JPH063866B2 - Tuning circuit device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a tuning circuit device using a variable capacitance diode.

[Outline of Invention]

The present invention prevents interference between a plurality of tuning circuits by using a special connection when a plurality of varactor diodes integrated into one chip are used for a plurality of tuning circuits in a radio receiver or the like. It is something that is done.

[Conventional technology]

When a varicap (variable capacitance diode) is used as a tuning element in the tuning circuit of an autodyne receiver (straight receiver) or a super-heterodyne receiver having a high-frequency amplifier in the input stage, the input stage is generally shown in FIG. It is configured as shown in.

That is, in the figure, the bar antenna coil L ₁ and
The varicap D ₁ and the bypass capacitor C _{1 form an} antenna tuning circuit (1) and a coil L ₂
And the varicap D ₂ and the bypass capacitor C ₂ constitute an interstage tuning circuit (2), and the tuning output of the tuning circuit (1) is supplied to the tuning circuit (2) through the high frequency amplifier (3). To be selected. Then, at this time, the tuning bias voltage (control voltage) Vc is applied to the varicaps D ₁ and D ₂ from the variable bias power source (5) through the decoupling resistors R ₁ and R _2.
Are supplied to control the capacities of the varicaps D ₁ and D ₂ , and thereby the reception frequency is changed.

Further, in the super-heterodyne receiver, its input stage is constructed as shown in FIG. 4, for example.

That is, in the figure, while the antenna tuning circuit (1) is constituted by the elements L ₁ , D ₁ , and C ₁ , the element L ₂ ,
D _2, C ₂ by the resonance circuit (2) the configuration of the local oscillation circuit (4), together with the tuning output of the tuning circuit (1) is supplied to the mixer circuit (6), the local local oscillation circuit (4) The oscillation signal is supplied to the mixer circuit (6). At this time, the tuning voltage V
burr c is via a resistor _R 1, _{R 2} caps _D 1, _{D 2}
Is supplied to.

In this way, when there are multiple tuning circuits (1) and (2),
As described above, it is necessary to separate the tuning circuits (1) and (2) at high frequencies by the bypass capacitors C ₁ and C ₂ and the decoupling resistors R ₁ and R ₂ so that mutual interference does not occur. .

By the way, as shown in FIG. 5 as a burr camp, a plurality of, for example, two burr caps D ₁ and D ₂ are formed on the same semiconductor chip CP, and their anode electrodes serve as terminals A ₁ and A _2. A plurality of varicaps D ₁₂ are manufactured which are independently taken out, but the cathode electrode is commonly taken out as the terminal K. According to such a composite varicap D ₁₂ , one semiconductor chip C
Since varicap D _1, D ₂ are formed adjacent to the P, it is possible to align the characteristics of varicap D _1, D _2, and conventional ranking or sorting the individual varicap as There is no need to use it. Moreover, there is an advantage that the manufacturing cost can be reduced.

However, when this composite varicap D ₁₂ is used in the tuning circuits (1) and (2) of FIG. 3 or 4, troubles will occur. That is, this composite varicap D
_{When 12} is used in the tuning circuits (1) and (2) of FIG. 3 or 4, the bypass capacitor C as shown in FIG.
₃ and the decoupling resistor R ₃ will be sustained. In this case, as a matter of course, in the composite varicap D ₁₂ , the impedance when the terminal K is viewed from the cathode electrodes of the varicaps D ₁ and D ₂ is set to be sufficiently small so that the varicap D _{1 is} And D ₂ are prevented from interfering with each other.

However, in the connection shown in FIG. 6, since the resonance current I ₁ of the tuning circuit (1) flows through the capacitor C ₃ and the resonance current I ₂ of the tuning circuit (2) also flows through the capacitor C ₃ ,
If the capacitor C ₃ has impedance, the tuning circuit
Interference will occur between (1) and (2). Therefore, the impedance of the capacitor C ₃ needs to be sufficiently small,
For that purpose, the capacitance of the capacitor C ₃ is sufficiently large,
Moreover, the equivalent series resistance needs to be sufficiently small, but when the reception frequency is low such as the medium wave band, it is difficult to completely satisfy such a condition, and as a result, the tuning circuit (1) and This causes interference with (2), which causes abnormal oscillation or unstable operation in the autodyne receiver. Alternatively, in the super-heterodyne receiver, the local oscillation signal is radiated to the outside through the tuning circuit (1).

Further, if the capacitance of the capacitor C ₃ were to be increased, the time constant with the resistor R ₃ would be increased, causing a time delay in the change of the varicaps D ₁ and D ₂ with respect to the music selection voltage Vc, and giving a feeling of tuning operation. It gets worse.

Therefore, a technology that solves such problems is disclosed in Japanese Patent Application No. 60-4.
Proposed in issue 2380.

That is, for example, as shown in FIG. 7, a bar antenna coil L ₁ and a decal lip ring resistor R ₁ are connected in series between the anode terminal A ₁ of the composite varicap D ₁₂ and ground. The bypass capacitor C ₁ is connected between the connection midpoint of the elements L ₁ and R ₁ and the cathode terminal K of the composite varicap D ₁₂ to form the antenna tuning circuit (1).

Further, a local coil or an interstage coil L ₂ is connected between the anode terminal A ₂ of the composite varicap D ₁₂ and the ground, and a bypass capacitor C ₂ is connected between the cathode terminal K and the ground. A tuning circuit (2) is constructed.

Furthermore, the tuning voltage Vc from the variable bias power supply (5) is
It is supplied to the cathode terminal K through the decoupling resistor R ₃ .

According to such a configuration, the coil L ₁ and the varicap D
_{Since 1} and ₁ are connected in parallel via the capacitor C ₁ , these elements L ₁ and D ₁ act as a tuning circuit (1). Further, since the coil L ₂ and the varicap D ₂ are connected in parallel via the capacitor C ₂ , these elements L 2
₂ , D ₂ act as a tuning circuit (2).

At this time, the tuning voltage Vc is supplied to the varicap D ₁ by the line of power supply (5) → resistor R ₃ → varicap D ₁ → coil L ₁ → resistor R ₁ → power supply (5). The tuning voltage Vc is supplied to the varicap D ₂ through the line of power supply (5) → resistor R ₃ → varicap D ₂ → coil L ₂ → power supply (5).

Therefore, the tuning frequency of the tuning circuits (1) and (2) is the tuning voltage Vc.
Changes in conjunction with.

And in this case, the resistors R ₁ and R ₃ are connected to the capacitor C ₁
Since the impedance is sufficiently large compared to
The resonance current I ₁ of (1) flows through the loop of the elements L ₁ , D ₁ , and C ₁ , and the resonance current I ₂ of the tuning circuit (2) is the elements L ₂ and D 1.
_2, the flow of _{C 2} loop, or current _{I 1} flows through the capacitor _{C 2,} the current _{I 2} does not flow through the capacitor _{C 1.} Therefore, even if the capacitors C ₁ and C ₂ have some impedance, interference does not occur between the tuning circuits (1) and (2). Therefore, abnormal oscillation occurs or the operation becomes unstable. There is nothing to do.

Further, the local oscillation signal is not radiated to the outside and the feeling during tuning operation is not deteriorated. Moreover, the structure therefor is remarkably simple.

In the example shown in FIG. 8, the elements L ₂ , D ₂ , C ₂ and R are
₂ is connected in the same manner as the elements L ₁ , D ₁ , C ₁ , and R ₁ to form the tuning circuit (2), and the bypass capacitor C ₃ is connected between the cathode terminal K and the ground. This is the case.

Therefore, since the coil L ₁ and the varicap D ₁ are connected in parallel via the capacitor C ₁ , these elements L ₁ and D ₁ act as a tuning circuit (1). Further, since the coil L ₂ and the varicap D ₂ are connected in parallel via the capacitor C ₂ , these elements L ₂ and D ₂ act as a tuning circuit (2).

At this time, the tuning voltage Vc is supplied to the varicap D ₁ by the loop of the power supply (5) → resistor R ₃ → varicap D ₁ → coil L ₁ → resistor R ₁ → power supply (5). , Power supply (5) → resistor R ₃ → varicap D ₂ → coil L ₂ → resistor R ₂ → power supply (5) loop selection voltage V
c is supplied to the varicap D ₂ .

Therefore, the tuning frequency of the tuning circuits (1) and (2) is the tuning voltage Vc.
Changes in conjunction with.

Then, in this case, the resonance current I ₁ of the tuning circuit (1) flows through the loop of the elements L ₁ , D ₁ , and C ₁ , and the resonance current I ₂ of the tuning circuit (2) changes to the elements L ₂ , D ₂ , Through the C ₂ loop,
Current _{I 1} or flows through capacitor _{C 2,} the current _{I 2} does not flow through the capacitor _{C 1.} Therefore, the capacitor C
Tuning circuit even if C ₁ and C ₂ have some impedance
No interference occurs between (1) and (2), and therefore abnormal oscillation does not occur and the operation does not become unstable.

In addition, the local oscillation signal does not radiate to the outside, and the feeling during tuning operation does not deteriorate.

[Problems to be solved by the invention]

However, it has been found that the above-mentioned configuration alone causes a trouble.

That is, when the varicaps D ₁ and D ₂ are respectively independent, by devising their arrangement, the varicaps D ₁ and D ₂ are not bonded to each other. However, in the composite varicap D ₁₂ , since the varicaps D ₁ and D ₂ are formed on the same semiconductor chip CP, as shown by the broken line in FIG. 9, there is a gap between the terminals A ₁ and A _2. A stray capacitance C _s is generated. Therefore, the tuning circuit
The resonance voltage generated in (2) leaks to the tuning circuit (1) through the stray capacitance C _s , which causes abnormal oscillation, unstable operation, or radiation of a local oscillation signal.

The present invention intends to solve such a problem as well.

[Means for solving problems]

In the present invention, a neutralizing capacitor is connected between the tuning circuits (1) and (2).

[Action]

The stray capacitance C _S is canceled and equivalently no longer exists.

〔Example〕

In FIG. 1, the tuning circuits (1) and (2) are constructed as described in FIG. 7, for example. Furthermore, the terminal A ₂
A neutralizing capacitor C _n is connected between the common connection point of the elements L ₁ , C ₁ , and R ₁ . In this case, C _n = C ₁ · C _s / C _v (i) C _v : the capacity of the varicap D ₁ .

With such a configuration, the equivalent circuit becomes a bridge circuit as shown in FIG. And at this time, (i)
Since the bridge circuit is balanced by the formula, the resonance voltage generated in the tuning circuit (2) does not appear across the coil L ₁ , that is, equivalently, the resonance voltage generated in the tuning circuit (2). Does not leak to the tuning circuit (1) through the stray capacitance C _S. Therefore, abnormal oscillation, unstable operation, radiation of a local oscillation signal, or the like does not occur.

In order for the bridge circuit of FIG. 2 to be perfectly balanced, it is necessary to change the capacitance C _v of the varicap D ₁ , that is, the capacitance of the capacitor C _n according to the change of the reception frequency. , since the impact of higher stray capacitance C _S capacity C _v is small increases, the capacity C _v
It suffices to set the capacitance of the capacitor C _n so that the expression (i) is satisfied in the vicinity of the minimum.

For example, when the reception band is the medium wave band, the range of the capacitance C _v is 500 pF to 30 pF as the varicap D ₁ , and the stray capacitance C is
_S having a value of 30 mpF to 50 mpF is used, and an external capacitor is added to this to set the minimum value of the capacity (combined capacity) C _v to 45 pF. Further, since the capacitor C ₁ needs to be sufficiently larger than the capacitance C _v , it is set to 6800 pF. Then,
(When _{C S} = _30mpF) from equation (i) _{C n = 6800 × 30 × 10} -3 / 45 4.5pF ( when _{C S} = _{50mpF) C n 7.6pF} Tosureba well, suspended in a relatively small volume The capacity C _S can be canceled.

Thus, according to the present invention, even if the composite varicap D ₁₂ is used, the influence of the stray capacitance C _S can be reduced, and abnormal oscillation, unstable operation, radiation of a local oscillation signal, etc. do not occur, and The good characteristics of the burr cap D ₁₂ can be fully utilized. Further, it is only necessary to add the capacitor C _n , which is low cost.

Incidentally, in the above, the resistor R ₃ may not be connected.

〔The invention's effect〕

According to the present invention, even if the composite varicap D ₁₂ is used, the influence of the stray capacitance C _S can be reduced, and abnormal oscillating, unstable operation or radiation of a local oscillation signal does not occur, and the composite varicap is The good characteristics of D ₁₂ can be fully utilized. Further, it is only necessary to add the capacitor C _n , which is low cost.

[Brief description of drawings]

FIG. 1 is a connection diagram of an example of the present invention, and FIGS. 2 to 9 are diagrams for explaining the same. (1) and (2) are tuning circuits, and D ₁₂ is a composite varicap.

Claims (1)

[Claims] 1. A first variable capacitance diode and a second variable capacitance diode, wherein one electrode of each of the first and second variable capacitance diodes is taken out as an independent terminal, and the other electrode is taken out as a common terminal. Using the composite variable capacitance diode described above, the first and second variable capacitance diodes are connected to the first and second tuning coils as tuning elements, respectively, and the first and second tuning circuits are provided. In the configured tuning circuit device, the independent terminals of the first and second variable capacitance diodes are directly connected to one terminals of the first and second tuning coils, respectively. The common terminal of the two variable capacitance diodes is connected to the other terminals of the first and second tuning coils through the first and second bypass capacitors, respectively. A control voltage is supplied in parallel to the first and second variable capacitance diodes, the tuning frequency of the first and second tuning circuits is changed in conjunction with the control voltage, and the second variable capacitance diode is also operated. And the independent terminal of
A tuning circuit device in which a capacitor having a predetermined value related to a stray capacitance between the first and second variable capacitance diodes is connected between a connection point of the first tuning coil and the bypass capacitor.