JPH11243348A - High frequency signal receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress mutual modulation interferences without decreasing an NF(noise factor) in a receiver suitably used for television broadcasting which converts a high frequency signal to an intermediate frequency signal of a desired frequency. SOLUTION: The device 21 is provided with trap filters Faa to FMc which have center frequencies fa to fc respectively that correspond to an interference signal, such as an FM band, a VHF low channel band and a VHF high channel band. The device 21 selectively connects these filters to a high frequency signal stage with a switchign circuit 23 in response to a band switch of a phase-locked loop(PLL) circuit 28 and also connects an LPF 24 that can change a cutoff frequency to the high frequency signal stage by using a turning voltage VT from the circuit 28 to a local oscillator circuit 29. Thus, it is possible to suppress the entry of components of bands higher or lower than the band of a tuning channel into a mixer 27 and to prevent distortions due to mutual modulation interferences from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for receiving a high frequency signal such as a television broadcast.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional CATV (Cable Te
FIG. 2 is a block diagram illustrating an electrical configuration of a receiving device 1 in a receiver for broadcasting. The receiving device 1 once up-converts the received high-frequency signal to a higher frequency side than the band of the received high-frequency signal, removes the image frequency from the high-frequency signal band, removes the image frequency with an intermediate frequency filter, and then down-converts the image frequency. This is a double conversion type receiving device that performs conversion.

In this receiving apparatus 1, a received high-frequency signal input to an input terminal 2 is transmitted to a fixed-frequency band-pass filter (hereinafter abbreviated as BPF) 3, for example, from 54 to 806 (MHz) in the United States. After the frequency band component is extracted, the gain is limited to a predetermined level range by an amplifier circuit 4 whose gain is automatically controlled by a feedback circuit (not shown), further amplified by a high frequency amplifier circuit 5 and input to a first mixer 6. Is done. A phase lock loop (hereinafter abbreviated as PLL) circuit 7 is provided in the mixer 6.
Accordingly, a local oscillation signal from the first local oscillation circuit 8 whose oscillation frequency is stably controlled to a desired frequency is input. When the frequency f _LO1 of the local oscillation signal is f _RF , the frequency of the first intermediate frequency signal in a predetermined frequency band to be created is f _IF1 , f _LO1 = f _RF + f _IF1 . The control is performed by the PLL circuit 7 in response to a tuning data signal from the tuning data signal generating circuit 9 output corresponding to the frequency of the broadcasting station to be tuned.
Thus, the mixer 6 outputs the first intermediate frequency signal of the frequency f _{IF1 obtained} by up-converting the high-frequency signal.

In the first intermediate frequency signal, only a signal component of a selected channel is filtered in a fixed frequency BPF 10, amplified by a first intermediate frequency amplifier circuit 11, and then again output to a fixed frequency BPF 12. The signal component of the selected channel is subjected to a filtering process and input to the second mixer 13. The intermediate frequency filter is connected to the BP
By dividing into two stages as in F10 and F12, a steep filter characteristic can be obtained with a small insertion loss.

Similarly, in the second mixer 13, the BPF 1
PLL circuit 14 for the first intermediate frequency signal from
Thereby, the local oscillation signal from the second local oscillation circuit 15 whose oscillation frequency is stably controlled to a desired frequency is mixed, and a second intermediate frequency signal is created. This second
When the frequency of the local oscillation signal from the local oscillation circuit 15 is f _LO2 , the frequency f _IF2 of the intermediate frequency signal becomes f _IF2 = f _IF1 −f _LO2 . That is, in the mixer 13, the first intermediate frequency signal has a frequency f defined by television broadcasting.
_The signal is down-converted to the second intermediate frequency signal of _IF2 .
The center frequency f _IF2C of the second intermediate frequency signal is, for example, 57 (MHz) in Japan and 44 (MH) in the United States.
z).

The second intermediate frequency signal is output from an output terminal 18 after the signal component of the selected channel is filtered and amplified by a BPF 16 and a second intermediate frequency amplifying circuit 17, and is output from a subsequent detection circuit. And demodulated into video and audio signals.

[0007]

The receiving apparatus 1 configured as described above is for CATV broadcasting as described above,
Therefore, the high-frequency signal received from the input terminal 2 is managed so as to have a predetermined level range so that there is not much difference between the levels of the channels. Therefore, in the BPF 3 corresponding to the entire reception frequency band as described above, components outside the reception frequency band are removed and the BPF 1
At 0, 12, and 16, channel components other than the selected channel are removed. In CATV broadcasting,
The risk of interfering signals is small, and the receiving device 1
It is possible to faithfully extract only the components of the selected channel without being affected by the interference signal.

However, when the receiving apparatus 1 is used as a receiver for terrestrial television broadcasting, the level of the broadcasting wave is, for example, several tens of dB outside the band of a television broadcasting wave such as frequency modulation broadcasting. The high-frequency interference signal is mixed into the received high-frequency signal, and the BPF 3 in the fixed frequency band cannot sufficiently remove the interference signal.
Even 0, 12, 16 could not be removed,
13, there is a problem that distortion due to intermodulation interference is generated. Also, for example, a VHF channel and a UHF
As in the case of the channel, the level difference between the selected channels becomes large, and when the level of the adjacent channel becomes too large with respect to the selected channel, the BPFs 10, 1
Even with Nos. 2 and 16, the adjacent channel components cannot be removed.

[0009] In this regard, if the variable cut-off frequency of the BPF 3, for example, in the United States with respect to the high-frequency signal frequency f _RF of fifty-four to eight hundred and six (MHz), the cut-off frequency 1
It is necessary to change it by 0 times or more, and the passband characteristics and the filter attenuation characteristics change greatly depending on the selected channel, and the configuration of a bias circuit for realizing such a large change in the cutoff frequency becomes complicated. Is not practical.

On the other hand, a filter having a fixed pass band is used,
Japanese Patent Laid-Open No. 7-15368 discloses a configuration for switching between them.
No. in the publication. In this prior art, a plurality of types of intermediate frequency filters (that is, BPFs 10, 12, and 16 in FIG. 6) of the first and second intermediate frequency stages are provided, and these are selectively switched and used. It is shown.

However, in such a configuration, two change-over switches are inserted in series in the high-frequency signal line before and after each filter, so that the loss at the change-over switches is large and noise is increased. Index NF (Noise Fi
gure) is worsened.

An object of the present invention is to provide a high-frequency signal receiving apparatus capable of removing the influence of an interfering signal without causing deterioration of NF.

[0013]

According to a first aspect of the present invention, there is provided a high-frequency signal receiving apparatus, comprising:
In a high-frequency signal receiving device that converts to an intermediate frequency signal by the frequency conversion means, a plurality of trap filters arranged in parallel with each other, each having a center frequency in a plurality of interference signal bands for a high-frequency signal to be received, A switching means for selectively connecting a plurality of trap filters to a front stage of the frequency conversion unit; a low-pass filter interposed at a front stage of the frequency conversion unit and capable of changing a cutoff frequency; A control means for changing a switching mode of the switching means and a cutoff frequency of the low-pass filter in conjunction with the switching.

According to the above configuration, for example, in a television broadcast receiver, a plurality of trap filters are provided corresponding to bands which become disturbing signals such as frequency modulated broadcasts.
In conjunction with the switching of the reception frequency band such as the high channel or the UHF channel, the control means controls the switching mode of the switching means, and the component of the interference signal band is bypassed and removed by one or more trap filters. Therefore, the interference signal on the low frequency side can be removed without causing deterioration of NF.

Corresponding to this, on the high frequency side, the control means changes the cutoff frequency of the low-pass filter, thereby removing the interfering signal. The cut-off frequency of the low-pass filter is set to 470 (MHz), which is the lower limit frequency of the UHF band, so that the UHF band can be removed when the VHF band is selected in the United States. Sometimes, the frequency is set to 806 (MHz), which is the upper limit frequency of the UHF band, whereby the rate of change of the frequency of the low-pass filter can be made relatively small.

Further, in the high frequency signal receiving apparatus according to the present invention, the control means controls the oscillation frequency of the local oscillation circuit in the frequency conversion means so as to correspond to the frequency of the high frequency signal to be received. A low-pass filter that changes the cutoff frequency in response to the tuning voltage.

According to the above configuration, noting that the frequency change rate of the low-pass filter is small, the tuning voltage output from the phase-locked loop circuit to the local oscillation circuit realized by a voltage-controlled oscillation circuit or the like is adjusted. It is used as it is to control the cutoff frequency of the low-pass filter.

Accordingly, there is no need to separately provide a bias voltage source for changing the cutoff frequency, and the configuration can be simplified.

Further, in the high frequency signal receiving apparatus according to the third aspect of the present invention, the control means controls the oscillation frequency of the local oscillation circuit in the frequency conversion means to correspond to the frequency of the high frequency signal to be received. A phase lock loop circuit to be controlled, wherein a switching mode of the switching means is controlled by a band switch originally provided in the phase lock loop circuit.

According to the above configuration, similarly to the second aspect, the switching control of the trap filter can be performed by using the existing phase lock loop circuit without any special configuration.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
This will be described below with reference to FIGS.

FIG. 1 is a block diagram showing an electrical configuration of a receiving apparatus 21 according to one embodiment of the present invention. The receiving device 21 is a double conversion type receiving device suitably used as a receiving device of a terrestrial television broadcasting receiver.

In the receiving apparatus 21, the received high-frequency signal input to the input terminal 22 is first selectively connected to the high-frequency signal stage by the switching circuit 23 before frequency conversion.
Each center frequency f
a, fb, and trap filters Fa, Fb,
By Fc, the interfering signal component on the low frequency side is removed,
Next, a low-pass filter (hereinafter abbreviated as LPF) 24
As a result, a component in a band that becomes a disturbance signal on the high frequency side is removed.

The trap filters Fa, Fb, Fc
Are arranged in parallel with each other, and each have a center frequency in a band that becomes an interference signal with respect to a high-frequency signal to be received, such as a band of frequency modulation broadcasting, for example.
3, one or more of them are combined and selectively connected to the high-frequency signal stage. The cutoff frequency of the LPF 24 is variable as described later.

Thus, the trap filters Fa, Fb,
Band tuned by Fc and LPF 24,
For example, only a high-frequency signal component in the VHF low channel band is extracted, and the high-frequency signal component is limited to a predetermined level range by an amplifier 25 whose gain is automatically controlled by a feedback circuit (not shown). And input to the first mixer 27. The mixer 27 is implemented by a voltage controlled oscillator circuit, in response to the tuning voltage V _T from the PLL circuit 28, the first local oscillation circuit 29 whose oscillation frequency is stably controlled to the frequency of the desired Is input. Frequency f _LO1 of the local oscillation signal, when the frequency of the RF signal and f _RF, the frequency of the first intermediate frequency signal in a predetermined frequency band to be created and f _IF1, and f _LO1 = f _RF + f _IF1 The control is performed by the PLL circuit 28 in response to a tuning data signal from the tuning data signal generating circuit 30 output corresponding to the frequency of the broadcasting station to be tuned. Thus, the mixer 27 outputs the first intermediate frequency signal of the frequency f _{IF1 obtained} by up-converting the high frequency signal.

In the first intermediate frequency signal, only the signal component of the selected channel is filtered in a fixed frequency BPF 31, amplified by a first intermediate frequency amplifier circuit 32, and then again supplied to a fixed frequency BPF 33. The signal components of the selected channel are subjected to a filtering process and input to the second mixer 34. The intermediate frequency filter is connected to the BP
By dividing into two stages as in F31 and F33, a steep filter characteristic can be obtained with a small insertion loss.

Similarly, in the second mixer 34, the BPF 3
PLL circuit 35 for the first intermediate frequency signal from
Thus, the local oscillation signal from the second local oscillation circuit 36 whose oscillation frequency is stably controlled to a desired frequency is mixed, and a second intermediate frequency signal is created. This second
Frequency f _IF2 of the intermediate frequency signal is the frequency of the local oscillation signal from the local oscillator circuit 36 when the f _LO2, the f _IF2 = f _IF1 -f _LO2. That is, in the mixer 34, the first intermediate frequency signal has a frequency f defined by television broadcasting.
_The signal is down-converted to the second intermediate frequency signal of _IF2 .
The center frequency f _IF2C of the second intermediate frequency signal is, for example, 57 (MHz) in Japan and 44 (MH) in the United States.
z).

The second intermediate frequency signal is output from an output terminal 39 after a signal component of the selected channel is filtered and amplified by a BPF 37 and a second intermediate frequency amplifier circuit 38, and is output from a subsequent detection circuit. And demodulated into video and audio signals.

FIG. 2 is a block diagram showing a specific configuration of the PLL circuit 28. For example, a tuning data signal as shown in FIG. 3 is input from the tuning data signal generating circuit 30.
At 1, the data is decoded into band switch data and frequency data. The band switch data includes, for example, VHF low channel, VHF high channel and UH
The band switch data is data representing the band of a channel to be tuned such as the F channel. The band switch 42 supplies switching control signals Sa, Sb, Sc corresponding to the band switch data to the switches in the switching circuit 23 individually corresponding to the trap filters Fa, Fb, Fc, respectively.

Thus, for example, when the VHF low channel is selected, the trap filter Fa corresponding to the frequency modulation broadcast band is connected to the high frequency signal stage,
The component of the band is bypassed and removed, and at the time of VHF high channel selection, a trap filter Fb corresponding to the band of the VHF low channel is connected together with the trap filter Fa, and the band component of the VHF low channel is Removed from high frequency signals. Similarly, UH
When selecting the F channel, a trap filter Fc corresponding to the VHF high channel is connected to the high frequency signal stage, thereby removing the band component of the VHF high channel.

The decoder 41 decodes the frequency data of the channel selection data signal and sets a frequency division ratio corresponding to the frequency of the channel to be selected in the programmable frequency divider 43. A first local oscillation signal from the local oscillation circuit 29 is input to the programmable frequency divider 43, and the programmable frequency divider 43 sets the frequency division ratio of the first local oscillation signal to a predetermined frequency. Divided by the phase comparator 4
Output to 4. The phase comparator 44 compares an output from the programmable frequency divider 43 with a reference signal from a reference signal generator 45 realized by a crystal oscillator or the like, and outputs a signal corresponding to a phase difference between the two to a loop filter. Output to 46. The loop filter 46 is realized by an LPF or the like, and removes a high-frequency component of an output from the phase comparator 44,
The DC tuning voltage V _T is created and output to the local oscillation circuit 29 and the LPF 24.

On the other hand, the LPF 24 can be configured, for example, as shown in FIG. In this example, the coil L
1 to L7, capacitors C1 to C8, variable capacitance diodes D1 to D4, and bias resistors R1 to R3. The tuning voltage application terminal 51
The tuning voltage V _T is applied, and the pass band in the high-frequency signal line between the input terminal 52 and the output terminal 53 changes.

As shown in FIG. 5 (a), the higher the tuning voltage V _T, the variable capacitance diode D1~D
4 the capacitance C _D is reduced. The tuning voltage V _T increases as the frequency of the channel to be tuned increases. Therefore, for example, when a VHF low channel is tuned, as shown by reference numeral α1 in FIG.
Whereas the passband of the LPF24 is relatively low frequency side, for example, at the time of channel selection of the UHF channels, the so tuning voltage V _T is increased, the passband of the LPF24, as indicated by reference symbol α2 Shift to higher frequencies.

Thus, the trap filter F
a, Fb, Fc, and LPF 24 extract only the band components of the channel to be selected from the high-frequency signal, and reliably remove the remaining interference signal, even if its level is large, and input it to mixer 27. Thus, it is possible to prevent the occurrence of distortion due to intermodulation interference in the mixer 27.

The trap filters Fa, Fb, Fc
Is not interposed in series with the high-frequency signal line,
Since the frequency components to be trapped are bypassed and removed in parallel, even if the switching circuit 23 is provided, the effect of the loss in the switching circuit 23 on the high-frequency signal to the subsequent stage does not occur.

Further, even if the cutoff frequency of the LPF 24 is changed, changes in the pass band characteristics and filter attenuation characteristics are small, and the frequency change rate is determined by the cutoff frequency, for example, the VHF band selection in the United States. UH in office
When the F band is removed, the lower limit frequency of the UHF band is set to about 470 (MHz), and when the UHF band is selected, the upper limit frequency is set to 806 (MHz). , the variable capacitance diode D1~D due to a change in the tuning voltage V _T
4 can sufficiently respond.

[0037] Thus, the change in the cutoff frequency of the LPF 24, by using the tuning voltage V _T of the local oscillation circuit 29 from the PLL circuit 28, it is possible to eliminate special configuration for the bias voltage generator . Similarly, when the switching mode of the switching circuit 23 is switched, PL
Since the band switch 42 of the L circuit 28 is used, the switching mode can be controlled without adding a new configuration.

The LPF 24 is not limited to the configuration shown in FIG. 4, and similarly, the PLL circuit 28 and the channel selection data signal are not limited to the configurations shown in FIGS. Needless to say, it may be. Two or four or more trap filters Fa, Fb, and Fc may be provided. Further, the trap filters Fa, Fb, and Fc and the LPF 24 are provided at a high-frequency signal stage before the mixer 27. If so, it may be inserted in any of them. In addition, trap filter F
As described above, a, Fb, Fc and LPF 24 are not only switched in accordance with the band of the selected channel such as the VHF low channel, VHF high channel, etc.
The switching may be performed according to a specific channel.

[0039]

As described above, the high-frequency signal receiving apparatus according to the first aspect of the present invention includes a plurality of traps respectively corresponding to a band serving as an interference signal such as a frequency modulation broadcast in a television broadcast receiver. A filter is provided, and one or a plurality of trap filters are selectively connected to the front side of the frequency conversion means in conjunction with switching of a reception frequency band such as a VHF low channel, a VHF high channel, or a UHF channel. By removing the interference signal on the high frequency side by bypassing and changing the cutoff frequency of the low-pass filter inserted before the frequency conversion means in conjunction with the switching of the reception frequency band, the interference signal on the high frequency side is removed. Is removed.

Therefore, it is possible to remove the interfering signal without deteriorating the NF. The cutoff frequency of the low-pass filter is 470 (MH), which is the lower limit frequency of the UHF band so that the UHF band can be removed when the VHF band is selected in the United States.
z), and when the UHF band is selected, the frequency is set to 806 (MHz), which is the upper limit frequency of the UHF band, whereby the frequency change rate of the low-pass filter can be made relatively small.

Further, the high frequency signal receiving apparatus according to the second aspect of the present invention focuses on the fact that the low-pass filter has a small rate of change in frequency, as described above, from the phase lock loop circuit in the frequency conversion means to the local oscillation. The tuning voltage output to the circuit is used as it is to control the cutoff frequency of the low-pass filter.

Therefore, it is not necessary to separately provide a bias voltage source for changing the cutoff frequency, and the configuration can be simplified.

Further, in the high frequency signal receiving apparatus according to the third aspect of the present invention, the switching of the plurality of trap filters is originally provided in the phase lock loop circuit of the frequency conversion means. Performed by band switch.

Therefore, the switching control of the trap filter can be performed by using the existing phase lock loop circuit as it is, without providing a special configuration, as in the second aspect.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an electrical configuration of a receiving device in a television broadcast receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a specific configuration of a PLL circuit used in the receiving device shown in FIG.

FIG. 3 is a diagram illustrating an example of a configuration of a tuning data signal used for controlling a tuning channel in the receiving device illustrated in FIG. 1;

FIG. 4 is an electric circuit diagram showing one configuration example of an LPF in the receiving device shown in FIG. 1;

FIG. 5 is a graph for explaining the operation of the LPF shown in FIG. 4;

FIG. 6 is a block diagram showing an electrical configuration of a receiving device in a conventional CATV broadcast receiver.

[Explanation of symbols]

 Reference Signs List 21 receiver 23 switching circuit (switching means) 24 LPF 25 amplifier circuit 26 high-frequency amplifier circuit 27 mixer (frequency conversion means) 28 PLL circuit (frequency conversion means, control means) 29 local oscillation circuit (frequency conversion means) 30 tuning data Signal generation circuit (control means) 31 BPF 32 Intermediate frequency amplifier circuit 33 BPF 34 Mixer 35 PLL circuit 36 Local oscillation circuit 37 BPF 38 Intermediate frequency amplifier circuit 41 Decoder 42 Band switch 43 Programmable frequency divider 44 Phase comparator 45 Reference signal generation Filter 46 Loop filter C1 to C8 Capacitor D1 to D4 Variable capacitance diode Fa, Fb, Fc Trap filter L1 to L7 Coil R1 to R3 Bias resistance

Claims (3)

[Claims] 1. A high-frequency signal receiving apparatus for converting an input received high-frequency signal into an intermediate frequency signal by a frequency converting means, wherein each of the plurality of interference signal bands for a high-frequency signal to be received has a center frequency. A plurality of trap filters arranged in parallel with each other; a switching means for selectively connecting the plurality of trap filters to a front stage of the frequency conversion unit; and a cutoff frequency interposed at a front stage of the frequency conversion unit. A high-frequency signal receiving apparatus comprising: a low-pass filter that can be changed; and a control unit that changes a switching mode of the switching unit and a cutoff frequency of the low-pass filter in conjunction with switching of a reception frequency band. . 2. The phase lock loop circuit for generating a tuning voltage for controlling an oscillation frequency of a local oscillation circuit in the frequency conversion means so as to correspond to a frequency of a high-frequency signal to be received. 2. The high frequency signal receiving device according to claim 1, wherein the low pass filter changes the cutoff frequency in response to the tuning voltage. 3. The control means is a phase-locked loop circuit for controlling an oscillation frequency of a local oscillation circuit in the frequency conversion means so as to correspond to a frequency of a high-frequency signal to be received. The high frequency signal receiving device according to claim 1 or 2, wherein the frequency is controlled by a band switch in the phase lock loop circuit.