JPH067644B2 - UHF television circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to coupling of a UHF tuner double-tuned circuit and a next-stage mixed circuit using a lumped constant (inductance coil).

(Prior Art) FIG. 8 is a schematic diagram of a distributed constant type tuner, in which a coupling loop C to a mixer is arranged between the tuning inductance lines A and B, and its characteristics are shown. As shown in FIG. 9, it was possible to form a trap at a position corresponding to the image frequency of the tuner.

(Problems to be Solved by the Invention) However, there is a problem that the size of the resonance circuit is inevitably increased if the resonance circuit is constituted by the inductance line A or B.

Therefore, it is possible to configure a UHF double-tuned circuit with a lumped-constant type coil, but with this circuit configuration, a mixer coupling coil is provided between the primary side coil and the secondary side coil. It was virtually impossible to form a trap in the band because the original selectivity Q was significantly lowered.

Also, as shown in FIGS. 10 and 11, the secondary side coil L
It was considered to provide the mixer coupling coil L _{3 on} the outside of ₂ . FIG. 10 shows a circuit configuration of a conventional example, and FIG. 11 shows an example of mounting an inductance coil. C ₁ and C ₂ are variable capacitors and D ₁ is a mixer diode.

In this case, the image disturbance ratio is 20 to 30 dB inferior to the distributed constant type inductance line,
No further improvement was possible.

The present invention solves such conventional problems,
It is intended to reduce the image disturbance while using the lumped element to achieve miniaturization.

(Means for Solving the Problem) In order to achieve this object, a UHF television tuner circuit of the present invention includes a primary side coil that forms a double-tuned circuit of the UHF tuner, and a coil next to the primary side coil. A secondary side coil provided, a mixer coupling coil provided next to the secondary side coil, and a mixer diode connected to the mixer coupling coil, wherein the secondary side coil is a primary side coil And the mixer coupling coil, and the coils on the secondary side and the mixer coupling coil are wound in opposite directions.

(Operation) With this configuration, the inductance of the double-tuned circuit and the coupling circuit of the UHF tuner is configured by the coil that is a lumped constant element, and the primary side coil, the secondary side coil, and the mixer coupling coil are implanted in this order. So UHF
The tuner can be downsized.

Further, since the windings of the secondary coil and the mixer coupling coil are opposite to each other, there is a phase relationship between the signal due to the mutual inductance of the both coils and the signal due to the stray capacitance formed between the two coils and the printed circuit board or the like. Since the transmitted signals cancel each other out in substantially opposite directions, image interference can be greatly reduced.

Further, in order to achieve the above-mentioned object, a mixer coupling coil (L ₃ ) in which the polarity (winding direction) of the coil (L ₂ ) on the secondary side of the double-tuned circuit of the UHF tuner of the present invention is inverted. ) Using a diode type mixing circuit (D ₁ )
It is connected with.

With this configuration, the image rejection capability of the UHF tuner can be greatly improved, and in the ultra-compact tuner,
That has become possible.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

FIG. 1 is a mounting example of the coil of the present invention, and FIG. 2 is a tuner circuit using the coil. The coil L ₁ and the variable capacitor C _{1 form} a primary side resonance circuit. Coil L ₂
The variable capacitance C ₂ constitutes a secondary side resonance circuit. The primary and secondary resonant circuits have mutual inductance M
They are connected by ₁₂ , forming a double-tuned circuit. Next, the coupling with the mixer diode is coupled to the coils L ₂ and L _3.
And the mutual inductance M _{23 with} . As the coil L ₃ , a coil whose polarities are inverted from those of the coils L ₁ and L ₂ (winding direction is opposite) is used. In addition, 10 is an RF amplifier, 11 is an IF tuning circuit, L. O. Is a local oscillator circuit. With such a configuration, as shown in FIG. 3, it becomes possible to form traps in the vicinity of the image frequency in the UHF band, and as a result, image interference is improved as shown in FIG. The reason why the image disturbance is improved will be described in detail with reference to FIGS.

FIG. 5 (A) is an equivalent circuit of the coupling portion between the interstage secondary side and the mixing circuit, which includes the floating resistance r _s and the floating capacitance C _s . Here, as shown in FIG. 5 (B), there are two routes for transmission from the interstage secondary side to the mixing circuit. One is due to the mutual inductance M _23, and the other is due to the floating element (r _s , C _s ). In particular, the influence of floating elements in the UHF band is unavoidable and cannot be ignored in circuit design. The present invention positively
The floating element is used. That is, FIG. 5 (B) shows that the transmission amount transmitted from the port 1 to the port 2 by the floating element 12 and the transmission amount transmitted from the port 1 to the port 2 by the inductive element 13 are opposite to each other. By making the phase and adding at the port 2, the canceling effect is utilized.

In FIG. 6, the canceling effect in each of the case of the original desired signal frequency and the case of the image interference frequency will be described using a vector. FIG. 6 (A) is a vector diagram at a near signal frequency. I ₁ ( ₀ ) is a current flowing into L ₂ , and I ₂ ′ ( ₀ ) is a current induced and flowing in the secondary side coil (mixer coupling coil) L ₃ .
I ″ ₂ ( ₀ ) is a current flowing from the floating element to the secondary-side coil L _{3. 2} = ′ ₂ + ″ ₂ , and ₂ represents a current flowing into the next-stage mixing circuit.

It can be seen that the current ₂ ( ₀ ) at the desired signal frequency is guided to the mixing circuit without a large loss.

Next, FIG. 6 (B) is a vector diagram at the image frequency _im . That is, at the frequency in the high frequency band of the UHF band, the impedance is extremely lowered due to the frequency characteristics shown in FIG. This means that the current I ″ ₂ ( _im ) due to the floating element increases, and the absolute values of ′ ₂ ( _im ) and ″ ₂ ( _im ) become closer to each other in the higher region of the UHF band.

Moreover, if the phase relationships are opposite, they cancel each other out completely, and transmission from port 1 to port 2 is lost. That is, the image interference frequency generated in the high frequency band of the UHF band is not transmitted from the port 1 to the port 2. At this time, the phase conditions are as follows.

(However, v ₀ represents the voltage of the input port 1.) As described above, according to the present embodiment, the polarity of the inductance coil to be inductively coupled to the interstage secondary side is reversed by the lumped constant type UHF tuner. As a result, the deterioration of the interference characteristics (image interference ratio, IF / 2 interference ratio) is greater than before,
With respect to the reception channel in the high frequency band, which has been a problem, it is possible to significantly improve the interference rejection characteristics.

(Effects of the Invention) As described above, according to the UHF television tuner circuit of the present invention, the inductances of the double tuning circuit and the coupling circuit of the UHF tuner are configured by the coil which is a lumped element, and the primary side coil is Since the secondary coil and the mixer coupling coil are implanted in this order, there is an effect that the UHF tuner can be downsized.

Further, since the windings of the secondary coil and the mixer coupling coil are opposite to each other, there is a phase relationship between the signal due to the mutual inductance of the both coils and the signal due to the stray capacitance formed between the two coils and the printed circuit board or the like. Since the signals are transmitted in the opposite directions to cancel each other, the image interference can be significantly reduced.

Furthermore, by the arrangement of the coils as described above, the adjustment of the mixer coupling coil does not affect the adjustment of the coils of the double tuning circuit, and the image frequency can be adjusted independently of the tuning frequency. It has the effect of making it easier.

Further, since the primary side coil, the secondary side coil and the mixer coupling coil can be firmly implanted in the printed board, there is an effect that the adjustment frequency does not change even when vibration or the like is applied.

[Brief description of drawings]

1 is a mounting diagram showing an example of mounting a coil according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing an embodiment of a tuner circuit using the coil of FIG. 1, and FIG. 3 is a selectivity characteristic. FIG. 4 is a characteristic diagram showing the image interference rejection characteristic, and FIG. 5 is a secondary side of the double-tuned circuit of FIG. 2 and an inductance L.
_{3 is} a circuit diagram of its vicinity and its equivalent circuit diagram, FIG. 6 is a vector diagram of each current in the equivalent circuit of FIG. 5, FIG. 7 is a frequency characteristic diagram of stray impedance, and FIG. 8 is a conventional distributed constant type tuner. FIG. 9 is a selectivity characteristic diagram of the interstage double-tuned circuit of the tuner of FIG. 8, FIG. 10 is a conventional lumped-constant type tuner circuit diagram, and FIG. 11 is a conventional coil mounting diagram. L ₁ , L ₂ , L ₃ ... Inductance coil, C ₁ , C
₂ ... Variable capacitance, M ₁₂ , M ₂₃ ... Mutual inductance,
r _s ... Floating resistance, C _s ... Stray capacitance, D ₁ ... Mixer diode, 10 ... RF amplifier, 11 ... IF tuning circuit, 12 ... Floating element, 13 ... Inductive coupling element, L. O. …
… Local oscillator circuit.

Claims (1)

[Claims] 1. A primary coil forming a double-tuned circuit of a UHF tuner, a secondary coil provided next to the primary coil, and a mixer coupling provided next to the secondary coil. A coil and a mixer diode connected to the mixer coupling coil, wherein the secondary side coil is provided between the primary side coil and the mixer coupling coil, and the secondary side coil is provided. A UHF television tuner circuit characterized in that the winding directions of the coil and the mixer coupling coil are opposite to each other.