JPH0424662Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a tuner used in television receivers and the like.

(b) Prior art Figures 3 and 4 show the main circuit diagrams of a conventional tuner, in which 1 is a high frequency amplifier circuit, 2 is a local oscillation circuit, C ₁ and C ₂ are coupling capacitors, and TR ₁ is a frequency conversion transistor, and the high frequency signal and local oscillation signal injected into the transistor TR ₁ via the coupling capacitors C ₁ and C ₂ are converted to an intermediate frequency by using the nonlinear characteristics of the transistor TR ₁ . This intermediate frequency output is supplied to the intermediate frequency amplification transistor _TR2 , where it is amplified and applied from the terminal T to the intermediate frequency circuit.

In the circuit shown in FIG. 3 above, a low-pass filter circuit 3 consisting of a coil L ₁ and a capacitor C ₃ is provided to couple the frequency conversion transistor TR ₁ and the intermediate frequency amplification transistor TR ₂ . Impedance matching between TR ₁ and TR ₂ and passing only signals below the intermediate frequency band contribute to eliminating interference caused by frequencies above the intermediate frequency band.

In addition, in the conventional example shown in FIG. 4, coils L 2 _and L as described in Japanese Patent Publication No. 53-39104 are used to couple the frequency conversion transistor TR ₁ and the intermediate frequency amplification transistor TR ₂ . _3. A double tuning circuit 4 consisting of capacitors C ₄ and C ₅ and resistors R ₁ and R ₂ is provided to increase the selectivity of the intermediate frequency band.
Efforts are being made to improve interference rejection capability and smoothen frequency characteristics. In addition, in FIGS. 3 and 4, R ₃ ,
_R4 is an emitter resistor, _C6 , _C7 , and _C8 are bypass capacitors, _C9 is a coupling capacitor, and _R5 is a bias resistor, which is the base of frequency conversion transistor _TR1 and intermediate frequency amplification transistor _TR2. The bias circuit is omitted.

By the way, among the nonlinear distortion disturbances that are a major problem in tuners, 6 in the US channel
One type of channel color beat disturbance occurs at the following frequency relationship.

In other words, the video carrier frequency of 6 channels in the United States is _6p (83.25MHz), the audio carrier frequency is _6S (87.75MHz), and the local oscillation frequency is _6L (129M
Hz), an interference signal u ₁ is generated according to the following equation.

u ₁ = _6p + _6S − _6L ...(1) Here, in equation (1), u ₁ is 42MHz, a value close to the color intermediate frequency of 42.17MHz,
This is an interference signal that can become a color intermediate frequency depending on the deviation of the local oscillation frequency _6L .

The relationship in equation (1) above is due to third-order nonlinear distortion occurring in frequency conversion transistor TR ₁ in FIGS. 3 and 4, but second-order nonlinear distortion also occurs in intermediate frequency amplification transistor TR ₂ . Another cause of 6-channel beat disturbance is due to non-linear distortion.
An interference signal u ₂ having the same frequency component as u ₁ is generated.

That is, when the video intermediate frequency is p and the audio intermediate frequency is s, u ₂ is generated from the following relationship.

u ₂ = _6L − (p + s) ... (2) Here, p is 45.75MHz and s is 41.25MHz, so u ₂ is 42MHz.

The relationship in equation (2) above means that the component of the sum of p and s of the video and audio intermediate frequency signals output from the output _terminal T is
Returning to the input side of the transistor TR ₂ , this is thought to be established due to the relationship between the leakage of the local oscillation signal and the second-order nonlinear distortion of the transistor TR ₂ .

For this reason, as a conventional countermeasure against interference caused by equations (1) and (2), constants such as the input level to the transistor with a local oscillation frequency of _6L and the bias condition of the transistor are set to optimal values in the circuit shown in Figure 3 or Figure 4. Improvements in performance have been made through selection.

However, the above-mentioned improvement method has a limit to variations in the nonlinearity of the transistor itself, and has the disadvantage that it is difficult to obtain steady performance.

(c) Problems to be Solved by the Invention The present invention attempts to provide a tuner that is devised to significantly improve interference caused by nonlinear distortion of transistors with a simple configuration.

(d) Means for solving the problem The present invention uses a frequency conversion transistor and an intermediate frequency amplification transistor in a double-tuned circuit that can provide an opposite-phase output to the secondary-side tuned circuit with respect to the primary-side tuned circuit. A small capacitor is provided for coupling and transmitting the signal obtained in the primary side tuning circuit to the secondary side tuning circuit in the same phase.

(e) Effect The frequency conversion transistor and the intermediate frequency amplification transistor are coupled by a double-tuned circuit that provides an opposite phase output to the secondary side tuning circuit with respect to the primary side tuning circuit. The current phase of the interference signal u ₁ caused by the next nonlinear distortion becomes opposite in phase on the input side of the intermediate frequency amplification transistor due to the double tuning circuit. Therefore, the interference signal u ₁ obtained in the primary side tuning circuit is transmitted to the secondary side tuning circuit in the same phase by the minute capacitance, so that it is canceled out by the interference signal of the opposite phase.

In addition, the current phase of the intermediate frequency obtained by frequency conversion with the frequency conversion transistor is also phase-inverted in the secondary side tuning circuit by the above-mentioned double tuning circuit.
The interference signal u ₂ generated by the following nonlinear distortion and fed back to the input side of the intermediate frequency amplification transistor is also in the opposite phase, and is therefore transmitted from the primary side tuning circuit by the minute capacitance mentioned above. positive phase interference signal
u ₁ and cancel each other out.

(F) Embodiment Hereinafter, an embodiment of the present invention will be explained with reference to FIGS. 1 and 2. In FIG. 1, the same parts as in FIG. do.

That is, in the present invention, the double tuning circuit 4 that couples the frequency conversion transistor TR ₁ and the intermediate frequency amplification transistor TR ₂ is connected to the tuning coil L _{2 ' of the primary side tuning circuit 4a and the tuning coil L 2} ' of the secondary side tuning circuit 4b. The coil L ₃ ' is configured to be inductively coupled to the secondary side with a polarity that provides a reverse phase output. In addition, a minute capacitance Cx of about 1 _P F or less is provided between point A of the primary side tuning circuit 4a and point B of the secondary side tuning circuit 4b, and this minute capacitance Cx corrects a slight signal from point A. The phase is transmitted to point B as is. Said minute capacity
Cx is the capacitor parts such as chip capacitors A,
Of course, it can be formed by connecting between points B, but it can also be formed using a conductive pattern on the tuner's printed circuit board. Figure 2 shows that such a conductive pattern creates a small capacitance.
This shows the case where Cx is formed. In the case of the figure a, the pattern 6 on the point B side is in contact so as to half surround the pattern 5 connected to the point A, and in the figure b, the pattern on the side of the point A is simply Parts attachment pattern 7
Using this, pattern 8 on the B point side is added to this pattern 7.
are in contact and form a capacitor. Also, Figure 2c
In the case of , component mounting pattern 9 connects to point A.
A bar-shaped pattern 9a extending from point B and a bar-shaped pattern 10a extending from a component mounting pattern 10 connected to point B are arranged parallel to each other, and the gap 1
1 forms a minute capacitance. Note that 12 is a chip capacitor forming capacitor _C4 .

With the above configuration, the current phase of the interference signal u1 generated at point A due to the third-order nonlinear distortion of the frequency conversion transistor _TR1 is phase-inverted in the double-tuned circuit 4, and the current phase of the interference signal _u1 generated at the point A due to the third-order nonlinear distortion of the frequency conversion transistor TR1 is phase-inverted by the double-tuned circuit 4. On the input side of _{No. 2} [point B], the phase is reversed. However, since the interference signal u ₁ generated at point A is transmitted in phase to point B by the minute capacitor Cx, it is canceled out by the interference signal -u ₁ of opposite phase generated at point B.

Further, the current phases of the intermediate frequencies p and s obtained by frequency conversion by the frequency conversion transistor TR ₁ are also transferred to the secondary side tuning circuit 4b by the double tuning circuit 4.
Since the phase is inverted, the interference signal u ₂ generated by the second-order nonlinear distortion in the intermediate frequency amplification transistor TR ₂ and returned to point B is also in the opposite phase. Positive phase interference signal transmitted from the primary side tuning circuit 4a by the capacitor Cx
As a result, 6-channel color beat interference in the United States can be significantly suppressed without considering transistor bias conditions.

In the above embodiment, it has been explained that the interference signal generated in the primary side tuning circuit 4a by the minute capacitance Cx is injected from point A to point B, but the interference signal generated at point B injects the minute capacitance Cx. It is clear that the explanation can also be made such that it flows into point A through the channel.

(g) Effects of the invention According to the invention, interference signals caused by nonlinear distortion of the frequency conversion transistor and the intermediate frequency amplification transistor connected thereto can be significantly suppressed with a simple configuration, which is extremely useful. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a main part of a tuner embodying the present invention, and FIG. 2 is an explanatory diagram thereof. Figures 3 and 4
Each figure is a circuit diagram of a main part of a conventional tuner. 4...Double tuned circuit, 4a...Primary side tuned circuit,
4b... Secondary side tuning circuit, TR ₁ ... Transistor for frequency conversion, TR ₂ ... Transistor for intermediate frequency amplification, Cx... Micro capacitance.

Claims (1)

[Claims for Utility Model Registration] (1) In order to convert the high frequency signal of television to an intermediate frequency, this high frequency signal and a local oscillation signal are injected, and at the same time, the first interference signal u ₁ is generated by nonlinear distortion. a frequency conversion transistor TR ₁ that generates a signal, and an intermediate frequency that amplifies the signal from this transistor TR ₁ and generates a second interference signal _{u 2 having} the same frequency as the first interference signal u 1 due to nonlinear distortion. In a tuner including an amplification transistor TR ₂ , the frequency conversion transistor TR ₁ and the intermediate frequency amplification transistor TR ₂ are coupled, and the secondary side tuning circuit 4b is connected to the primary side tuning circuit 4a. A tuner comprising: a double-tuned circuit 4 capable of obtaining an opposite phase output; and a minute capacitor Cx that transmits the signal obtained in the primary-side tuned circuit 4a to the secondary-side tuned circuit 4b in phase. . (2) The tuner according to claim 1, wherein the minute capacitance Cx is formed of a conductive pattern on a printed circuit board.