced integrated circuit; accordingly, size-reduced radio-frequency receiver 10 a.

According to the structure of the present invention, the oscillation circuit constituting the oscillator section can be formed of half the number of tuning circuits. The integrated circuit containing the oscillator section can be formed into a compact structure, and accordingly, a size-reduced radio-frequency receiver is obtained.

The structure of the second embodiment is built on the basic idea described in the first exemplary embodiment. Although the first and the second embodiments describe the frequency of the digital broadcasting signal based on the ch-assignment in Japan, it is not limited thereto; the idea is also applicable to the ch-assignment for a foreign country. Employing a similar structure based on the idea provides improvements, such as a shared-use of oscillation circuits and size-reduced inductors.

The radio-frequency receiver of the present invention has an oscillator section shareable between the two radio-frequency receiver sections. This allows the radio-frequency receiver to have a compact structure.