JPH11312954A - Variable tuning frequency filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a filter which is small-sized, low in cost, has high breakdown voltage and can continuously vary a tuning frequency. SOLUTION: A variable tuning frequency filter is equipped with a main turning circuit 3 consisting of a parallel resonance circuit of a main inductance and a main capacitor and plural additional capacitor switching circuits 10, 20... which consist of a serial circuit of an additional capacitor 11 and a pin diode 12 that are connected in parallel to the tuning circuit 3. Turning on/off of the pin diode 12 is made to change switching additional capacitance of the additional capacitor 11 and to change the tuning frequency. Values of the additional capacitors 11, 21... of plural additional capacitor switching circuits 10, 20... and set to be a value which can perform geometric multiple switching from a minimum variable capacitance corresponding to a minimum variable unit of the frequency so that the tuning frequency can continuously vary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tunable frequency variable filter used in a transceiver for frequency hopping communication,
In particular, the present invention relates to a filter capable of continuously changing a tuning frequency.

[0002]

2. Description of the Related Art FIG. 7 shows a conventional tuning frequency variable filter in which a filter having a required variable width in which the tuning frequency is different continuously by a minimum unit is prepared, and each filter is entirely switched. . In the figure, reference numerals 1a and 1b denote connection points with input / output connectors or other circuit elements.
The input / output direction is determined by the characteristics of the filter or other circuit elements. Reference numerals 2a and 2b denote matching circuits for controlling matching with other circuit elements. A plurality of filters 3a to 3n are provided in parallel between matching circuits 2a and 2b. Each filter is composed of a parallel resonance circuit of an inductance L and a capacitor C,
The tuning frequency slightly changes in the minimum change unit, and a filter of a required variable width is connected. For example, 1MHz
Are arranged in units of 25 KHz, 41 filters are provided. To switch between them, one of the filters 3a to 3n is selected by an n-to-1 switch. In this constituent filter, since each of the filters 3a to 3n is already tuned to a predetermined frequency, only the switching time by the switch controls the tuning time. Therefore, by setting this switch to a high speed, a high-speed tuning frequency variable filter can be configured. In order to increase the speed of the switch, the technology of an electronic switch using a pin diode is used.

FIG. 8 shows an example of a filter using a variable capacitor to change the tuning frequency. In the figure, input / output connectors 1a and 1b are the same as those in FIG. 2
a and 2b are matching circuits with other circuit elements. Reference numeral 3 denotes a resonator, which is equivalent to an LC (inductance / capacitor) parallel resonance circuit configuration. Reference numeral 4 denotes a capacitor that blocks direct current from the bias circuit of the variable capacitor 5. The variable capacitor 5 is a capacitor composed of a variable diode and having a characteristic that the capacitance changes by changing the bias voltage Vc7. According to this configuration, by changing the bias voltage Vc, the total capacitance of the resonator 3 and the variable capacitor 5 changes, and the tuning frequency changes. In this way, a desired tuning frequency is obtained. Note that the resistor 6 of the bias circuit is a resistor for giving sufficient impedance to high frequencies.

[0004]

According to the tuning frequency variable filter shown in FIG. 7, a filter having a desired variable width is required, and the configuration becomes large and the cost is increased. Also, the switch circuit needs to be selected from a large number of channels, which complicates the circuit.

Further, according to the latter method shown in FIG. 8, if the passing power is large, a voltage due to the passing power is applied, so that there is a problem that the tuning frequency is shifted.

SUMMARY OF THE INVENTION An object of the present invention is to solve the conventional problems of large size, increase in cost, and inability to handle large power, and to continuously change the tuning frequency which is small, low cost, and excellent in high withstand voltage. It is an object of the present invention to provide a tunable frequency variable filter.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of switching the value of an additional capacitor of a plurality of additional capacitor switching circuits from a value which can be switched by a geometric series from a minimum variable capacitance corresponding to a minimum variable unit of a tuning frequency. Achieved by doing

Further, the above object is achieved by using an additional capacitor as an air capacitor and arranging a plurality of additional capacitor switching circuits composed of the air capacitor radially around the coaxial inner conductor.

Further, the above object is achieved by arranging additional capacitors and pin diodes of a plurality of additional capacitor switching circuits in a required multiple of a predetermined unit in parallel.

According to the above means, when the tuning frequency of the filter is changed by changing the additional capacitance by switching the additional capacitor of the main tuning circuit, the value of the plurality of additional capacitors is changed from the minimum variable capacitance. By setting the value so that the ratio can be switched, it is easy to continuously change the required tuning frequency variable width in minimum variable units.

Further, since the additional capacitor is an air capacitor, the filter can be constructed without deteriorating the Q of the filter. Further, a plurality of additional capacitor switching circuits are radially arranged around the center of the internal conductor, and the additional capacitor and the pin diode are disposed. Are arranged in a predetermined multiple in parallel in a predetermined unit, and the on-resistance when turning on / off the pin diode is reduced, so that the transmission loss of the filter can be reduced, and
A low cost, high withstand voltage tuning frequency variable filter can be provided.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.
The input / output connectors 1a and 1b, the matching circuits 2a and 2b, the main tuning circuit 3, and the DC blocking capacitor 4 are the same as those described in the related art. The capacitor 11 is an additional capacitor for determining the tuning frequency, and is added to the equivalent capacitance of the main tuning circuit 3 to determine the tuning frequency. Of course, the capacitance of the capacitor 11 is determined in consideration of the stray capacitance of circuit components such as the on / off control pin diode 12 connected in series. The resistor 13 inserted in the bias voltage circuit of the pin diode 12 is a resistor that has a high impedance to a high frequency (a passing signal) and is determined so that a predetermined current flows from the bias power supply Vc8 to the pin diode 12. is there. Switch 14
Is a switch that operates when tuning to a desired frequency and controls whether or not a current flows through the pin diode 12, and is selectively controlled by the control circuit 9 in accordance with the tuning frequency.
When a predetermined current flows from the bias power supply Vc, the pin diode 12 turns on because the high-frequency impedance is close to 0 and turns on when no current flows.

A switching circuit block (stage) 10 for determining a tuning frequency including the additional capacitor 11, the pin diode 12, the pin diode bias circuit, and the like;
,..., The tuning frequency continuously changes by the minimum variable unit, and they are arranged for a required tuning frequency variable width.

The tuning frequency is selected by the control circuit 9. The control circuit 9 selects the switching circuits 10, 20,... Corresponding to the desired tuning frequency, for example, selects the switching circuit 10 and turns on the switch 14. Let it. Then, a current flows from the bias power supply Vc to the pin diode 12, and the pin diode 12 is turned on. Therefore, the desired tuning frequency is determined by inputting the additional capacitor 11 to the main tuning circuit 3 in parallel.

Each of the switching circuits 10, 20,... Provided with an additional capacitor 11, 21,... For determining a tuning frequency has a geometric series multiple of the minimum variable capacitance corresponding to the minimum variable unit of the tuning frequency. The switching frequency is set and arranged so that the tuning frequency can be equivalently continuously varied in minimum variable units.

The tuning frequency ω is determined by equation (1).

[0018]

(Equation 1)

In this configuration, since L is constant, ω is given by
Will follow.

[0020]

(Equation 2)

Further, C is decomposed into a fixed amount C _Fix and a change amount ΔC turned on / off by a pin diode. Therefore, it is represented by Equation 3.

[0022]

(Equation 3)

Each of the switching circuits 10, 20,..., Is set such that ΔC becomes a geometric series (Expression 4) times the root 2 of the minimum variable capacity.
Are set as the capacitances of the additional capacitors 11, 21,..., The tuning frequency can be continuously varied in a desired minimum variable unit.

[0024]

(Equation 4)

As described above, the value of the capacitor is set to the equation (4) (n = 0, 0) so that the variable center frequency shifts at equal intervals.
1, 2, 3,...), I.e., each switching circuit 10, 20,.
By arranging the capacitances of the additional capacitors, the tuning frequency can be continuously varied equivalently. The control circuit 9 includes switching circuits 10, 20, corresponding to the predetermined frequency.
The frequency is varied by selecting...

Air capacitors are used for the additional capacitors 11, 21,... Of the switching circuits 10, 20,.
This can be realized without lowering the Q of the filter by the air condenser.

FIG. 2 shows an embodiment of the additional capacitor switching circuit according to the present invention. The mechanism comprises a substrate 31, an internal conductor 32 and an external conductor 33. Substrate 3
1 is a substrate 31 such as Teflon as shown in a top view in FIG.
Has a circular hole 31a in the center of the hole 31a.
A plurality of patterns are formed radially around a. A capacitance switching circuit such as a pin diode and a resistor is mounted on this pattern, and additional capacitors 41 to 49 are respectively connected to spaces formed between the internal conductor 32 and each of the patterns 1 to 3 as shown in FIG.

FIG. 4 shows the structure of the inner conductor 32 and the outer conductor 33. The inner conductor 32 and the outer conductor 33 are coaxially formed, one end is short-circuited, the other end is opened, and the open end is opened. The substrate 31 is bonded to the side. FIG. 5 shows the structure of additional capacitors (air capacitors) 41 to 49 arranged in the gaps between the internal conductor 32 and each pattern of the substrate 31. FIG. 1A is a perspective view, and FIG. 2B is a top view. A capacitance is formed by an electrode plate B obtained by bending a metal plate into a U-shape and an electrode plate A inserted in parallel into the electrode plate B. .

FIG. 6 is a circuit configuration diagram of additional capacitors 41 to 49 and a capacitance switching circuit of each capacitor. The additional capacitor 41 has a minimum variable capacitance, which is connected between the internal conductor 32 and the substrate 31. The pin diode 50 and the resistor 60 of the additional capacitor capacitance switching circuit are mounted on the pattern of the substrate 31 by soldering or the like. Capacitance of the additional capacitor 42 is twice the route of the capacitor 41, the capacitance of the additional capacitor 43 is root 2 ^double condenser 41, the capacity of the route 2 ³ times ...... additional capacitor 49 of the capacitance of the additional capacitor 44 capacitor 41 capacitor 41 Route ²⁸ times. For this purpose, a capacitor having a minimum variable capacitance and a route twice as large as a predetermined unit capacitor is prepared.
By arranging the unit capacitors of each type in multiple multiples in parallel, it is possible to switch the geometric series of the route 2 having the minimum variable capacity by multiples. Of course, geometric series multiplication is not limited to route 2.

Also, as shown in FIG. 6, by arranging a plurality of pin diodes 50 of the capacitance switching circuit mounted on each pattern on the substrate in accordance with the number of capacitors arranged in parallel, the pin diodes 50 are turned on / off. The on-resistance at the time of turning off can be made as small as possible. This is because, in a circuit with a large switching amount of capacitance, the insertion loss of the entire resonator sharply increases when the circuit changes from the OFF state to the circuit ON state, but the transmission loss of the filter unit is reduced by reducing the ON resistance. be able to.

When the number of pin diodes 50 of the capacitance switching circuit is increased in parallel with the number of capacitors arranged in parallel, as shown in FIG. Since the area is gradually increased from the pattern in accordance with the number of pin diodes arranged in parallel, and the pattern is formed to have the maximum area, each capacitance switching circuit having a plurality of pin diodes arranged in parallel can be easily mounted on each pattern.

As shown in FIG. 2, a plurality of capacitance switching circuits including the additional capacitors 41 to 49 are connected to the internal conductor 32.
Are arranged radially around the center, a large number of additional capacitor switching circuits are compactly mounted, the filter section is small and the resistance is small, and transmission loss is reduced.

[0033]

As described above, according to the filter of the present invention, the tuning frequency can be continuously varied in minimum variable units. Further, the on-resistance of the capacitance switching can be reduced, and the transmission loss can be reduced. Further, the configuration can be reduced in size and cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a perspective view of a mounted state of an additional capacitor switching circuit unit according to the embodiment of the present invention.

FIG. 3 is an enlarged view of a substrate part of FIG. 2;

FIG. 4 is a detailed view of an inner conductor and an outer conductor of FIG. 2;

FIG. 5 is a detailed structural view of the air condenser of FIG. 2;

FIG. 6 is an additional capacitor switching circuit diagram.

FIG. 7 is a configuration diagram of a conventional filter.

FIG. 8 is a configuration diagram of a conventional filter.

[Explanation of symbols]

1a, 1b: input / output connector, 2a, 2b: matching circuit,
3: Main tuning circuit, 4: DC blocking capacitor, 8: Bias power supply, 9: Control circuit, 10, 20: Additional capacitor switching circuit, 11, 21: Additional capacitor, 12, 50 ...
Pin diode, 13, 60 ... resistor, 14 ... switch,
31 ... substrate, 32 ... inner conductor, 33 ... outer conductor, 41-
49: Additional condenser (air condenser), ... pattern.

Claims (3)

[Claims] 1. A main tuning circuit comprising a parallel resonance circuit of a main inductance and a main capacitor, and a plurality of additional capacitor switching circuits comprising a series circuit of an additional capacitor and a pin diode connected in parallel to the main tuning circuit. In a tuning frequency variable filter that switches an additional capacitor by turning on / off the pin diode and changes an additional capacitance to change a tuning frequency, the value of the additional capacitor of the plurality of additional capacitor switching circuits is used as a minimum variable unit of the tuning frequency. A tuning frequency variable filter characterized in that the value can be switched from a corresponding minimum variable capacity to a geometric series. 2. The tunable frequency variable filter according to claim 1, wherein said additional capacitor is an air capacitor, and a plurality of additional capacitor switching circuits comprising said air capacitor are arranged radially around a coaxial inner conductor. 3. A plurality of additional capacitors and pin diodes of said plurality of additional capacitor switching circuits each being arranged in a required multiple of a predetermined unit in parallel.
A tunable frequency variable filter as described.