JPH01166655A - Double superheterodyne television receiver - Google Patents

Abstract

PURPOSE:To reduce the disturbance by in-band signal by providing a trap circuit attenuating a high frequency signal when a low frequency signal in the band is received and attenuating a low frequency signal when a high frequency signal in the band is received. CONSTITUTION:An input filter circuit 27 is provided with switching circuits 28, 29, a band pass filter 30 passing a VHF low band signal, a high pass filter 31 passing a VHF high band signal, and a high pass filter 32 passing a UHF band signal, and outputs the signal of each band to a trap circuit 34. In the reception of the low frequency in the band, the trap circuit 34 attenuates a high frequency signal and in the reception of the high frequency in the band, the trap circuit 34 attenuates a low frequency signal to eliminate the disturbance of the 3-dimensional distortion caused in the reception of three signals arranged at an equal interval in the same pass band.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a double-sub one type receiver for receiving television signals, etc., and particularly relates to a Chener circuit structure [IC] with improved interference characteristics.

[Conventional technology]

The double super one type chainer circuit configuration for receiving television signals is described in JP-A-55-83549 or JP-A-60-74731, but these input sections have interference characteristics. In order to improve this, it is common to provide an input filter circuit in which a plurality of bandpass filters having n passbands are connected in parallel. This input filter circuit accepts VHF low band signals,
The Vl(F) band signals are received through a VHF low band band pass filter or a VHF high band band pass filter, respectively.

[Problem that the invention seeks to solve]

In the conventional tuner described above, when there is a strong imbalance in the signal level of the signal in the VHF low band or the signal level in the VHF high band, third-order distortion interference due to the in-band signal (for example, twice and four times the signal two channels away from the receiving channel)
(An interference signal is generated in the reception channel due to a signal from a different channel), which deteriorates the interference characteristics of the tuner and deteriorates the television reception screen.

An object of the present invention is to improve the interference characteristics of the above-mentioned conventional chainer due to in-band signals, and to provide a chainer with good interference characteristics. It is to provide.

[Means for solving problems]

The above object is achieved by dividing the VHF low band or V) IF', -i band and providing a trap circuit that switches the trap frequency to suppress interfering signals within the band.

[Effect]

The trap circuit operates to attenuate the high frequency signal when receiving a low frequency signal within the band, and attenuates the low frequency signal when receiving a high frequency signal. This reduces interference caused by internal signals. The circuit configuration has two tuning points, VHF' low band and V)
The number of parts is reduced by adopting a circuit with a shaped bottom trap in the IF high band.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 3. FIG. 1 shows a trap circuit diagram, FIG. 2 shows its characteristic diagram, and FIG. 3 shows the countries in which the double super one-type Chinana using the trap circuit of FIG. 1 is constructed. First, the operation of the trap circuit shown in diagram t41 will be explained.

1 is a signal input terminal, 2 is an output terminal, 3 to 5 are power supply terminals, and 6.7 is a switching diode. 8-1
4 is a capacitor, of which 10 and 11 are bypass capacitors for blocking direct current. Also, 15-19
is a coil, and 20 to 24 are resistors.

The circuit composed of the capacitor 8.9 and the coil 15, 16, 17 has two resonance points, and when this circuit is provided between the signal line and the ground, two traps are generated. The coil 16.
The trap frequency can be changed by switching the inductance provided by 17. That is, when a voltage is applied to the power supply terminal 3, the diode 6 becomes conductive, the coil 17 is short-circuited, and the two traps have a higher frequency than when no voltage is applied to the terminal 3. In this way, this circuit can change the trap frequencies of the two traps by switching the switching diode 6 into a conductive state and a non-conductive state. In addition, the circuit composed of capacitors 12, 13, 14 and coils 18 and 19 is also a circuit that develops a resonance point ft29, and it is recommended that this be installed between the input and output of the signal line.
Two traps occur. Depending on whether or not a voltage is applied to the power supply terminal 4, the diode 7 is made conductive or non-conductive, and the capacitance of the capacitors 13 and 14 is changed to change the two trap frequencies. In this case, the trap frequency becomes high when no voltage is applied to the power supply terminal 4. Note that a bias is always applied to power supply terminal 5.
The diode 6 or 7 is configured to be biased in the reverse direction when no voltage is applied to the power supply terminal 3 or 4. The circuit shown in FIG. 1 is a circuit in which two circuits each having two trap points are connected in an inverted configuration, and this configuration effectively obtains a sufficient amount of trap attenuation.

FIG. 2 shows an attenuation characteristic diagram of the circuit shown in FIG. 1.

This figure shows the case where two trap points are provided in the VHF low band and VHF high band of the American channel. Apply voltage to power terminal 3, apply voltage to power terminal 4,
The solid line shows the characteristics when no voltage is applied to power supply terminal 4.
The dotted line shows the characteristics when a voltage is applied to the power supply terminal 3 and no voltage is applied to the power supply terminal 3.

Next, the structure and function of a double super one type chainer provided with the trap circuit shown in FIG. 1 in FIG. 3 will be explained. The received signal is inputted from the antenna terminal 25, passes through the input filter circuit 27, is amplified by the wideband amplification circuit 53 with variable gain attenuation, and is inputted to the first mixer 35 through the trap circuit 34.

The input signal is converted by the first mixer into an 11F frequency higher than the received signal by the local oscillation signal input from the frequency variable first local oscillation circuit 36, and is input to the second mixer 38 through the band pass filter 37. do. The input signal is frequency-converted to the normal IF frequency by the second mixer using a local oscillation signal that is also input to the second local oscillation circuit 39, and the I
The signal is amplified by the F' amplifier circuit 40 and outputted from the output signal 26.

The input filter circuit 27 includes switching circuits 28 and 29,
Bandpass filter 3 that passes VHF low band signals
o. It is composed of a band pass filter 61 that passes VHF high band signals and a high pass filter 32 that passes UHF band signals, thereby improving interference caused by signals outside the receiving band. Double super one type 4
- If a variable tuning circuit using a tuning diode is used as the input filter circuit, it is difficult to track the local oscillation circuit, so a method is generally adopted in which filters with different passbands are switched.

The trap circuit 34 having the circuit configuration shown in FIG.
and the first mixer 35.

This is because the input signal 1M is amplified by the wideband amplifier circuit and interference occurs at the first mixer where it is input at the strongest signal level, and the increase in the Chainer noise figure due to the loss of the trap circuit is to be minimized as much as possible.

Next, interference within the band will be described in detail and band division within the band will be explained.

The interference caused by signals within the band includes third-order distortion interference caused by two waves of interference signals or three waves of interference signals. This is interference that occurs when the received signal frequency and the interference signal frequency are at equal intervals.If the reception signal frequency is fd and the frequency interval is Δf, the interference signal generates an interference signal in the damaged signal band as shown below.

(In the case of 2 waves of 11 interference signals, 2x(fd*Δf)-(fd*2xΔf)-fd (same order of decoding) )−(fd*3Δf)
−fd (same order of decoding) (2).

Interference caused by two waves of interference signals is strongly influenced by signals close to the received signal, that is, interference signals that are difficult to remove with a filter.The interference level of interference caused by two waves of interference signals is higher than that caused by three waves of interference signals, It is necessary to consider intra-band division in consideration of interference caused by two signal waves. (As shown in Equation 11, when three signals lined up at equal intervals are received in the same passband, third-order distortion interference occurs.

Band division is performed according to the above. However, the channels of the television broadcast waves are arranged every other channel, and the band division is made to be as small as possible.

(1) American, Rica Channel VHF high band 70H
(Video carrier frequency fp-175, 25MH2) ~ 13
CH (fp-21t25MHz), and the most signal assignments are 7CH, 9CH, 11CH113C
This is a case of 4 channels of H. 70H and 9C in the band
The band may be divided into two so that H is in the same passband and 11CH and 13C) are in the same passband.

(21 American channels VHF low band 20H (fp
-55,25MHz)~6CHCfp-83,25M
Hz) but dc) ((fp-67, 25MHz)
and 5C) i (fp-77, 25MHz) is 10MHz
z apart, and aCHlsCH may be placed simultaneously. 3-arrow distortion occurs when JCH 2 is received when 2CH is received.
Within the 2CH band (54~
60MH2) when an interference signal occurs (6725X2)
- When an interference signal is generated within the 5CH band (76 to 82MH2) due to a signal twice as large as 4CH and a 20H signal in 77.25-57.25MH2 and sCHC borrowing (6
7,25x2-55.25-79.25Mf(z)
There is a 't'.

2CH1scH14CH is in the same passband, 5C"Hl
It is sufficient to divide the band into 42 so that bcH has the same passband.

131 Japan Channel V) IF High Band 4CH (f
p-17125MHz ) ~12eH (fp-217
, 25MHz), and the most signal allocation is 4.
This is a case of 5 channels of CH16cH, 8CH, 1oCH, and 12CH, and in order to have two or less channels in the same pass band, it is necessary to divide the band into three.

(41 Japan channel vHF low band ICH (fp-9t25MHz)"3CH (103,2
5MHz), and no third-order distortion disturbance occurs.

For the above reasons, the characteristics of the American channel trap circuit shown in Figure 2 are such that the VHF low band is
CH is the same passband, 5CH16CH is the same passband, the trap circuit is divided into two ICs. The band is divided into two by a trap circuit, and the characteristics in that case are shown.

In this way, in addition to band dividing filters for the VHF low band and VHF no. It is possible to improve the third-order distortion disturbance that occurs. The trap circuit configuration uses a circuit with two resonance points to configure traps for VHF low band and VHF high band, and by switching one switching diode, it is possible to switch the passband between VHF low band and VHF no band. The trap circuit can also be simplified.

In the embodiment shown in FIG. 1, the trap frequency is changed by switching the inductance of the coil 16.17 or the capacitance value of the capacitor 15.14, but in order to change the trap frequency formed between the signal line and the ground, the capacitor 8 .9 or switch coil 15, and
The trap frequency formed between the signal lines can be switched by switching the capacitor 12 or the coils 18 and 19. Which capacitor or coil to switch can be selected depending on the frequency range to be changed. Here, trap circuits are provided between the signal line and the ground and on the signal line, but if the amount of attenuation required is small, either one of the 10,000 trap circuits may be used.

FIG. 4 shows another circuit with two resonance points. 41
-48 are lakes, 49-56 are capacitors, and 57-64 are coils. Lol! , 4 When the circuits in Figures 1al and lbl are installed between the signal line and ground, two traps are created, and when the circuits in tel and (di are installed on the signal line, two traps are created. By switching one of them, you can change the two trap frequencies.Of course, if you switch two or more elements, you can change the trap frequency even more.
It is also possible to divide the frequency into three or more.

FIG. 5 shows another embodiment of the trap circuit.

65 and 66 are input/output terminals, and 67 is a voltage supply terminal.

Further, 68 to 71 are switching diodes, 71 to 7
9 is a capacitor, 80-87 is 1 coil, 88-90
is the resistance, and 75.75.77.79 of the capacitor
is a bypass capacitor for DC blocking. The structure of the trap circuit is such that a series resonant circuit consisting of a capacitor and a coil is provided between the signal line and ground, and a parallel resonant circuit consisting of a capacitor and a coil is provided on the signal line, and these circuits are provided in two stages. The first stage is for V) IF cloning, and the fifth stage is for VHF high band. Each resonant circuit changes the trap frequency by switching the inductance of the coil using a switching diode. When a voltage is applied to the power supply terminal 67, each switching diode becomes conductive and the trap frequency becomes high; when no voltage is applied, each switching diode becomes non-conductive and the trap frequency becomes low. Although the circuit of the embodiment shown in FIG. 5 has a larger circuit scale than the circuit of the embodiment shown in FIG. 1, it is easier to design and adjust. Here, the trap frequency was changed by switching the coil, but the trap frequency may also be changed by switching the capacitor.

FIG. 6 shows another example of the configuration of a tuple super one-way cheese provided with a trap circuit. Components in FIG. 6 that have the same functions as those in FIG. 3 are given the same reference numerals. In the configuration example shown in FIG. 3, the trap circuit 34 is provided after the wideband amplification circuit 53 to reduce deterioration of Chener's noise figure due to loss in the trap circuit, but in the configuration shown in FIG. It is provided before the circuit 33 to prevent interference from occurring in the broadband amplifier circuit.

FIG. 7 shows a third example of the circuit configuration from the antenna input of the double super one-type chainer to the first mixer input end. In FIG. 7, parts having the same functions as those in FIG. 3 are given the same reference numerals. 91 is an input terminal, 92 is an output terminal, 93 to 96 are switching circuits, 97 is a filter circuit that passes the CATV signal, and 98 is an amplifier circuit that amplifies the U) IP band signal. In the configuration shown in Fig. 7, a filter circuit for receiving CATV signals is added, and the UHF band signal is amplified by a newly installed amplifier circuit.
The trap circuit is provided after the VHF low band and VHF high band bandpass filters 31% 52, and
It operates only when receiving F low band and VHF high band, and is configured so that there is no trap circuit loss when receiving UHF band or CATV band signals.

FIG. 8 shows a fourth configuration example. @ Also in figure 8, r
Components with the same functions as in Figure g7 have the same symbols. What is different in Fig. 8 from Fig. 7 is the VHF high band bandpass filter! A trap circuit 99 for the VHF high band is provided after the VHF high band, and a trap circuit 100 for the VHF high band is provided after the band pass filter 30 for the VHF low band. In this way, loss can be further reduced during VHF low band reception or vHF no-band reception.

Note that the trap circuits shown in Figures 91 and 3 are on the input side,
The output side may be connected in the opposite direction, and if the impedance of the load on the input side and the output side is different, the connection may be made in the direction that increases the amount of trap attenuation.

〔Effect of the invention〕

According to the present invention, in a double super tuner, I
It is possible to improve the 5rK distortion disturbance characteristics due to in-band signals when receiving VHF low band and VHF' high band which are a@. The trap circuit adopted as a countermeasure includes VHF low band and VHF high band.

The circuit is simplified by using a circuit having a wrap point ft.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of one embodiment of the trap circuit of the present invention, Fig. 2 is its characteristic diagram, Fig. 3 is a schematic diagram of a tuner using the trap circuit of Fig. FIG. 5 is a circuit diagram of a second embodiment of the trap circuit, and FIG. 6, FIG. 7, and FIG. 2nd, 3rd, @ of the tuner used
FIG. 4 is a block diagram showing a configuration example of No. 4; 6.7...Switching diode, 8,9.12.
13.14... Capacitor, 15-19... Coil, 3A199.100... Trap circuit. 10th 2nd 60th ? 2. 7. mouth

Claims (1)

[Claims] 1. A first mixer and a second mixer are provided, and the first mixer has at least a first band-pass filter having the same pass band as the VHF low-band signal and a VHF high-band signal on the input side. In a double super type receiver having an input filter circuit section equipped with a second band pass filter having the same pass band, a VH is installed at a stage before the first mixer.
A double super television receiver characterized by being provided with a trap circuit whose passband is switched within the F low band or within the VHF high band.