JPS5838646Y2 - UHF Chu-Nano Hatsushin Sochi - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an oscillation device for a UHF tuner.

More specifically, the present invention relates to a λ/2 type oscillator equipped with an automatic frequency adjustment circuit, which has a function of correcting inter-channel deviations in automatic frequency adjustment sensitivity.

FIG. 1 shows a circuit diagram of a general λ/2 type oscillator in a UHF tuner, and numeral 1 in the figure is a transistor for oscillation.

Reference numeral 2 denotes a resonance line connected to the collector electrode of the transistor 1 via a DC cut capacitor 3;
A tuning variable capacitance element 4 is connected to the other end.

Reference numeral 5 denotes a bar J cap diode for automatic frequency adjustment (hereinafter referred to as AET), to which the voltage for AFT is supplied as a reverse bias from a terminal 6 via a resistor 7, and to the resonant line 2 via a DC cut capacitor 8. are connected as shown in the figure.

9 is a terminal capacitor, and 10 is a correction capacitor which will be described later.

By the way, in the conventional λ/2 type oscillator, the inter-channel deviation in AFT sensitivity is corrected by a correction capacitor 10 connected in circuit parallel to the tuning variable capacitor 4, as shown in FIG.
at a predetermined distance l from one end of the resonance line 2 on the variable capacitance element 4 side.
This was done by connecting to the location.

However, in the conventional device described above, positioning of the correction capacitor 10 connected to the resonant line 2 is delicate and difficult, which is unfavorable in terms of workability and tuner performance.

That is, when installing the capacitor 10, the position of the point a that creates the distance LD corresponding to the return circuit of the capacitor 10 is located in the case 1.
1, but the capacity 1
When attaching the other end of 0, that is, coupling to the resonance line 2, the setting of the point that expresses the distance l is likely to vary, and the effect of correcting the AFT sensitivity deviation will be destroyed by this slight variation, so it is especially important to determine the position of the point mentioned above. was difficult.

Further, the oscillation frequency changes greatly depending on the processing of the connection point between the resonant line 10 and the resonance line 2 (for example, variations in the amount of solder), and the influence on the tracking of the tuner cannot be ignored.

The present invention proposes a new and useful oscillation device for a UHF tuner that is devised to eliminate these drawbacks.

That is, in the present invention, as shown in FIG. 3, the correction capacitor 10 is attached to the end of the resonant line 2 instead of near the center.

A connection point a between the capacitor 10 and the tuner housing 11
' is the tuning variable capacitance element 4 and the termination capacitance 9 of the resonant line 2
The length L2 of the return path between the tuning variable capacitance element 4 and the termination capacitor 9 of the resonant line 2 is selected to be sufficiently longer than the length L1 of the return path between the correction capacitor 10 and the termination capacitor 9 of the resonant line 2.

Since the correction capacitor 10 connected in parallel to the tuning variable capacitor 4 has almost no effect in the low band, the return circuit length in the low band is defined by the variable capacitor 4 and the terminating capacitor 9, while in the high band The capacitance 10 and the terminal capacitance 9
The length of the return path is defined by the distance Ll between the two.

In this way, in the present invention, since the correction capacitor 10 is connected to the end of the resonant line 2, the installation work, especially the positioning work, is easier than before, and the performance of the product can be made uniform. This makes the present invention extremely useful in combination with improved workability.

In addition, the inter-channel deviation of the automatic frequency adjustment sensitivity is also shown in Figure 5, with the horizontal axis representing the oscillation frequency f and the vertical axis representing the sensitivity △f. In contrast, the characteristics of the present invention shown in FIG. 3 are better.

[Brief explanation of drawings]

FIG. 1 shows a general circuit configuration of a λ/2 type oscillation device for a UHF tuner, and FIG. 2 is a plan view of the conventional oscillation device. FIG. 3 is a plan view of the oscillation device of the present invention, FIG. 4 is a plan view of the oscillation device for comparing and explaining the effects of the present invention, and FIG. 5 is a plan view of the oscillation device of the present invention. It is a characteristic diagram shown for comparison. 2...Resonance line, 4...Tuning variable capacitance element, 9...Terminal capacitor, 10...Correction capacitor.

Claims (1)

[Scope of utility model registration request] In a λ/2 type oscillator with an automatic frequency adjustment circuit, a tuning variable capacitor and an automatic frequency adjustment sensitivity correction capacitor are connected in parallel between one end of the resonance line and the ground, and the other end of the resonance line is connected in parallel. An oscillation device for a UHF tuner, characterized in that a return path length determined by a terminating capacitor connected between and ground and the correction capacitor is sufficiently shorter than a return path length determined by the tuning variable capacitor and the terminating capacitor.