JPS6029077A - Tuner - Google Patents

Abstract

PURPOSE:To improve spurious characteristics, to permit miniaturization and to plan to make integrated circuits possible by selecting the first intermediate frequency in its upper limit from 3-5 times of the receiving frequency band. CONSTITUTION:The oscillation signal frequency of a frequency variable oscillator 65 is made higher than the first intermediate frequency; the first intermediate frequency is made higher than the oscillation frequency of a frequency fixed oscillator 69, and also made between 3-5 times of the upper frequency of the input signals. The band width is rendered 5MHz by using dielectric BPF for a frequency-fixed filter 67, preventing adjacent channel interruption in the following circuits.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a tuner for a TV receiver which receives a TV signal, selects a desired TV channel, and converts the frequency to an intermediate frequency. This invention relates to a tuner using the super)heterodyne method.

Conventional configuration and problems thereof FIG. 1 is a block diagram of a conventionally used VHF electronic tuner.

An input signal is input from an input terminal 1o to an input filter 11, where intermediate frequency band interference signals that interfere with the TV intermediate frequency signal, FM signals, etc. are removed.

The signal is input to the single tuning circuit 12. In the single tuning circuit 12, a desired reception channel is selected using one varactor as a variable resonant element, and the signal is input to the RF amplifier 13 and amplified. The amplified signal is input to a double-tuned circuit 14 using two varactors as variable resonance elements, unnecessary signals are removed, and the mixer circuit 15
V? : Input.

The mixing circuit 15 includes a variable frequency oscillator 1 using a varactor.
An oscillation signal from 6 is added. A frequency-converted intermediate frequency signal is extracted from the output of the mixer 16 and amplified by an intermediate frequency amplifier 17.

In the conventional tuner as mentioned above, a single tuning circuit,
Tuning varactors are required for each of the double-tuned circuit and the oscillation circuit, and traversing adjustment between each circuit is required.

Furthermore, two circuits are required to receive -VHF and UHF TV signals. Furthermore - for VHF low band and high band reception - each frequency is tuned using a switching diode.

and it is necessary to change the oscillation frequency.

1. The configuration shown in FIG. 1 has the disadvantage that it cannot support confidential teletext when used as a CATV tuner.

In order to eliminate the above drawbacks - double super
Various heterodyne all-channel tuners have been proposed.

Double super-hetero gain tuners that have already been proposed include: ``The output frequency of the mixer on the input side,
That is, the selection of the first intermediate frequency and the mixing method in the mixer determine the first local oscillation signal (frequency: fLl
) and the received signal (frequency: fs) is the first intermediate frequency (fLlfB = flyl) - the sum of the first local oscillation signal and the received signal is the first intermediate frequency (ft, 1 + fs = fryl), but both of these methods have drawbacks.

These drawbacks will be explained below. Figure 2 shows the basic circuit configuration of a double super-heterodyne tuner. In the figure, -21 is the input terminal -22 is V
Fixed band bass filter on the input side with the required bands such as HF and UHF, 23 is a variable attenuator, 24 is R
F amplifier.

26 is a first mixer for converting one desired TV channel of the amplified high-frequency input signal to a suitable first intermediate frequency; 26 is a first local oscillator with variable frequency;
Select the desired TV channel input in step 6. 27 is a frequency-fixed band pass filter 28 for selecting the tuned and frequency-converted first intermediate frequency as an F wave to eliminate interference from other channels in the circuits after the first one;
is a second mixer for converting the frequency from the first intermediate frequency to the intermediate frequency of the TV receiver, and the output of the fixed oscillator 29 is inputted thereto. 3o is an intermediate frequency amplifier for amplifying the signal frequency-converted to the intermediate frequency of the -TV receiver.

In the above basic circuit configuration, the characteristics of each circuit are very important in determining the overall characteristics of the tuner, and the interference characteristics of the system are determined by the frequency chosen for the first intermediate frequency. will change greatly.

Now, the first intermediate frequency is set to 300 to 400M 2 bands, and the mixing method of the first mixer is to combine the variable oscillator signal (frequency: fLl) input to the first mixer and the high frequency input signal. (Frequency: fu) to obtain the first intermediate frequency signal (frequency: fxy+).

Considering a channel other than the desired channel as an interfering signal, the frequency band of the interfering signal is, for example, 160 M1z to 450 MHz, assuming the case of 0ATV. (
Hereinafter, the frequency of the interference signal will be abbreviated as fu. ) Harmonic interference, such as fLl-2fl and fLl-3ru, which is converted to fItl when receiving a desired channel, will inevitably occur no matter what first intermediate frequency is selected. However, this interference can be removed by adding fixed band pass filters to one input terminal for each of the VHF, VHF, and UHF/Z ends.

However, if the first intermediate frequency and mixing method are set as described above, -2fu * 2fufp1+ 2fL1-fu
, 2fL1-2fu, etc. become interference. This interference is the difference between the second harmonic or fundamental wave of the interfering signal and the second or lower harmonics of the local oscillation signal of the first mixer, and therefore causes a large amount of interference.

For example, a certain desired reception frequency ′! f−fR, and the 1st′
If the intermediate frequency is fj, then the frequency of the local oscillation signal of the first mixer is fu-1-fxpj. fx
When pj is set to 300 to 400 MIIz, by mixing the harmonics below the second order of the frequency f of the signal other than the desired wave (interfering wave) and the harmonics below the second order of the local oscillation signal of the first mixer. , harmonic components of the second order or lower of the video carrier wave of the signal fu other than the desired wave exist within the first intermediate frequency band of the desired channel. FIG. 3 shows this situation.

In FIG. 3, 31 is the audio carrier signal (frequency - f
xpj-Δf1), 32 is the frequency-converted video carrier signal of the desired channel (frequency, fIFi+Δf2
). Note that Δf1+Δf2=a, esMHz. 33 is an interference signal due to harmonics of second order or lower of a signal other than the desired wave. (Frequency f'-2fu- or 2
fu-fLi- or 2fLi-fu- or 2fLj
-2fu) 0 or more interference -TV channel signal 300-400
This always occurs when converting to the first intermediate frequency of the MMz band, and will cause beat disturbance on the TV screen.

Next, the output signal frequency of the first mixer, that is, the first intermediate frequency is set to, for example, 2000 M Mz.

As a mixing method of the first mixer, consider a case where the sum of the first local oscillation signal frequency (fLi) and the received signal frequency (fR) is set as the first intermediate frequency (for+).

In this case also + f'L1 +2fu, fL1+3
fu etc.

Although harmonic interference converted to frFl occurs when the desired channel is received, countermeasures can be taken in the same manner as in the previous example. In addition, 2fL1-3f11 become interference. Since this interference is also the difference between the second harmonic of the local oscillation signal of the first mixer and the third harmonic of the first interfering wave, it causes a large amount of interference. In this case as well, one interference wave enters the first intermediate frequency band as shown in FIG.

Purpose of the Invention The purpose of the present invention is to solve the above-mentioned problems and to provide a double solution.
The object of the present invention is to provide a double super-heterodyne tuner suitable for a TV receiver, which minimizes spurious interference caused by channels other than the desired channel due to the super-heterodyne gain method.

Structure of the Invention To achieve this object, the present invention selects a suitable first intermediate frequency between 3 times and 6 times the upper limit of the receiving frequency band, and selects an optimal mixing method as the first intermediate frequency. The first intermediate frequency is obtained by the difference between the first local oscillation signal frequency having a frequency higher than the first intermediate frequency and the received signal frequency, and the first intermediate frequency and the second local oscillation signal frequency having a lower frequency than the first intermediate frequency. A second intermediate frequency is obtained by the difference, and an input filter and a first intermediate frequency are provided on the received signal input side to reduce spurious interference and beat interference, and to vary or switch the frequency of the selective filter depending on the desired receiving channel. DESCRIPTION OF EMBODIMENTS As described above, by setting the first intermediate frequency, the mixing method, and the filter format, the conventional example The interference mentioned above will be removed. Below - we will describe in detail how these interferences are removed.
Considering the V signal, what is the frequency band of the interfering signal?

For example, assuming the case of -0ATV, etc., 60 to 450M
IIZ.

The spurious interference generated in the first mixer is determined by the local oscillation signal frequency (hereinafter abbreviated as -fLi) and the interference signal frequency (hereinafter abbreviated as fu) of the first mixer, except for the beat interference between channels. The spurious caused by harmonic mixing of is the first intermediate frequency of the desired reception channel (hereinafter fIFj
), and this relationship is expressed by the following equation.

l mfL1±nfu1. −fT, 1 (m, n
:o, 1.2°3,) The harmonics of fLj and fu are considered here up to the third order.

It is meaningless to consider higher orders than that unless the intermodulation cup characteristics are extremely poor.

When the above-mentioned interference components are arranged according to the order of harmonics of the first local oscillation signal frequency fLj, they are as follows. ■ The second and third harmonics of the interference signal themselves fall within the first intermediate frequency band. .

2fB, 3f11 ■ The fundamental wave of the first local oscillation signal and the secondary and 3rd order of the interference signal
Due to mixing with the next harmonic O 1fL1±2t”ul, l fL1±3ful■
a second harmonic of the first local oscillation signal and a fundamental wave of the interference signal;
By mixing with 2nd harmonic and 3rd harmonic.

12fLl±ful, l 2fLi±2fll.

12f'+, 1±3fu1 ■ Caused by mixing of the third harmonic of the first local oscillation signal and the fundamental wave, second harmonic, and third harmonic of the interference signal.

+3fl±ful　, 13fL1±2ful.

13fL+±3ful Here, the high frequency input signal (frequency: fR) - and the first
The variable oscillator signal input to the mixer (frequency: fL
l) and the first intermediate frequency signal (frequency: fIyl)
Normalized by −F1=fR/fryl.

Let F 2 = f Ll / f engineering v1.

Then, spurious in general.

mFl + nF2 = 1 (m, n=o, ±1.±2.±3−=).

The frequency relationship of spurious up to the third order is shown in FIG. 4. For a certain desired wave frequency fD, -fXν1== fLl-fn by the mixing method of the first mixer
'F or flFj = fh'1+fn, so fL
l or Uf'+, 1 becomes a constant value, and F2 becomes a constant value.O At this time, the high frequency input signal frequency fn is
The lower limit is F + m1n (= fRm
tn/ fIp+ ), and the upper limit is F+max (= f
RmaX/fry+), then - for a constant F2
When changing from Flmin to FjmaXY by -11'Fc.

It is determined from the value of Fl that intersects mFl-4-nF2,=1. In reality, the frequencies of high-frequency input signals do not exist continuously, but at regular frequency intervals (6M
IIz interval), so the frequency from the crossing point to the F1 existence point at 6M1lz interval in the vicinity is a frequency that is far from the first intermediate frequency, and enters the band of the first intermediate frequency and causes interference. .

However, -a 0trl F2-F1 = 1 and flF
According to j = fr, +-f'n, the frequency relationship of the desired wave when the difference between the reaching part of the flute 1 and the desired wave is fxyl, 41 nF2+F+ = 1 tear e fXv1
=f'L1+fD When the sum of the first local oscillation frequency and the desired wave is rryl, 042, which is the frequency relationship of the desired wave, is 72-2F+ = 1- a 3 is F
2+2F1. = 1, and both have a frequency relationship of fx = fn/2, and 44 = 22-3F1-1 + 46
is F2-t-3F1=1, and both are fR=fo/3. These 42 to 45 frequency relationships, that is, the spurious relationship in which the harmonics of the interference wave become the desired wave, occur no matter what first intermediate frequency or mixing method is adopted, and the harmonics on the input side It is necessary to suppress interference signals that generate spurious interference due to waves.

These 40 to 46 desired waves are sure to occur.

Determine the mixing method of the first mixer from the spurious relationship, excluding the spurious frequency relationship that can be countered. For example, if the frequency range of the interference wave is f□ifi=50M
lz, fRmaz = a 50 Mllz, in Fig. 4, 46 is the difference between the first local oscillation frequency and the desired wave as fTFl, and fIFl = 1GI
[For the frequency range 47f to be considered in the case of z, let the sum of the first local oscillation frequency and the desired wave be fiFl -fIFl-
1. For G11z.

48, the difference between the first local oscillation frequency and the desired wave is frl, and when -fr+z = 2 GHz, 49 is the sum of the first local oscillation frequency and the desired wave, r□, 1, and flFl-
This is the frequency range to be considered in the case of 2Gllz.

Comparing 46.48 when the difference between the first local oscillation frequency and the desired wave is fIFl and 47.49 when the sum of the first local oscillation frequency and the desired wave is fIFl, the spurious The frequency relationship becomes less when the difference between the first local oscillation frequency and the desired wave is fIFl. Furthermore, it can be confirmed that the thickness of the spurious level is smaller when the difference between the first local oscillation frequency and the desired wave is fIFl, due to the difference between 1 and 2.

Therefore, in the mixing method, the difference between the first local oscillation frequency and the desired wave is expressed as fIFl, that is, fI
It is preferable to set Fl=fLl-fs because both the number and level of spurious signals generated are small.

However, FIG. 6 shows the principle, and 25 is a first mixer, 26 is a first local oscillator, 27 is a bandpass filter, 28 is a second mixer, and 29 is a second local oscillator. It is.

Now, in that case - since the desired wave is subtracted from the first local oscillation frequency, the frequency relationship of the desired wave is reversed, and the signal corresponding to the audio intermediate frequency is higher than the signal corresponding to the video intermediate frequency in the first intermediate frequency band. becomes higher in frequency.

At the second intermediate frequency, in order to use the intermediate frequency band of the television, in order to perform frequency variation without changing the above frequency relationship, the first intermediate frequency flF+ is changed to the fixed frequency second intermediate frequency as shown in Fig. 6. A second intermediate frequency is obtained by selecting a frequency higher than the local oscillation frequency fL2 and taking the difference.

f ty2=fr+z f+, + selection) Necessary power O Next, consider the selection of the first intermediate frequency.

Figure 6 shows the difference fI between the first local oscillation frequency and the desired wave.
This figure shows the frequency relationship for spurious harmonics of the sixth order or lower when a mixing method is adopted. However, regarding the spurious mF1-)-nF2-1, when -m and n are both 3rd order or less, the solid line is shown, and when -m or n is 4th to 6th order, and the other is 6th order or less, the dashed line is shown. ing.

40 is 12-F1=1, the desired wave, 42 is y2-2Fj
=i, fR-fD/2+44 shows a frequency relationship such that F2-31h=1 and fi=fn/3.

Also, 5Q is Fl-1 and f'a=fty1. ” is 2F1-
1 R = frp + / 2-52 is 3Fj = 1 and -fn engineering fry + / 3-53 is 4F4 = 1 and +f'
R= fry 1/4-54id6F1 =ITfR
”=f!+z15 and L This:/l are the harmonics of the interference wave that directly become frF1. Also, -56 is 2F
2-3F+ =1-56 3F1-F2=1+67 is 2
F2-2F1 = 1-581d3F2-3F1 = 1
It is.

Cocoa, "F+ +nl'2=1(m, n-〇
, ±1°±2.・・・・・・±, ni=2.3・・・・
), except for the case where n=1, kF1=1(
F+=1/k).

mFl-1-nF2=1 (F1=(1-ny2)7m
) and.

In the range of F+,>o, F2)1, the value of Fl is always smaller when kF1=1 than when my1+ny2=1.

1, desired wave of fl=1 and fR=fD/&
Except for the spurious (a=2.3...),
F1=1/, that is, fH= fIy1/k (k
= 2, 3...) will occur at the lowest frequency among the k-order or lower spurious. The spurious frequency relationship that should actually be considered is +F,)o
, narrower than the range of F2>1, 46 in Figure 6 is fIF
The range when l = 1@Ilz, 48 is fIFj = 2
This is the range for Glrz. These ranges are F+
mtn (= fRmtn/fry1) <F+ <F
+max (=fnmax/fIFl) and F2m1n (-1+fRmtn/fIy+)<F
2 <F2max(-1-1-fRmax/fIFl
) is given by

Therefore, fR−fn/a (a −2
, 3...), and if the spurious should be considered at the order of 1 or less, then if k is not only an integer but also a positive number in general, F i maX〈
If 1/', that is, -k'·fnmax<fIFl, the following spurious will not occur within the frequency range of one high-frequency input signal.

Next, consider the factors that determine the value of ', that is, the order of the spurious that no longer exists within the frequency range. There are three main factors: As a mixed method, consider the case where + fXFi = fLl - fD.

(1) Cross-modulation distortion characteristics Adjacent adjacent channels that give 1% cross-modulation distortion to the desired receiving channel.
Alternatively, when the tuner input level of the adjacent channel has a cross-modulation distortion characteristic of -5 dBm in the entire tuner, the level of the interference wave is 30 dB higher than the desired wave in the input signal.

What is the level of the desired wave relative to the level of the third-order spurious interference wave that enters the first intermediate frequency band?

This is about 26 dB or more. The level of the desired signal relative to the level of the fourth-order spurious interference wave is -5 odB.
There is no problem since it exceeds.

Under the same conditions, if the tuner input level of the adjacent channel that causes 1% cross-modulation distortion to one desired receiving channel or the tuner input level of the adjacent channel has a cross-modulation characteristic of 116 dBm, the third-order spurious It is about 10 dB or more, and about +40 dB or more for fourth-order spurious.

(2) Filter characteristics First, let's talk about the input filter characteristics.If the level of the interference wave can be lowered on the input side when receiving the desired signal, then
This is advantageous in terms of spurious characteristics. Spurious wave whose harmonics of the interference wave become the desired wave - fH - fn/a (a = 2, 3
・River...), since they always occur and primary and secondary spurious signals also exist, it is necessary to remove them with an input filter. In this case, the desired wave and the interference wave are fn - fn/a
Because it's just far away.

If only these spurious signals need to be removed, the filter configuration is relatively easy. If other spurious signals also need to be removed by the one-person filter, the configuration of the one-person filter becomes complicated. 0 Note that the harmonic of the interference wave is the first intermediate frequency fn = fty+/k
(k = 2, 3-・----) Regarding o-y spurious, if it enters the first intermediate frequency band, both the desired wave and spurious interference wave on the input side are within the reception band, so , cannot be removed by an input filter. Therefore, in order to prevent these spurious from becoming a problem, it is necessary to select the order k of the spurious that does not enter the band, determine the first intermediate frequency, and ensure cross-modulation distortion characteristics. .

Regarding beats, it is easy to deal with secondary beats because the frequency interval of the two waves is fD apart, but for 3rd order intermodulation, it is easy to deal with it because the frequency interval between the two waves is fD. Since the desired wave is only separated by a frequency interval, processing by the input filter becomes quite difficult and depends largely on the selection of the first intermediate frequency and ensuring the intermodulation distortion characteristics.

Next, let us describe the filter characteristics of the first intermediate frequency.
Of the various signals generated by the first mixer, it is necessary to provide a fixed frequency filter that selects the first intermediate frequency band and selects the p-wave.It is necessary to reduce the interference caused by signals of other channels in the subsequent circuits. be. In that case, what is suitable for the purpose of realizing a filter that is as small as possible and that does not pass signals from other channels as much as possible at 1 to several GHz is a resonant element with a high dielectric constant and a high Q. Dielectric type band pass filter using dielectric material, especially dielectric constant 35, no load Q, outer diameter 1mmφ
This is a coaxial dielectric filter as shown in FIG. 7 using a dielectric material 59 of .800.

In addition, in FIG. 7, 59a is an input/output terminal.

69b is a tuning screw, and 69C is a bonding board.

(3) Frequency dependence of initial characteristics When the first intermediate frequency is selected high, the first local oscillation frequency also becomes high. Generally, the gain of a transistor is -6dB10at with respect to frequency - and
The noise figure (NF) also deteriorates as the frequency increases; for example, at -IGllz, NF = 1.8 dB (+7) becomes -2
G[Z NF=2. It will be about sdB. Also, from an industrial perspective, the higher the frequency.

This tends to be disadvantageous in terms of manufacturing and cost.

Considering the above-mentioned factors, it is preferable that the value of -ni' be linear.

In other words, in order to obtain a good quality screen on the TV screen with almost no influence, the level of the desired wave against spurious interference within the first intermediate frequency band must be at least a 5 dB. As mentioned in the section on modulation characteristics, if the tuner input level of the adjacent or adjacent channel that has a 1% cross-modulation distortion characteristic for the desired reception channel is -es
In the case where the signal has cross-modulation characteristics of dBm, there is no problem if it is 4th order or higher, but 3rd order and stronger 2nd order spurious can only be removed by an input filter, which is difficult.

Therefore, as described above, it is preferable to set the value to ')3 so that, except for the spurious of fR=fD/a, which always occurs, spurious of the third order or lower order does not occur within the band. At that time,
As the first intermediate frequency, 3-fRmax < fzy
If o fimaX = a50 MHz, which will be selected as 1, it will be -136 o MHz (rt+ 1).

υ, and the tuner input level of the adjacent channel that causes 1% cross-modulation distortion on the desired receiving channel or the adjacent channel is m.
-5dBm - For example, Itf -1tsdBt
In the case of cross-modulation distortion characteristics of n, it may not be possible to maintain the level of the desired signal over 45 dB with respect to the spurious interfering waves in the band, even for 14th-order spurious. Also, it is not necessary to set k<5 so that spurious of the sixth order or lower does not exist in the band. In that case, it is thought that the effects of an increase in the beat generation level due to poor cross-modulation characteristics and an increase in one frequency will be more severe.

At this time, the first intermediate frequency is Its −'5 fy+
max > frpl (O fRma)
(=460M1lz + t'IF1 <2.25
It becomes 0 MIIZ. Even if the cross-modulation distortion is poor, if the input filter can reduce the beat, by selecting a high first intermediate frequency, you can construct a tuner with excellent spurious characteristics. This is extremely advantageous in terms of gain and noise figure characteristics.

As mentioned above, the value of +k' is -3(k'(s- that is, the first intermediate frequency f□, 1 is -3XfRma
X< fr F 1 < 5 X fRmax, which means that the upper limit of the high frequency input signal may be set between 3 and 5 times. In fact, where to set fIFi between them can be determined by taking into account the intermodulation φ characteristics, input filter, frequency, etc., and performing optimization according to the requirements of each case.

Examples according to the present invention will be described in detail below.

FIG. 8 is a block diagram of a double super-heterodyne tuner for an 0ATV converter in one embodiment of the present invention.

The input signal input from the terminal 60 is input to the single filter circuit 61. This filter 61 includes a trap circuit and a high-pass filter for removing FM signals and the like. The output of the input filter circuit is input to a variable attenuator 62 composed of a pin diode. The loss in the passband of this variable attenuator is approximately 1 to 1.6 dB, and the maximum attenuation is.

It is approximately 60 dB. The output of the variable attenuator 42 [-] is amplified by the RF amplifier 63 and then input to the first input terminal of the first mixer 64 configured with a diode single balanced mixer. The second input terminal of the mixer 64 includes:
The output of the voltage controlled oscillator 66 is amplified to a required level by the amplifier 66 and input. Voltage controlled oscillator 6
6 generates a necessary oscillation signal corresponding to a desired channel by voltage control. The first mixer 64 receives the oscillation signal from the voltage-controlled oscillator 66, receives the TV multiplied signal input to the first input terminal of the mixer 64, and generates a predetermined first intermediate frequency 1.
The frequency is converted to 360~22cs□MHz. - As an example, 1500 M[lz is selected, and as described above as the mixing method, the difference between the local oscillation signal frequency of the first mixer, that is, the oscillation signal frequency of the voltage controlled oscillator, and the frequency of the received TV channel signal is the first If you set it to be an intermediate frequency.

The required oscillation frequency band of the voltage controlled oscillator is 1660~1
950MH2 and Naru.

The output of the first mixer 64 is 1500 MI (Z(7)
The TV channel signal frequency-converted to the first intermediate frequency is input to a frequency-fixed band pass filter 67 that selects one. The frequency-fixed bandpass filter 67 is a coaxial dielectric filter with a bandwidth of 6M to avoid adjacent channel interference as much as possible in the circuits after the first one.
Hz. The output of the fixed band pass filter 67 is input to a first input terminal of a second mixer 68. The output of the fixed oscillator 69 is input to the second input terminal of the second mixer 68 . The second mixer 68 receives the first F-wave selected by the fixed no-band pass filter 67.
frequency converting the intermediate frequency signal to a second intermediate frequency. As described above, the mixing method is set so that the difference between the frequency of the second fixed oscillator 69 and the first intermediate frequency is calculated to obtain the second intermediate frequency.

70 selects the intermediate frequency frequency signal in order to suppress adjacent channel interference in the intermediate frequency amplifier on the output side, and fixes it to attenuate the video carrier signal and audio carrier signal components of the upper and lower adjacent channels. A band pass filter and a trap circuit. The output of the filter 7o is amplified to a required level by an intermediate frequency amplifier 71 that amplifies the second intermediate frequency frequency-converted by the second mixer 68.

Terminals 72 and 73 [, respectively terminals for AGO voltage supply end,
This is a terminal for supplying channel selection voltage.

According to the embodiments of the present invention as described above, it is possible to prevent the generation of low first-order spurious as much as possible as described above, and the spurious characteristics are excellent.

A compact double super-heterodyne tuner, which is industrially advantageous, can be constructed relatively easily.

DETAILED DESCRIPTION OF THE INVENTION One aspect of the present invention provides a first local oscillator signal having a frequency higher than a first intermediate frequency.

The first intermediate frequency is obtained by the difference between the received signal frequency and the output signal of the input filter that reduces spurious interference and beat interference, and the first intermediate frequency is set to 6 times the upper limit of the received input frequency. It is set up to double.

Therefore, by selecting the first intermediate frequency, generation of low-order spurious, at least third-order or lower spurious, can be prevented, and filter characteristics for these spurious are not required. However, the harmonics of the interference wave become the desired wave - the level of the spurious that always occurs must be attenuated by an input filter. 'For example, even if the cross-modulation distortion characteristics are poor due to requirements such as gain and noise figure that conflict with the cross-modulation distortion characteristics, the first intermediate frequency may be set to 3 to 6 times the upper limit frequency of the received signal. If one of these is set high, for example, 4.6 times, spurious of the 4th order or lower will not occur, which is advantageous in terms of spurious characteristics.If the input filter is used to attenuate the beat frequency relationship, a tuner with good interference characteristics can be created. can be configured. L
, therefore, depending on the superiority of the cross-modulation distortion characteristics.

There is a degree of design freedom in that it is only necessary to select the first intermediate frequency and determine the input filter characteristics.

Further, by taking the difference between the second local oscillation frequency and the first intermediate frequency, the second intermediate frequency can be obtained, so that the relationship between the output frequency and the first intermediate frequency can be set as the intermediate frequency of the television.

Furthermore, by using a dielectric material for a band pass filter with a fixed frequency, it is possible to reduce interference in other channels in subsequent circuits, despite the small size.

After all, according to the present invention, it is possible to prevent the generation of low-order spurious signals with strong interference as much as possible, so the spurious characteristics are excellent, and since the first intermediate frequency is in the GIIz band, it can be configured compactly. Since the circuit configuration has few adjustment points and many parts that can be integrated into integrated circuits, it has advantages such as good mass production, and its industrial value is extremely high.

[Brief explanation of the drawing]

Figure 1 is a lock diagram of a conventional VHFHF electronic tuner, Figure 2 is a block diagram showing the basic configuration of a conventional double super-heterodyne tuner, and Figure 3 is a block diagram showing the basic configuration of a conventional double super-heterodyne tuner. Explanatory diagram showing that interference signals from other channels are generated in the fourth
Figure 6 is a frequency relationship diagram of third-order or lower spurious generated in the first mixer - Figure 6 is a block wiring diagram showing the mixer method of chews in an embodiment of the present invention; Figure 6 is the same as Figure 4; A partially enlarged view, FIG. 7 is a perspective view of a dielectric band-pass filter, and FIG. 8 is a block diagram of a tuner in an embodiment of the present invention. 61... Input filter circuit-64...
First mixer, 65... Voltage controlled oscillator, 66
······amplifier. 67...Dielectric hand pass filter, 68
...Second mixer, 69...Fixed oscillator. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure 6 Figure 2 4 Figure F+←4tz/f IFI) 2￥ 5 Figure hr:t fhFz Brush 6 Figure Ft (=sug/fxH di

Claims (4)

[Claims] (1) On the input signal side, there is an input filter that selects the input signal by varying or switching the frequency - the signal from the output of the input filter and the signal from the variable frequency oscillator are mixed and the first a first mixer for converting the frequency into an intermediate frequency signal; a fixed frequency filter for selectively converting the first intermediate frequency signal; and an output signal of the fixed frequency filter and a signal from the fixed frequency oscillator. a second mixer that mixes the oscillation signal frequency from the variable frequency oscillator to obtain a second intermediate frequency signal;
and the first intermediate frequency is a frequency higher than the oscillation frequency of the fixed frequency oscillator - and between 3 and 5 times the upper limit frequency of the input signal, and the first intermediate frequency is set to be between 3 and 5 times the upper limit frequency of the input signal, and A tuner characterized in that a dielectric bandpass filter is used as a filter. (2) If the input signal frequency is 50 MI (z to 450 M1 (
Z-7', between 3 and 5 times the upper limit frequency 4esoMtlz, i.e. 1350Ml (from Z to 2250MH
2. The tuner according to claim 1, wherein the first intermediate frequency is selected between z and z. (3) Claim 1, characterized in that the input filter includes a Trakub circuit for removing FM signals, etc., and a high-pass F-wave device whose frequency can be varied using a varactor diode. Tuner listed. (4) The tuner according to claim 1, wherein a coaxial dielectric filter is used as the dielectric band-pass filter.