Voltage-controlled oscillator

Abstract

A voltage-controlled oscillator (10) according to the present invention comprises: an oscillation circuit which includes a transistor, an inductor and a capacitor, and in which a portion of the output of the transistor is fed back to the input of the transistor by means of a circuit composed of the inductor and the capacitor; a load impedance that is connected to a collector of the transistor; and a variable capacitor that is connected to the collector of the transistor in parallel with the load impedance.　Due to this configuration, the present invention can provide a voltage-controlled oscillator with which output fluctuations can be suppressed.

Description

Voltage Controlled Oscillator

[0001] The present invention relates to a voltage controlled oscillator capable of suppressing output fluctuations.

[0002] In order to transmit and receive data in communication systems, especially wireless communication, a sine wave signal is required as a carrier wave for modulation and demodulation by a frequency mixer. A phase-locked loop (PLL) with high frequency purity is usually used to generate this sine wave signal. A voltage-controlled oscillator (VCO) is required to configure a PLL. To support wireless communication over a wide frequency range, it is necessary to widen the output frequency range from the PLL and also the output frequency range of the VCO.

[0003] Furthermore, to maintain constant signal quality in wireless communications, it is necessary to maintain constant power of the sine wave signal that serves as the carrier throughout the entire frequency range. Therefore, it is necessary to minimize the fluctuation range of the PLL (VCO) output power. While adding a variable attenuator or saturated amplifier after the PLL (VCO) can stabilize the output power, large fluctuations in the PLL (VCO) output power increase power loss and increase the performance requirements for the additional circuitry.

[0004] This section explains the case where a variable attenuator is added to the output stage of the PLL. This method stabilizes the output power by adjusting it to the lower limit of the PLL output over the entire frequency range. This results in power loss at frequencies where the PLL output power is high, reducing power efficiency.

[0005] Furthermore, since the variable attenuator is required to adjust the attenuation amount according to the fluctuation range of the PLL output power, the larger the fluctuation range of the PLL output power, the higher the performance required of the variable attenuator. Therefore, in order to keep the PLL output power constant, it is better to have a small fluctuation range of the PLL (VCO) output power.

[0006] L. Dauphinee, et al., “A Balanced 1.5GHz Voltage Controlled Oscillator with an Integrated LC Resonator,” 1997 ISSCC, pp. 390-391. S. Voinigescu, “Design of voltage-controlled oscillators,” in High-Frequency Integrated Circuits,” in High-Frequency Integrated Circuits, New York, NY, USA: Cambridge Univ. Press, 2013, pp. 641-643.

[0007] Figure 9 shows a Colpitts VCO, one of the common VCO configurations (Non-Patent Document 1). Figure 10 shows a small-signal equivalent circuit of a Colpitts VCO. In the circuits of Figures 9 and 10, the output frequency and output power are expressed by equations (1) and (2) (Non-Patent Document 2).

[0008]

[0009]

[0010] Here, I ＢＩＡＳ is the bias current of the transistor, G ｍ is the large signal transconductance of the transistor, and Q is the Q value of the resonant circuit.

[0011] The Colpitts type VCO is ２ This is a circuit configuration that makes it possible to adjust the frequency by making the C variable. ２ is controlled by the voltage V ｃｔｒｌ If the oscillation frequency f ｏｓｃ is expressed by equation (3).

[0012]

[0013] In addition, the output power P ｏｕｔ is expressed by equation (4).

[0014]

[0015] Control voltage Vｃｔｒｌ When the variable capacitance C ２ Not only G ｍ , Q, C １ Therefore, it is difficult to derive the actual amount of change in output power only by a calculation formula. ２ is C ２ =C ２ａ ・V ｃｔｒｌ +C ２ｂ It changes linearly as shown in G ｍ , Q, C １ is V ｃｔｒｌ In this case, f ｏｓｃ and P ｏｕｔ are expressed by equations (5) and (6), respectively.

[0016]

[0017]

[0018] FIG. 11 shows the output power P obtained from equation (6). ｏｕｔ V of ｃｔｒｌ The calculation results of the dependency are shown below. ＢＩＡＳ = 10mA, G ｍ =2・0.01 / 0.8Ω －１ , Q=25, L=25pH, C １ = 40 fF, C ２ａ = -2fF / V, C ２ｂ = 10 fF, Z Ｌ = 50Ω.

[0019] Output power P ｏｕｔ is V ｃｔｒｌ = 2.5V, minimum value 23.3dBm, V ｃｔｒｌ = -0.5V and the maximum value is 25.1dBm. ｃｔｒｌ = -0.5-2.5V, the output power change range ΔP ｏｕｔ The output power is about 109.6 mW (40.7%). As described above, the large fluctuation range of the output power has been a problem in conventional VCOs.

[0020] In order to solve the above-mentioned problems, the voltage-controlled oscillator according to the present invention comprises an oscillation circuit including a transistor, an inductor, and a capacitor, and feeding back a portion of the output of the transistor to the input of the transistor via a circuit consisting of the inductor and the capacitor, a load impedance connected to the collector of the transistor, and a variable capacitor connected to the collector of the transistor in parallel with the load impedance.

[0021] Furthermore, a voltage-controlled oscillator according to the present invention comprises a transistor, a first capacitance, a second capacitance, an inductor, a resistor, a load impedance, another variable capacitance, and a variable capacitance, wherein the first capacitance is connected between the emitter and base of the transistor, the second capacitance is connected between the collector and base of the transistor, an inductor and a resistor are connected in series to the base of the transistor, another variable capacitance is connected to the emitter of the transistor, a load impedance is connected to the collector of the transistor, and the variable capacitance is connected in parallel to the load impedance.

[0022] According to the present invention, it is possible to provide a voltage controlled oscillator capable of suppressing fluctuations in output.

[0023] FIG. 1 is a circuit diagram showing the configuration of a voltage-controlled oscillator according to a first embodiment of the present invention. FIG. 2 is a diagram showing a small-signal equivalent circuit of the voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 3 is a diagram for explaining the effects of the voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 4 is a circuit diagram showing an example of the configuration of a voltage-controlled oscillator according to the first embodiment of the present invention. FIG. 5 is a circuit diagram showing the configuration of a voltage-controlled oscillator according to a second embodiment of the present invention. FIG. 6 is a circuit diagram showing an example of the configuration of a voltage-controlled oscillator according to the second embodiment of the present invention. FIG. 7 is a diagram for explaining the effects of the example of the configuration of the voltage-controlled oscillator according to the second embodiment of the present invention. FIG. 8 is a diagram for explaining the effects of the example of the configuration of the voltage-controlled oscillator according to the second embodiment of the present invention. FIG. 9 is a circuit diagram showing the configuration of a conventional voltage-controlled oscillator. FIG. 10 is a diagram showing a small-signal equivalent circuit of the conventional voltage-controlled oscillator. FIG. 11 is a diagram for explaining the operation of the conventional voltage-controlled oscillator.

[0024] First Embodiment A voltage controlled oscillator according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG.

[0025] <Configuration of Voltage-Controlled Oscillator> A voltage-controlled oscillator 10 according to this embodiment includes a transistor, a load impedance connected to the collector of the transistor, and a variable capacitance connected to the collector of the transistor in parallel with the load impedance.

[0026] 1 shows an example of the configuration of a voltage-controlled oscillator 10. In the voltage-controlled oscillator 10, a variable capacitance is connected in parallel with a load impedance to the collector of a transistor of a Colpitts type VCO. １ and a transistor Q １ In this case, the capacitance C １ , a capacitance C between the collector and base ｂｃ is connected to the transistor Q １ At the base of ｓ are connected in series, and a bias voltage V ＢＩＡＳ is applied to the transistor Q １ The emitter of ２ is connected. Also, the transistor Q １ A current source is connected to the emitter of ＢＩＡＳ is supplied. Transistor Q １ The collector of the load impedance Z Ｌ is connected. Also, the transistor Q １ The collector of Ｌ In parallel with Ｔ is connected.

[0027] <Effects> The effects of the voltage controlled oscillator 10 according to this embodiment will be described below. FIG.

[0028] In general, a voltage controlled oscillator is obtained by calculating ω that satisfies equation (7).

[0029]

[0030] In this embodiment, in the voltage controlled oscillator 10, Z Ｌ does not include an imaginary part (pure resistance). In this case, the output frequency is expressed by equation (8). The output power is expressed by equation (9). Here, the variable capacitance C T Also C ２ is the control voltage V ｃｔｒｌ It changes depending on the １ , C ｂｃ also changes.

[0031]

[0032]

[0033] Z Ｌ is the pure resistance (Z Ｌ =R), C ２ is C ２ =C ２ａ ・V ｃｔｒｌ +C ２ｂ C T Also C ２ Similarly, C T =C Ｔａ ・V ｃｔｒｌ +C Ｔｂ G ｍ , Q, C １ , C ｂｃ V ｃｔｒｌ Assuming that the output power is independent of the input power, the output power is expressed by equation (10).

[0034]

[0035] Here, the conventional VCO and the VCO are controlled by the same control voltage V ｃｔｒｌ It is assumed that the output power of the conventional VCO is operated in the range of P ｏｕｔ１ (V ｃｔｒｌ１ ) and P ｏｕｔ１ V when is maximum ｃｔｒｌ１ The value of V ｃｔｒｌ１＿ｍａｘ , when V is minimum ｃｔｒｌ１ The value of V ｃｔｒｌ１＿ｍｉｎ Let the output power of the VCO be P ｏｕｔ２ (V ｃｔｒｌ２ ) and P ｏｕｔ２ V when is maximumｃｔｒｌ２ The value of V ｃｔｒｌ２＿ｍａｘ , when V is minimum ｃｔｒｌ２ The value of V ｃｔｒｌ２＿ｍｉｎ Let's say.

[0036] In the VCO according to this embodiment, the fluctuation range of the output power can be suppressed by setting each parameter so as to satisfy the formula (11). For example, C1, Cbc, L, Rs, and the variable capacitance C Ｔ Coefficient C that determines Ｔａ , C Ｔｂ and other parameters are set, and the control voltage V ｃｔｒｌ The variable capacitance C Ｔ By changing the value of the output voltage, the fluctuation range of the output power can be suppressed.

[0037]

[0038] FIG. 3 shows the output power P obtained from equation (10) in the VCO. ｏｕｔ V of ｃｔｒｌ The results of the dependency calculation are shown below.

[0039] In the calculation, I ＢＩＡＳ = 10mA, G ｍ =2・0.01 / 0.8Ω －１ , Q=25, L=25pH, C １ = 40 fF, C ２ａ = -2fF / V, C ２ｂ = 10 fF, Z Ｌ = 50Ω, C Ｔａ = -4fF / V, C Ｔｂ = 20 fF, C ｂｃ = 10 fF.

[0040] For comparison, the output power P ｏｕｔ V of ｃｔｒｌ The dependency is also shown (dotted line in the figure, same as in FIG. 11).

[0041] In the conventional VCO, as described above, V ｃｔｒｌ = -0.5-2.5V, the output power change range ΔP ｏｕｔ is about 109.6 mW (40.7%).

[0042] On the other hand, in the VCO, the output power P ｏｕｔ is V ｃｔｒｌ = 2.5V, minimum value 21.7dBm, Vｃｔｒｌ = 0.76V and the maximum value is 22.1 dBm. ｃｔｒｌ = -0.5-2.5V, the output power change range ΔP ｏｕｔ is about 14 mW (8.98%).

[0043] In this way, the VCO can suppress the variation range of the output power compared to a conventional VCO.

[0044] In this embodiment, the variable capacitance C ２ , C Ｔ However, the present invention is not limited to this. For example, as shown in Fig. 4, an E-B diode with B-C shorted may be used as the variable capacitance. Alternatively, a B-C diode with B-E shorted, an E-B diode with C open, a B-C diode with E open, or a mirror variable capacitance may be used as the variable capacitance.

[0045] An LC resonator may be used as the load impedance in the VCO according to this embodiment, and the frequency may be adjusted by changing the capacitance C of the LC resonator.

[0046] Second Embodiment A voltage controlled oscillator according to a second embodiment of the present invention will be described with reference to FIGS.

[0047] <Configuration of Voltage-Controlled Oscillator> As shown in FIG. 5, a voltage-controlled oscillator (VCO) 20 according to this embodiment has a differential circuit configuration in which the voltage-controlled oscillators (VCOs) according to the first embodiment are combined.

[0048] In the voltage-controlled oscillator 20, the base of the transistor Q1 in one circuit and the base of the transistor Q2 in the other circuit are connected via their respective inductors L and resistors Rs. The resistor Rs in one circuit is connected to the resistor Rs in the other circuit, and the node is connected to a voltage terminal (V ＢＩＡＳ ) bias impedance Z ＢＩＡＳ１ is connected, and a bias impedance Z ＢＩＡＳ２ A current source is connected to the emitter of the transistor Q1 in one circuit and the emitter of the transistor Q2 in the other circuit, and a bias current 2I ＢＩＡＳ is supplied.

[0049] In the VCO 20, the impedance Z of the bias circuit at the VCO oscillation frequency is set to be differential oscillation rather than common-phase oscillation. ＢＩＡＳ１ and Z ＢＩＡＳ２ It is desirable to set the value of .

[0050] Z in VCO20 ＢＩＡＳ１ and Z ＢＩＡＳ２ A resistor or an inductor may be used for Z, or a combination of these may be used. ＢＩＡＳ１ is the inductor, Z ＢＩＡＳ２ It is desirable to make the information available to the public.

[0051] In the VCO 20, the load impedance Z Ｌ A common-base (CB) buffer circuit may be inserted between the VCO and the LC tank circuit, which can suppress the effects of changes in load impedance on the LC tank circuit and avoid problems such as oscillation halting due to a circuit connected to the VCO load (post-stage).

[0052] In this configuration, a variable capacitance may be added to the node where the collector terminal of the transistor in the LC tank circuit and the emitter terminal of the transistor in the CB buffer circuit are connected (see FIG. 6). Alternatively, the collector terminal of the transistor in the CB buffer circuit and the load impedance Z Ｌ A variable capacitance may be added to the node to which

[0053] In this embodiment, the core oscillator (Z in FIG. Ｌ and C ＴAlthough an example using a Colpitts oscillator circuit in a circuit other than the above has been shown, the present invention is not limited to this. An oscillator circuit may be used that includes a transistor, an inductor, and a capacitor, and feeds back a portion of the transistor's output to the transistor's input via a circuit (LC circuit) consisting of an inductor and a capacitor. In this oscillator circuit, only a signal of a specific frequency may be fed back via the LC circuit (for example, this may be referred to as a selective feedback oscillator circuit). An oscillator circuit in which an admittance consisting of at least an inductor and a capacitor is connected in parallel between the base and emitter, the base and collector, or the collector and emitter of the transistor may also be used. Circuits with configurations other than a circuit topology that changes frequency by changing the capacitance C of an LC circuit used as a load impedance may also be used. For example, oscillators such as a Clapp oscillator, a Hartley oscillator, or a Pierce oscillator may also be used, or oscillators with a combination of these may also be used.

[0054] As an example of a voltage-controlled oscillator according to this embodiment, a configuration using a VCO that uses a Colpitts-Clapp oscillator as its core oscillator (Colpitts-Clapp VCO) will be described below. Figure 7 shows the calculation results of the output power of this VCO.

[0055] The calculation was performed for a 100 GHz band differential Colpitts-Clapp VCO (with a CB buffer circuit) using the software "Advanced Design System (ADS, Keysight Corporation)." The parameters used in the calculation were V ＣＣ (power supply voltage) = 4.5 V, Z ＢＩＡＳ２ = 200 pH, Z ＢＩＡＳ = Open, I ＢＩＡＳ = 60mA.

[0056] C Ｔ VCO (solid line in the figure), C Ｔ Calculations were also performed for a VCO with no capacitance (dotted line in the figure) and a VCO with a constant capacitance (=60 fF, fixed capacitance) (dashed line in the figure).

[0057] C Ｔ In a VCO without ｏｕｔis 26.6 mW (74.5%). For a VCO with a constant C (fixed capacitance), ΔP ｏｕｔ is 21.3 mW (53.9%).

[0058] On the other hand, C Ｔ For a VCO with ｏｕｔ is 19.2 mW (51.8%). Ｔ By adding ｏｕｔ can be reduced.

[0059] Figure 8 shows the calculation results of the output frequency of a VCO using a Clapp oscillator as the load impedance. As in the above, a 100 GHz band differential Colpitts-Clapp VCO (with a CB buffer circuit) was used for the calculation. Ｔ VCO (solid line in the figure), C Ｔ The output frequencies of a VCO without a constant capacitance (dotted line in the figure) and a VCO with a constant capacitance (=60 fF, fixed capacitance) (dashed line in the figure) are also shown.

[0060] C Ｔ For a VCO without ｏｓｃ is 17.2 GHz. For a VCO with a constant C (fixed capacitance), Δf ｏｓｃ is 19.1 GHz. On the other hand, C Ｔ For a VCO with ｏｓｃ is 19.4 GHz. Ｔ By adding ｏｓｃ In this way, in this embodiment, the range of output frequencies f ｏｓｃ may be expanded.

[0061] In this embodiment, the variable capacitance C ２ , C Ｔ However, the present invention is not limited to this. For example, an E-B diode with B-C shorted may be used as the variable capacitance. Alternatively, a B-C diode with B-E shorted or a mirror variable capacitance may be used as the variable capacitance.

[0062] In the present embodiment, an example in which bipolar transistors are used has been shown, but the present invention is not limited to this, and the circuit may be configured by combining bipolar transistors and CMOS transistors.

[0063] In the embodiments of the present invention, examples of the structure, dimensions, materials, etc. of each component in the configuration and manufacturing method of the voltage-controlled oscillator are shown, but the present invention is not limited to these. Anything that can demonstrate the function and effect of the voltage-controlled oscillator may be used.

[0064] It should be noted that the present invention is not limited to the above-described embodiments, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0065] 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.

[0066] (Supplementary Note 1) A voltage-controlled oscillator comprising: an oscillation circuit including a transistor, an inductor, and a capacitor, wherein a portion of the output of the transistor is fed back to the input of the transistor via a circuit consisting of the inductor and the capacitor; a load impedance connected to the collector of the transistor; and a variable capacitor connected to the collector of the transistor in parallel with the load impedance.

[0067] (Supplementary Note 2) The voltage-controlled oscillator according to Supplementary Note 1, wherein fluctuations in the output of the voltage-controlled oscillator are suppressed.

[0068] (Supplementary Note 3) A voltage-controlled oscillator comprising two voltage-controlled oscillators according to Supplementary Note 1 or Supplementary Note 2, one of the voltage-controlled oscillators and the other of the voltage-controlled oscillators forming a differential circuit.

[0069] (Supplementary Note 4) A voltage-controlled oscillator comprising a transistor, a first capacitance, a second capacitance, an inductor, a resistor, a load impedance, another variable capacitance, and a variable capacitance, wherein the first capacitance is connected between the emitter and base of the transistor, the second capacitance is connected between the collector and base of the transistor, an inductor and a resistor are connected in series to the base of the transistor, another variable capacitance is connected to the emitter of the transistor, a load impedance is connected to the collector of the transistor, and the variable capacitance is connected in parallel to the load impedance.

[0070] (Supplementary Note 5) A voltage-controlled oscillator comprising two voltage-controlled oscillators according to Supplementary Note 4, the voltage-controlled oscillator comprising a voltage terminal, a first bias impedance, and a second bias impedance, one of the voltage-controlled oscillators and the other of the voltage-controlled oscillators constituting a differential circuit, the base of the transistor of one of the voltage-controlled oscillators being connected to the base of the transistor of the other of the voltage-controlled oscillators via the inductor and the resistor, respectively, the first bias impedance being connected between the voltage terminal and a node between the one resistor and the other resistor, and the second bias impedance being connected between the node and ground.

[0071] (Supplementary Note 6) A voltage-controlled oscillator according to Supplementary Note 5, wherein a first transistor is connected between the collector of the transistor in one of the voltage-controlled oscillators and the load impedance, a second transistor is connected between the collector of the transistor in the other of the voltage-controlled oscillators and the load impedance, and the base of the first transistor and the base of the second transistor are connected.

[0072] The present invention relates to a voltage-controlled oscillator, and can be applied to communication devices and communication systems.

[0073] 10 Voltage Controlled Oscillator

Claims

1. A voltage-controlled oscillator comprising: an oscillation circuit having a transistor, an inductor, and a capacitor, wherein a portion of the output of the transistor is fed back to the input of the transistor via a circuit consisting of the inductor and the capacitor; a load impedance connected to the collector of the transistor; and a variable capacitor connected to the collector of the transistor in parallel with the load impedance.

2. The voltage controlled oscillator according to claim 1, wherein the change in capacitance value of said variable capacitor suppresses fluctuations in the output of said voltage controlled oscillator.

3. A voltage-controlled oscillator comprising two voltage-controlled oscillators according to claim 1 or 2, one of which and the other of which constitute a differential circuit.

4. A voltage controlled oscillator comprising: a transistor; a first capacitance; a second capacitance; an inductor; a resistor; a load impedance; another variable capacitance; and a variable capacitance, wherein the first capacitance is connected between the emitter and base of the transistor; the second capacitance is connected between the collector and base of the transistor; an inductor and a resistor are connected in series to the base of the transistor; another variable capacitance is connected to the emitter of the transistor; a load impedance is connected to the collector of the transistor; and a variable capacitance is connected in parallel to the load impedance.

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