JPS5823979B2 - Chuyuna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Conventionally, as shown in FIG. 1, in a VHF tuner for a television receiver, a broadcast wave signal received by an antenna 1 is passed through a bandpass filter 2 on the input side, and is subjected to high-frequency amplification. It is supplied through a circuit 3 to a mixer 5 through an interstage bandpass filter 4, and in the mixer 5 it is supplied to a local oscillator 6.
The local oscillation signal and multiplication are combined and frequency converted,
The output signal is extracted as an intermediate frequency signal through an intermediate frequency band pass filter 7.

The band pass filters 2 and 4 are designed so that their passbands can be switched by the channel selection operation for each channel. occurs in 2
This is to remove unnecessary signals such as harmonic components.

As described above, the conventional tuner has a frequency selection circuit that can be switched for each channel, which has the disadvantage that the configuration is complicated.

In view of this point, the present invention has been devised so that it is possible to remove the above-mentioned unnecessary signals and receive only the desired channel with a simple configuration, without providing a frequency selection circuit that can be switched for each channel. Hereinafter, a specific example will be explained using FIG. 2 and subsequent figures.

As shown in FIG. 2, the tuner according to the present invention supplies a broadcast wave signal received by an antenna 11 directly to a mixer 15, multiplies it with a local oscillation signal from a local oscillator 16, and converts the frequency. The configuration is such that the output signal is extracted as an intermediate frequency signal through an intermediate frequency band pass filter 17, and for this purpose, the mixer 15 has a special circuit configuration as follows.

That is, FIG. 3 shows an example of a specific configuration of the mixer 15, in which 21
is a switching circuit, which includes first to fourth diodes D1. D2. D3 and D4 are connected in series to form a loop, and the connection point P1 between the first and fourth diodes D1 and D4 and the connection point P2 between the second and third diodes D2 and D3 are connected to one of the input terminals and The connection point P3 between the first and second diodes D1 and D2 and the connection point P4 between the third and fourth diodes D3 and D4 are used as one and the other of the output ends.

The broadcast wave signal from the antenna 11 is supplied to one input terminal P1 and the other input terminal P2 of the switching circuit 21 in phase with each other, and a local oscillation signal is transmitted between one input terminal P1 and the other input terminal 22 of the switching circuit 21. The diodes D1 and D2 and the diodes D3 and D4 of the switching circuit 21 are turned on and off in the opposite direction by this local oscillation signal.

In the illustrated example, the antenna 11 is connected to one of the input terminals P□ of the circuit 21 via the secondary side 22b of the bifilar-wound input quadrature transformer 22, and the antenna 11 is connected to one of the input terminals P□ of the circuit 21 via the primary side 22a of the input quadrature transformer 22. It is connected to the other input terminal P2, so that the broadcast wave signal SF (FIG. 5A) is supplied in phase to one input terminal P1 and the other input terminal P2, and the local oscillator 16 is connected to the primary side 23a of the transformer 23. One end of the secondary side 23b of the transformer 23 is connected to the base of the transistor 24, the other end is connected to the base of the transistor 25, and the emitters of these transistors 24 and 25 are connected in common, The connection point thereof is grounded via a resistor 26, and the power supply terminal 27 from which a positive DC voltage is obtained is grounded via resistors 28 and 29, and the grounding points of the resistors 28 and 29 are connected via resistors 30 and 31, respectively. is connected to the bases of transistors 24 and 25 to constitute a differential current source 32 for local oscillation signals, and the collectors of transistors 24 and 25 are connected to one input terminal P1 and the other input terminal P2 of switching circuit 21, respectively.

Note that 33 is the transistor 2 that constitutes the differential current source 32.
A choke coil for passing a bias current through 4 and 25, which may be a resistor.

Furthermore, the signals obtained at one output terminal P3 and the other output terminal P4 of the switching circuit 21 are extracted differentially,
In the example shown in the figure, an intermediate frequency bandpass filter 17 consisting of a secondary side 34a of a transformer 34 and a capacitor 35 is connected between one output terminal P3 and the other output terminal 24, and one end of the secondary side 34b of this transformer 34 is connected. An output end 36 is led out.

Therefore, in the positive section of the local oscillation signal So (FIG. 5B), the diode D1 is connected so that the current flowing through the transistor 24 decreases and the current flowing through the transistor 25 increases.
and D2, current flows through these diodes D1 and D
2 becomes conductive, the broadcast wave signal SF appears at one of the output terminals P3, and in the negative section of the local oscillation signal So, the transistor 2
Current flows through diodes D3 and D4 so that the current flowing through transistor 4 increases and the current flowing through transistor 25 decreases, these diodes D3 and D4 become conductive, and a broadcast wave signal SF appears at the other output terminal P4, The output terminal 36 receives an output signal obtained by subtracting the signal 5FA obtained at one output terminal P3 (FIG. 5 C) from the signal 5FB obtained at the other output terminal P4 (FIG. 5 D), that is, the broadcast wave signal SF and local oscillation. Signal So
The combined intermediate frequency signal S (FIG. 5E) is obtained.

In the example of FIG. 4, a differential amplifier 39 consisting of transistors 37 and 38 is provided, and the signal SFA obtained at one output terminal P3 of the switching circuit 21 and the signal SFB obtained at the other output terminal P4 are applied to the bases of the transistors 37 and 38. In this case, the intermediate frequency bandpass filter 17 is connected to the collector sides of the transistors 37 and 38.

According to the above-described tuner according to the present invention, the broadcast wave signals are supplied to the switching circuit 21 in phase with each other, and
Since the output side of the switching circuit 21 is configured differentially, the diodes D1 to D4 of the switching circuit 21
No broadcast wave signal current flows through these diodes D.
The impedances of 1 to D4 are not affected by the broadcast wave signal, so an output signal without linear distortion can be obtained.

Therefore, generation of harmonic components of the broadcast wave signal can be prevented, and interference due to harmonic signals will not occur.

The image frequency interference can be removed by selecting the frequency of the intermediate frequency signal as follows.

For example, when using the upper heterodyne system, as shown in Figure 6, the lowest frequency of the channel occupying the lowest band of the low channel of the broadcast wave signal is flL, the highest frequency is ftHl, and the lowest channel of this low channel is The local oscillation frequency when receiving is fl, the lowest frequency in the channel that occupies the highest band of the low channel is fsL, and the highest frequency is f3.
H1 The local oscillation frequency when receiving the highest channel of this low channel is f3, and the lowest frequency of the channel occupying the lowest band of the high channel is f4.
L, the highest frequency is f4H1, the local oscillation frequency when receiving the lowest channel of this high channel is f4,
The lowest frequency in the channel occupying the highest band of the high channel is f12L, and the highest frequency is f12H1
The local oscillation frequency when receiving the highest channel of this high channel is f1□, the bandwidth of one channel of the broadcast wave signal is fB, the lowest frequency of the intermediate frequency signal is fL, and the highest frequency is fH (= fL + fB).

First, in order to avoid image frequency interference based on the signals of other channels in the low channel when receiving the low channel, it is necessary to The signal obtained by multiplying the local oscillation signal at the time is f
It is sufficient that it does not fall within the band from L to fH, therefore,
As shown in FIGS. 7A and B, fL=fl-fH> f3H-fl...
・・・・・・ke) is fine.

Next, in order to prevent image frequency interference from occurring in the high channel signal when receiving the low channel, when receiving the highest channel of the low channel, the signal of the lowest channel of the high channel and the local oscillation signal at this time must be When receiving the lowest channel of the low channel, the signal of the difference frequency between the highest channel signal of the high channel and the local oscillation signal at this time becomes lower than fH. Therefore, as shown in Fig. 8 A and B or Fig. 9 A and B, fH'' f3 f3L < f4L f3
・・・・・・・・・(2) Or fL=ft ftH>ft2Hfx ・・・・
...(3) is sufficient.

Furthermore, in order to prevent image frequency interference from occurring in the signals of other channels of the high channel when receiving the high channel, when receiving the lowest channel of the high channel, it is necessary to The combined signal is f
It is sufficient that it does not fall within the band from L to fH, therefore,
As shown in Figure 10 A and B, fL-f4-f4H>f1□□-f4...
... (4) is sufficient.

If this condition is met, image frequency interference based on low channel signals will not occur during high channel reception.

And from equation (1), 2f1〉f1H+f3H to this Substitute fl-f1L + fH 2 fH> f1H+f3H-2ftL Therefore, becomes.

Also, from equation (2), 2 f3<f3L +f+L By substituting f3-f3L + fH into this, 2fH<f4L fsL=f4L (f3HfB) Therefore, it becomes.

Also, from equation (3), 2 fl> f1H + ft2H to this Substitute f1=fIL+fH 2fH>fIH+f1□H2ftL Therefore, becomes.

Furthermore, from equation (4), 2 f4> f, H+f1□H to this Substitute f4= f4L+ fH 2fH>f4H+f12I(-2f4L Therefore, becomes.

Here, (5) to (8) derived from equations (1) to (4)
Looking at the formula, as is clear from Figure 6, (7)
Since the right-hand side of equation (5), (6), and (8) are larger than the right-hand sides of equations (5), (6), and (8), in order for image frequency interference not to occur, the following three conditions must be simultaneously satisfied, or the following conditions must be met: The intermediate frequency, and therefore the local oscillation frequency, should be selected so as to satisfy the following.

Specifically, let us show what values should be set for a tuner that receives VHF broadcasting in Japan today.

The signal status of each channel of VHF broadcasting in Japan is as shown in Figure 11, and the specific frequency values are as shown in the table above, f B = 6 MHz.

Therefore, from equation (5), fH > 12 MHz From equation (6), fH × 34 MH2 From equation (8), fH > 29 MHz From equation (7), fH > 69 M) (z, so it is sufficient that If the intermediate frequency is fp, then fp=
Since fH-1,25■h, it is sufficient.

The selection can be made in the same manner when using the lower heterodyne method.

As described above, according to the present invention, by using a mixer with a special configuration and by carefully selecting the intermediate frequency, unnecessary signals can be eliminated with a simple configuration without the need for a frequency selection circuit that can be switched for each channel. can be removed to receive only the desired channel.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a conventional tuner, Fig. 2 is a system diagram of a tuner according to the present invention, Figs. 3 and 4 are connection diagrams of specific examples thereof, and Fig. 5 is a waveform for explaining its operation. Figure, 6th
Figures 1 to 11 are diagrams for explaining frequency relationships. 11 is an antenna, 15 is a mixer, 21 is a switching circuit thereof, D1 to D4 are first to fourth diodes, 1
6 is a local oscillator, and 17 is an intermediate frequency band pass filter.

Claims (1)

[Claims] 1 The first to fourth diodes are connected in series to form a loop, and the connection point between the first and fourth diodes and the connection point between the second and third diodes are connected to one of the input terminals and and a switching circuit in which a connection point between the first and second diodes and a connection point between the third and fourth diodes are one output terminal and the other output terminal,
A local oscillation signal is supplied between one and the other of the input terminals of the switching circuit, and the first to fourth diodes are turned on and off by this local oscillation signal, and the first to fourth diodes are turned on and off, and the first to fourth diodes are turned on and off by the local oscillation signal. Broadcast wave signals are supplied to the other side in phase with each other, and the signals obtained at one and the other of the output terminals of the switching circuit are differentially extracted to obtain an intermediate frequency signal, and the frequency of this intermediate frequency signal is A tuner in which the frequency of the local oscillation signal is selected so as to have a predetermined value.