Amplifier circuit

Abstract

To provide an amplifier circuit capable of establishing impedance matching without using an open / close switch.SOLUTION: An amplifier circuit includes an impedance matching circuit at either or both of the input and output of a basic circuit, the impedance matching circuit includes a variable capacitance circuit whose capacitance can be freely varied by a control voltage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an amplifier circuit.

Background Art

[0002] Patent Document 1 below discloses a low-noise amplifier (LNA) for high-frequency signals having an impedance matching circuit at its input and output. This low-noise amplifier employs a series resonance circuit in which an inductor and a capacitor are directly connected as an impedance matching circuit, and by connecting an open / close switch in series to this series resonance circuit, it enables connection / disconnection of the impedance matching circuit to the input and output of the source-grounded circuit. Such a low-noise amplifier can adjust the frequency band and achieve impedance matching of the input impedance and the output impedance by connecting / disconnecting the impedance matching circuit.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the above low-noise amplifier (amplifier circuit), since a series resonance circuit in which an open / close switch is connected in series to the input and / or output of the source-grounded circuit is provided, when the open / close switch is set to the ON state and the series resonance circuit is connected to the input and / or output of the source-grounded circuit, power loss (power loss) occurs in the input signal and / or output signal due to the ON resistance of the open / close switch.

[0005] In addition, in the above low-noise amplifier, since the on-off switch has an ON resistance, the on-off switch acts as a noise source with respect to the input signal and / or the output signal. For example, in the frequency band of the millimeter-wave band, due to the ON resistance of the on-off switch, the gain reduction and the deterioration of the noise characteristics become remarkable.

[0006] The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an amplifier circuit capable of establishing impedance matching without using an on-off switch.

Means for Solving the Problems

[0007] In order to achieve the above object, in the present invention, as a first solution means related to the amplifier circuit, an amplifier circuit including an impedance matching circuit in either one or both of the input and output of the basic circuit, wherein the impedance matching circuit includes a variable capacitance circuit whose capacitance can be variably controlled by a control voltage.

[0008] In the present invention, as a second solution means related to the amplifier circuit, in the first solution means, the variable capacitance circuit includes a MOS transistor in which a source terminal and a drain terminal are connected as a variable capacitance element.

[0009] In the present invention, as a third solution means related to the amplifier circuit, in the first or second solution means, the impedance matching circuit includes a first impedance matching circuit connected in parallel to the output of the basic circuit and a second impedance matching circuit connected in series to the output of the basic circuit.

[0010] In the present invention, as a fourth solution means related to the amplifier circuit, in the third solution means, the second impedance matching circuit includes an inductor in addition to the variable capacitance circuit.

[0011] In the present invention, as a fifth solution means related to the amplifier circuit, in the above-described third or fourth solution means, a pair of the second impedance matching circuits is provided, and each of the pair of control voltages is set in a voltage region where the temperature characteristics are reversed.

[0012] In the present invention, as a sixth solution means related to the amplifier circuit, in the above-described fourth or fifth solution means, a pair of the second impedance matching circuits share one of the inductors.

[0013] In the present invention, as a seventh solution means related to the amplifier circuit, in any of the above-described third to sixth solution means, a pair of the first impedance matching circuits is provided, and each of the pair of control voltages is set in a voltage region where the temperature characteristics are reversed.

Advantages of the Invention

[0014] According to the present invention, it is possible to provide an amplifier circuit capable of establishing impedance matching without using an open / close switch.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0016] Hereinafter, with reference to the drawings, the first embodiment and the second embodiment of the present invention will be described. 〔First Embodiment〕 First, the first embodiment will be described with reference to FIG. 1. As shown in FIG. 1, the high-frequency amplification circuit A according to the first embodiment includes an RF input terminal 1, an input capacitor 2, a bias resistor 3, a bias terminal 4, a transistor 5, an output inductor 6, a first output capacitor 7, a first impedance matching circuit 8, a second output capacitor 9, a second impedance matching circuit 10, an RF output terminal 11, and a load resistor 12.

[0017] Note that this high-frequency amplification circuit A corresponds to the amplification circuit according to the present invention. Among these multiple components, the RF input terminal 1, the input capacitor 2, the bias resistor 3, the bias terminal 4, the transistor 5, and the output inductor 6 constitute the basic circuit M of the high-frequency amplification circuit A.

[0018] Also, as shown in the figure, the first impedance matching circuit 8 includes a first variable capacitance element 8a, a first control resistor 8b, and a first control terminal 8c. Further, as shown in the figure, the second impedance matching circuit 10 includes a second variable capacitance element 10a, a matching inductor 10b, a second control resistor 10c, and a second control terminal 10d.

[0019] The RF input terminal 1 is a connection terminal for receiving a high-frequency signal Vin with a predetermined frequency (predetermined wavelength) from the outside. This RF input terminal 1 is connected to the source of the high-frequency signal Vin outside the high-frequency amplification circuit A and is also connected to one end of the input capacitor 2 inside the high-frequency amplification circuit A. Note that the high-frequency signal Vin is an input signal having a frequency band in the millimeter-wave band, for example.

[0020] One end of the input capacitor 2 is connected to the RF input terminal 1, and the other end is connected to one end of the bias resistor 3 and the input terminal (gate terminal) of the transistor 5. This input capacitor 2 has a predetermined capacitance and is a coupling capacitor that transmits only the AC component of the high-frequency signal Vin from one end to the other end. That is, the DC component of the high-frequency signal Vin is blocked by the input capacitor 2 and is not applied to one end of the bias resistor 3 and the input terminal (gate terminal) of the transistor 5.

[0021] The bias resistor 3 has one end connected to the other end of the input capacitor 2 and the input terminal (gate terminal) of the transistor 5, and the other end connected to the bias terminal 4. This bias resistor 3 has a predetermined resistance value and applies the bias voltage Vb applied from the bias terminal 4 to the input terminal (gate terminal) of the transistor 5.

[0022] The bias terminal 4 is a connection terminal that receives a bias voltage Vb of a predetermined voltage (DC voltage) from the outside. This bias terminal 4 is connected to the source of the bias voltage Vb outside the high-frequency amplification circuit A and is also connected to the other end of the bias resistor 3 inside the high-frequency amplification circuit A.

[0023] The transistor 5 is an N-channel MOS (Metal Oxide Semiconductor) type field effect transistor as shown in the figure. This transistor 5 has its input terminal (gate terminal) connected to the other end of the input capacitor 2 and one end of the bias resistor 3, its source terminal connected to the ground potential (GND), and its drain terminal (output terminal) connected to one end of the output inductor 6, one end of the first output capacitor 7, and one end of the second output capacitor 9.

[0024] That is, this transistor 5 is an amplification transistor in a source-grounded connection form. This transistor 5 inverts and amplifies the high-frequency signal Vin input to the gate terminal via the input capacitor 2 and outputs it to the drain terminal in a state where the gate bias voltage is set by the bias voltage Vb.

[0025] The output inductor 6 has one end connected to the drain terminal of the transistor 5, one end of the first output capacitor 7, and one end of the second output capacitor 9, and the other end connected to the power supply V DD is connected thereto. This output inductor 6 has a predetermined inductance and functions as a load (inductive load) of the transistor 5. Also, this output inductor 6 is connected to the power supply V DDA predetermined DC voltage (power supply voltage) supplied from [source] is applied to the drain terminal of transistor 5.

[0026] The basic circuit M in the first embodiment is a source-grounded inverting amplifier circuit composed of the input capacitor 2, bias resistor 3, bias terminal 4, transistor 5, and output inductor 6 described above. That is, this basic circuit M mainly inverts and amplifies the high-frequency signal Vin based on the bias voltage Vb and the inductance of the output inductor 6, and outputs it to one end of the first output capacitor 7 and one end of the second output capacitor 9.

[0027] One end of the first output capacitor 7 is connected to the drain terminal of the transistor 5, one end of the output inductor 6, and one end of the second output capacitor 9, and the other end is connected to one end of the first impedance matching circuit 8. This first output capacitor 7 has a predetermined capacitance and is a coupling capacitor that transmits only the AC component of the output signal Vout from one end to the other end.

[0028] The first impedance matching circuit 8 is a circuit for matching (matching) the output impedance of the high-frequency amplifier circuit A with the subsequent circuit of the high-frequency amplifier circuit A. One end is connected to the other end of the first output capacitor 7, and the other end is connected to the ground potential (GND). The first impedance matching circuit 8 is connected in parallel to the drain terminal of the transistor 5, that is, the output of the basic circuit M.

[0029] The first variable capacitance element 8a is an N-channel MOS field-effect transistor with its source terminal and drain terminal connected as shown in the figure. One end (gate terminal) of the first variable capacitance element 8a is connected to the other end of the first output capacitor 7 and one end of the first control resistor 8b, and the other end (source terminal and drain terminal) is connected to the ground potential (GND).

[0030] **Note**: The word "から" in is translated as "[source]" here because its specific meaning depends on the context. If there is more context information, a more accurate translation can be provided.One end of the first control resistor 8b is connected to the other end of the first output capacitor 7 and one end of the first variable capacitor 8a, and the other end is connected to the first control terminal 8c. The first control resistor 8b has a predetermined resistance value and applies the first control voltage Vb1 input from the first control terminal 8c to one end of the first variable capacitor 8a.

[0031] The first control terminal 8c is a connection terminal for receiving the first control voltage Vb1 from the outside. The first control terminal 8c is connected to the source of the first control voltage Vb1 outside the high-frequency amplification circuit A and connected to the other end of the first control resistor 8b inside the high-frequency amplification circuit A. The first control voltage Vb1 is a DC voltage within a predetermined range.

[0032] In such a first impedance matching circuit 8, the capacitance of the first variable capacitor 8a changes within a predetermined range according to the first control voltage Vb1 applied to one end of the first variable capacitor 8a via the first control resistor 8b. That is, the first impedance matching circuit 8 is a first variable capacitance circuit in which the capacitance of the first variable capacitor 8a can be freely changed by the first control voltage Vb1 and has a first variable capacitance.

[0033] One end of the second output capacitor 9 is connected to the drain terminal of the transistor 5, one end of the output inductor 6, and one end of the first output capacitor 7, and the other end is connected to one end of the second impedance matching circuit 10. The second output capacitor 9 has a predetermined capacitance and is a coupling capacitor that transmits only the AC component of the output signal Vout from one end to the other end.

[0034] The second impedance matching circuit 10 is a circuit for matching (matching) the output impedance of the high-frequency amplification circuit A with the subsequent circuit of the high-frequency amplification circuit A, similar to the first impedance matching circuit 8. One end of the second impedance matching circuit 10 is connected to the other end of the second output capacitor 9, and the other end is connected to one end of the RF output terminal 11 and the load resistor 12. Also, the second impedance matching circuit 10 is connected in series to the output of the basic circuit M.

[0035] The second variable capacitance element 10a is an N-channel MOS field-effect transistor with its source terminal and drain terminal connected, similar to the first variable capacitance element 8a in the first impedance matching circuit 8. One end (gate terminal) of the second variable capacitance element 10a is connected to the other end of the second output capacitor 9 and one end of the second control resistor 10c, and the other end (source terminal and drain terminal) is connected to one end of the matching inductor 10b.

[0036] One end of the matching inductor 10b is connected to the other end of the second variable capacitance element 10a, and the other end is connected to one end of the RF output terminal 11 and the load resistor 12. This matching inductor 10b has a predetermined inductance and forms a series resonance circuit with the second variable capacitance element 10a.

[0037] One end of the second control resistor 10c is connected to the other end of the second output capacitor 9 and one end of the second variable capacitance element 10a, and the other end is connected to the second control terminal 10d. The second control resistor 10c has a predetermined resistance value and applies the second control voltage Vb2 input from the second control terminal 10d to one end of the second variable capacitance element 10a.

[0038] The second control terminal 10d is a connection terminal for receiving the second control voltage Vb2 from the outside. The second control terminal 10d is connected to the source of the second control voltage Vb2 outside the high-frequency amplification circuit A and to the other end of the second control resistor 10c inside the high-frequency amplification circuit A. The second control voltage Vb2 is a DC voltage within a predetermined range.

[0039] In such a second impedance matching circuit 10, the capacitance of the second variable capacitor element 10a changes within a predetermined range in response to a second control voltage Vb2 applied to one end of the second variable capacitor element 10a via the second control resistor 10c. That is, the second impedance matching circuit 10 is a second variable capacitance circuit in which the capacitance of the second variable capacitor element 10a can be freely varied by the second control voltage Vb2, and has a second variable capacitance.

[0040] Further, the second impedance matching circuit 10 variably sets the resonance frequency of the series resonance circuit by the second variable capacitance that is varied by the second control voltage Vb2. That is, the resonance frequency determined by the capacitance of the second variable capacitor element 10a (second variable capacitance) and the inductance of the matching inductor 10b changes according to the set value of the second variable capacitance.

[0041] The RF output terminal 11 is a connection terminal for delivering the output signal Vout to the outside. That is, this RF output terminal 11 is connected to the subsequent-stage circuit of the output signal Vout outside the high-frequency amplification circuit A, and is also connected to the other end of the second impedance matching circuit 10 and one end of the load resistor 12 inside the high-frequency amplification circuit A.

[0042] One end of the load resistor 12 is connected to the other end of the second impedance matching circuit 10 and the RF output terminal 11, and the other end is connected to the ground potential (GND). This load resistor 12 has a predetermined resistance value and functions as a load of the second impedance matching circuit 10.

[0043] Subsequently, the operation of the high-frequency amplification circuit A according to the first embodiment will be described in detail.

[0044] First, in this high-frequency amplification circuit A, the basic circuit M inverts and amplifies the high-frequency signal Vin input from the outside to the RF input terminal 1, and outputs the output signal Vout from the output terminal (the drain terminal of the transistor 5) to one end of the first output capacitor 7 and one end of the second output capacitor 9.

[0045] Then, the output signal Vout is input to the first impedance matching circuit 8 via the first output capacitor 7, and is also input to the second impedance matching circuit 10 via the second output capacitor 9. The first impedance matching circuit 8 sets the first variable capacitance to a desired value by the first control voltage Vb1 applied from the outside to the first control terminal 8c.

[0046] On the other hand, the second impedance matching circuit 10 sets the second variable capacitance to a desired value by the second control voltage Vb2 applied from the outside to the second control terminal 10d. That is, the first variable capacitance in the first impedance matching circuit 8 and the second variable capacitance in the second impedance matching circuit 10 are set so that the output impedance of the high-frequency amplification circuit A matches the input impedance of the subsequent circuit.

[0047] Here, in the high-frequency amplification circuit A according to the first embodiment, instead of using an open / close switch to match the output impedance to the input impedance of the subsequent circuit, the first impedance matching circuit 8 and the second impedance matching circuit 10 that do not use an open / close switch are used to match the output impedance to the input impedance of the subsequent circuit.

[0048] That is, according to the first embodiment, it is possible to provide a high-frequency amplification circuit A (amplification circuit) capable of establishing impedance matching without using an open / close switch. And according to the first embodiment, since an open / close switch is not used, it is possible to suppress a decrease in gain and deterioration of noise characteristics.

[0049] Further, this high-frequency amplification circuit A includes a first impedance matching circuit 8 connected in parallel to the output of the basic circuit M and a second impedance matching circuit 10 connected in series to the output of the basic circuit M. Therefore, according to the first embodiment, it is possible to accurately achieve impedance matching between the output impedance of the high-frequency amplification circuit A and the input impedance of the subsequent circuit.

[0050] Also, this high-frequency amplification circuit A includes two N-channel MOS transistors, that is, a first variable capacitance element 8a and a second variable capacitance element 10a, with their source terminals and drain terminals connected as variable capacitance elements. That is, according to the first embodiment, it is possible to achieve impedance matching with excellent high-frequency characteristics.

[0051] Furthermore, this high-frequency amplification circuit A has the second impedance matching circuit 10 including a matching inductor 10b in addition to the second variable capacitance circuit. According to such a first embodiment, it is possible to more accurately match (match) the output impedance with the input impedance of the subsequent circuit as compared with the case where the matching inductor 10b is omitted.

[0052] 〔Second Embodiment〕 Next, a second embodiment of the present invention will be described with reference to FIG. 2. In this second embodiment, the same reference numerals are given to the same components as in the first embodiment.

[0053] As shown in FIG. 2, the high-frequency amplification circuit B according to the second embodiment includes a third output capacitor 7X and a fourth output capacitor 7Y in place of the first output capacitor 7 of the first embodiment, and a fifth output capacitor 9X and a sixth output capacitor 9Y in place of the second output capacitor 9.

[0054] Further, this high-frequency amplification circuit B includes a third impedance matching circuit 8X, a fourth impedance matching circuit 8Y, a fifth impedance matching circuit 10X, and a sixth impedance matching circuit 10Y in place of the first impedance matching circuit 8 and the second impedance matching circuit 10 of the first embodiment. This high-frequency amplification circuit B corresponds to the amplification circuit according to the present invention.

[0055] A pair of variable capacitance circuits, that is, a third impedance matching circuit 8X and a fourth impedance matching circuit 8Y, are connected in parallel to the output of the basic circuit M in this high-frequency amplification circuit B. Also, a pair of series resonance circuits, that is, a fifth impedance matching circuit 10X and a sixth impedance matching circuit 10Y, are connected in series to the output of the basic circuit M in this high-frequency amplification circuit B.

[0056] One end of the third output capacitor 7X is connected to the drain terminal of the transistor 5, one end of the output inductor 6, one end of the fourth output capacitor 7Y, one end of the fifth output capacitor 9X, and one end of the sixth output capacitor 9Y, and the other end is connected to one end of the third impedance matching circuit 8X. This third output capacitor 7X has a predetermined capacitance and is a coupling capacitor that transmits only the AC component of the output signal from the transistor 5 from one end to the other end.

[0057] One end of the fourth output capacitor 7Y is connected to the drain terminal of the transistor 5, one end of the output inductor 6, one end of the third output capacitor 7X, one end of the fifth output capacitor 9X, and one end of the sixth output capacitor 9Y, and the other end is connected to one end of the fourth impedance matching circuit 8Y. This fourth output capacitor 7Y has a predetermined capacitance and is a coupling capacitor that transmits only the AC component of the output signal from the transistor 5 from one end to the other end.

[0058] The fifth output capacitor 9X has one end connected to the drain terminal of the transistor 5, one end of the output inductor 6, one end of the third output capacitor 7X, one end of the fourth output capacitor 7Y, and one end of the sixth output capacitor 9Y, and the other end is connected to one end of the fifth impedance matching circuit 10X. This fifth output capacitor 9X has a predetermined capacitance and is a coupling capacitor that transmits only the AC component of the output signal from the transistor 5 from one end to the other end.

[0059] The sixth output capacitor 9Y has one end connected to the drain terminal of the transistor 5, one end of the output inductor 6, one end of the third output capacitor 7X, one end of the fourth output capacitor 7Y, and one end of the fifth output capacitor 9X, and the other end is connected to one end of the sixth impedance matching circuit 10Y. This sixth output capacitor 9Y has a predetermined capacitance and is a coupling capacitor that transmits only the AC component of the output signal from the transistor 5 from one end to the other end.

[0060] As shown in the figure, the third impedance matching circuit 8X includes a third variable capacitance element 8ax, a third control resistor 8bx, and a third control terminal 8cx. The fourth impedance matching circuit 8Y includes a fourth variable capacitance element 8ay, a fourth control resistor 8by, and a fourth control terminal 8cy.

[0061] Also, as shown in the figure, the fifth impedance matching circuit 10X includes a fifth variable capacitance element 10ax, a common matching inductor 10bxy, a fifth control resistor 10cx, and a fifth control terminal 10dx. Furthermore, the sixth impedance matching circuit 10Y includes a sixth variable capacitance element 10ay, a common matching inductor 10bxy, a sixth control resistor 10cy, and a sixth control terminal 10dy.

[0062] Here, a single common matching inductor 10bxy is a circuit element used in both the fifth impedance matching circuit 10X and the sixth impedance matching circuit 10Y as shown in the figure. The fifth impedance matching circuit 10X includes a first series resonance circuit having the common matching inductor 10bxy as a component, and the sixth impedance matching circuit 10Y includes a second series resonance circuit having the same common matching inductor 10bxy as a component.

[0063] The third impedance matching circuit 8X is a circuit for matching (matching) the output impedance of the high-frequency amplification circuit B with the subsequent circuit of the high-frequency amplification circuit B. One end is connected to the other end of the third output capacitor 7X, and the other end is connected to the ground potential (GND). Such a third impedance matching circuit 8X is connected in parallel to the output of the basic circuit M.

[0064] The third variable capacitance element 8ax is an N-channel MOS field-effect transistor with its source terminal and drain terminal connected as shown in the figure. One end (gate terminal) of the third variable capacitance element 8ax is connected to the other end of the third output capacitor 7X and one end of the third control resistor 8bx, and the other end (source terminal and drain terminal) is connected to the ground potential (GND).

[0065] One end of the third control resistor 8bx is connected to the other end of the third output capacitor 7X and one end of the third variable capacitance element 8ax, and the other end is connected to the third control terminal 8cx. The third control resistor 8bx has a predetermined resistance value and applies the third control voltage Vb1x input from the third control terminal 8cx to one end of the third variable capacitance element 8ax.

[0066] The third control terminal 8cx is a connection terminal for receiving the third control voltage Vb1x from the outside. The third control terminal 8cx is connected to the source of the third control voltage Vb1x outside the high-frequency amplification circuit B and to the other end of the third control resistor 8bx inside the high-frequency amplification circuit B. Note that the third control voltage Vb1x is a DC voltage within a predetermined range.

[0067] In such a third impedance matching circuit 8X, the capacitance of the third variable capacitance element 8ax varies within a predetermined range according to a third control voltage Vb1x applied to one end of the third variable capacitance element 8ax via a third control resistor 8bx. That is, the third impedance matching circuit 8X is a third variable capacitance circuit in which the capacitance of the third variable capacitance element 8ax can be freely varied by the third control voltage Vb1x, and has a third variable capacitance.

[0068] The fourth impedance matching circuit 8Y is a circuit for matching (matching) the output impedance of the high-frequency amplifier circuit B with the subsequent circuit of the high-frequency amplifier circuit B, similar to the third impedance matching circuit 8X. One end of the fourth impedance matching circuit 8Y is connected to the other end of the fourth output capacitor 7Y, and the other end is connected to the ground potential (GND). Such a fourth impedance matching circuit 8Y is connected in parallel to the output of the basic circuit M, similar to the third impedance matching circuit 8X.

[0069] The fourth variable capacitance element 8ay is an N-channel MOS type field effect transistor in which the source terminal and the drain terminal are connected, similar to the third variable capacitance element 8ax. One end (gate terminal) of the fourth variable capacitance element 8ay is connected to the other end of the fourth output capacitor 7Y and one end of the fourth control resistor 8by, and the other end (source terminal and drain terminal) is connected to the ground potential (GND).

[0070] One end of the fourth control resistor 8by is connected to the other end of the fourth output capacitor 7Y and one end of the fourth variable capacitance element 8ay, and the other end is connected to the fourth control terminal 8cy. The fourth control resistor 8by has a predetermined resistance value and applies a fourth control voltage Vb1y input from the fourth control terminal 8cy to one end of the fourth variable capacitance element 8ay.

[0071] The fourth control terminal 8cy is a connection terminal for receiving the fourth control voltage Vb1y from the outside. The fourth control terminal 8cy is connected to the source of the fourth control voltage Vb1y outside the high-frequency amplifier circuit B, and is connected to the other end of the fourth control resistor 8by inside the high-frequency amplifier circuit B. Note that the fourth control voltage Vb1y is a DC voltage within a predetermined range.

[0072] In such a fourth impedance matching circuit 8Y, the capacitance of the fourth variable capacitance element 8ay changes within a predetermined range according to the fourth control voltage Vb1y applied to one end of the fourth variable capacitance element 8ay via the fourth control resistor 8by. That is, the fourth impedance matching circuit 8Y is a fourth variable capacitance circuit in which the capacitance of the fourth variable capacitance element 8ay can be freely varied by the fourth control voltage Vb1y, and has a fourth variable capacitance.

[0073] The fifth impedance matching circuit 10X is a circuit for matching (matching) the output impedance of the high-frequency amplifier circuit B with the subsequent circuit of the high-frequency amplifier circuit B. One end of the fifth impedance matching circuit 10X is connected to the other end of the fifth output capacitor 9X, and the other end is connected to the RF output terminal 11 and one end of the load resistor 12. Such a fifth impedance matching circuit 10X is connected in series to the output of the basic circuit M.

[0074] The fifth variable capacitance element 10ax is an N-channel MOS field-effect transistor in which the source terminal and the drain terminal are connected, similar to the third variable capacitance element 8ax and the fourth variable capacitance element 8ay described above. One end (gate terminal) of the fifth variable capacitance element 10ax is connected to the other end of the fifth output capacitor 9X and one end of the fifth control resistor 10cx, and the other end (source terminal and drain terminal) is connected to one end of the common matching inductor 10bxy and the other end of the sixth variable capacitance element 10ay.

[0075] The common integration inductor 10bxy has one end connected to the other end of the fifth variable capacitor 10ax and the other end of the sixth variable capacitor 10ay, and the other end connected to the RF output terminal 11 and one end of the load resistor 12. This common integration inductor 10bxy has a predetermined inductance, forms a first series resonance circuit with the fifth variable capacitor 10ax, and forms a second series resonance circuit with the sixth variable capacitor 10ay.

[0076] One end of the fifth control resistor 10cx is connected to the other end of the fifth output capacitor 9X and one end of the fifth variable capacitor 10ax, and the other end is connected to the fifth control terminal 10dx. The fifth control resistor 10cx has a predetermined resistance value and applies the fifth control voltage Vb2x input from the fifth control terminal 10dx to one end of the fifth variable capacitor 10ax.

[0077] The fifth control terminal 10dx is a connection terminal for receiving the fifth control voltage Vb2x from the outside. The fifth control terminal 10dx is connected to the source of the fifth control voltage Vb2x outside the high-frequency amplification circuit B and connected to the other end of the fifth control resistor 10cx inside the high-frequency amplification circuit B. Note that the fifth control voltage Vb2x is a DC voltage within a predetermined range.

[0078] In such a fifth impedance matching circuit 10X, the capacitance of the fifth variable capacitor 10ax changes within a predetermined range according to the fifth control voltage Vb2x applied to one end of the fifth variable capacitor 10ax via the fifth control resistor 10cx. That is, the fifth impedance matching circuit 10X is a fifth variable capacitance circuit in which the capacitance of the fifth variable capacitor 10ax can be freely varied by the fifth control voltage Vb2x and has a fifth variable capacitance.

[0079] The sixth impedance matching circuit 10Y is a circuit for matching (matching) the output impedance of the high-frequency amplifier circuit B with the subsequent circuit of the high-frequency amplifier circuit B, similar to the fifth impedance matching circuit 10X. One end of the sixth impedance matching circuit 10Y is connected to the other end of the sixth output capacitor 9Y, and the other end is connected to one end of the RF output terminal 11 and the load resistor 12. Such a sixth impedance matching circuit 10Y is connected in series to the output of the basic circuit M, similar to the fifth impedance matching circuit 10X.

[0080] The sixth variable capacitance element 10ay is an N-channel MOS field-effect transistor in which the source terminal and the drain terminal are connected, similar to the fifth variable capacitance element 10ax described above. One end (gate terminal) of the sixth variable capacitance element 10ay is connected to the other end of the sixth output capacitor 9Y and one end of the sixth control resistor 10cy, and the other end (source terminal and drain terminal) is connected to one end of the common matching inductor 10bxy and the other end of the fifth variable capacitance element 10ax.

[0081] One end of the sixth control resistor 10cy is connected to the other end of the sixth output capacitor 9Y and one end of the sixth variable capacitance element 10ay, and the other end is connected to the sixth control terminal 10dy. The sixth control resistor 10cy has a predetermined resistance value and applies the sixth control voltage Vb2y input from the sixth control terminal 10dy to one end of the sixth variable capacitance element 10ay.

[0082] The sixth control terminal 10dy is a connection terminal for receiving the sixth control voltage Vb2y from the outside. The sixth control terminal 10dy is connected to the source of the sixth control voltage Vb2y outside the high-frequency amplifier circuit B and to the other end of the sixth control resistor 10cy inside the high-frequency amplifier circuit B. Note that the sixth control voltage Vb2y is a DC voltage within a predetermined range.

[0083] In such a sixth impedance matching circuit 10Y, the capacitance of the sixth variable capacitance element 10ay varies within a predetermined range according to the sixth control voltage Vb2y applied to one end of the sixth variable capacitance element 10ay via the sixth control resistor 10cy. That is, the sixth impedance matching circuit 10Y is a sixth variable capacitance circuit in which the capacitance of the sixth variable capacitance element 10ay can be freely varied by the sixth control voltage Vb2y, and has a sixth variable capacitance.

[0084] Subsequently, the operation of the high-frequency amplifier circuit B according to the second embodiment will be described in detail with reference to FIG. 3.

[0085] This high-frequency amplifier circuit B includes a third impedance matching circuit 8X and a fourth impedance matching circuit 8Y connected in parallel to the output of the basic circuit M. Among these third impedance matching circuit 8X and fourth impedance matching circuit 8Y, the third impedance matching circuit 8X has its third variable capacitance set by the third control voltage Vb1x, and the fourth impedance matching circuit 8Y has its fourth variable capacitance set by the fourth control voltage Vb1y.

[0086] FIG. 3 shows the relationship between the third control voltage Vb1x and the third variable capacitance and the relationship between the fourth control voltage Vb1y and the fourth variable capacitance when the ambient temperature is 150°C, 25°C, and -40°C. Looking at this FIG. 3, it can be seen that based on about 0V, the temperature characteristics of the capacitance are reversed in the voltage regions before and after that.

[0087] Both the third variable capacitance element 8ax in the third impedance matching circuit 8X and the fourth variable capacitance element 8ay in the fourth impedance matching circuit 8Y are constituted by the same N-channel MOS type field effect transistor. Such third variable capacitance element 8ax and fourth variable capacitance element 8ay tend to increase in capacitance as the ambient temperature rises in the positive voltage region, but tend to decrease in capacitance as the ambient temperature rises in the negative voltage region.

[0088] By utilizing the temperature characteristics of such a third variable capacitance element 8ax and a fourth variable capacitance element 8ay, that is, by setting the third control voltage Vb1x and the fourth control voltage Vb1y in different voltage regions (positive voltage region or negative voltage region) where the temperature characteristics are reversed, it is possible to ensure the temperature stability of the third variable capacitance and the fourth variable capacitance.

[0089] In FIG. 3, as indicated by the arrows, it shows that the third control voltage Vb1x is set in the positive voltage region and the fourth control voltage Vb1y is set in the negative voltage region. However, alternatively, the third control voltage Vb1x may be set in the negative voltage region and the fourth control voltage Vb1y may be set in the positive voltage region.

[0090] Since the fifth variable capacitance element 10ax and the sixth variable capacitance element 10ay are also N-channel MOS type field effect transistors, they have temperature characteristics similar to those of the third variable capacitance element 8ax and the fourth variable capacitance element 8ay.

[0091] Therefore, also for the fifth impedance matching circuit 10X and the sixth impedance matching circuit 10Y, by setting the fifth control voltage Vb2x and the sixth control voltage Vb2y in different voltage regions, it is possible to ensure the temperature stability of the fifth variable capacitance and the sixth variable capacitance.

[0092] According to such a second embodiment, in addition to being able to establish impedance matching without using an open / close switch, it is possible to provide a high-frequency amplification circuit B (amplification circuit) capable of ensuring the temperature stability of impedance matching.

[0093] Note that the present invention is not limited to the above embodiments, and for example, the following modification examples can be considered. (1) In the above embodiment, the first impedance matching circuit 8 and the second impedance matching circuit 10 are provided only at the output of the basic circuit M, but the present invention is not limited thereto. The first impedance matching circuit 8 and the second impedance matching circuit 10 may be provided at the input of the basic circuit M, or may be provided at both the input and the output of the basic circuit M.

[0094] Note that when the first impedance matching circuit 8 and the second impedance matching circuit 10 are provided at the input of the basic circuit M, the first impedance matching circuit 8 and the second impedance matching circuit 10 are for matching the input impedance of the high-frequency amplification circuit A with the output impedance of the preceding-stage circuit connected to the input side of the high-frequency amplification circuit A.

[0095] (2) In the above embodiment, the first impedance matching circuit 8 connected in parallel to the output of the basic circuit M and the second impedance matching circuit 10 connected in series to the output of the basic circuit M are provided, but the present invention is not limited thereto. That is, either one of the first impedance matching circuit 8 or the second impedance matching circuit 10 may be provided.

[0096] (3) In the above embodiment, the series resonance circuit is provided only in the second impedance matching circuit 10, but the present invention is not limited thereto. A series resonance circuit may also be provided in the first impedance matching circuit 8. Further, if necessary, the second impedance matching circuit 10 may be made to have the same circuit configuration as the first impedance matching circuit 8, and the series resonance circuit may be removed from the second impedance matching circuit 10.

[0097] (4) In the above embodiment, an N-channel MOS field-effect transistor with its source terminal and drain terminal connected is adopted as the variable capacitance element, but the present invention is not limited thereto. A general varicap (variable capacitance diode) that can be used for high frequencies may be adopted.

Description of Reference Numerals

[0098] A, B... high-frequency amplification circuit (amplification circuit), M... basic circuit, 1... RF input terminal, 2... input capacitor, 3... bias resistor, 4... bias terminal, 5... transistor, 6... output inductor, 7... first output capacitor, 8... first impedance matching circuit, 8a... first variable capacitor element, 8b... first control resistor, 8c... first control terminal, 9... second output capacitor, 10... second impedance matching circuit, 10a... second variable capacitor element, 10b... matching inductor, 10c... second control resistor, 10d... second control terminal, 11... RF output terminal, 12... load resistor

Claims

1. An amplifier circuit comprising an impedance matching circuit in either or both of the input and output of a basic circuit, wherein the impedance matching circuit comprises a variable capacitance circuit whose capacitance is variable by a control voltage. The amplifier circuit is characterized by this.

2. The amplifier circuit according to claim 1, wherein the variable capacitance circuit comprises a MOS transistor having a source terminal and a drain terminal connected as variable capacitance elements.

3. The amplifier circuit according to claim 1, wherein the impedance matching circuit has a first impedance matching circuit connected in parallel to the output of the basic circuit and a second impedance matching circuit connected in series to the output of the basic circuit.

4. The amplifier circuit according to claim 3, wherein the second impedance matching circuit comprises an inductor in addition to the variable capacitance circuit.

5. The amplifier circuit according to claim 4, wherein a pair of the second impedance matching circuits are provided, and the pair of control voltages are respectively set in a voltage region where the temperature characteristics are reversed.

6. The amplifier circuit according to claim 5, wherein the pair of second impedance matching circuits share one inductor.

7. The amplifier circuit according to any one of claims 3 to 6, wherein a pair of the first impedance matching circuits are provided, and the pair of control voltages are respectively set in a voltage region where the temperature characteristics are reversed.

Images