JPH08330871A - Variable attenuating circuit - Google Patents

Abstract

PURPOSE: To reduce the chip area of an intergrated circuit by respectively omitting a exclusive power source for generating an attenuation quantity control voltage and an inductor for increasing an input/output impedance when a variable attenuator circuit for a high frequency signal route is incorporated in the integrated circuit. CONSTITUTION: The high frequency signal route is provided with a depression- type FET 30 which is serially inserted between drain sources. FET 30 is provided with first resistance element 11 and the second resistance element 12 whose respective one ends are connected to the drain sources, whose respective other ends are connected to a prescribed positive voltage power source node 15 and which is for obtaining the required impedance characteristic in the high frequency signal route. A system is constituted by connecting the third resistance element 13 between the gate of FET 30 and an attenuation quantity control voltage impression node 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a variable attenuation circuit formed in, for example, a microwave integrated circuit, and more particularly to a MESF.
The present invention relates to a variable attenuation circuit for high frequency signals using ET (metal-semiconductor junction type field effect transistor), and is used for wireless communication equipment such as personal handyphones and digital cordless telephones.

[0002]

2. Description of the Related Art FIGS. 4 and 5 show a depletion type ME formed in a GaAs (gallium arsenide) integrated circuit.
A conventional example of a variable attenuation circuit for a high frequency signal using an SFET will be shown. In the variable attenuation circuit shown in FIG. 4, the drain-source of the depletion-type FET 30 for variable resistance is inserted in series in the high-frequency signal path, and between the both ends (drain-source) of the FET and the ground node. Inductors 41 and 42 are connected to each other. As a result, the drain and source of the FET 30 are set to the ground potential in terms of direct current. The gate of the FET 30 is connected to the control node 44 via the resistance element 43, and the control voltage Vcont is applied to the control node 44.

In FIG. 5, the drain-source of a depletion type FET 30 for variable resistance is connected between a high frequency signal path and a ground node, and an inductor 45 is provided between the high frequency signal path and the ground node. It is connected. As a result, the drain / source of the FET 30 is set to the ground potential in terms of direct current. And the FE
The gate of T30 is connected to the control node 44 via the resistance element 43.
Connected to the control node 44.
cont is applied.

In the configurations shown in FIGS. 4 and 5 as described above, in order to variably control the drain-source resistance of the FET 30, control in a voltage range lower than the drain-source voltage (here, a negative voltage range) is performed. It is necessary to apply a voltage. When the absolute value of the negative control voltage is larger than a predetermined value, the drain-source resistance of the FET 30 is maximum, and as the absolute value of the negative control voltage becomes smaller, the drain-source resistance of the FET 30 gradually decreases. . Thereby, it is possible to variably control and output the attenuation amount with respect to the input signal (high frequency signal) of the high frequency signal path.

In this case, in the configuration of FIG. 4, it is possible to control so that the attenuation amount for the input signal increases as the absolute value of the negative control voltage increases, and in the configuration of FIG. 5, the negative control voltage can be controlled. It is possible to control in such a direction that the amount of attenuation with respect to the input signal becomes larger as the absolute value of becomes smaller.

By the way, the output of the negative power source 50 is input to the voltage variable circuit 51 in order to generate the control voltage in the negative range, and the negative power source 50 is connected to the high frequency signal path. A positive power supply voltage Vcc externally supplied to the integrated circuit as an operating power supply for the above is generated by a DD converter (DC-DC conversion circuit). This complicates the configuration of the power supply circuit of the integrated circuit and increases the chip area of the integrated circuit.

Further, the inductors 41, 42, 45
Is provided such that the input impedance or the input / output impedance of the variable attenuation circuit is higher than that of a high frequency signal of a predetermined frequency.
Alternatively, by incorporating 45 in the integrated circuit, the chip area of the integrated circuit increases.

[0008]

As described above, the conventional variable attenuating circuit using the depletion type FET requires a power supply circuit dedicated to the generation of the control voltage, which complicates the structure of the power supply circuit. However, there is a problem in that the chip area becomes large when it is built in, and the chip area also becomes large in the point that the inductor is used.

The present invention has been made to solve the above-mentioned problems, and the operating power supply of the circuit connected to the high-frequency signal path is also used as the power supply for generating the attenuation control voltage, so that the power supply dedicated to the control voltage generation is provided. Can be omitted, and by having a high resistance element for increasing the input / output impedance, the inductor can be omitted, and the chip area can be reduced when incorporated in an integrated circuit. The purpose is to provide.

[0010]

The variable attenuator circuit of the first invention is such that a depletion type FET in which a drain and a source are inserted in series in a high-frequency signal path and one end of each is connected to the drain and the source of the FET. First and second resistance elements each having the other end connected to a predetermined positive voltage power supply node and having a high resistance value for obtaining desired impedance characteristics of the high frequency signal path, The FE
A third resistance element is connected between the gate of T and the attenuation control voltage application node.

The variable attenuating circuit of the second invention is connected between a depletion type FET in which one of a drain and a source is connected to a high frequency signal path and the other of the drain and the source of the FET and a ground node. One end is connected to the capacitor and the drain / source of the FET, and the other end is connected to a predetermined positive voltage power supply node, and has a high resistance value for obtaining desired impedance characteristics of the high frequency signal path. And a third resistance element connected between the gate of the FET and the attenuation control voltage application node. A variable attenuator circuit of a third invention is characterized in that the variable attenuator circuit of the first invention and the variable attenuator circuit of the second invention are cascade-connected.

[0012]

In the variable attenuation circuit of the present invention, since a positive voltage is applied to the drain and source of the FET through the first resistance element and the second resistance element correspondingly, the FE
In order to variably control the drain-source resistance of T, a control voltage in a positive voltage range lower than the drain-source voltage may be applied. That is, when the absolute value of the positive control voltage is smaller than a predetermined value (for example, 0V), the drain of the FET
The resistance between the sources is the maximum, and the resistance between the drain and the source of the FET gradually decreases as the absolute value of the positive control voltage increases. Thereby, it is possible to variably control and output the attenuation amount with respect to the input signal (high frequency signal) of the high frequency signal path.

Therefore, by using the operating power source of the circuit connected to the high frequency signal path also as the power source for generating the attenuation amount control voltage, it becomes possible to omit the power source dedicated to the control voltage generation, and the input / output impedance is also reduced. Since it has a high resistance element for increasing the input voltage, it is possible to omit the inductor for increasing the input / output impedance.
When incorporated in an integrated circuit, the chip area can be reduced.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a variable attenuator circuit for a high frequency signal using a depletion type MESFET formed in a GaAs integrated circuit as a first embodiment of the variable attenuator circuit of the present invention.

This variable attenuator circuit has a depletion-type FET 30 for variable resistance in which a drain and a source are inserted in series in a high-frequency signal path, and one end is connected to the drain and the source of the FET 30, and each has a predetermined positive voltage. A voltage (for example, 5 V) is applied, and the first resistance element 11 and the second resistance element 12 formed to have high resistance values for obtaining desired impedance characteristics of the high-frequency signal path, and the FET 30. The third resistance element 13 is connected between the gate and the attenuation amount control voltage application node 14. In this case, the first resistance element 11 and the second resistance element 12 have the same resistance value, for example, and the other ends thereof are commonly connected to the positive voltage power supply node 15.

The positive power supply voltage Vcc supplied to the positive voltage power supply node 15 serves both as a power supply for operating a circuit connected to the high frequency signal path, for example, an amplifier circuit 16 and a power supply for generating an attenuation amount control voltage. , And the positive power supply voltage V
A voltage variable circuit 17 is provided which receives cc and generates an attenuation amount control voltage + Vcont to be applied to the attenuation amount control voltage application node 14.

In the configuration of FIG. 1 as described above, the FE
The same positive voltage is applied to the drain and source of T30 through the first resistance element 11 and the second resistance element 12 correspondingly. Therefore, in order to variably control the drain-source resistance of the FET 30, the control voltage + Vcont in a positive voltage range lower than the drain-source voltage may be applied.

That is, when the absolute value of the positive control voltage + Vcont is smaller than a predetermined value (for example, 0V), the FET 3 is
The drain-source resistance of 0 is the maximum, and as the absolute value of the positive control voltage + Vcont increases, the above FET3
The drain-source resistance of 0 gradually decreases. Thereby, it is possible to variably control and output the attenuation amount with respect to the input signal (high frequency signal) of the high frequency signal path. In this case, it is possible to control the attenuation amount for the input signal to increase as the absolute value of the positive control voltage + Vcont decreases.

According to the variable attenuation circuit of the first embodiment,
A positive power supply voltage Vcc externally supplied to the integrated circuit as an operating power supply for the amplifier circuit 16 connected to the high frequency signal path.
Is also used as the power supply for generating the attenuation control voltage, and this is input to the voltage variable circuit 17 to generate the control voltage Vcont, so that the power supply dedicated to the control voltage generation can be omitted, so that the chip of the integrated circuit can be omitted. It becomes possible to reduce the area. Further, since the high resistance elements 11 and 12 for increasing the input / output impedance are provided, the inductor for increasing the input / output impedance can be omitted, and in this respect also, the chip area of the integrated circuit can be reduced. It will be possible.

FIG. 2 shows, as a second embodiment of the variable attenuator circuit of the present invention, a variable attenuator circuit for high frequency signals using a depletion type FET formed in a GaAs integrated circuit.

The variable attenuator circuit 20 includes a depletion-type FET 30 for a variable resistor in which one of a drain and a source (a drain in this example) is connected to a high-frequency signal path, and the other of the drain and the source of the FET (the present example). Then the source)
A capacitor 21 connected between the FE and the ground node,
One end is connected to the drain / source of T30, and the other end is applied with a predetermined positive voltage (for example, 5 V) to have a high resistance value for obtaining desired impedance characteristics of the high-frequency signal path. First resistance element 1
It comprises first and second resistance elements 12 and a third resistance element 13 connected between the gate of the FET 30 and the attenuation amount control voltage application node 14. In this case, the first
The resistance element and the second resistance element have the same resistance value, and the other ends thereof are commonly connected to the positive voltage power supply node 15.

In the configuration of FIG. 2 as described above, the FE
The same positive voltage is applied to the drain and source of T30 via the first resistance element 11 and the second resistance element 12 corresponding to each other, and the source of the FET 30 is cut off from the ground node in terms of direct current by the capacitor 21. However, it is grounded in terms of alternating current (high frequency) due to the capacity. Therefore, in order to variably control the drain-source resistance of the FET 30, the control voltage + Vcont in a positive voltage range lower than the drain-source voltage may be applied.

That is, when the absolute value of the positive control voltage + Vcont is smaller than a predetermined value (for example, 0V), the drain-source resistance of the FET is maximum, and the positive control voltage +
The drain-source resistance of the FET 30 gradually decreases as the absolute value of Vcont increases. Thereby, it is possible to variably control and output the attenuation amount with respect to the input signal (high frequency signal) of the high frequency signal path. In this case, it is possible to control the attenuation amount for the input signal to increase as the absolute value of the positive control voltage + Vcont increases.

In the variable attenuator circuit 20 of the second embodiment as well, similar to the variable attenuator circuit 10 of the first embodiment, the operating power source such as the amplifier circuit 16 connected to the high frequency signal path is used to generate the attenuation amount control voltage. Since it can be omitted as a power supply dedicated to control voltage generation by also serving as a power supply for the IC, the chip area of the integrated circuit can be reduced and a high resistance element for increasing the input / output impedance can be provided. Since it has, the inductor can be omitted, and the chip area of the integrated circuit can be reduced also in this respect.

FIG. 3 shows a variable attenuator circuit for high frequency signals using a depletion type FET formed in a GaAs integrated circuit as a third embodiment of the variable attenuator circuit of the present invention.

In this variable attenuator circuit, the variable attenuator circuit (first variable attenuator circuit) 31 shown in FIG. 1 and the variable attenuator circuit (second variable attenuator circuit) 32 shown in FIG. 15 are shared and are cascade-connected. In this case, the second resistance element 12 of the first variable attenuation circuit 31 and the first resistance element 11 of the second variable attenuation circuit 32 can be integrated into one.

Further, the control voltage is independently applied to the attenuation amount control voltage application node 141 of the first variable attenuation circuit 31 and the attenuation amount control voltage application node 142 of the second variable attenuation circuit 32, so that the first It is possible to independently control the attenuation amount of the variable attenuation circuit 31 and the attenuation amount of the second variable attenuation circuit 32. For example, by controlling each attenuation amount to the maximum state, the variable attenuation circuit of FIG. It becomes possible to almost completely prevent the high-frequency signal from leaking from the input node to the output node of the circuit.

In the variable attenuator circuit of the third embodiment, as in the variable attenuator circuits of the first and second embodiments, the operating power supply 17 such as the amplifier circuit 16 connected to the high frequency signal path is attenuated. Since the power supply dedicated to the control voltage generation can be omitted by also serving as the power supply for the quantity control voltage generation, the chip area of the integrated circuit can be reduced and the input / output impedance can be increased. Since the high resistance element is provided, the inductor can be omitted, and the chip area of the integrated circuit can be reduced also in this respect.

[0029]

As described above, according to the variable attenuation circuit of the present invention, the operating power source of the circuit connected to the high frequency signal path is also used as the power source for generating the attenuation amount control voltage, so that the power source dedicated to the control voltage generation is used. Can be omitted,
By having a high resistance element for increasing the input / output impedance, the inductor can be omitted, and the chip area can be reduced when incorporated in an integrated circuit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a variable attenuation circuit for a high frequency signal according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a variable attenuator circuit for high frequency signals according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a variable attenuation circuit for high frequency signals according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing an example of a conventional variable attenuation circuit for high-frequency signals.

FIG. 5 is a circuit diagram showing another example of a conventional variable attenuation circuit for high frequency signals.

[Explanation of symbols]

11 ... 1st resistance element, 12 ... 2nd resistance element, 13 ...
3rd resistance element, 14, 141, 142 ... Attenuation control voltage application node, 15 ... Positive voltage power supply node, 16 ... Amplifier circuit, 17 ... Voltage variable circuit, 20, 30 ... Depletion type MESFET for variable resistance, 21 ... Capacitance, 31 ... 1st variable attenuation circuit, 32 ... 2nd variable attenuation circuit.

Claims (5)

[Claims] 1. A depletion type field effect transistor in which a drain and a source are inserted in series in a high frequency signal path, and one end is connected to the drain and the source of the field effect transistor, and the other end is a predetermined positive electrode. First and second resistance elements connected to a voltage power supply node and having high resistance values for obtaining desired impedance characteristics of the high-frequency signal path, gates of the field-effect transistors, and attenuation control A variable attenuation circuit, comprising: a third resistance element connected between the voltage application node and the third resistance element. 2. A depletion type field effect transistor in which one of a drain and a source is connected to a high frequency signal path, a capacitor connected between the other of the drain and the source of the field effect transistor and a ground node, One end is connected to the drain / source of the field effect transistor, and the other end is connected to a predetermined positive voltage power supply node, and is formed to have a high resistance value for obtaining desired impedance characteristics of the high frequency signal path. The first and second
Variable resistance circuit, and a third resistance element connected between the gate of the field effect transistor and an attenuation amount control voltage application node. 3. The variable attenuation circuit according to claim 1 and claim 2.
A variable attenuation circuit comprising the variable attenuation circuit described in a cascade connection. 4. The variable attenuation circuit according to claim 1, wherein the first resistance element and the second resistance element are provided.
2. The variable attenuation circuit, wherein the resistance elements have the same resistance value and the other ends are commonly connected to the positive voltage power supply node. 5. The variable attenuator circuit according to claim 1, wherein the positive power supply voltage supplied to the positive voltage power supply node is an operating power supply of a circuit connected to the high frequency signal path. And a power supply for generating an attenuation amount control voltage, and further comprises a voltage variable circuit which receives the positive power supply voltage and generates an attenuation amount control voltage to be applied to the attenuation amount control voltage applying node. A variable attenuation circuit characterized in that