VCO Gain Control Method and Circuit

Abstract

To provide a VCO gain control circuit that can separate and control the nonlinearity of the VCO gain and the variability of the VCO gain, does not increase the circuit scale, and has high versatility.SOLUTION: A VCO gain control circuit according to the present invention is a VCO gain control circuit that controls the VCO gain of VCO 103, and includes a feedback circuit that amplifies a difference between a monitor voltage Vfmo and a reference voltage Vset according to the output frequency of the VCO 103 by a variable first gain α and feeds back the difference to the input voltage Vcont to the VCO 103, and the reference voltage Vset is a voltage obtained by amplifying or attenuating the input voltage Vcont with a second gain β (112).SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a VCO gain control method and its circuit that enable adjustment of the VCO gain.

Background Art

[0002] A voltage-controlled oscillator (VCO: Voltage-controlled oscillator; hereinafter referred to as VCO) in which the frequency of an output signal changes with respect to an input voltage is used in a phase-locked loop (PLL: phase locked loop; hereinafter referred to as PLL), a frequency demodulation circuit, etc., and is widely used in wireless transmission devices, sensors, etc.

[0003] An important factor representing the performance of a VCO is the relationship between the input control voltage and the output frequency.

[0004] The relationship between the input control voltage (V cont ) of the VCO and the output frequency is shown as the VCO gain (K v ). K v is a value representing the change amount of the output frequency (fo) with respect to the change amount of the input control voltage, and the unit is [Hz / V]. The basic equation showing the relationship between the input control voltage and the output frequency of the VCO is, when the VCO offset frequency is f offvco ,

Equation

[0005] Ideally, the characteristic of the VCO gain is that the VCO gain is a constant value in the oscillation frequency band of the VCO. That is, it is desirable that the input control voltage and the output frequency are linear in the oscillation frequency band of the VCO as in the above equation.

[0006] (First Problem) However, generally, the characteristics of the VCO gain are non-linear. In the case of a PLL circuit, for example, Patent Document 1 shows that problems due to the non-linearity of the VCO gain can cause loop oscillation due to an increase in phase noise and a decrease in loop stability. Also, Patent Document 2 shows that when generating a frequency-modulated continuous wave (FMCW) used in a radar system with a VCO, the range resolution deteriorates due to the non-linearity of the VCO gain.

[0007] (Second problem) In addition to the linearity of the VCO gain, the value of the VCO gain is also an important factor representing the performance of the VCO. The magnitude of the VCO gain is an important factor particularly in a PLL that changes the output frequency in a short time.

[0008] In a PLL that changes the output frequency in a short time, in order to solve the conflicting requirements of reducing the lock-up time and reducing the phase noise, the open-loop gain (or closed-loop gain) of the PLL is made high (or wide) at the time of lock-up and low (or narrow) after lock-up. For example, Patent Document 3 describes a method of making the VCO gain of a VCO using a varactor variable to make the open-loop gain of the PLL variable, thereby realizing reduction of the lock-up time and reduction of the phase noise.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] ·Regarding Patent Document 1 As a method for improving the non-linearity of the VCO gain, Patent Document 1 converts the output signal from the loop filter, which is a component of the PLL, from an analog signal to a digital signal, detects the non-linearity of the VCO gain by digital signal processing, and adjusts the gain of the phase converter, which is a component of the PLL, and the capacitance and resistance of the loop filter to solve the degradation of characteristics caused by the non-linearity of the VCO gain by adjusting the loop gain.

[0011] Although not specified in Patent Document 1, since it is a method for adjusting the loop gain, it can also be applied as a method for reducing the lock-up time and reducing the phase noise.

[0012] On the other hand, an analog-digital converter and a digital signal processing circuit are required for detecting the non-linearity of the VCO gain, and there is a problem that the circuit scale increases. Also, the method shown in Patent Document 1 is an effective method in the PLL circuit configuration, and its application is difficult when the VCO is used for other purposes.

[0013] That is, the technology of Patent Document 1 can solve the above-described first and second problems, but new problems regarding the circuit scale and versatility will occur.

[0014] ·Regarding Patent Document 2 Patent Document 2 describes means for correcting the non-linearity of the VCO gain for the purpose of generating an FMCW signal. However, similar to Patent Document 1, an analog-digital converter and a digital signal processing circuit are required for detecting the non-linearity of the VCO gain, and there is a problem that the circuit scale increases. Also, it only corrects the non-linearity of the VCO gain, and does not describe the technology and effects for controlling the magnitude of the VCO gain.

[0015] That is, the technology of Patent Document 2 can solve the above-described first problem, but cannot solve the second problem, and new problems regarding the circuit scale will occur.

[0016] · Regarding Patent Document 3 In Patent Document 3, a technique is disclosed in which by making the VCO gain variable, reduction of lock-up time and reduction of phase noise are achieved. The technique of Patent Document 3 is limited to a VCO using a varactor for the circuit configuration of the VCO, and also does not describe the technique and effect for improving the non-linearity of the VCO gain.

[0017] That is, the technique of Patent Document 3 can solve the above-described second problem, but cannot solve the first problem, and new problems regarding versatility will occur.

[0018] · Regarding Patent Document 4 As a means for correcting the non-linearity of the VCO gain, Patent Document 4 discloses a method in which the output frequency signal of the VCO is converted into a voltage signal corresponding to the input frequency via a frequency-voltage converter (F / V converter: Frequency / Voltage converter), compared with the control voltage of the VCO to obtain an error, and the control voltage of the VCO is controlled so that this error signal disappears. However, the technique of Patent Document 4 can only realize a method for correcting the non-linearity of the VCO gain.

[0019] That is, the technique of Patent Document 4 can solve the above-described first problem, but cannot solve the second problem.

[0020] Therefore, an object of the present invention is to provide a VCO gain control method and circuit that can separately control the non-linearity and variability of the VCO gain, do not increase the circuit scale, and have high versatility in order to solve all of the above problems.

Means for Solving the Problems

[0021] In order to achieve the above object, in the VCO gain control method and circuit according to the present invention, when amplifying the difference between the monitor voltage corresponding to the output frequency of the VCO and the reference voltage and feeding it back to the input voltage to the VCO, the variable gain and linearity improvement of the VCO are achieved by the amplification amount.

[0022] Specifically, the VCO gain control method according to the present invention is a VCO gain control method for controlling the gain of a voltage controlled oscillator (VCO), which amplifies the difference between a monitor voltage corresponding to the output frequency of the VCO and a reference voltage with a variable first gain and feeds it back to the input voltage to the VCO, and amplifies or attenuates the input voltage with a second gain to obtain the reference voltage.

[0023] Further, the VCO gain control circuit according to the present invention is a VCO gain control circuit for controlling the gain of a voltage controlled oscillator (VCO), which includes a feedback circuit that amplifies the difference between a monitor voltage corresponding to the output frequency of the VCO and a reference voltage with a variable first gain and feeds it back to the input voltage to the VCO, and is characterized in that the reference voltage is a voltage obtained by amplifying or attenuating the input voltage with a second gain.

[0024] Although specific explanations will be given later, by adjusting the first gain α of the feedback circuit, the variability and linearity of the VCO gain can be improved. Also, by setting the second gain β, the linearity and variability of the VCO gain can be separately controlled. Since this circuit does not require an analog-to-digital converter and a digital signal processing circuit, the circuit scale does not increase. In addition, since this circuit can be applied to any type of VCO, it has high versatility.

[0025] Therefore, the present invention can provide a VCO gain control method and circuit that can separately control the non-linearity and variability of the VCO gain, do not increase the circuit scale, and have high versatility.

Advantages of the Invention

[0026] The present invention can provide a VCO gain control method and circuit that can separately control the non-linearity and variability of the VCO gain, do not increase the circuit scale, and have high versatility.

Brief Description of the Drawings

[0027]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0028] Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, components having the same reference numerals indicate the same components as each other.

[0029] (Embodiment 1) FIG. 1 is a block diagram for explaining the VCO gain control circuit 100 of the present embodiment. The VCO gain control circuit 100 is a VCO gain control circuit that controls the VCO gain of the VCO 103, and A monitor voltage V corresponding to the output frequency of the VCO 103 fmo and a reference voltage V set The difference between them is amplified by a variable first gain α to obtain an input voltage V to the VCO 103 cont characterized by comprising a feedback circuit for feeding back to In FIG. 1, the feedback circuit is a closed-loop circuit composed of an F / V converter 108 that outputs a voltage corresponding to the frequency, an adder 107, an amplifier 106, and an adder 102.

[0030] The VCO 103 takes an input signal Vo (109) as an input and outputs a signal having a frequency fo (104) corresponding to Vo. The frequency fo becomes the input of the F / V converter 108, and a voltage V fmo (111) is output.

[0031] The adder 107 generates a signal obtained by subtracting V set (105) of the reference voltage from V fmo . The amplifier 106 amplifies the signal by α times to generate a voltage V re (110). The adder 102 adds the input control voltage V cont (101) that indicates the frequency output by the VCO 103 and the voltage V re to generate a voltage Vo and input it to the VCO 103. In this embodiment, the reference voltage V set (105) is a constant value.

[0032] The voltage Vre is represented by equation (1).

Equation

Equation

Equation

Equation

[0033] Substituting Equation (4) into Equation (3) gives Equation (5).

Equation

Equation

Equation

[0034] Assuming that the input signal frequency and the output signal of the F / V converter 108 are linear, Lv becomes a constant and 1 / Lv also becomes a constant. Also, since Lv is a quantity with the unit of [V / Hz], the unit of 1 / Lv is [Hz / V].[[]END]]

[0035] In Equation (6), V cont , V set , and Vo are quantities with the unit of voltage, so the three terms each have the unit of [Hz] and match the frequency of fo. However, since Vo is a function of V cont from Equation (5), Equation (6) can be expressed as Equation (7).

Equation

[0036] Here, the overall gain K vtotal (frequency change amount per unit voltage; sensitivity characteristic) of the gain control circuit 100 is the input control signal Vcont Since it is the ratio of the change in the output signal frequency fo of the VCO 103 with respect to V, (7) is obtained by differentiating with respect to V and becomes (8). cont and is obtained by differentiating the formula (7) with respect to V, resulting in the formula (8).

Equation

Equation

[0037] In the formula (8)

Equation

[0038] Also, in the formula (8)

Equation

[0039] Therefore, the gain control circuit 100 can adjust the gain K of the gain control circuit 100 with the gain α of the amplifier 106, and can also reduce the influence of the non-linearity of the VCO 103 by increasing the gain α. vtotal can be adjusted, and by increasing the gain α, the influence of the non-linearity of the VCO 103 can also be reduced.

[0040] (Example 1) FIG. 2 is a specific circuit example of the gain control circuit 100. FIG. 3 is the VF characteristic (control voltage V contOutput frequency f with respect to o is a diagram for explaining the gain α-dependence of the gain characteristics (control voltage V cont with respect to the VCO gain (K v )) of the gain control circuit 100 of FIG. 2.

[0041] As shown in FIG. 3, the slope (gain) between the input control voltage and the output frequency can be adjusted with the gain α. Also, as shown in FIG. 4, increasing the gain α decreases the VCO gain (Kv), and the non-linearity between the input control voltage and the VCO gain is also improved. Therefore, if α shown in FIG. 3 is further increased and approaches infinity, it converges to a constant frequency (in the VF characteristics of FIG. 3, fo ≒ 2.5 GHz in the entire range of V cont = -1 to +1 V). As a result, in FIG. 4, the gain approaches 0.0 [GHz / V] in the entire range of V cont = -1 to +1 V. That is, the VCO gain control circuit according to the present invention can adjust the slope (gain) of the VF characteristics of the VCO by adjusting the gain α, and can also improve the non-linearity of the gain.

[0042] (Embodiment 2) In the VCO gain control circuit 100 of Embodiment 1, the larger the gain α, the gentler the slope of the VF characteristics as shown in FIG. 3, and the non-linearity of the VCO gain is also improved as shown in FIG. 4. However, as shown in FIG. 4, the value of the VCO gain (Kv) varies depending on the gain α. That is, if the gain α is increased to improve the non-linearity of the VCO gain, the value of the VCO gain (Kv) is determined by the value of the gain α.

[0043] Therefore, in the present embodiment, a circuit for improving the variation of the VCO gain depending on the gain α will be described. FIG. 5 is a diagram for explaining the VCO gain control circuit 150 of the present embodiment. The VCO gain control circuit 150 is different from the VCO gain control circuit 100 of FIG. 1 in that the reference voltage V set is a voltage obtained by amplifying or attenuating the input voltage V cont with a second gain β (112).

[0044] The operating principle of the VCO gain control circuit 150 will be described. The Vo in FIG. 5 is expressed by equation (5) shown in the VCO gain control circuit 100. In the VCO gain control circuit 100, a reference voltage V set (constant value) was applied. In the VCO gain control circuit 150, the reference voltage V set is proportional to the input control voltage V cont . That is, the reference voltage V set in this embodiment is expressed by equation (9) which is β times the input control voltage V cont .

Equation

[0045] Substituting equation (9) into equation (5) gives equation (10).

Equation

[0046] As described in Embodiment 1, since V o is a function of V cont , equation (10) can be expressed by equation (11).

Equation

[0047] Since the gain of the entire VCO gain control circuit 150 is the ratio of the change in the VCO output signal frequency (f cont ) with respect to the input control signal (V o ), it is obtained by differentiating equation (11) with respect to V cont , resulting in equation (12).

Equation

[0048] For the first term of equation (12)

Equation

[0049] Therefore, α in the first term can be used to suppress non-linearity. By increasing α, the non-linearity of the first term contributing to Δf o becomes smaller, and Δf o approaches the value of the second term β / Lv. As a result, Δf o becomes constant with respect to the change in V cont . Even if there is non-linearity in the VCO as this component, it operates as a circuit having a linear gain as the entire system.

[0050] As is clear from the above description, by using the circuit configuration of the VCO gain control circuit 150, the value of the VCO gain can be adjusted by the gain β, and separately from the gain adjustment, the non-linearity of the VCO gain can be corrected by the gain α.

[0051] (Embodiment 2) FIG. 6 is a specific circuit example of the VCO gain control circuit 150. FIG. 7 is a diagram for explaining the gain α dependence of the VF characteristic (characteristic of the output frequency f cont with respect to the control voltage V o ) in the VCO gain control circuit 150 of FIG. 6 (gain β = 0.095 fixed). FIG. 8 is a diagram for explaining the gain α dependence of the gain characteristic (characteristic of the VCO gain (K cont with respect to the control voltage V v ) in the VCO gain control circuit 150 of FIG. 6 (gain β = 0.095 fixed). FIG. 9 is a diagram for explaining the gain β dependence of the VF characteristic (characteristic of the output frequency f cont with respect to the control voltage V o ) in the VCO gain control circuit 150 of FIG. 6 (gain α = 10 fixed). FIG. 10 is a diagram for explaining the gain β dependence of the gain characteristic (characteristic of the VCO gain (K cont with respect to the control voltage V v) is a diagram for explaining the gain β-dependency of the characteristics) (gain α = 10 fixed).

[0052] As described above, the gain α can adjust the error in the feedback circuit, and by increasing its value, the linearity of the VF characteristics of the VCO 103 can be improved. On the other hand, the gain β determines the gain (slope) at which the VF characteristics converge, and when its value is decreased, the gain becomes smaller. That is, with the gain α and the gain β, the non-linearity of the VCO gain and its value can be adjusted.

[0053] In FIGS. 7 and 8, when the gain α is further increased and approached to infinity in the same manner as the description of Embodiment 1, it converges to a VF characteristic with a certain slope where β = 0.095, different from the VCO gain control circuit 100. For example, in the case of the VF characteristic of FIG. 7, even if the gain α is approached to infinity, the VF characteristic has the same slope as α = 20 in FIG. 7. As a result, in FIG. 8, V cont The VCO gain is constant at ≒ 2.5 [Hz / V] in the range of V ≒ -0.7 to +0.7 V.

[0054] In FIGS. 9 and 10, when β is further decreased to 0, the characteristics of the VCO gain control circuit 150 become the same as those of the VCO gain control circuit 100 described in Embodiment 1 (α = 10 in FIGS. 3 and 4). Here, when α is further increased and approached to infinity for each β in FIG. 9, the VF characteristics converge with the error improved near the respective slopes in FIG. 9. For example, in the case of FIG. 10, it becomes a constant value with the following gains. β = 0.095 (dotted line) Gain ≒ 2.5 [Hz / V] β = 0.055 (broken line) Gain ≒ 2.0 [Hz / V] β = 0.025 (dash-dotted line) Gain ≒ 1.5 [Hz / V]

[0055] Summarizing the characteristics of the VCO gain control circuit with respect to the gains α and β through Embodiments 1 and 2 is as follows. The VCO gain control circuit 100 corresponds to β = 0 in the VCO gain control circuit 150. Therefore, FIG. 3 explains that the slope of the VF characteristic can be adjusted by the gain α, and FIG. 4 explains that the VCO gain varies with the gain α and suppresses the nonlinearity of the VCO gain. And it is explained that if the gain α is infinite, it converges to the VCO gain = 0.0 [GHz / V] determined by β = 0.000.

[0056] FIG. 7 also explains that the slope of the VF characteristic can be adjusted by the gain α, and FIG. 8 explains that the nonlinearity of the VCO gain can be suppressed by the gain α. And it is explained that if the gain α is infinite, it converges to the VCO gain ≒ 2.5 [GHz / V] determined by β = 0.095.

[0057] FIGS. 9 and 10 explain that the slope of the VF characteristic changes with the gain β and the VCO gain changes.

[0058] (Embodiment 3) FIG. 11 is a block diagram for explaining the VCO gain control circuit 160 of the present embodiment. The VCO gain control circuit 160 is different from the VCO gain control circuit 150 in FIG. 5 in that it further includes an addition circuit 114 that adds an offset voltage V set to the reference voltage V oft .

[0059] For example, even if the input signal frequency and the output signal of the F / V converter 108 are linear, there may be an offset. There may also be an offset in the functional units constituting the feedback circuit other than the F / V converter 108. In such a case, the VCO 103 cannot be correctly controlled. Therefore, the VCO gain control circuit 160 adds the offset voltage V set to the reference voltage V oft to correct the offset.

[0060] That is, the VCO gain control circuit 160 offsets the offset existing in the feedback circuit by the offset voltage V oftIt can be corrected. In FIG. 11, although it is configured to add the offset voltage V to the output of the gain amplifier 112 of the VCO gain control circuit 150 in FIG. 5, it may be configured to add the offset voltage V to the reference voltage V of the VCO gain control circuit 100 in FIG. 1. oft However, it may be configured to add the offset voltage V to the reference voltage V of the VCO gain control circuit 100 in FIG. 1. set to the reference voltage V of the VCO gain control circuit 100 in FIG. 1. oft It may be configured to add the offset voltage V.

[0061] (Embodiment 4) FIG. 12 is a block diagram for explaining the VCO gain control circuit 170 of this embodiment. The gain control circuit 170 is different from the gain control circuit 150 in FIG. 5 in that the feedback circuit generates the monitor voltage V based on the frequency obtained by dividing the output frequency of the VCO 103. Specifically, the VCO gain control circuit 170 further includes a divider 115 with respect to the VCO gain control circuit 150 in FIG. 5. fmo Specifically, the VCO gain control circuit 170 further includes a divider 115 with respect to the VCO gain control circuit 150 in FIG. 5.

[0062] By dividing the output frequency f of the VCO 103 by the divider 115, o a low-frequency F / V converter 108 can be used, and the cost of the VCO gain control circuit can be reduced. In FIG. 12, although the divider 115 is arranged in the feedback circuit of the VCO gain control circuit 150 in FIG. 5, it may be arranged in the feedback circuit of the VCO gain control circuit 100 in FIG. 1.

[0063] (Advantages of the Invention) As is clear from the above description, according to the present invention, without relying on digital signal processing that requires an analog-to-digital converter as a means for detecting the non-linearity of the VCO gain, the output frequency signal of the VCO is converted into a voltage signal corresponding to the input frequency via an F / V converter, the error is obtained by comparing the input voltage with the increased or decreased reference voltage and the output of the F / V converter, and this error signal is added or subtracted from the input control voltage to obtain the control voltage of the VCO. Based on this method, it is possible to provide a VCO gain adjustment method and circuit that can adjust the value of the VCO gain and correct the non-linearity of the VCO gain regardless of the circuit form of the VCO.

[0064] (Appendix) The differences between the VCO gain control method and its circuit according to the present invention and Patent Document 4 are summarized below. The structure of the VCO gain control circuit of the present invention is different from the circuit described in Patent Document 4. Specifically, the circuit described in Patent Document 4 includes an error amplifier, a first slope / offset adjuster, and a feedback circuit including a variable voltage device, and a second slope / offset adjuster that adjusts an input control voltage (frequency modulator). Therefore, the circuit described in Patent Document 4 needs to adjust a total of six parameters, namely, the "gain" of the error amplifier, the "slope" and "offset" of the first slope / offset adjuster, the "slope" and "offset" of the second slope / offset adjuster, and the "variable voltage device", considering the relationship between the output and input (frequency modulator) of the frequency-voltage converter and the operating characteristics of the error amplifier. On the other hand, the VCO gain control circuit of the present invention is composed of a feedback circuit including one amplifier 106 in the case of FIG. 1, and a circuit including a gain device 112 that adjusts the input control voltage (V cont ) in the case of the circuit of FIG. 5. Therefore, since the VCO gain control circuit of the present invention does not require adjustment based on the performance of the F / V converter 108, it only needs to adjust a maximum of three parameters, namely, "gain α", "reference voltage V set or V oft ", and "gain β". As described above, the VCO gain control circuit of the present invention can improve the non-linearity between the input control voltage V cont and the VCO gain with fewer parameters compared to the circuit described in Patent Document 4. Furthermore, the VCO gain control circuit of the present invention can also adjust the VCO gain value, which was impossible with the circuit described in Patent Document 4 (solving the second problem).

Industrial Applicability

[0065] The present invention is used in industries that manufacture oscillators that require a VCO with a wide linearity and a VCO gain value that is a specific value or variable.

Explanation of Reference Numerals

[0066] 100, 150, 160, 170: VCO gain adjustment circuit 101: Input control voltage 102: 2-input adder / subtractor 103: VCO 104: VCO output signal (f o ) 105: Reference voltage (V set ) 106: Amplifier (gain α) 107: 2-input adder / subtractor 108: F / V converter 109: VCO input signal (Vo) 110: Voltage (Vre) 111: Monitor voltage (V fmo ) 112: Gain device (gain or attenuation β) 113: Offset voltage (V ofs ) 114: 2-input adder / subtractor 115: Divider

Claims

1. A VCO gain control method for controlling the gain of a voltage-controlled oscillator (VCO), comprising: amplifying the difference between a monitor voltage corresponding to the output frequency of the VCO and a reference voltage with a variable first gain and feeding it back to the input voltage to the VCO; and amplifying or attenuating the input voltage with a second gain to obtain the reference voltage A VCO gain control method characterized by the above.

2. A VCO gain control circuit for controlling the gain of a voltage-controlled oscillator (VCO), comprising: a feedback circuit that amplifies the difference between a monitor voltage corresponding to the output frequency of the VCO and a reference voltage with a variable first gain and feeds it back to the input voltage to the VCO, wherein the reference voltage is a voltage obtained by amplifying or attenuating the input voltage with a second gain. A VCO gain control circuit characterized by the above.

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