JPS58984Y2 - tuned circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a tuning circuit that facilitates compensation adjustment for deviations of elements constituting the circuit.

In general, when switching to multiple frequencies by changing the voltage using a resonant circuit that changes the capacitance of a variable capacitance diode and tunes to a desired frequency by changing the voltage, the specified tuning voltage is In order to resonate at the frequency of , due to manufacturing and element deviations, in the case of an LC resonant circuit, L and C are adjusted to obtain the desired characteristics.

For this reason, in the past, L in the resonant circuit as shown in Fig.
A tuning circuit that directly varies C and C was used.

In FIG. 1, 1 is a coil, 2 is a variable capacitance diode, 3 is a DC blocking capacitor, 4 is a tracking semi-fixed capacitor, 5 is a choke coil, and 6 is a terminal for applying a tuning voltage.

When a tuning voltage is applied to the terminal 6, the variable capacitance diode 2 has a capacitance corresponding to the tuning voltage.

A tracking semi-fixed capacitor 4 is connected to the variable capacitance diode 2, which forms a resonant capacitance with the DC blocking capacitor 3, and resonates at a frequency determined by the inductance of the coil 1 and this resonant capacitance.

Let us now consider a case in which the circuit is adjusted so that it resonates at the frequency fl when the tuning voltage is v4, f2 when the tuning voltage is v2, . . ., at the frequency fn when the tuning voltage is Vn.

In Fig. 1, if the capacitance of the DC blocking capacitor 3 is sufficiently larger than the variable capacitance diode capacitance and the tracking capacitance, the resonant frequency fi of the resonant circuit is given by where, L: coil inductance (9), Cs , stray capacitance F), Cv: variable capacitance diode face F), Ct;) ranking capacitance (F').

Normally, there are deviations in coil inductance, variable capacitance diode capacitance, and stray capacitance, and the following conditions are possible as a result.

■ When the resonance frequency stretches differently.

However, the extension of the resonant frequency here is Defined by

■ When the growth of the resonant frequency is constant and only the absolute value of the frequency differs.

Regarding 1), since the expansion of the resonant frequency is given by the ratio of the capacitance from equation (1), it is sufficient to change the tracking capacitance to make the expansion constant, and then vary the following to match the specified curve.

In addition, in the case of (2), by fixing the capacity and adjusting L, it is possible to adjust the elongation without changing it.

This type of adjustment method directly adjusts the elements in the resonant circuit to obtain tracking, so changes in the adjustment element directly result in changes in the resonant frequency, and when used in oscillation circuits, the mechanical adjustment of the adjustment element Oscillation frequency changes due to vibration.

That is, vibration causes FM modulation, which causes a significant decrease in S/N.

In general, resonant circuits are constructed on a single board and are often housed in a shielding case, which makes it difficult to adjust them from the outside, and it is difficult to adjust them from the outside if they are housed in a case after being adjusted. etc., characteristics change due to changes in environmental conditions.

This idea was made in view of this point, and instead of adjusting the elements in the resonant circuit, one power supply is divided by resistance and connected in series to the dividing resistor of a voltage generating circuit to generate multiple tuned voltages. By adjusting and setting two or more variable resistors,
The present invention provides a tuning circuit in which a resonant circuit is caused to resonate at a specified multifrequency.

An embodiment of this invention shown in FIG. 2 will be described below.

FIG. 2 shows a tuning circuit in which adjustment is performed using two variable resistors.

In FIG. 2, a coil 1, a variable capacitance diode 2, and a DC blocking capacitor 3 constitute a resonant circuit.

5 is a choke coil that supplies a tuning voltage to the variable capacitance diode 2;

A resistor 7 acts as a filter together with an electrolytic capacitor 8 and a high frequency capacitor 9.

10 is a switch group composed of relays and the like.

11 is a resistance divider circuit, 12 is an adjustment variable resistor that adjusts the frequency of the highest resonant frequency, and 13 is an adjustment variable resistor that adjusts the lowest resonant frequency.
．． A voltage generating circuit 14 is configured by the adjusting resistors 12 and 13.

15 is a power supply terminal connected to a power supply. Do not disconnect, power terminal 1
5 is divided by the voltage generating circuit 14,
Several tuning voltages are created and supplied to the switch group 10.

In the switch group 10, one desired switch is closed, and a voltage corresponding to the switch terminal is generated as a tuning voltage.

The tuning voltage obtained in this way attenuates the power supply noise contained therein and the noise generated from the resistor by a filter composed of a resistor 7, an electrolytic capacitor 8, and a high frequency capacitor 9, and then passes through a choke coil 5 to a variable capacitor. applied to diode 2.

The variable capacitance diode generates a capacitance corresponding to the applied tuning voltage, and the resonant circuit resonates with the inductance of the coil and the capacitance determined by the variable capacitance diode 2 and the DC blocking capacitor 3.

Now suppose that the variable capacitance diode 2 has the following characteristics with respect to the terminal voltage: Cv: variable capacitance diode capacitance, Co: initial capacitance, K: constant ■: terminal voltage, and the capacitance of the switched DC blocking capacitor 3 is It is assumed that the capacitance is sufficiently larger than that of the variable capacitance diode 2.

The tuning voltage V1 generated when the first switch 10-1 is closed in this state is given by R=ΣRi l20■d; power supply voltage.

The resonant frequency f1 at this time is becomes.

Then, the variable resistor 12 is adjusted so that fl in equation (4) becomes the highest resonance frequency f1 (rnax) of the selected frequency (or desired adjustment frequency range), and this is set to fo (max
).

Next, switch 10-1 is opened, and the nth switch 1 is opened.
Close 0-n.

The tuning voltage Vn applied to this variable capacitance diode 2 is given by, The resonant frequency fn in this case is Tonarro.

In this case, the variable resistor 13 is adjusted so that fn in equation (6) becomes the lowest resonance frequency fn (min) of the selected frequency, and is set to fn (min).

In this case, by adjusting the variable resistor 13, the switch 10-
Since a setting deviation occurs in the tuning voltage Vo at 1, the next step is to adjust the variable resistor 12 and reset its resonant frequency f1 to the highest resonant frequency f1 (max).

In this way, by alternately repeating the adjustment of both the variable resistors 12 and 13, fl and fn are gradually brought closer to the highest and lowest resonance frequencies ft (max), (n (min), and the switch 10- Both variable resistors 12.1 are set so that fl (max) is set when switch 1 is closed, and fn (min) is set when switch 10-1 is closed.
Adjust 3.

Here, regarding the deviation (variation) of the elements that affects the resonance frequency in equations (4) and (6), A is the variable capacitance diode 20, that is, C (capacitance) -
When the differential coefficients (slopes) of V (voltage) characteristics are different.

B If the initial value Co of variable capacitance diode 2 is different, When the values of C stray capacitance Cs are different.

D: When the value of inductance L of coil 1 is different.

is possible.

That is, the above A and D correspond to the above I, and the dimensions B and C correspond to ■.

Therefore, in the case of A and D, by increasing or decreasing the potential difference between v1 and Vml according to the C-■ characteristic of the variable capacitance diode 2 or the value of the inductance L of the coil 1, B, C place what jttV
By moving 1 and Vn in one direction (0 or -) on the voltage axis according to the initial value Co of variable capacitance diode 2 or the value of stray capacitance Cs, the deviation can be absorbed. The setting operation is done using variable resistor 1.
This can be done by adjusting 2°130.

Note that the intermediate tuning voltage ■2. ■３・・・・・・Vn −
1, if the voltage dividing resistor 11 is set in advance as R1, R2...Rn-1 with a predetermined resistance value and resistance ratio, a desired frequency (for example, equally spaced frequency) can be generated according to the voltage dividing ratio. Resonant frequencies f2tf3...fn-1 are obtained.

In this way, even if there are variations in the characteristics or circuit constants of the variable capacitance diode 2, the variable resistor 12.
13, the highest and lowest resonance frequency f1 (max),
Just by adjusting and setting fn (min), the desired resonance frequency fl (max), f2, f3...
fn(min) can be generated.

As described above, according to this invention, the highest and lowest resonant frequencies of the resonant circuit are set to predetermined frequencies by two variable resistors connected in series at both ends of the voltage dividing resistor circuit. A desired resonant frequency corresponding to the divided voltage of the voltage dividing resistor circuit, that is, each voltage dividing resistance value, can be easily and selectively obtained without being affected by variations in the characteristics of the capacitor diodes or variations in the power supply voltage.

This invention can be widely used as a tuning circuit for an oscillation circuit having a resonant circuit or a circuit that adjusts the resonant frequency by voltage such as an amplifier.The principle of the invention will be explained based on the case where two variable resistors are used. However, similar adjustment is also possible when two or more variable resistors are used in the dividing resistor, and the adjustment principle is based on the case of two variable resistors.

Further, although a variable capacitance diode having a 1/2 power characteristic is used, the same adjustment can be made when the variable capacitance diode is given by a general function f&) with respect to the terminal voltage.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventionally used resonant circuit, and FIG. 2 is a circuit diagram showing an embodiment of this invention. In the diagram, 1... Coil, 2... Variable capacitance diode, 3... DC blocking capacitor, 5...
...Choke coil, 7...Resistor, 8...
... Electrolytic capacitor, 9 ... High frequency capacitor, 10 ... Switch group, 11 ... Resistance divider circuit, 12.13 ... Variable resistor 14・
. . . Voltage generation circuit, 15 . . . Power supply application terminal. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] A variable capacitance element whose capacitance value changes depending on the applied voltage, a resonant circuit formed by a coil, and both ends of the voltage dividing resistor circuit are supplied with power through variable resistors, and each of the voltage dividing resistor circuits is A voltage generation circuit selectively applies a divided voltage to the variable capacitance element, and adjusts both the variable resistors to set the highest and lowest resonance frequencies of the resonant circuit to predetermined frequencies. A tuned circuit characterized by: