JPH10294929A - Catv reception equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve performance and reduce cost by improving the phase noise, LO leak or return loss of low-pass offset. SOLUTION: In order to reduce phase noises, a tuner 101 for CATV is basically constituted by adopting a single version type system having one local oscillator and one mixer or the like. In this case, an additional circuit composed of an AGC circuit 70 for controlling the gain of input signal frequency, an amplifier 80 and an LPF 90 is inserted between an HPF/LPF 41 and a switch 42 on the preceding stage of tracking filters (43, 49 and 55). Thus, since the isolation of input to each mixer is improved, the occurrence of LO leak and return loss or the like is suppressed, performance can be improved and costs can be reduced. Besides, since frequency division is performed by a variable frequency divider 67 without using the fixed frequency division prescaler of the PLL circuit, the phase noises caused by the low-pass offset of local oscillation frequency are reduced as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV receiver capable of receiving CATV broadcasts, and more particularly, to prevent local oscillation leakage and return loss, thereby improving the equipment performance of a high-frequency unit tuner and realizing a low cost. The present invention relates to a CATV receiving apparatus suitable for performing the above.

[0002]

2. Description of the Related Art With the recent digitalization and multimedia, in the field of broadcasting, not only the current radio broadcasting but also cable television broadcasting (hereinafter referred to as CATV) in which broadcasting and communication are integrated. ) Is drawing attention.

[0003] CATV has been widely used as a cable-based broadcasting form, and recently, with the realization of the CATV interactive service business in the United States, which is a CATV advanced nation, in Japan, CATV interactive services have been developed. Commercialization of the service is underway.

[0004] In CATV, the retransmission of existing terrestrial television and BS / CS satellite television and the like, and the spread of urban-type cable television that provides independent programs in cities are remarkable. Broadcasting service systems, such as cable Internet and cable karaoke, that use TV are also very popular.

[0005] By the way, a CA capable of receiving an analog or digital CATV capable of receiving CATV.
The TV receiver incorporates a tuner that receives a signal in a desired transmission band from a transmission signal transmitted via a transmission medium such as a cable or a radio wave. Such a tuner is generally called a double super system. And two frequency oscillators and two local oscillators. FIG. 4 shows such a double super type CATV tuner.

FIG. 4 is a block diagram showing a conventional CATV receiving apparatus and showing an example of a double super system CATV tuner.

As shown in FIG. 4, the CATV tuner is provided with an input terminal 1a for receiving an input signal. The input terminal 1a receives a signal from a center facility called a head end (not shown) and a cable or the like. Signal (RF signal) transmitted through the transmission medium
Is supplied. The RF signal input via the input terminal 1a is supplied to the AGC circuit 2 after passing only a predetermined frequency band by the LPF and HPF1.

The AGC circuit 2 receives an input RF signal based on an RFAGC signal from an AGC circuit control unit (not shown).
The signal gain is limited to an optimum level and output. That is, when the input radio wave is strong, the gain of the high-frequency amplifier circuit is controlled while keeping the gain of the video intermediate amplifier circuit (not shown) at a constant small gain, thereby suppressing the occurrence of cross-modulation interference and the like.

The output signal of the AGC circuit is amplified by an amplifier 3 and then applied to a first mixer (described as MIX in the figure) 4. The first mixer 4 is provided with a first local oscillator (hereinafter referred to as LO) which is provided separately and can vary the oscillation frequency.
An oscillation frequency supplied from 13 and a frequency of the supplied RF signal are mixed to generate and output a beat signal having a beat frequency equal to the difference between the two original frequencies. That is, the mixer 4 is a first frequency converter, and up-converts the input signal from the amplifier 3 by using the oscillation frequency from the first local oscillator 13 to generate a 1st IF signal (intermediate frequency signal). And given to HPF5.

The HPF 5 passes the high-frequency component of the input 1st IF signal and supplies it to the BPF 6, and the 1st IF signal of the high-frequency component passed therethrough is limited in a predetermined band by the BPF 5, so that a band corresponding to one CATV channel is obtained. Signal. After that, the output signal of the BPF 5 is amplified by the amplifier 7 and then supplied to the second mixer 8.

The second mixer 8 is a second frequency converter, which down-converts the input signal from the amplifier 7 using the oscillation frequency from the second local oscillator 15 to obtain a second frequency.
The signal is converted into a stIF signal (intermediate frequency signal) and supplied to the LPF 9.

The LPF 9 passes the low-frequency component of the input 2st IF signal and supplies it to the amplifier 10. Amplifier 10
Amplifies the input signal, and the amplified signal is
The band is limited to a predetermined band, and after being amplified by the amplifier 12, the band is output to a signal processing unit (not shown).

With such a configuration, for example, by converting the input frequency to a higher frequency by the first frequency converter of the first stage, the oscillation frequency of the local oscillator can be set outside the band of the input RF. It is possible to reduce the frequency change ratio of the oscillator. Further, by providing and using a fixed frequency filter (also referred to as a band-pass filter) such as BPF6 between the first frequency converter and the second frequency converter, the output waveform of any input signal can be stabilized. It becomes possible.

By the way, CA in recent digital broadcasting
The use of the single version type has been reconsidered because TV tuners tend to have low cost and advantageous advantages because they are each provided with one frequency converter and local oscillator. In general, as a single version type tuner currently used, a tuner employed in a television receiver (hereinafter abbreviated as TV) is well known. FIG. 5 shows an example of such a single version type TV tuner.

FIG. 5 shows an example of the configuration of a conventional single-version type TV tuner. FIG. 5 (a) is a block diagram showing the configuration of the tuner, and FIG. 5 (b) is a specific example of a PLL circuit used in the tuner. FIG. 3 is a block diagram illustrating a configuration. Note that the description of the configuration includes only one band out of three bands for simplification of the description.

As shown in FIG. 5A, the TV tuner is provided with an input terminal 11a for receiving an input signal, and the input terminal 11a is provided with a reception signal (not shown) received by a reception antenna (not shown). A television signal,
Hereinafter, referred to as an RF signal). The RF signal input via the input terminal 11a is L
After passing only a predetermined frequency band by the PF and HPF1, the signal is supplied to the switch 12.

The switch 12 switches the input RF signal to three in accordance with the respective frequencies, and outputs the three to the corresponding variable trunking filters (13, 19, 25). For example, if the band is switched to the band based on the input terminal b 1 by the switch 12, the input RF
The signal is supplied to a variable tracking filter 19 synchronized with the local oscillation, and a predetermined band is limited by the variable tracking filter 19 so that an amplifier (FET AMP)
Give to 20.

The amplifier 20 receives an input signal from an AG (not shown).
The level is adjusted so that the signal is amplified at a level based on the gain control signal from the C circuit, and is provided to the variable tracking filter 21 at the subsequent stage. The tracking filter 21 further limits the band of the input signal and outputs the signal. This output signal is then amplified by an amplifier 22 and then applied to a mixer (frequency conversion unit) 23.

The mixer 23 converts the input signal from the amplifier 22 into an IF signal (intermediate frequency signal) using the oscillation frequency from the local oscillator 24 and outputs the IF signal. This IF signal is thereafter given to a BPF (single tuned filter) 31 so that a predetermined band is limited, further amplified by an amplifier 32, and then output to a signal processing unit (not shown) via an output terminal 32a. .

A PLL circuit 34 shown in the figure generates a control signal based on the oscillating frequencies of the local oscillators 18, 24 and 30, and transmits the control signal to the local oscillators 18, 24.
And 30 to control the oscillation frequency of each oscillator.

More specifically, as shown in FIG.
The LL circuit 34 detects an oscillation frequency from any of the local oscillators 18, 24, and 30, divides the frequency by a fixed frequency dividing prescaler 38, further divides the frequency by a variable frequency divider 37, and divides the frequency. The phase of the signal and a signal from a fixed frequency divider 35 for dividing a signal from a high-precision fixed oscillator (not shown) are compared by a phase comparator 36, and a control voltage VT is determined based on the phase comparison result. Generates and varies the oscillation frequency of any of the local oscillators. That is, by using the PLL circuit 34, the local oscillators 18, 24 and 30
Can be controlled.

Therefore, in the TV tuner, which is a single-version type tuner having the above configuration, the PLL
Since the circuit 34 is provided with the prescaler 38 having a fixed frequency division, the selected step width of the local oscillation and the comparison frequency of the PLL have different values.

When the above two types of tuners are compared, there are the following differences. For example, the current double conversion type of analog and digital CATV tuners has two local oscillators for performing the frequency conversion process twice. It is disadvantageous in price as compared with the conversion type tuner. That is, there is a disadvantage that the cost is high.

In the double-conversion type, the frequency of the two local oscillations is as high as 1-2 GHz and the variable width is as wide as 1 GHz, so that the frequency sensitivity to the voltage is increased (about 35 MHz / V). Phase noise tends to deteriorate. As for the phase noise of the output signal, since the phase noises of the two local oscillators are added and output, there is only one local oscillator and the frequency is as low as 100 to 900 MHz (ex. 15 MHz /
It is disadvantageous when compared with the single version type.

In digital broadcasting CATV, which has been put into practical use in recent years, especially in multilevel QAM transmission (256 QAM transmission) for transmitting a large amount of data at a high rate, the interval between symbols in a constellation (signal arrangement diagram) is narrow. That is, if the eye pattern is small and the phase noise is bad, each symbol has a spread in the phase direction, and consequently, the constellation is blurred (the eye pattern is broken), which causes an increase in fixed deterioration. Therefore, in order to avoid such inconveniences, considering the use of a single version type tuner having only one local oscillator to improve phase noise and the like, the single version type tuner as described above is considered. Has a tuner for TV.

However, in the configuration of the conventional TV tuner, the isolation between the input oscillation frequency of the mixer and the input signal is not sufficient, and the two tracking filters at the preceding stage eliminate the influence of the oscillation frequency. Processing is not enough. Furthermore, because the isolation between the input and output of the amplifier is not sufficient, the leakage performance of the oscillation frequency to the input terminal (hereinafter referred to as LO leakage) is insufficient, or the return loss outside the band due to a variable filter is reduced. Since the state is close to total reflection, the return loss performance in the entire region may be insufficient, or the performance level required for CATV may not be reached. For this reason,
It may interfere with the subscribers connected via the transmission cable, resulting in the inconvenience of image degradation, and it is not possible to use it as it is .

On the other hand, in the single version type tuner, since the PLL circuit is provided with the fixed frequency dividing prescaler for LO as described above, the local oscillation tuning S
The TEP width and the comparison frequency for comparing the PLL are:
It has different values. For example, at present, a 4 MHz reference is frequency-divided by 512 to operate a PLL at a comparison frequency of 7.8125 KHz.
If the fixed frequency division for the channel is reduced to １ ／, the LO tuning channel STEP width becomes 62.5 KHz. In other words, in the current tuner, the comparison frequency is 1 / (fixed frequency division) of the tuning step width, is reduced by several KHz, and the PLL fluctuation is multiplied by the fixed frequency division for the LO fixed frequency division. As a result, the carrier is in a state where FM is applied. Therefore, low phase noise at a low-frequency offset of about 1 KHz is difficult to realize and is one of the causes of an increase in fixed deterioration.

[0028]

As described above, the conventional C
If an ATV receiver uses a double-conversion type tuner, it is more expensive than a single-version type tuner, and the phase noise due to the local oscillation frequency also deteriorates. In order to avoid such inconvenience, it is optimal to use a single version type.
If a TV reception signal is tuned, inadequate isolation causes problems such as LO leakage and return loss. As a result, other subscribers connected to the transmission cable may experience ghost or ghost. Flicker etc. occurs,
There is a problem that the image is deteriorated.

Therefore, the present invention has been made in view of the above problems, and realizes high performance by improving low frequency offset phase noise, LO leak and return loss, and realizes low cost. It is an object of the present invention to provide a CATV receiving apparatus capable of performing such operations.

[0030]

According to a first aspect of the present invention, there is provided a CATV receiving apparatus comprising: an input terminal to which a high-frequency signal is input; and a signal input to the input terminal, which is controlled to a predetermined level and output. Possible gain control means, amplifying means connected to the gain control means for amplifying a signal of controlled gain, voltage-controlled local oscillator and mixing means, the output signal from the amplifying means and the local oscillator A frequency converting means for mixing the signal with a local oscillation signal to generate an intermediate frequency signal, and a pass band limited by a control voltage for controlling the local oscillator which is arranged between the amplifying means and the frequency converting means. Variable filter means.

In the present invention, a high-frequency signal is input to the input terminal. The gain control means is capable of controlling the signal input to the input terminal to a predetermined level and outputting the signal. The amplification means is connected to the gain control means and amplifies the signal whose gain is controlled. The frequency conversion means includes a voltage-controlled local oscillator and a mixing means,
An output signal from the amplifying unit and a local oscillation signal from the local oscillator are mixed to generate an intermediate frequency signal. The variable filter means is disposed between the amplifying means and the frequency converting means, and has a pass band limited by a control voltage for controlling the local oscillator. As a result, it is possible to improve the isolation of the input of the variable filter means, so that it is possible to suppress LO leakage, return loss, and the like, to improve the performance, and to reduce the cost. Therefore, it is possible to prevent image deterioration of another connected subscriber.

According to a second aspect of the present invention, there is provided a CATV receiving apparatus as set forth in the first aspect, wherein the PL can control a local oscillation frequency of the local oscillator.
The PLL circuit is configured to include an L circuit unit, wherein the PLL circuit performs a phase comparison so that a value of a PLL comparison frequency matches a value of a local oscillation frequency based on a tuning step width of the local oscillator. It is assumed that.

According to a second aspect of the present invention, there is provided the CATV receiving apparatus according to the first aspect, further comprising a PLL circuit unit capable of controlling a local oscillation frequency of the local oscillator. Performs a phase comparison so that the value of the comparison frequency of the PLL matches the value of the local oscillation frequency based on the tuning step width of the local oscillator. As a result, it is possible to suppress the phase noise at a low-frequency offset of the local oscillation frequency as compared with the conventional TV tuner, and it is possible to improve the fixed deterioration.

[0034]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a CATV receiver according to the present invention.

As shown in FIG. 1, the CATV according to the present invention
The receiving apparatus (which may be described as a tuner for CATV) 101 is a single version type in which phase noise can be improved by having only one local oscillator as described in the related art in order to improve phase noise. It is configured by adopting the ones. That is, the circuit configuration is similar to that of a TV tuner. However, if the TV tuner is used as it is as a CATV tuner, the LO
In some cases, problems due to leakage, return loss, and the like, and problems such as phase noise at a low-frequency offset may occur. Therefore, the CATV receiving apparatus according to the present invention is provided with means for solving the above-mentioned problem. A specific circuit configuration employing these means will be described below.

As shown in the figure, the CATV tuner 10
1 is provided with an input terminal 41a for receiving an input signal. The input terminal 41a receives a reception signal received by a center facility called a headend (not shown) and transmitted via a transmission medium such as a cable. (RF
Signal). Input terminal 41a
Is supplied to the HPF and the LPF 41.

The HPF and LPF 41 perform a wide-band filtering process on the input RF signal and output it. This HPF, L
The output of the PF 41 is thereafter supplied to an AGC circuit 70 as an additional circuit newly provided in the present embodiment.

The additional circuit is disposed, for example, between the input terminal 41a and a tuner main part, which will be described later, and has a configuration in which an AGC circuit 70, an amplifier 80, and an LPF 90 are sequentially connected to the input terminal 41a. I have.

The AGC circuit 70 receives an input R signal based on an RFAGC signal from an AGC circuit control unit (not shown).
The F signal gain is limited to an optimum level and output. That is, when the input radio wave is strong, the gain of the high-frequency amplifier circuit is controlled while keeping the gain of the video intermediate amplifier circuit (not shown) at a constant small gain, thereby suppressing the occurrence of cross-modulation interference and the like.

The output signal of the AGC circuit 70 is
After amplification by LPF90. LPF9
0 passes the low frequency component of the input signal and supplies it to the input terminal of the switch 42 which operates in the same manner as in the prior art. That is,
Improving the input isolation in the mixers 47, 53, and 59 at the subsequent stage by using the input signal supplied to the main part of the tuner after the switch 42 as the output RF signal of the additional circuit. Becomes possible.

The switch 42 switches the input RF signal to three in accordance with the respective frequencies, and outputs the three to the corresponding variable trunking filters (43, 49, 55). For example, if the band is switched to the band based on the input terminal b 1 by the switch 42, the input RF
The signal is supplied to a variable tracking filter 49 whose frequency pass band is adjusted by a control voltage (tuning voltage Vt) for controlling the local oscillator 54, and a predetermined band is limited by the tracking filter 49 so that an amplifier (FET)
AMP) 50.

The amplifier 50 receives an input signal from an AG (not shown).
The level is adjusted so that the signal is amplified at a level based on the gain control signal from the C circuit, and is supplied to the variable tracking filter 51 at the subsequent stage. The tracking filter 51 has a frequency pass band adjusted by a control voltage (tuning voltage Vt) for controlling the local oscillator 54, similarly to the tracking filter 49, and further restricts and outputs the band of the input signal. . This output signal is then applied to the amplifier 52
After being amplified by a mixer (frequency conversion unit) 53.

The mixer 53 converts an input signal from the amplifier 52 into an IF signal (intermediate frequency signal) using the oscillation frequency from the local oscillator 54 and outputs the IF signal. The IF signal is thereafter given to a BPF (single tuned filter) 61 to restrict a predetermined band, and is further amplified by an amplifier 62 before being output to a signal processing unit (not shown) via an output terminal 62a. .

The other bands, ie, the switches 42
When the band is switched to the band based on the input terminal a and the input terminal c, the operation is substantially the same as in the case of the band described above, and the output IF signal of the mixer 47 or the mixer 59 becomes B
The signal is output from the output terminal 62a via the PF 61 and the amplifier 62.

According to such a configuration, it is possible to effectively reduce the phase noise at a wide-range offset as compared with the double conversion type.
In particular, in multi-valued QAM such as 256 QAM, it is possible to suppress an increase in fixed deterioration.

As described above, by providing the additional circuit blocks of the AGC circuit 70, the amplifier 80, and the LPF 90 before the variable tracking filters 43, 49, and 55, the input isolation in each mixer can be improved. Therefore, as a result, it is possible to suppress the occurrence of the LO leak. Also, as for the return loss, only the reception channel is good and the others are not close to total reflection as in the conventional TV tuner. By providing an additional circuit block, the influence of the variable tracking filter at the input terminal is reduced. As a result, good return loss performance can be obtained in all bands.

On the other hand, the PLL circuit 64 shown in the figure generates a control signal based on the oscillating frequencies of the local oscillators 48, 54 and 60, and transmits the control signal to the local oscillators 48 and 54.
And 60 to control the oscillation frequency of each oscillator.

The PLL circuit 64 in this embodiment is devised in order to reduce the phase noise of the low-frequency offset of the local oscillation frequency.

For example, as shown in FIG. 2, the PLL circuit 64 includes a fixed frequency dividing prescaler 38 used in the related art.
(See FIG. 5B). That is, by removing the fixed frequency dividing prescaler, P
This is because the comparison frequency of LL and the step frequency of LO (local oscillator) are set to the same value.

Therefore, the PLL in this embodiment is
In the circuit 64, as shown in FIG.
And 60, and divides the frequency by (n / 1) / (1 / n + 1) by a variable frequency divider 67. The frequency-divided signal and a high-precision fixed oscillator (not shown) ) Is compared with the signal from the fixed frequency divider 65 obtained by dividing the frequency of the signal from the local oscillator 65, and the phase comparison result is used as a control voltage to vary the oscillation frequency of any of the local oscillators. Thus, the PLL circuit 64 controls the oscillation frequency of the local oscillators 48, 54 and 60.

Thus, in the single-version type tuner for digital transmission, the frequency divider uses the variable frequency divider 67 instead of eliminating the fixed frequency division prescaler of the PLL circuit caused by the generation of the phase noise at the low frequency offset. By circulating, the comparison frequency of the PLL and the tuning step width of the local oscillation can be matched, and as a result, the phase noise at the low frequency offset can be reduced.

Note that the PLL circuit 64 may employ the ordinary PLL circuit configuration including the fixed frequency dividing prescaler shown in the prior art (FIG. 5) to constitute the CATV receiver shown in FIG. In the case where the PLL circuit 64 shown in FIG. 2 is adopted, the fixed deterioration can be more effectively improved.

FIG. 3 is a block diagram showing another embodiment of the CATV receiving apparatus according to the present invention, showing an application example of the receiving apparatus. FIG. 3 (a) shows an IF signal demodulation type. 3 (b) shows an I and Q signal signal demodulation type. It is assumed that the tuner 101 shown in FIG. 3 has the same configuration requirements as the tuner shown in FIG.

In this embodiment, an additional circuit group is further added at the subsequent stage of the CATV receiving apparatus shown in FIG. 1 so that a CATV tuner capable of performing two kinds of different demodulation processes, that is, an IF output type is provided. , I, and Q output types.

More specifically, as shown in FIG.
The F-type tuner includes a BPF 102 that inputs an output IF signal from the output terminal 62a of the CATV tuner 101 shown in FIG. The BPF 102 limits a predetermined band of the input IF signal and supplies the signal to the amplifier 103. The amplifier 103 amplifies the output signal of the BPF 102 and supplies it to a further provided mixer (described as MIX in the figure) 104.

The mixer 104 further down-converts and outputs the input IF signal by mixing the local oscillation frequency of the local oscillator 107 and the output signal from the amplifier 103. At this time, an A / D converter (not shown) (an A / D converter connected to the tuner) directly operates.
Down-convert to the frequency of the F signal.

The IF signal further frequency-converted by the mixer 104 passes only the low-frequency component of the signal by the LPF 105, is thereafter amplified by the amplifier 106, and is output to a signal processing unit (not shown). In this manner, by further down-converting and demodulating, it is possible to obtain an IF signal to be provided to a signal processing unit (not shown).

On the other hand, as shown in FIG. 3B, another I / Q output type tuner is a BPF 102 for inputting an output IF signal from the output terminal 62a of the CATV tuner 101 shown in FIG. Is provided. BPF10
2 restricts a predetermined band of the input IF signal, and
Supply 3 The amplifier 103 amplifies the output signal of the BPF 102 and supplies the amplified signal to a distributor 108 that distributes an input IF signal according to the frequency.

The distributor 108 distributes the input IF signal according to the frequency, and outputs one to the mixer 109 and the other to the other mixer 112. These mixers 109, 11
2 is supplied with a local oscillation frequency signal whose phase is shifted by 90 degrees by the phase shifter 115 provided with the phase of the local oscillation frequency from the local oscillator 117.

The mixers 109 and 112 mix the input IF signal and the local oscillation frequency signals having different phases, respectively, to perform frequency conversion, and obtain the obtained IF signal.
The signal is supplied to the connected LPFs 110 and 113, respectively. Then, after the low-frequency components of the input signal are passed by the LPFs 110 and 113, respectively,
1 and 114 are amplified by the respective output terminals 11
From 1a and 114a, it is supplied to a signal processing circuit (not shown). By performing the demodulation processing in this manner, it is possible to obtain an I signal and a Q signal that are 90 degrees out of phase.

Therefore, according to this embodiment, FIG.
In addition to the same effects as those of the above-described embodiment, two types of tuners that perform different demodulation processes can be configured, and a high-performance CATV tuner can be realized with a simple circuit configuration. Can be planned.

In the embodiment according to the present invention,
In the tuner configuration shown in FIG. 1, a description has been given of a three-band system capable of switching to three bands. However, the present invention is not limited to this. Alternatively, it may be configured as a two-band system. Even in such a case, it is possible to obtain the same effect as the embodiment.

[0064]

As described above, according to the present invention, A
By providing an additional circuit block composed of the GC circuit 70, the amplifier 80, and the LPF 90 in front of the variable tracking filter, the input isolation of the mixer can be improved. In addition to reducing the influence of the noise, phase noise can be suppressed, which contributes to higher performance and lower cost. As a result, it is possible to prevent image degradation for other subscribers connected via the transmission cable. Further, by causing the PLL circuit to perform a phase comparison so that the value of the PLL comparison frequency matches the value of the tuning step width of the local oscillation frequency, phase noise at a low-frequency offset of the local oscillation frequency can be reduced. In addition, it is possible to improve the fixed deterioration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a CATV receiver according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a PLL circuit in FIG. 1;

FIG. 3 is a block diagram showing another embodiment.

FIG. 4 is a block diagram showing an example of a conventional double conversion type tuner.

FIG. 5 is a block diagram showing an example of a conventional single conversion type tuner.

[Explanation of symbols]

41a: input terminal, 42: switch, 43, 45, 4
9, 51, 55, 57: variable tracking filter, 4
4, 50, 56 ... amplifier (FET AMP), 47, 5
3, 59: mixer (MIX), 48, 54, 59: local oscillator (LO), 61: BPF, 64: PLL circuit, 6
2a ... output terminal.

Claims (2)

[Claims] 1. An input terminal to which a high-frequency signal is input, a gain control unit capable of controlling a signal input to the input terminal to a predetermined level and outputting the signal, and a gain control unit connected to the gain control unit for controlling a gain. Amplifying means for amplifying the amplified signal, a voltage-controlled local oscillator and a mixing means, and a frequency converter for mixing an output signal from the amplifying means and a local oscillation signal from the local oscillator to generate an intermediate frequency signal. And a variable filter means disposed between the amplifying means and the frequency converting means and having a pass band limited by a control voltage for controlling the local oscillator. 2. A PLL circuit comprising a PLL circuit unit capable of controlling a local oscillation frequency of the local oscillator.
2. The CATV receiver according to claim 1, wherein the LL circuit performs a phase comparison so that a value of a comparison frequency of a PLL and a value of a local oscillation frequency based on a tuning step width of the local oscillator match.