JPS624014B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present application relates to a tuner that selects a tuning frequency by varying C and L of a tuning circuit, and particularly relates to a tuner that selects a tuning frequency by varying C and L of a tuning circuit.
The purpose of this system is to facilitate tracking adjustment between tuning circuits by using a variable capacitance diode and a variable capacitor that sets the combined capacitance of the diode, and to improve the performance of the receiver.

Generally, L variable tuners made of variable inductance elements are widely used in car radios and the like. The reason for this is that the strong input characteristics are extremely good, and the reception characteristics do not change or the operation becomes unstable due to external vibrations, large changes in temperature and humidity, or the influence of dust, and the product is uniform. This is because it has an advantage over a C variable tuner in that it can be easily tuned. However, the problem with variable inductance tuners is that it is extremely difficult to accurately adjust the tracking between the tuned circuits, and the gain decreases at higher frequencies, while the gain becomes abnormal at lower frequencies. As a result, the operation of the receiver becomes unstable, and it is impossible to improve the performance of the receiver by increasing the number of tuning circuits.

That is, as is well known, a variable inductance tuner is equipped with a variable inductance element in each tuning circuit of the antenna circuit, RF circuit, and OSC circuit.
This method achieves tuning by manually operating each variable inductance element using the same sliding member to vary the L of each tuning circuit.
There are differences in the frequency characteristic curves of each variable inductance element due to manufacturing errors, etc., and conventionally, this difference in frequency characteristic curves has been corrected by adjusting the protruding and retracting base position of the high frequency magnetic core with respect to the coil body, or by adjusting the μ Tracking adjustment between the tuned circuits was achieved by exchanging different high-frequency magnetic cores. However, in the former case, even if the position of the protruding and retracting base point is adjusted, the frequency characteristic curve of the variable inductance element is almost always shifted in parallel, so the frequency characteristic curve is shifted in parallel and the frequency characteristic curve of other variable inductance elements is shifted in parallel. Even if it is tuned to a certain point, the frequency curves will not match for the frequencies before and after that point.Therefore, even if the position of the protrusion and retrieval base point of the high frequency magnetic core with respect to the coil body is adjusted, the frequency characteristic curve between the tuned circuits will not match. are only approximate to each other, and the variable stroke of the variable inductance element is determined by the mechanical sliding stroke of the sliding member in the tuner. When the base position is adjusted, both the upper and lower limit positions of the tuned frequency change, and therefore it is extremely difficult to perform accurate tracking adjustment only by adjusting the base position of the magnetic core relative to the coil body.

For example, as shown in Fig. 4, suppose that the frequency characteristic curve of one tuned circuit is A, and the frequency characteristic curve of another tuned circuit is B, and in this relationship, the coil of the variable inductance element has the frequency characteristic curve B. Assuming that the position of the origin of the magnetic core relative to the body is adjusted and both characteristic curves are adjusted to the vicinity of point P,
The frequency characteristic curve B only moves in parallel as shown by the broken line, but the two curves never match.Moreover, because the variable strokes are the same, its upper limit position F ₁ becomes F ₁ ' and its lower limit position F ₂ changes to F ₂ ', and therefore it is extremely difficult to accurately adjust tracking.

In addition, in the latter case, the task of measuring and classifying the μ characteristics of the high frequency magnetic core into numerous ranks and exchanging them is extremely troublesome and greatly lacks workability. Furthermore, the variable inductance tuner has the disadvantage that the gain decreases at higher frequencies, making it impossible to obtain a stable and uniform gain over the entire tuning frequency band.

Therefore, the present application is intended to improve such defects, and examples thereof will be described in detail below with reference to the drawings. Figure 1 shows the basic tuning circuit of the present application.
is a variable inductance element that varies L by making a high frequency magnetic core appear and disappear from a coil body, and by connecting a variable capacitance diode 2 and a variable capacitor 3 such as a trimmer capacitor in parallel to this, one It constitutes a tuned circuit. Reference numeral 4 denotes a variable voltage circuit consisting of a variable resistor that varies the voltage applied to the variable capacitance diode 2, which is mechanically connected to the variable inductance element 1 and is commonly varied.

However, now the lower limit of the bandwidth of the tuning frequency is
If min is the upper limit and max is the upper limit, then the resonant frequency is Since it is expressed as However, Lmin is the minimum value of variable inductance Lmax is the maximum value of variable inductance Cmin is the minimum combined capacitance of variable capacitance diode 2 and variable capacitor 3 Cmax is the maximum combined capacitance of variable capacitance diode 2 and variable capacitor 3, The relationship between the variable magnification of LC and the tuning frequency is Lmax・Cmax/Lmin・Cmin=(max
x/min) ² ......

In the above formula, the variable magnification Lmax/Lmin of L and the variable magnification Cmax of C
The purpose is to adjust the band width of the tuning frequency by the product of x/Cmin, and as a specific example, a case where numerical values are substituted and applied to the AM band will be described in detail below.

Now, if min is 510KHz and max is 1650KHz, and if this AM band width is covered by, for example, an L variable tuning circuit, then Lmax/Lmin=(max/min) ² =
(1650/510) ² ... From the formula, the variable magnification of L is approximately 10.47.

By the way, as mentioned earlier, there are variations in the frequency characteristic curve of the variable inductance element due to manufacturing errors, so the following disadvantages arise when only the L variable tuning circuit is used.

That is, when the protrusion and retraction stroke of the high-frequency magnetic core with respect to the coil body is constant, and the variable range of a certain variable inductance element is 500KHz to 1690KHz due to manufacturing errors, the variable magnification is (1690/500) ² = 11.42 ......, and when the variable range of a certain variable inductance element is 520 KHz to 1610 KHz, the variable magnification is (1610/520) ² = 9.56 ......

In the case of the above formula, if the base position of the high-frequency magnetic core relative to the coil body is adjusted to the desired lower limit frequency of 510 KHz, the frequency at the upper limit position is calculated from the formula (max/510) ² = 11.42, max = 1723.8KHz, and in the case of the above formula, if the base point position of the high frequency magnetic core relative to the coil body is adjusted to 510KHz, the frequency at the upper limit position becomes max=1579KHz from the formula (max/510) ² = 9.56.

From this, when trying to adjust the tracking only by varying L as in the past, since the variable stroke of the high frequency magnetic core is the same, there is a large difference at the higher tuning frequency, and the required band width is This has the disadvantage that channel selection cannot be effectively achieved.

Therefore, in the present application, the above-mentioned variable magnification of L is set to 10.47 or less, and the deficiency in the magnification is supplemented by the variable magnification of C to obtain the required bandwidth.

That is, let us now assume that the magnification of L is set to 7, for example. Then, from the formula (X/510) ² = 7, X or max becomes 1349KHz, and AM
There is a lack of tuning frequency selection in the band width range of 1349KHz to 1650KHz. Therefore, this shortfall in bandwidth is supplemented by the variable magnification of C. (1650/510) ² = 7 x becomes. Therefore, if we assume that the lower limit capacitance of the variable capacitance diode 2 is 5PF and its upper limit capacitance is 20PF, and that the capacitance of the variable capacitor 3, which can be manually adjusted from the outside and is semi-fixed, is Co, the variable magnification of C is 1.5. Therefore, the following formula is obtained: 20+Co/5+Co=1.5 From this formula, Co becomes 25PF.

That is, when the above-mentioned equations are combined, from the equation (X/510) ² =7×1.5, X, that is, max, becomes 1652, and a tuning circuit that sufficiently covers the AM band width can be obtained.

Furthermore, in the above, if the variable magnification of L is, for example, 7.5 or 6.5 due to manufacturing errors, the required band width of 10.47 can be obtained by setting the variable magnification of C to 1.396 or 1.610, respectively, from the above formula. , C can be easily adjusted by varying Co from the above equation.

That is, as is clear from the above explanation, by arbitrarily variably adjusting the variable capacitor 3 to set the combined capacitance with the variable capacitance diode 2, and thereby variably adjusting the variable magnification of C, the variable capacitor 3 can be variably adjusted. It is possible to sufficiently cover the band width that could not be selected by the magnification, and this shows that the variable magnification of L and C
This means that the bandwidth of the tuning frequency can be arbitrarily varied by mutual selection with the variable magnification.

As described above, according to the present application, for example, there is variation in the lower limit frequency of the tuning frequency characteristic curve, and this variation can be made to match the desired frequency by adjusting the protrusion/retraction reference point position of the high frequency magnetic core with respect to the coil body. Even in this case, since the variable magnification of the tuning frequency is constant, the upper limit frequencies of the characteristic curves also match, which has the advantage that tracking adjustment can be performed accurately over the entire reception band width.

Note that FIG. 2 shows a tuning circuit in which a fixed temperature compensation capacitor 5 for the purpose of temperature compensation of the variable capacitance diode 2 is connected in parallel in FIG. The temperature characteristics of No. 2 are improved. In this case, Co in the above equation is set by the variable capacitor 2 and the temperature correction capacitor 5.

Figure 3 also shows a plurality of tuning circuits that are variable by the high frequency magnetic core, namely ANT circuit A, first stage RF circuit B,
This figure shows a tuner in which a tuning circuit having the configuration shown in FIG. 2 is applied to each tuning circuit of a variable inductance tuner equipped with a second stage RF circuit A circuit 4 is commonly connected to each tuned circuit.

Furthermore, although the above example shows the case where the variable capacitor 3 and the temperature compensation capacitor 5 are both connected in parallel to the variable capacitance diode 2, it goes without saying that the capacitors 3 and 5 may be combined in series or in series and parallel. It is.

As described above, the present application provides a tuner including a plurality of tuning circuits that are varied by a high-frequency magnetic core, in which at least one of the tuning circuits has a variable capacitance diode, and sets a composite capacitance with the variable capacitance diode. Since it includes a variable capacitor and a variable voltage circuit that varies the voltage applied to the variable capacitance diode in conjunction with the variation of the magnetic core, it has the following advantages.

In other words, as is well known, in a tuned circuit with variable L, the gain (Q) is high at low frequencies (when the magnetic core is immersed in the coil body), and high at high frequencies (when the magnetic core has escaped from the coil body). )
However, the C variable tuning circuit has a gain characteristic that is opposite to that of the L variable tuning circuit, and therefore, according to the present application,
Since it is a tuning circuit with variable L and C, the gain can be obtained almost uniformly over the entire tuning frequency band width, and stable gain characteristics can be obtained. When selecting the full width of , the variable magnification of L had to be about 10 times, but in this application, the tuning frequency is set by multiplying it by the variable magnification of C, and the variable magnification of L is the above-mentioned value. Since it is obtained smaller than in the case of
It is possible to shorten the variable stroke of the variable length inductance element and is effective in downsizing the tuner;
According to the present application, a variable capacitance diode whose capacitance changes via a variable voltage circuit linked to a high frequency magnetic core of a variable inductance element and a semi-fixed variable capacitor that can be manually adjusted from the outside are connected in parallel or in series. By connecting and adjusting the capacitance of the variable capacitor at the reference point for tracking adjustment and adjusting the combined capacitance, the bandwidth of the tuning frequency can be arbitrarily varied. It is possible to easily adjust the tracking between the tuning circuits by adjusting the position of the protruding and retracting base point of the magnetic core and the capacitance of the variable capacitor. It becomes possible to use an inductance element or a variable capacitance diode with variations, and an inexpensive tuner can be obtained.
In addition, as mentioned above, since the tracking of the tuning circuit can be performed extremely accurately and easily, it is possible to increase the number of tuning circuits, thereby improving the selectivity of the radio receiver, eliminating interference waves, improving sensitivity, stable operation, and even more. It is also extremely effective in improving various characteristics.

Further, according to the present invention, since a temperature compensation capacitor of a variable capacitance diode is connected, good temperature characteristics can be obtained, and there is an advantage that a tuner with stable operation as a whole can be provided.

[Brief explanation of the drawing]

The drawings show an embodiment of the present application, and FIGS. 1 and 2 are circuit diagrams showing the basic configuration of a tuning circuit, and FIG.
The figure is an overall circuit diagram of the manual tuner, and FIG. 4 is an explanatory diagram of the frequency characteristic curve. In the figure, 1 is a variable inductance element, 2 is a variable capacitance diode, 3 is a variable capacitor, 4 is a variable voltage circuit, and 5 is a temperature correction capacitor.

Claims (1)

[Scope of Claims] 1. A tuner including a plurality of tuning circuits variable by a high-frequency magnetic core, wherein at least one tuning circuit has a variable capacitance diode, and
A tuner comprising: a variable capacitor that sets a combined capacitance with the variable capacitance diode; and a variable voltage circuit that varies the voltage applied to the variable capacitance diode in conjunction with variable capacitance of the magnetic core. 2. The tuner according to claim 1, wherein the variable voltage circuit is constituted by a variable resistor. 3. In a tuner equipped with a plurality of tuning circuits variable by a high frequency magnetic core, at least one tuning circuit has a variable capacitance diode, and
A variable capacitor that sets a combined capacitance with the variable capacitance diode, and a variable voltage circuit that varies the voltage applied to the variable capacitance diode in conjunction with the variable capacitance of the magnetic core, and a variable capacitor that is variable in the one tuning circuit. A tuner characterized by a capacitance diode connected to a temperature compensation capacitor. 4. The tuner according to claim 3, wherein the variable voltage circuit is constituted by a variable resistor.