JPH0770940B2 - Variable capacity device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable capacitance device that switches a capacitance value by turning on / off a switch used in a radio device or an oscillator.

[Conventional technology]

FIG. 3 is a circuit diagram showing a basic circuit of a conventional variable capacitance device, in which 1 is an inverter for inverting an input signal, 2 is a P-channel transistor as a switch provided on a substrate, and 3 is a switch. When an "H" level signal is input to the gate of the N-channel transistor 3 and the gate wiring 8 in the N-channel transistor, N
The resistance value between the source of the channel transistor 3 or the diffusion layer 16 and the end portion 17 of the diffusion layer 16 decreases, and a short-circuit state occurs. Further, when an "L" level signal is input to the gate wiring 8, its resistance value increases and the switch is turned off. The operation of the P-channel transistor 2 is the reverse of the above. When the “H” level signal is input to the gate of the P-channel transistor 2 and the gate wiring 11, the switch is disconnected, and when the “L” level signal is input. It becomes a short state.

Reference numeral 4 is a capacitor, which is formed between the aluminum electrode 10 and the substrate by using the polysilicon 9 as a dielectric. 5 is an aluminum wiring for applying the potential of the polysilicon 9 to a negative voltage power supply terminal which will be described later, 6 is a connection between the above transistors 2 and 3,
A control terminal for applying a control signal of "L" or "H" level for cutting, 7 is a common terminal, 8 is the above gate and gate wiring, 9 is the above polysilicon as a dielectric, and 10 is the above An aluminum electrode, 11 is the above gate and gate wiring, 12 is an N region (N layer) of the semiconductor substrate, 13 is a P region (P layer), 14 is a connection contact between the aluminum wiring 5 and the polysilicon 9, and 15 is A connection contact between a transistor and a wiring, 16 is a source or drain region (diffusion layer) of the N-channel transistor 3, 17 is the end of the source or drain region, 18 is a source or drain region of the P-channel transistor 2, and 19 is this. It is the edge of the source or drain region.

Further, FIG. 4 is an equivalent circuit of the basic circuit constituting the variable capacitance device shown in FIG. 3, and the same circuit parts as those shown in FIG. The description is omitted.

Further, FIG. 5 shows a conventional variable capacitance device in which a plurality of basic circuits 21 to 24 similar to the basic circuit shown in FIG. 3 are arranged side by side on the same substrate. In the figure, reference numeral 25 is a capacitance reference point in the P region including the N-channel transistor 3 and the capacitance 4, that is, a reference capacitance point, which is fixed to a negative voltage potential. Reference numeral 26 is a reference capacitance point in the N region, which is fixed to a positive voltage potential. Further, 6a to 6d are switch control terminals of the respective basic circuits 21 to 24.

Since the power supply (positive voltage power supply, negative voltage power supply) and the ground terminal are AC short-circuited in the electronic circuit with a low impedance that can be neglected AC, they are at the same distance from the adjacent basic circuit. The reference point of the capacitance (capacitor capacitance value) on the basic circuit is the above reference capacitance point.

31 is a negative voltage power supply terminal for fixing the potentials of the polysilicon 9 and the reference capacitance point, and 32 is a common terminal 7 of the basic circuit 21.
The common terminal is connected to the switch control terminals 6a to 6d, and the capacity of the common terminal 32 is changed. 33 is a positive voltage power supply terminal for fixing the potential of the reference capacitance point 26, 34 is a capacitance connected to the common terminal 32, and is a parasitic capacitance on the common terminal 32 side in the variable capacitance device when the transistors 2 and 3 are off. It is the capacity including. The variable capacitance device shown in FIGS. 3 to 5 is connected to other circuits via the common terminal 7.

Next, the operation will be described. In FIG. 3 and FIG. 4, when the “L” level signal is applied to the switch control terminal 6, the output of the inverter 1 becomes “H” level, and the gate of the N-channel transistor 3 and the gate wiring are It goes to "H" level and P-channel transistor 2
The gate and the gate wiring 11 become "L" level, the transistors 2 and 3 are short-circuited, and the capacitor 4 is connected to the common terminal 7 through this switch circuit.

On the contrary, when the "H" level signal is applied to the switch control terminal, the "H" level signal is applied to the gate and gate wiring 11 of the P-channel transistor 2 and to the gate and gate wiring 8 of the N-channel transistor 3. Is applied with an "L" level signal. Therefore, the switch circuit is turned off and the capacitance is not connected to the common terminal 7.

Now, the variable capacitance value in the basic circuit 21 of this variable capacitance device in the short-circuited state and the off-state is the parasitic capacitances C _2-21 and C _{3-21 of the} transistors 2 and ₃ and the capacitance C of the capacitance 4.
It becomes the capacity C ₂₁ which added _4-21 . That is, it becomes like the following formula.

C ₂₁ = C _2-21 + C _3-21 + C _{4-21 In} FIG. 5, basic circuits 22 to 24 similar to the basic circuit 21 shown in FIG. 32 common terminal capacities are taken out according to the “H” level or “L” level applied signals input to the switch control terminals 6a to 6d. For example, when the basic circuits 21, 22, and 23 are on, the common terminal capacitance is C _C1 = C ₃₄ + C ₂₁ + C ₂₂ + C ₂₃ (1), and when only the basic circuit 21 is on, The common terminal capacitance is C _C2 = C ₃₄ + C ₂₁ , and the capacitance change amount is C ₂₂ + C ₂₃ .

[Problems to be solved by the invention]

Since the conventional variable capacity device is configured as described above, the capacities C _{21 to} C ₂₄ of the basic circuits ₂₁ to ₂₄ are the reference capacity points 2 respectively.
Although set based on 5,26, these are basic circuits 21 ~
Since the capacitors are connected via the resistors in the 24 semiconductor chips, the reference of the capacitance value is from the reference capacitance points 25 and 26 to each basic circuit 21.
There is a problem that the capacitance value is different due to the difference in the distance, even if the basic circuits 21 to 24 are the same, in proportion to the distance to.

That is, when explaining the circuit diagram equivalently shown in FIG. 6, the capacitance value C ₂₁ of the basic circuit is When the basic circuits 21 and 22 are the same, C ₂₁ ′ = C ₂₂ ′, and therefore C ₂₂ = C ₂₁ . On the other hand, the capacitance value of the basic circuit 23
C ₂₃ is Therefore, even if C ₂₁ ′ = C ₂₃ ′, C ₂₁ ≠ C ₂₃ .

That is, there is a problem in that the capacitance value is different due to the difference in the distance between the basic circuit and the reference capacitance point as described above.

The present invention has been made to solve the above problems, and to obtain a variable capacitance device capable of maintaining a constant capacitance value by making the distance between each basic circuit and the reference capacitance point the same. With the goal.

[Means for solving problems]

In the variable capacitance device according to the present invention, a reference capacitance point is arranged for each of a plurality of basic circuits at equidistant positions where the capacitance changes when the transistors of each basic circuit are turned on or off are equal. Is.

[Action]

In the present invention, one or two or more reference capacitance points are located at positions on the same semiconductor chip (substrate) that are equidistant to any of the basic circuits, so that the switches, which are transistors of each basic circuit, are It acts so that the capacitance change due to turning on and off, especially the capacitance change at the common terminal, can be set equally and highly accurately for each basic circuit.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 46 to 49 are basic circuits having the same structure as the basic circuit 21 shown in FIG. 3, and these internal circuits are shown in FIG.
The structure (pattern) is symmetrical with respect to the line C-D. Then, reference capacitance points 50 to 53 are arranged at positions equidistant from each of these basic circuits 46 to 49, respectively.
The capacitance change that changes when a transistor as a switch (semiconductor switch) that configures is turned on and off is made equal for all basic circuits.
Here, 41 to 44 are switch control terminals, 45 is a common terminal,
54 is a positive voltage power supply terminal and 55 is a negative voltage power supply terminal.

Here, equidistant means that the distance between the basic circuit and the basic circuit is equal. Electrically, in the case of a semiconductor, in the case of a semiconductor, there is an electrical connection between the substrate (bulk) connection point at the point where a hole is made in the semiconductor substrate and the reference capacitance point side electrode of the capacitor (capacitance value) in the substrate circuit. It shows that the impedances are equal.

The basic circuit and the reference capacitance point are mainly integrated circuits that can be easily and accurately formed on a silicon or gallium arsenide substrate. However, other than the integrated circuits, for example, FIGS. When the basic circuit shown in (1) is formed on one board, wiring is performed on this printed board to form an equivalent circuit similar to an integrated circuit, and similar effects can be obtained.

Next, the operation will be described. Since each of the basic circuits 46 to 49 shown in FIG. 1 is at the same distance from each of the reference capacitance points 50 to 53 at the same potential from the circuit portion such as these transistors and capacitors, the same circuit is provided in the same chip. Have the same bulk resistance. Therefore, if each of the basic circuits 46 to 49 has the same configuration, the same capacitance value can be set based on each reference capacitance point regardless of where they are located in the same chip. As a result, the capacitance value that changes when the transistor is turned on or off can be set equally and highly accurately for each basic circuit.

When the respective basic circuits 46 to 49 are not symmetrically arranged, for example, in FIG.
The circuit may be configured so that is symmetrical with respect to the line AB.

FIG. 2 shows another embodiment of the present invention. According to this
By connecting three basic circuits 47 to 49 other than the basic circuit 46 to the common switch control terminal 56, one basic circuit 46
It is possible to accurately control the capacity with a capacity value three times larger than that of

The above basic circuit can employ the same circuit configuration as that shown in FIG. 4, and one common terminal of the switches of the P-channel transistor 2 and the N-channel transistor 3 having complementary characteristics is connected to the common terminal 7. Connect to
It is possible to connect the capacitor 4 to the other common terminal. In addition, one of the P-channel transistor 2 and the N-channel transistor 3 is used as a semiconductor switch, one terminal of which is connected to the common terminal 7 to which a reference voltage is applied, and the other terminal is connected to the capacitor 4. It can be connected. The capacitance can be controlled by turning on / off each of these transistors 2 and 3.

Further, the capacitance 4 can be connected in series to the P-channel transistor 2 or the N-channel transistor 3 as a switch as described above, or can be connected in parallel (not shown) or can be connected in series-parallel.

〔The invention's effect〕

As described above, according to the present invention, the reference capacitance points are arranged at equidistant positions with respect to each of the plurality of basic circuits so that the capacitance changes when the switches of the respective basic circuits are turned on or off are equal. Since it is configured as described above, it is possible to equalize the capacitance change when the above switch is turned on or off for each basic circuit, and obtain a variable capacitance device with high capacitance value accuracy, and make a radio device or an oscillation device with stable operation. There is an effect that what can be obtained.

[Brief description of drawings]

FIG. 1 is a block connection diagram showing a variable capacitance device according to an embodiment of the present invention, FIG. 2 is a block connection diagram showing another embodiment of the present invention, and FIG. 3 is a basic circuit used in the prior art and the present invention. FIG. 4, FIG. 4 is an equivalent circuit diagram of a basic circuit, FIG. 5 is a block diagram showing a conventional variable capacitance device, and FIG. 6 is an equivalent circuit diagram of FIG. 2, 3 are switches (semiconductor switches), 4 are capacitors, 46-49
Is the basic circuit, 50 to 53 are the reference capacity points. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (5)

[Claims] 1. A plurality of basic circuits each consisting of a switch for connecting or disconnecting a circuit and a capacitor connected to the switch are connected in parallel and fixed to a set potential of a positive voltage power source or a negative voltage power source serving as a reference of the capacitance. In the variable capacitance device having the reference capacitance point, the reference capacitance point is arranged at an equal distance position with respect to each of the basic circuits so that the capacitance change due to the connection or disconnection of the switch is equal for each of the basic circuits. A variable capacitance device characterized in that 2. The variable capacitance device according to claim 1, wherein the switch is a semiconductor switch. 3. The variable capacitance device according to claim 1, wherein the basic circuit and the reference capacitance point are formed by an integrated circuit. 4. The switch is composed of two semiconductor switches having complementary characteristics and connected in parallel with each other, and one common terminal of each semiconductor switch is connected to a common terminal.
The variable capacitance device according to claim 1, wherein a capacitor having a predetermined capacitance is connected to the other common terminal. 5. The switch comprises one semiconductor switch, one terminal of which is connected to a common terminal to which a reference voltage is applied, and the other terminal of which is connected a capacitor. A variable capacitance device according to claim 1.