Amplifier circuit and voltage-controlled oscillator

Abstract

An amplifier circuit (11) according to the present invention comprises an inverting amplifier circuit (110), a first capacitor (111) connected in parallel with the inverting amplifier circuit (110), and a second capacitor (112) connected to the input of the inverting amplifier circuit (110), wherein the first capacitor (111) is a feedback capacitor, and the value of the second capacitor (112) is greater than the value of the first capacitor (111). Also, the value of the second capacitor (112) may be not less than triple the value of the first capacitor (111) and not greater than 10 pF.　With this configuration, the present invention can provide an amplifier circuit capable of operating over a wide band.

Description

Amplifier circuit and voltage-controlled oscillator

[0001] The present invention relates to an amplifier circuit and a voltage-controlled oscillator that operate over a wide band.

[0002] In signal transmission such as wireless communication, a sine wave signal is generated as a carrier wave. In order to make the carrier wave (sine wave signal) compatible with a wide frequency range, the output frequency of a signal generation circuit needs to be variable. In order to output a carrier wave (sine wave signal) over a wide frequency range from a signal generation circuit such as a PLL (Phase Locked Loop), it is necessary to widen the output frequency range of a voltage-controlled oscillator (VCO) in the PLL or the like.

[0003] In a voltage-controlled oscillator around 100 GHz, which is necessary for 100 GHz-band wireless communication, a configuration has been disclosed in which the output frequency is controlled using a variable capacitance that uses the parasitic capacitance of a MOS transistor or the reverse-bias capacitance of a diode-connected MOS transistor (Non-Patent Documents 1 and 2).

[0004] W. Badalawa, et al., “115GHz CMOS VCO with 4.4% tuning range,” 2009 European Microwave Integrated Circuits ConferenceW. Volkaerts, et al., “118GHz fundamental VCO with 7.8% tuning range in 65nm CMOS,” 2011 IEEE Radio Frequency Integrated Circuits Symposium

[0005] However, in the above-mentioned voltage controlled oscillator, the frequency control range is only a few percent at most, and it has not been possible to realize a wide frequency control range of 10% or more.

[0006] In order to solve the above-described problems, an amplifier circuit according to the present invention includes an inverting amplifier circuit, a first capacitor connected in parallel with the inverting amplifier circuit, and a second capacitor connected to the input of the inverting amplifier circuit, wherein the first capacitor is a feedback capacitor and the value of the second capacitor is larger than the value of the first capacitor.

[0007] According to the present invention, it is possible to provide an amplifier circuit and a voltage controlled oscillator that can be controlled over a wide frequency range.

[0008] FIG. 1A is a schematic diagram showing the configuration of an amplifier circuit according to a first embodiment of the present invention. FIG. 1B is a schematic diagram showing the configuration of a voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 2 is a diagram for explaining the operation of the amplifier circuit and voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 3 is a diagram for explaining the operation of the amplifier circuit and voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 4A is a diagram for explaining the operation of the amplifier circuit and voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 4B is a diagram for explaining the operation of the amplifier circuit and voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 5 is a diagram for explaining the effect of the amplifier circuit and voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 6 is a schematic diagram showing the configuration of an amplifier circuit according to a first example of the present invention. FIG. 7 is a schematic diagram showing an example of the configuration of an amplifier circuit according to the first example of the present invention. FIG. 8 is a schematic diagram showing the configuration of an amplifier circuit and voltage-controlled oscillator according to a second example of the present invention. FIG. 9 is a schematic diagram showing an example of the configuration of an amplifier circuit and voltage-controlled oscillator according to the second example of the present invention. FIG. 10 is a schematic diagram showing an example of the configuration of an amplifier circuit and voltage-controlled oscillator according to the second example of the present invention.

[0009] First Embodiment An amplifier circuit and a voltage-controlled oscillator according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG.

[0010] <Configuration of Amplifier Circuit and Voltage-Controlled Oscillator> FIGS. 1A and 1B each show a schematic diagram illustrating an example of the configuration of an amplifier circuit 11 and a voltage-controlled oscillator 10 according to this embodiment.

[0011] The amplifier circuit 11 includes an inverting amplifier circuit 110 , a first capacitor 111 connected in parallel to the inverting amplifier circuit 110 , and a second capacitor 112 connected in series to the input of the inverting amplifier circuit 110 .

[0012] The inverting amplifier circuit 110 has an amplification factor of −A.

[0013] The first capacitor (capacitance value: C) 111 exhibits a Miller effect when connected to the inverting amplifier circuit 110, and operates as a Miller capacitance (described later).

[0014] The value of the second capacitance 112 is larger than the value (C) of the first capacitance 111 and is x (a predetermined value) times the value of the first capacitance 111 (capacitance value: xC).

[0015] The voltage-controlled oscillator 10 includes a current source 12 and an inductor (inductance: L Ｐ ) 13 and a resistor (R Ｐ ) 14 and negative resistance (-R Ｐ ) 15.

[0016] Negative resistance (-R Ｐ ) 15 is a resistor (R Ｐ ) 14 and is realized by active elements.

[0017] Furthermore, the control circuit 16 is connected to the input of the inverting amplifier circuit 110. The control circuit 16 is connected to a control voltage source (voltage: V ｃｔｒｌ ) 160 in series with a first impedance (Z Ｂ１ ) 161 and the second impedance Z Ｂ２ ) 162 and the voltage V ｂｉａｓ Output.

[0018] <Operations of Amplifier Circuit and Voltage-Controlled Oscillator> The operations of the amplifier circuit 11 and voltage-controlled oscillator 10 according to this embodiment will be described.

[0019] First, a typical voltage-controlled oscillator will be described. In a typical voltage-controlled oscillator, the output frequency can be controlled by changing the impedance or capacitance with a voltage. FIG. 2 shows the configuration of a voltage-controlled oscillator 20 that controls the output frequency by changing the capacitance. In the voltage-controlled oscillator 20, an impulse current I is supplied from a current source 22. ｉｎ When is applied, the capacitor (capacitance value: C ＶＡＲ ) 21 and an inductor (inductance: L Ｐ Energy travels back and forth between the resistor 24 and the negative resistor (active circuit) 25, and the energy loss due to the resistor 24 is compensated for by the negative resistor (active circuit) 25. ｏｕｔA sine wave voltage signal is output to L Ｐ and C ＶＡＲ Since the resonant frequency is determined by ＶＡＲ By making the resistor 24 (R ｐ ) to compensate for the signal loss due to the negative resistance 25 (-R Ｐ ) is realized by active elements.

[0020] 3 shows an example of the configuration of a voltage-controlled oscillator 30 that controls the output frequency using a change in capacitance. ＶＡＲ A reverse bias V is applied to the diode-connected transistor 311 by a voltage source 312. ｃｔｒｌ When this configuration is used, the output frequency variable range that can be changed by the transistor 311 in a voltage controlled oscillator that oscillates in the 100 GHz band is at most a few percent. As such, it is difficult to control a wide output frequency with this configuration.

[0021] In the amplifier circuit and voltage-controlled oscillator according to this embodiment, the variable capacitance C ＶＡＲ This uses the Miller capacitance caused by the Miller effect generated in the inverting amplifier circuit. This makes it possible to vary the output frequency of the voltage-controlled oscillator and control the carrier wave (sine wave signal) over a wide range of frequencies. The Miller effect is explained below.

[0022] As shown in Figure 4A, a feedback capacitor (capacitance value: C) 111 is connected in parallel to an inverting amplifier 110 with a gain of -A. At this time, as shown in Figure 4B, a grounded capacitor (capacitance value: C') is connected to the input of the inverting amplifier. Here, C' = (1 + A) C. This capacitance value C' is called Miller capacitance.

[0023] In this circuit configuration, variable capacitance can be achieved by varying the gain A of the inverting amplifier circuit. By setting the gain A of the inverting amplifier circuit to A≧0, a variable capacitance value that is 1 or more times the capacitance value C of the feedback capacitance can be obtained. This makes it possible to vary the output frequency of the voltage-controlled oscillator, and to control the carrier wave (sine wave signal) over a wide frequency range.

[0024] In the amplifier circuit 11 according to this embodiment, as shown in FIG. 1A, a second capacitor (capacitance value: xC) 112 is connected in series to the input of an inverting amplifier circuit 110 having a feedback capacitor 111. The combined capacitance C １ is expressed by the formula (1).

[0025]

[0026] When inverting and amplifying is not performed (A=0), the capacitance value C １ is {x / (x+1)}×C.

[0027] Therefore, the capacitance variation ΔC is expressed by equation (2).

[0028]

[0029] As described above, the amplifier circuit according to this embodiment can increase the amount of capacitance variation compared to the conventional amplifier circuit.

[0030] When an amplifier circuit is configured with an inverting amplifier circuit and a first capacitor (feedback capacitor) (without a second capacitor), the deviation from the optimal bias point of the inverting amplifier circuit may become large, preventing it from operating properly. As a result, it becomes necessary to change the gain within a range where the bias point allows the inverting amplifier circuit to operate properly, which restricts the variable range of the gain. In the configuration of an inverting amplifier circuit and a first capacitor (feedback capacitor), the variable range of the capacitance becomes narrower than the expected range (ΔC = AC).

[0031] On the other hand, the amplifier circuit according to this embodiment includes the second capacitor 112 in addition to the inverting amplifier circuit 110 and the first capacitor 111, and therefore, by setting the capacitance value xC of the second capacitor 112 to an appropriate value, it is possible to suppress a shift in the bias point of the inverting amplifier circuit 110. Therefore, the shift in the bias point of the inverting amplifier circuit 110 is suppressed, and as described above, the variable range of the gain is not restricted. As a result, the effect of the Miller capacitance in the inverting amplifier circuit is fully reflected, and the variable range of the capacitance can be widened.

[0032] As shown in FIG. 1B, the voltage controlled oscillator according to this embodiment includes a current source 12, an inductor 13, a resistor 14, and a negative resistor 15 connected in parallel with an amplifier circuit 11.

[0033] Furthermore, the control circuit 16 is connected to the input of the inverting amplifier circuit 110. The control circuit 16 is connected to a control voltage source (control voltage: V ｃｔｒｌ ) 160 in series with a first impedance 161 (Z Ｂ１ ) and the second impedance 162 (Z Ｂ２ ) are connected. This allows the bias voltage expressed by equation (3) to be applied to the inverting amplifier circuit.

[0034]

[0035] The first impedance 161 (Z Ｂ１ ) and the second impedance 162 (Z Ｂ２ ) When a resistor having an impedance sufficiently larger than the input impedance of the inverting amplifier is used as the first capacitance (1 + A)C, the second capacitance xC, and the inverting amplifier, the minimum value of the output frequency f ｍｉｎ , maximum value f ｍａｘ are expressed by equations (4) and (5), respectively.

[0036]

[0037]

[0038] Here, L Ｐ is the value of the inductor 13.

[0039] From this, the variable width Δf of the output frequency of the voltage controlled oscillator 10 is f ｍａｘ -f ｍｉｎ Therefore, according to the voltage controlled oscillator of this embodiment, the output frequency of the voltage controlled oscillator can be made variable, and the carrier wave (sine wave signal) can be controlled over a wide frequency range.

[0040] <Effects> The effects of the amplifier circuit and voltage-controlled oscillator according to this embodiment will be described with reference to FIG.

[0041] FIG. 5 shows the results of a simulation of the output oscillation spectrum of the voltage-controlled oscillator 10 configured as shown in FIG. 1B.

[0042] The output oscillation spectrum was simulated using software (product name: "Advanced Design System (ADS)" manufactured by Keysight Technologies).

[0043] In the simulation, C = 13.05 fF, x = 15.32, xC = 200 fF, Z Ｂ１ = 200 pH, Z Ｂ２ =∞.

[0044] In the simulated output oscillation spectrum, when the amplification factor A=0, the oscillation frequency f ０ When the amplification factor A is sufficiently large (A=10 or more), the oscillation frequency f １ = 93 GHz (solid line in the figure). From this, the adjustable range of the frequency is ０ -f １ ) / {(f ０ +f １ ) / 2}]×100, we obtain 27.1%, which is larger than the adjustable range of the frequency of a conventional voltage-controlled oscillator (several %).

[0045] As described above, the amplifier circuit and voltage-controlled oscillator according to this embodiment make it possible to vary the output frequency of the voltage-controlled oscillator, and to control the carrier wave (sine wave signal) over a wide frequency range.

[0046] In the amplifier circuit according to this embodiment, when the variable range of the capacitance is about twice that of the feedback capacitance and A varies from 0 to 40, the value of x of the second capacitance is preferably 3 or greater. Furthermore, when the variable range of the capacitance is about 10 times that of the feedback capacitance and A varies from 0 to 40, the value of x of the second capacitance is preferably 15 or greater. Furthermore, it is preferable that the value xC of the second capacitance is set to be on the order of pF (for example, 10 pF or less).

[0047] In the voltage controlled oscillator according to this embodiment, Z Ｂ１ = 200 pH, Z Ｂ２ =∞ is shown as an example, but it is not limited to this and other values ​​may be used. ｃｔｒｌ It is sufficient to set so that no AC component is included in Z.Ｂ１ , Z Ｂ２ As the resistor, an inductor or a combination thereof may be used.

[0048] First Embodiment An amplifier circuit 41 and a voltage-controlled oscillator 40 according to a first embodiment of the present invention will be described with reference to FIG.

[0049] 6 shows a common-emitter amplifier circuit as an example of a specific configuration of the amplifier circuit 41 according to this embodiment. In the amplifier circuit 41, a Miller capacitance 411 is connected between the base and collector of a transistor 410 in one circuit. An input terminal (in) is connected to the base of the transistor 410, and an output terminal (out) is connected to the collector. A second capacitance (capacitance value: xC) 412 is connected between the base and the input signal terminal. A resistor 413 (R) is connected to the collector, and a power supply voltage Vcc is applied. A variable current source (2I) is connected to the emitter. ＶＡＲ ) 414 are connected.

[0050] Furthermore, a mirror capacitor 411_2 is connected between the base and collector of the transistor 410_2, and another circuit, in which a resistor 413_2 is connected to the collector, is connected in parallel to one circuit.

[0051] According to the amplifier circuit of this embodiment, it is possible to increase the variable amount of the combined capacitance of the capacitances (first capacitance and second capacitance) connected to the inverting amplifier circuit.

[0052] Therefore, according to a voltage controlled oscillator including the amplifier circuit of this embodiment, the output frequency of the voltage controlled oscillator can be made variable, and the carrier wave (sine wave signal) can be controlled over a wide frequency range.

[0053] Although the amplifier circuit according to this embodiment is configured by one circuit and the other circuit, the present invention is not limited to this and may be configured by only one circuit.

[0054] The amplifier circuit according to this embodiment may be an inverting amplifier circuit in which a feedback variable resistor is added to an operational amplifier, as shown in FIG.

[0055] Second Embodiment An amplifier circuit and a voltage-controlled oscillator according to a second embodiment of the present invention will be described with reference to FIGS.

[0056] FIG. 8 shows an example of a specific configuration of the voltage-controlled oscillator 50 according to this embodiment, in which a single-phase Colpitts oscillator circuit is used to achieve negative resistance.

[0057] In the voltage controlled oscillator 50, similarly to the first embodiment, a circuit having one transistor 410 and a circuit having the other transistor 410_2 are connected in parallel, and a first impedance Z Ｂ１ and the second impedance Z Ｂ２ The control circuits 56 and 56_2 are connected to each other.

[0058] The Colpitts oscillator circuit 55 is connected to the base of the transistor 410 via a second capacitor 412. In the Colpitts oscillator circuit 55, a grounded current source 551 is connected to the emitter of a transistor 550, and a grounded voltage source (V Ｂ ) 554 is connected to the collector, and an inductor (L Ｐ ) 552 and the output signal terminal (out) are connected. １ ) 553 is connected.

[0059] In the voltage controlled oscillator according to this embodiment, a Colpitts oscillator circuit is used, which improves the compatibility in connection with other circuits.

[0060] As shown in FIG. 9, a differential Colpitts oscillation circuit may be used in the voltage-controlled oscillator 50_2 to achieve negative resistance.

[0061] 10, a cross-coupled oscillator circuit may be used in the voltage-controlled oscillator 60 to achieve negative resistance. The voltage-controlled oscillator 60 includes the amplifier circuit according to the first embodiment as a basic configuration, and also includes a cross-coupled oscillator circuit. In detail, the voltage-controlled oscillator 60 includes the amplifier circuit according to the first embodiment, a control circuit 56, a current source 651, transistors 650 and 650_2, and an inductor (L Ｐ) 652, 652_2 and resistors (R Ｐ ) 653, 653_2.

[0062] In the voltage controlled oscillator according to this embodiment, a cross-coupled oscillation circuit is used, which improves the compatibility in connection with other circuits.

[0063] In the embodiments of the present invention, examples have been shown in which a single-phase Colpitts oscillator circuit, a differential Colpitts oscillator circuit, and a cross-coupled oscillator circuit are used to realize negative resistance, but the present invention is not limited to these and other circuits may also be used.

[0064] In the embodiments and examples of the present invention, examples using bipolar transistors have been shown, but the present invention is not limited to this, and the circuit may be configured using MOS transistors, or may be configured using both types of transistors.

[0065] In the embodiments and examples of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration of the amplifier circuit and voltage-controlled oscillator are shown, but the present invention is not limited to these. Anything that can demonstrate the functions and effects of the amplifier circuit and voltage-controlled oscillator may be used.

[0066] It should be noted that the present invention is not limited to the above-described embodiments and examples, and it is clear that modifications and combinations of the above-described embodiments and examples can be implemented by a person having ordinary knowledge in the art within the technical spirit of the present invention.

[0067] A part or all of the above-described embodiment or an example thereof can be described as, but is not limited to, the following supplementary notes.

[0068] (Supplementary Note 1) An amplifier circuit comprising: an inverting amplifier circuit; a first capacitor connected in parallel with the inverting amplifier circuit; and a second capacitor connected to an input of the inverting amplifier circuit, wherein the first capacitor is a feedback capacitor; and the value of the second capacitor is greater than the value of the first capacitor.

[0069] (Supplementary Note 2) The amplifier circuit according to Supplementary Note 1, wherein the value of the second capacitance is not less than three times the value of the first capacitance and not more than 10 pF.

[0070] (Supplementary Note 3) The amplifier circuit according to Supplementary Note 1 or Supplementary Note 2, wherein the inverting amplifier circuit includes a transistor, and the first capacitor is connected between the base and collector of the transistor.

[0071] (Supplementary Note 4) A voltage-controlled oscillator comprising: an amplifier circuit according to any one of Supplementary Notes 1 to 3; and a second resistor, a negative resistor, an inductor, and a current source connected in parallel with the amplifier circuit.

[0072] (Supplementary Note 5) The voltage controlled oscillator of Supplementary Note 4, wherein the negative resistance comprises a Colpitts oscillator circuit.

[0073] (Supplementary Note 6) The voltage controlled oscillator according to Supplementary Note 4, wherein the negative resistance comprises a cross-coupled oscillator circuit.

[0074] The present invention relates to an amplifier circuit and a voltage-controlled oscillator, and can be applied to communication systems such as wireless communication systems.

[0075] 11 Amplifier circuit 110 Inverting amplifier circuit 111 First capacitor 112 Second capacitor

Claims

1. An amplifier circuit comprising: an inverting amplifier circuit; a first capacitance connected in parallel to the inverting amplifier circuit; and a second capacitance connected to the input of the inverting amplifier circuit, wherein the first capacitance is a feedback capacitance; and the value of the second capacitance is greater than the value of the first capacitance.

2. The amplifier circuit according to claim 1, wherein the value of the second capacitance is greater than or equal to three times the value of the first capacitance and less than or equal to 10 pF.

3. The amplifier circuit according to claim 1 or 2, wherein the inverting amplifier circuit comprises a transistor, and the first capacitor is connected between the base and collector of the transistor.

4. A voltage controlled oscillator comprising: an amplifier circuit according to claim 1 or 2; and a second resistor, a negative resistor, an inductor, and a current source connected in parallel with said amplifier circuit.

5. The voltage controlled oscillator of claim 4, wherein said negative resistance comprises a Colpitts oscillator circuit.

6. The voltage controlled oscillator of claim 4, wherein said negative resistance comprises a cross-coupled oscillator circuit.