JP2004023762A - Oscillation circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oscillation circuit that reduces phase noise. <P>SOLUTION: A parallel resonant frequency has at least two parallel resonant frequencies. The parallel resonant frequency of a high frequency, a low frequency and a lowest frequency represent f<SB>+</SB>, f<SB>-</SB>and f', respectively. In this point, if either of parallel resonant frequencies f<SB>-</SB>and f<SB>+</SB>is allowed to be brought infinitely closer to either of series resonant frequencies f<SB>1</SB>, and f<SB>3</SB>, and X<SB>1</SB>and X<SB>3</SB>in the vicinity of the resonant frequency f<SB>1</SB>are inverted, the Q of the oscillation circuit and phase noise are allowed to be raised and reduced. Such a resonant frequency is in existence. The variable capacity of a first reactive element column X<SB>1</SB>is conditioned so that the lower parallel resonant frequency f-can be brought infinitely closer to the series resonant frequency f<SB>1</SB>. A targeted frequency represents the f<SB>1</SB>, and this eventually results in an increase in Q value in the frequency f<SB>1</SB>. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an oscillation circuit.
[0002]
[Prior art]
2. Description of the Related Art In the field of communication technology using an oscillation circuit, reduction of phase noise is demanded. Since the phase noise depends on the Q (Quality factor) value, the phase noise can be reduced by increasing the Q value in the resonance circuit forming the oscillation circuit. The Q value is an amount that indicates the sharpness of resonance of the resonance circuit, and is an amount that gives a bandwidth around the resonance frequency (a range in which the power is halved). In a conventional oscillation circuit, a parallel resonance circuit is coupled to a negative resistance circuit, and oscillation is sustained by supplementing power consumption in the parallel resonance circuit with the negative resistance circuit.
[0003]
[Problems to be solved by the invention]
However, in a normal parallel resonance circuit, for example, only one capacitor and one coil are connected in parallel, and the Q value is determined by the characteristics of the coil. No, and therefore phase noise cannot be reduced. More specifically, since the Q value is determined by the resistance of the oscillation circuit and the reactance of the resonance circuit at the time of parallel resonance, these values are finite, so that the Q value cannot be increased. The present invention has been made in view of such a problem, and has as its object to provide an oscillation circuit capable of reducing phase noise.
[0004]
[Means for Solving the Problems]
In order to solve the above problems, a first invention is an oscillation circuit having a resonance circuit coupled to a negative resistance circuit, wherein the resonance circuit includes a first reactance element row and a reference reactance element row connected in parallel with each other. A parallel resonance circuit, wherein the first reactance element row and the reference reactance element row each have a series resonance frequency, at least the first reactance element row has a variable capacitance capacitor, and the variable capacitance The movable range is set so that the series resonance frequency of the first reactance element row and the reference reactance element row can be relatively close to the parallel resonance frequency in the parallel resonance circuit.
[0005]
In other words, the inventors of the present application have made intensive studies on the parallel resonance circuit, and as a result, in the parallel resonance circuit, when the above-described element array is used, the parallel resonance frequency can be made as close as possible to the target series resonance frequency. I discovered that. Therefore, if the movable range of the variable capacitance of the first reactance element row is set as described above, the target series resonance frequency can be made as close as possible to the parallel resonance frequency. The Q value can be improved. In other words, since the Q value has a correlation with the phase noise in the oscillation circuit, the phase noise can be reduced.
[0006]
Note that the “row” in the above-described element row is defined to include a case where only a single element, for example, a capacitor is theoretically provided. The terms “abbreviated”, “near”, and “near” mean that the numerical value of the target parameter is set within a range of 30% or less of the target numerical value. ing.
[0007]
The second invention is characterized in that one of the reactances of the first reactance element row and the reference reactance element example near the parallel resonance frequency is inductive, and the other is capacitive.
[0008]
In this case, the resonance circuit has a parallel resonance frequency.
[0009]
Further, a third invention is characterized in that an additional reactance element array provided in parallel with the reference reactance element array is provided.
[0010]
That is, even if the additional reactance element row is provided, the same operation as the above-described operation is achieved. Such an additional reactance is composed of, for example, a parasitic capacitance of a transistor, a package, a pad, an ESD (electrostatic discharge) element or the like.
[0011]
A fourth invention is characterized in that the movable range of the variable capacitance is set such that the sum of the reciprocals of the reactances of the reactance element rows connected in parallel can be zero.
[0012]
In this case, by appropriately setting the value of the reactance, the approach of the frequency can be achieved as described above.
[0013]
That is, since the Q value of the resonance circuit is proportional to the reciprocal of the reactance, the Q value increases as the reactance approaches zero. There are combinations of capacitance and inductance where two of the reactances of each element array approach zero.
[0014]
When the reactance of the first reactance element row is positive (inductive), the reactance of the additional reactance element row is negative (capacitive), and the reactance of the reference reactance element row is negative (capacitive), or This is a case where the reactance of one reactance element row is negative (capacitive), the reactance of the additional reactance element row is negative (capacitive), and the reactance of the reference reactance element row is positive (inductive). If reactances with different signs are to match each other, even if there is a condition that these values are different, the reactance of the remaining element rows can give a solution, so the sum of the inverse of the reactance is zero. can do. Therefore, there is a combination of a capacitance and an inductance in which two of the reactances of each element row approach zero, that is, a combination of a capacitance and an inductance that theoretically makes the Q value infinite.
[0015]
This means that there is a solution that can make the parallel resonance frequency of the resonance circuit relatively close to the series resonance frequency of the target element row.
[0016]
When the first reactance element row is inductive and the reference reactance element row is capacitive, the Q value is proportional to the inverse of the equivalent parallel resistance or conductance of the resonance circuit, and increases in inverse proportion to the reactance of the first reactance element row. There is a tendency. Assuming that the series resonance frequency of the first reactance element row is one frequency, the parallel resonance frequency of the resonance circuit can be relatively close to this frequency, so that the Q value of the resonance circuit at this frequency can be increased. it can.
[0017]
A fifth invention is characterized in that, in the above invention, the reference reactance element row includes a variable capacitance capacitor. Even when the series resonance frequency of the first reactance element row cannot be made close to one parallel resonance frequency due to a wide band, it is possible to change the series resonance frequency by changing the capacitance of the reference reactance element row. Since the series resonance frequency of the reference reactance element row can be made closer to the series resonance frequency of the first reactance element row, the parallel resonance frequency can be made closer to the parallel resonance frequency. Therefore, the Q value at this parallel resonance frequency can be increased. .
[0018]
The variable capacitance capacitor of the first reactance element row and the variable capacitance capacitor of the reference reactance element row are held substantially equal in capacitance, and the inductance (L1) of the coil of the first reactance element row and the reference reactance element If the inductance (L3) of the coil in the row is substantially equal (L1 ≠ L3), the parallel resonance frequency can be moved while the interval between the series resonance frequencies of the first and reference reactance element rows is substantially fixed. Therefore, the Q value can be kept high in the entire range of the variable capacitance. Note that the first reactance element row may be either capacitive or inductive.
[0019]
That is, the oscillation circuit according to the sixth aspect of the invention can change the capacitances of the capacitors in the first reactance element row while keeping the capacitances of the capacitors in the reference reactance element row substantially equal, and The inductance of the coil of the first reactance element row and the inductance of the coil of the reference reactance element row are close to each other so as not to coincide with each other.
[0020]
In a seventh aspect of the present invention, in the case of the first to sixth aspects, the semiconductor device further comprises a bias circuit connected in parallel to the reference reactance element row, connecting a resistor, a capacitor, and a coil, and having a parallel resonance frequency. There are at least two parallel resonance frequencies of the parallel resonance circuit that gives a solution with a sum of zero, and the parallel resonance frequency of the bias circuit and the target parallel resonance frequency of the parallel resonance circuit are substantially matched. And
[0021]
When the conductance on the resonance circuit side at a specific frequency is large, the negativeness of the oscillation circuit decreases, and oscillation hardly occurs. In addition, when the conductance on the resonance circuit side at a specific frequency is small, oscillation becomes easy.
[0022]
Here, since the conductance on the resonance circuit side at a parallel resonance frequency other than the target of the parallel resonance circuit is set to be large, the parallel resonance circuit has negative polarity at the target parallel resonance frequency and can oscillate. At the parallel resonance frequency other than the target, the negative characteristic is eliminated and the oscillation can be suppressed.
[0023]
Conversely, conversely, by setting the values of the capacitance and inductance of the bias circuit to the target parallel resonance frequency, the conductance on the resonance circuit side can be reduced. In addition, resonance can be performed at a Q value higher than an undesired parallel resonance frequency.
[0024]
Further, by setting the parallel resonance frequency of the bias circuit between the series resonance frequency of the first reactance element row and the series resonance frequency of the reference reactance element row, the parallel resonance of the system consisting of the capacitance and inductance of the bias circuit is achieved. The frequency can be matched to the desired parallel resonance frequency.
[0025]
An oscillation circuit according to an eighth aspect is the oscillation circuit according to the seventh aspect, further comprising a coil that connects the bias circuit and the reference reactance element row. If a coil is connected between the bias circuit and the reference reactance element row, the Q value can theoretically be made infinite even when the reactance of the reference reactance element row becomes zero by inserting this coil.
[0026]
When such a coil is inserted, the Q value can be made infinite if the reference reactance element row is connected after the coil. As a coil, a parasitic coil can be considered, but even when a parasitic coil is not used, the value of the equivalent parallel resistance on the resonance circuit side can be increased and the value of the conductance can be reduced by connecting the coil to the bias circuit. it can.
[0027]
According to a ninth aspect, in the seventh or eighth aspect, there is provided a substrate on which a parallel resonance circuit is formed, and a package for accommodating the substrate (for example, an IC). Characterized by the following inductance. That is, the circuit of the present invention can sufficiently suppress the decrease in the Q value even by the parasitic coil formed by the package or the substrate. The reference reactance element row is connected to a parasitic coil.
[0028]
Further, the negative resistance circuit has a transistor, a predetermined element row is connected between a current path of the transistor and the ground potential, and the predetermined element row includes a coil and a capacitor, and includes a coil and a capacitor of the predetermined element row. The series resonance frequency of the system can be set to match the parallel resonance frequency of the parallel resonance circuit.
[0029]
A transistor is an element for giving a negative polarity to a resonance circuit, and a current flowing through the transistor changes depending on a current input to a base or a voltage input to a gate. The predetermined element array provided in parallel with this determines the series resonance frequency of the negative resistance circuit, and this series resonance frequency basically matches the target parallel resonance frequency of the parallel resonance circuit. Of course, in order to suppress unintended parallel resonance frequency components in the parallel resonance circuit, the series resonance frequency of the negative resistance circuit and the target parallel resonance frequency of the parallel resonance circuit can be shifted.
[0030]
That is, the series resonance frequency on the negative resistance circuit side preferably originally matches the target parallel resonance frequency in the parallel resonance circuit, but in this case, the negative resonance in the parallel resonance circuit outside the target in the parallel resonance circuit is negative. Can not be suppressed. Here, since the series resonance frequency of the negative resistance circuit determined from the series resonance frequency of the predetermined element row is shifted from the target parallel resonance frequency in the parallel resonance circuit, an unintended parallel resonance frequency in the parallel resonance circuit is not used. Can be eliminated.
[0031]
As the target frequency approaches the series resonance frequency of the reference reactance element row and the first reactance element row, the admittance conductance component on the resonance circuit side increases, and the negative property disappears.
[0032]
When considering the parasitic resistance connected in series to the reference reactance element row and the first reactance element row, when the target frequency approaches the series resonance frequency of the reference reactance element row and the first reactance element row, the conductance on the resonance circuit side increases. And oscillation becomes difficult. This problem can be solved by setting the inductance of the coil constituting the predetermined element row and the capacitance of the capacitor so that the reactance of the predetermined element row becomes zero at the target frequency, thereby increasing the negativeness. be able to.
[0033]
More specifically, it is originally desirable that the series resonance frequency of the predetermined element array and the target parallel resonance frequency of the parallel resonance circuit match each other. If the series resonance frequency is not matched with the target parallel resonance frequency, and if the total conductance of the oscillation circuit at the non-target parallel resonance frequency is positive, oscillation at the non-target parallel resonance frequency in the parallel resonance circuit will Be suppressed.
[0034]
A series resonance frequency of a system including a coil and a capacitor in a predetermined element row can be set to be shifted from the series resonance frequency of the reference reactance element row. Of course, the series resonance frequency of the system including the coil and the capacitor of the predetermined element row can also be set to be shifted from the series resonance frequency of the first reactance element row.
[0035]
In a tenth aspect based on the first to ninth aspects, the negative resistance circuit has a transistor, and a predetermined element row is connected between a current path of the transistor and a ground potential. And a capacitor, the parallel resonance circuit has at least two parallel resonance frequencies, the total conductance of the oscillation circuit at the target parallel resonance frequency becomes negative, and the parallel resonance frequency at the non-target parallel resonance frequency (one parallel resonance frequency) The value of the coil and the capacitor of the predetermined element row is set so that the total conductance of the oscillation circuit is positive.
[0036]
In this case, for the reasons described above, oscillation at an unintended resonance frequency is suppressed.
[0037]
An eleventh invention is characterized in that a coil connected in parallel to a capacitor included in the first reactance element row or the reference reactance element row is provided. In this case, since the conductance at each series resonance frequency is reduced by the coil and the capacitor, the Q value can be increased.
[0038]
At this time, two series resonance frequencies occur in each reactance element row of the first and reference reactance element rows. However, the reactances of the first reactance element row and the reference reactance element row are opposite to each other near the parallel resonance frequency. With a configuration in which one is inductive and the other is capacitive, the same effects as described above can be obtained.
[0039]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the oscillation circuit according to the embodiment will be described. Note that the same reference numerals are used for the same elements, and duplicate descriptions are omitted.
[0040]
FIG. 1 is a circuit diagram of the oscillation circuit according to the embodiment. The connection in the following circuit diagram is as shown, and this is an equivalent circuit of an actual circuit. This circuit has a bias circuit but is not shown. The circuit design and connection may be performed according to the equivalent circuit, or the actual circuit design and connection may be performed based on this. Also, the physical quantities of each element are indicated by the same reference numerals as the elements for convenience of explanation. Note that the “row” in the above-described element row is defined to include a case where only a single element, for example, only a capacitor is theoretically included.
[0041]
This oscillation circuit includes a resonance circuit coupled to a negative resistance circuit N via a terminal T. The resonance circuit includes a parallel resonance circuit S. The power consumption in the parallel resonance circuit S is supplemented by the negative resistance circuit N coupled thereto, and oscillation in the parallel resonance circuit S continues.
[0042]
The parallel resonance circuit S includes a first reactance element row X connected in parallel with each other. ₁ , Additional reactance element row X ₂ And reference reactance element row X ₃ It has. In this example, one of the two terminals connected in parallel is set to the ground potential, and oscillation occurs between the two terminals.
[0043]
The resistance value of the negative resistance circuit N is -Rv. Each element row X ₁ , X ₂ , X ₃ , A resistor Rr is inserted equivalently in parallel. The negative resistance -Rt of the entire oscillation circuit is a parallel combined resistance of -Rv and Rr, and is set to be negative at the target resonance frequency.
[0044]
First reactance element row X ₁ Has a variable capacitance capacitor, and by varying the capacitance, the reactance X ₁ And the series resonance frequency f ₁ Can be changed. The first reactance element row X ₁ Series resonance frequency f ₁ Is inversely proportional to the square root of the product of the capacitance and the inductance when a capacitor and a coil are used. Reference reactance element row X ₃ Is the series resonance frequency of f ₃ And
[0045]
f ₁ <F ₃ And set f ₁ And f ₃ , The first reactance element row X ₁ Reactance X ₁ Is inductive (L), and the reactance X ₁ Is positive. The terms inductive and capacitive refer to the characteristics of the reactance near the parallel resonance frequency of the resonance circuit.
[0046]
Additional reactance element row X ₂ Has a fixed-capacitance capacitor, and by changing the capacitance, the reactance X ₂ Can be changed.
[0047]
Reference reactance element row X ₃ Series resonance frequency f ₃ Is inversely proportional to the square root of the product of the capacitance and the inductance when a capacitor and a coil are used. Reference reactance element row X ₃ Reactance X ₃ Is f ₁ <F ₃ Then, it is capacitive (C property) and the reactance X ₃ Is negative. That is, the first reactance element row X ₁ And reference reactance element row X ₃ Are set to be inverse. In other words, reactance X ₁ And X ₃ Suffices if one is capacitive and the other is inductive.
[0048]
Series resonance frequency f ₁ Series resonance frequency f ₃ Is set to be large (f ₁ <F ₃ ), Then L ₁ C ₁ > L ₃ C ₃ (See FIG. 14 (3)), but in this case, near the parallel resonance frequency (f ₋ Reactance X) ₁ Is inductive, reactance X ₃ Becomes capacitive.
[0049]
Conversely, the series resonance frequency f ₁ Series resonance frequency f ₃ Is set to be small (f ₃ <F ₁ ), In this case, the reactance X near the parallel resonance frequency ₁ Is capacitive, reactance X ₃ Becomes inductive.
[0050]
When the bias circuit is not considered, in the parallel resonance circuit of this configuration, the parallel resonance frequency is f ₁ <F ₃ In two, f ₃ <F ₁ And there are two. Let the high frequency parallel resonance frequency be f ₊ , The lower parallel resonance frequency f ₋ And Here, for example, f ₁ <F ₃ , The parallel resonance frequency f ₋ With the series resonance frequency f ₁ , F ₃ , The Q of the resonance circuit at that frequency can be increased, and the phase noise can be reduced. Such a resonance frequency exists.
[0051]
Here, Q = | Rr / X ₁ | The lower parallel resonance frequency f ₋ With the series resonance frequency f ₁ , The first reactance element row X ₁ Is to be adjusted. By adjusting the variable capacitance, the series resonance frequency f ₁ Not only the parallel resonance frequency f ₋ Also shift, so the frequency shift is relative. The desired frequency is f ₁ Therefore, finally, the frequency f ₁ In the vicinity, the Q value increases.
[0052]
FIG. 15 is a graph showing the relationship between frequency and reactance. First reactance element row X ₁ By adjusting the variable capacitance of the series resonance frequency f ₁ Is the parallel resonance frequency f ₋ Can be approached. In this case, the first reactance element row X ₁ By adjusting the variable capacitance of the parallel resonance frequency f ₋ Also move. Series resonance frequency f ₁ To the series resonance frequency f ₃ As a result, the series resonance frequency f ₁ And f ₃ Is the parallel resonance frequency f ₋ It will be as close as possible. The phase noise is reduced by increasing the Q value.
[0053]
Note that the series resonance frequency f ₁ Is the frequency at which the reactance becomes zero, and the parallel resonance frequency f ₋ Is the frequency at which the sum of the reciprocals of the reactances connected in parallel becomes zero. The Q value is the series resonance frequency f ₁ And the parallel resonance frequency f ₋ It becomes higher as the distance between the and is smaller. In addition, Q value and reactance X _i Is shown in (1) of FIG. Where X _i Is X ₁ ~ X ₃ One of the following.
[0054]
f ₁ And f ₃ , The conditions under which the Q value theoretically diverges to infinity are as follows. Note that f ₁ <F ₃ And
(1) First reactance element row X ₁ Reactance X ₁ Is inductive (positive). (2) Reference reactance element row X ₃ Reactance X ₃ Is capacitive (negative). (3) The movable range of the variable capacitance is the first reactance element row X ₁ Reactance X ₁ Reciprocal of (1 / X ₁ ) And reference reactance element row X ₃ Reactance X ₃ Reciprocal of (1 / X ₃ ) Is set to be zero. Additional reactance element row X ₂ Is used, the reactance X ₂ Reciprocal of (1 / X ₂ ) Is set to be zero (see (2) in FIG. 14), and the parallel resonance frequency f ₋ Is f ₁ ~ F ₃ Variable up to.
[0055]
First reactance element row X ₁ And reference reactance element row X ₃ Is the series resonance frequency f ₁ , F ₃ And the reactance X ₁ And reactance X ₃ Is inverse, then f ₁ And f ₃ Is assumed to have a parallel resonance frequency.
[0056]
Note that f ₁ > F ₃ , The reactance X ₁ Is capacitive and the reactance X ₃ Becomes inductive.
[0057]
In this case, the above-described proximity of the frequencies can be achieved by appropriately setting the reactance value.
[0058]
More specifically, the Q value of the parallel resonance circuit is proportional to the reciprocal of the reactance, and is proportional to the equivalent parallel resistance Rr on the resonance circuit side. The Q value increases as the reactance approaches zero. f ₁ <F ₃ , The first reactance element row X ₁ Reactance X ₁ Is positive (inductive) and the additional reactance element row X ₂ Reactance X ₂ Is negative (capacitive) and the reference reactance element row X ₃ Reactance X ₃ Becomes negative (capacitive). That is, when the reactance of the three parallel lines is a combination of L, C, and C, respectively, f ₁ <F ₋ <F ₃ Exists, and the above value that satisfies the above condition exists. Such parameters can be obtained by performing a numerical analysis.
[0059]
Also, f ₃ <F ₁ , The first reactance element row X ₁ Reactance X ₁ Is negative (capacitive) and the additional reactance element row X ₂ Reactance X ₂ Is negative (capacitive) and the reference reactance element row X ₃ Reactance X ₃ Becomes positive (inductive). That is, when the reactance of the three parallel lines is a combination of C, C, and L, respectively, f ₃ <F ₋ <F ₁ Exists, and the above value that satisfies the above condition exists.
[0060]
When reactances having different signs are to coincide with each other, even if there is a condition that these values are different, the reactances of the remaining element rows can give a solution. ₁ , X ₂ , X ₃ Can be zero.
[0061]
Therefore, the reactance X of each element row ₁ , X ₃ There is a combination of a capacitance and an inductance that approaches zero, that is, since the Q value is inversely proportional to the reactance, a combination of a capacitance and an inductance that theoretically makes the Q value infinite exists.
[0062]
This means that there is a solution that can make the parallel resonance frequency of the parallel resonance circuit S relatively close to the series resonance frequency of the target element row.
[0063]
As an example, the first reactance element row X ₁ Series resonance frequency f ₁ Is the target frequency, f ₁ And f ₃ , And consequently, f ₁ And f ₋ Can be approached, so that the Q value of the resonance circuit at this frequency can be increased. Conversely, f ₁ And f ₋ Cannot be brought close alone, f ₁ F to move ₃ Also synchronized ₋ Approach.
[0064]
FIG. 2 is a circuit diagram showing a preferred example of the resonance circuit shown in FIG.
[0065]
First reactance element row X ₁ Is the coil L connected in series ₁ And variable capacitor C ₁ Comprising. Reference reactance element row X ₃ Is the coil L connected in series ₃ And variable capacitor C ₃ Comprising. Additional reactance element row X ₂ Is the capacitor C ₂ Comprising.
[0066]
As described above, the inductive first reactance element row X ₁ Is the reactance X by changing the capacitance. ₁ And the series resonance frequency f ₁ Can be changed, but similarly, the capacitive reference reactance element row X ₃ Also variable capacitor C ₃ Includes Capacitor C ₃ Of the series resonance frequency f ₃ Can be changed. Broadband capacitor C ₁ Series resonance frequency f due to capacitance fluctuation of ₁ Of the capacitor C so as to follow the change of ₃ , A high Q value can always be obtained.
[0067]
Capacitor C ₁ And the capacitance of the capacitor C ₃ These capacitances are changed while the capacitances of the coils L ₁ Inductance and coil L ₃ Are close to each other so that they do not match with each other. In this case, the series resonance frequency f ₁ , F ₃ Is substantially fixed, and the parallel resonance frequency f ₋ Can be moved, so that the Q value can be kept high in the entire range of the variable capacitance.
[0068]
FIG. 3 is a circuit diagram showing another preferred example of the resonance circuit shown in FIG. In this circuit, the reference reactance element row X in the resonance circuit shown in FIG. ₃ And a bias circuit B which is connected in parallel to the first and second resistors and connects a resistor, a capacitor, and a coil. The bias circuit B includes a resistor R between both terminals of the resonance circuit S, that is, in parallel with each element row. ₀ And insert a resistor R ₀ Between the capacitor and the ground potential ₀ And insert the capacitor C ₀ Coil L in parallel with ₀ Are connected.
[0069]
As described above, the parallel resonance frequency of the parallel resonance circuit S that gives a solution in which the reciprocal sum becomes zero is f ₋ And f ₊ There are at least two of Capacitor C of bias circuit B ₀ Capacity C ₀ And coil L ₀ Inductance L ₀ Is one of the parallel resonance frequencies (f ₊ ), The conductance G of the admittance of the bias circuit B (f = f ₊ ) Is the other of the parallel resonance frequencies (f ₋ ), The conductance G of the admittance of the bias circuit B (f = f ₋ ) Is set to be relatively large with respect to minutes.
[0070]
That is, when the conductance on the side of the resonance circuit at a specific frequency is large, the negativeness of the oscillation circuit decreases, and oscillation hardly occurs. In addition, when the conductance on the resonance circuit side at a specific frequency is small, oscillation becomes easy. Here, L ₀ , C ₀ Is the parallel resonance frequency (f) which is the target of the parallel resonance circuit S. ₋ ), So that an unintended parallel resonance frequency (f ₊ In (2), oscillation can be suppressed. Conversely speaking, such L ₀ , C ₀ By using the parallel bias circuit B, the target parallel resonance frequency (f ₋ ), The parallel resonance frequency (f ₊ ), Resonance can be performed with a higher Q value.
[0071]
Note that the parallel resonance frequency of the bias circuit B and the target parallel resonance frequency (f ₋ ) Approximately matches.
[0072]
That is, oscillation at an undesired parallel resonance frequency can be prevented. The capacitance C of the parameters constituting the conductance G of the bias circuit B ₀ And coil L ₀ Is set to an appropriate value, the resonance frequency f ₊ At the resonance frequency f ₋ Can be increased.
[0073]
Further, the third element row X ₃ Series resonance frequency f ₃ And C ₁ Is the minimum value of the series resonance frequency f ₁ By setting it larger than ₁ , Ie, the Q value increases in the higher parallel resonance frequency range. C ₁ Following the value of ₃ Also, by varying, the Q value can always be increased over a wide band.
[0074]
FIG. 4 is a circuit diagram showing another preferred example of the parallel resonance circuit shown in FIG. In this circuit, the bias circuit B and the reference reactance element row X in the parallel resonance circuit S shown in FIG. ₃ Parasitic coil L connecting between ₅ It has. Bias circuit B and reference reactance element row X ₃ And the parasitic coil L ₅ Can theoretically make the Q value infinite.
[0075]
That is, a substrate (not shown) on which the parallel resonance circuit S shown in FIG. 4 is formed and a package (not shown) for accommodating the substrate (for example, IC) are provided. ₅ Is the inductance of the substrate and the package. That is, even if there is a parasitic coil due to the package or substrate, ₃ And X ₁ With this configuration, the circuit can sufficiently suppress a decrease in the Q value.
[0076]
FIG. 5 is a circuit diagram of a parallel resonance circuit according to a comparative example. In the case of this circuit, the coil L ₅ X with or without ₁ Is inductive, Q = ωC ₂ Rr (ω: angular frequency, Rr: equivalent parallel resistance on the resonance circuit side), and the Q value becomes a finite value.
[0077]
FIG. 6 is a circuit diagram showing a preferred example of the oscillation circuit shown in FIG. 1, in which the oscillation circuit shown in FIG. 4 is configured to take a differential from the output terminal OUT. Therefore, in the bias circuit B, the resistance R ₀ 'Are added in series.
[0078]
Here, an example of the negative resistance circuit N will be described. The negative resistance circuit N includes a predetermined element array X connected between the current path of the transistor Q and the ground potential. ₄ It has. Since the transistor Q is a bipolar transistor, the current flowing between the emitter and the collector changes according to the current input to the base. When the transistor Q is a field-effect transistor such as a MOSFET, the current flowing between the source and the drain changes according to the voltage input to the gate. Since the functions are the same in both cases, description will be made here assuming that the transistor Q is a bipolar transistor having excellent high-frequency characteristics. As such a transistor, a transistor using a compound semiconductor in the GHz band can be used.
[0079]
Reference reactance element row X ₃ Is the coil L connected in series ₃ And capacitor C ₃ , But similarly, a predetermined element row X ₄ Coil L connected in series ₄ And capacitor C ₄ Includes The negative resistance circuit N is a circuit for supplying a current in inverse proportion to the input voltage, and can be constituted by, for example, a bipolar transistor Q having a common emitter as shown in the figure.
[0080]
This oscillation circuit employs a differential configuration. The capacitor C is inserted between the base of the transistor and both terminals of the resonance circuit, and the input of the DC voltage to the base is suppressed. By adopting the differential configuration, in-phase noise can be removed. The DC bias voltages VB and VB ′ are input to the base of the transistor Q. Note that the effects of the present invention can be sufficiently obtained even when a differential circuit is not used.
[0081]
Predetermined element row X ₄ Coil L connected in series ₄ And capacitor C ₄ Series resonance frequency f ₄ Is ideally the oscillation frequency f ₋ Is preferably set to the value of ₊ F to prevent oscillation ₋ If it is set to be shifted from the value of ₊ Can be eliminated.
[0082]
That is, in this oscillation circuit, the negative resistance circuit N has a bipolar transistor Q, and a predetermined element row X is connected in parallel with the emitter resistance of the bipolar transistor Q. ₄ Are connected, and a predetermined element row X ₄ Is the coil L connected in series ₄ And capacitor C ₄ And a predetermined element row X ₄ Coil L connected in series ₄ And capacitor C ₄ Series resonance frequency f ₄ Is the parallel resonance frequency f of the parallel resonance circuit S ₋ It is set out of alignment.
[0083]
Note that f ₁ > F ₃ , The first reactance element row X ₁ Is the resonance frequency f ₋ Is capacitive near the reference reactance element row X ₃ Is inductive.
[0084]
Also, f ₁ <F ₃ , The first reactance element row X ₁ Is inductive and the reference reactance element row X ₃ Is capacitive. Note that f ₄ And f ₋ Can be made to have a larger negativeness by essentially matching.
[0085]
The transistor Q is an element for giving the parallel resonance circuit S a negative polarity, and a current flowing through the transistor Q changes according to a current input to the base or a voltage input to the gate. A predetermined element row X connected to this ₄ Is the series resonance frequency f of the negative resistance circuit N ₄ Is determined, this series resonance frequency f ₄ Is, in principle, the parallel resonance frequency f of the parallel resonance circuit S. ₋ Matches. As described above, one parallel resonance frequency component f in the parallel resonance circuit S ₊ In this example, the series resonance frequency f of the negative resistance circuit N ₄ And the parallel resonance frequency f of the parallel resonance circuit S ₋ Has been shifted.
[0086]
The series resonance frequency f on the negative resistance circuit N side ₄ Is originally the other parallel resonance frequency f in the parallel resonance circuit S. ₋ , But in this case, one parallel resonance frequency f in the parallel resonance circuit S ₊ Cannot be suppressed. Here, the predetermined element row X ₄ Series resonance frequency f of the negative resistance circuit N determined from the series resonance frequency ₄ With the other parallel resonance frequency f in the parallel resonance circuit S ₋ , One parallel resonance frequency f in the parallel resonance circuit S ₊ Can be eliminated.
[0087]
The target parallel resonance frequency, that is, the oscillation frequency is equal to the reference reactance element row X ₃ And the first reactance element row X ₁ Series resonance frequency f ₃ , F ₁ , The conductance of the admittance of the parallel resonance circuit S increases, and the negative effect disappears.
[0088]
Reference reactance element row X ₃ And the first reactance element row X ₁ Considering the parasitic resistance connected in series with the reference reactance element row X ₃ And the first reactance element row X ₁ Series resonance frequency f ₃ , F ₁ , The conductance of the parallel resonance circuit S increases, and oscillation becomes difficult. At the oscillation frequency, a predetermined element row X ₄ Reactance X ₄ So that the predetermined element row X ₄ Coil L constituting ₄ Inductance and capacitor C ₄ This problem can be solved by setting the capacity of, and the negativeness can be increased.
[0089]
Predetermined element row X ₄ Series resonance frequency f ₄ And the parallel resonance frequency f ₋ It is originally desirable that they match, but one parallel resonance frequency f in the parallel resonance circuit S ₊ In order to eliminate the negative in ₄ Series resonance frequency f at ₄ Is not matched with the oscillation frequency, and the parallel resonance frequency f ₊ Assuming that the total conductance of the oscillation circuit at is positive, the parallel resonance frequency f ₊ Is suppressed. Note that the desired parallel resonance frequency f ₋ Is set to be negative.
[0090]
In the circuit shown in FIG. ₁ > F ₃ , F ₁ <F ₃ In either case, a similar effect can be obtained.
[0091]
Also in this case, the series resonance frequency f ₄ With the series resonance frequency f ₃ Or series resonance frequency f ₁ Needless to say, the same effect can be obtained.
[0092]
In the above-described oscillation circuit, the resonance frequency f ₊ The predetermined element row X is set so that the total conductance of the oscillation circuit at ₄ Coil L ₄ And capacitor C ₄ Is set. In this case, f ₊ Is negative at f ₋ Is relatively suppressed as compared with
[0093]
A specific example is as follows.
f ₋ = 2.84 GHz
f ₊ = 4.34 GHz
f ₊ Total conductance at 13.24 mS (S = 1 / Ω)
f ₋ Total conductance at −14.92 ms (S = 1 / Ω)
L ₄ = 4nH
C ₄ = 0.6 pF
f ₄ = 3.24 GHz
[0094]
When the setting is performed in the negative resistance circuit N, the reference reactance element row X ₃ , First reactance element row X ₁ The oscillation frequency is f ₃ , F ₁ As the distance approaches, even when the admittance conductance of the parallel resonance circuit increases, the negativeness can be increased. Therefore, the energy is sufficiently replenished with respect to the attenuation of the resonance, and oscillation is facilitated.
[0095]
Further, the parallel resonance circuit S includes a first reactance element row X ₁ Or reference reactance element row X ₃ Capacitor C included in ₁ , C ₃ May be provided with a coil connected in parallel. In this case, this coil and the capacitor C ₁ , C ₃ , The respective series resonance frequency f ₁ , F ₃ , The conductance at the point becomes small, so that the Q value can be increased.
[0096]
At this time, the first reactance element row X ₁ And reference reactance element row X ₃ , Two series resonance frequencies occur in each reactance element row, but the first reactance element row X ₁ And reference reactance element row X ₃ The same effect can be obtained by a configuration in which the reactance of (1) becomes inverse (one is inductive and the other is capacitive) near the target parallel resonance frequency.
[0097]
In order to increase the Q value by reducing the parasitic resistance, a multilayer chip inductor may be used as the above-described coil. As the multilayer chip inductor, a spiral inductor in which a spiral internal conductor is formed in an element and terminal electrodes are provided at both ends can be used. In this case, the parasitic resistance is minimized, and low loss and high Q characteristics can be realized. The above-described oscillation circuit can be used for a signal processing circuit in the gigahertz band in a mobile phone or the like.
[0098]
FIG. 7 is a graph showing a simulation result of data relating to the resonance circuit (the present invention) of FIG.
[0099]
FIG. 7A is a graph showing the relationship between frequency and impedance (| Z |: Ω).
[0100]
First reactance element row X ₁ Series resonance frequency f ₁ Is 2.63 GHz (C ₁ = 0.65 pF), and the reference reactance element row X ₃ Series resonance frequency f ₃ Is 3.75 GHz, and the predetermined element row X ₄ Series resonance frequency f ₄ Is set to 2.65 GHz. Note that f ₁ <F ₃ It is. The resonance frequencies of this resonance circuit are 2.84 GHz and 4.34 GHz.
[0101]
Peak A is X ₁ Is inducible (L), X ₂ Is capacitive (C), X ₃ Is capacitive (C), X ₄ Is the case of capacitive (C).
[0102]
Peak B is X ₁ Is inducible (L), X ₂ Is capacitive (C), X ₃ Is inducible (L), X ₄ Is the case of capacitive (C).
[0103]
Peak C is X ₁ Is capacitive (C), X ₂ Is capacitive (C), X ₃ Is capacitive (C), X ₄ Is inductive (L-type).
[0104]
FIG. 7B is a graph showing the relationship between the total admittance conductance (real part) and frequency. When this value becomes positive, the negative value is lost and oscillation stops. Note that the lowest resonance frequency is f ′. In the present invention, the resonance frequency f ₋ And f 'and f ₊ , The negativity of this point must be positive. This contrivance exists on the bias circuit B and the negative resistance circuit N side, and the frequency f ₋ The negative of the above can be sufficiently secured. f 'and f ₊ Is positive. When the negative value of the present invention is compared with a comparative example described later, the negative value of the present invention is larger.
[0105]
FIG. 7C is a graph showing the relationship between frequency and phase noise. At 10 kHz, the phase noise is -100 dBc / Hz.
[0106]
FIG. 8 is a graph showing a simulation result of data relating to the resonance circuit (the present invention) of FIG.
[0107]
FIG. 8A is a graph showing the relationship between frequency and impedance (| Z |: Ω).
[0108]
First reactance element row X ₁ Series resonance frequency f ₁ Is 2.03 GHz (C ₁ = 6 pF), and the reference reactance element row X ₃ Series resonance frequency f ₃ Is 3.75 GHz, and the predetermined element row X ₄ Series resonance frequency f ₄ Is set to 2.65 GHz. Note that f ₁ <F ₃ It is. The resonance frequencies of this resonance circuit are 2.47 GHz and 4.34 GHz.
[0109]
Peak A is X ₁ Is inducible (L), X ₂ Is capacitive (C), X ₃ Is capacitive (C), X ₄ Is inductive (L-type).
[0110]
Peak B is X ₁ Is inducible (L), X ₂ Is capacitive (C), X ₃ Is inducible (L), X ₄ Is the case of capacitive (C).
[0111]
Peak C is X ₁ Is capacitive (C), X ₂ Is capacitive (C), X ₃ Is capacitive (C), X ₄ Is inducible (L-type).
[0112]
FIG. 8B is a graph showing the relationship between the total admittance conductance (real part) and frequency. Comparing the negative value of the present invention with a comparative example described later, the negative value of the present invention is larger.
[0113]
FIG. 8C is a graph showing the relationship between frequency and phase noise. At 10 kHz, the phase noise is -95 dBc / Hz.
[0114]
FIG. 9 is a graph showing a simulation result of data when the bias circuit of the comparative example is used without using the bias circuit B in the resonance circuit of FIG.
[0115]
FIG. 9A is a graph showing the relationship between frequency and impedance (| Z |: Ω). C ₁ = 0.65 pF. Also in this resonance circuit, three peaks appear.
[0116]
FIG. 9B is a graph showing the relationship between the total admittance conductance (real part) and frequency. Comparing the negative value of the present invention with a comparative example described later, the negative value of the present invention is larger. Further, the circuit shown in FIG. 7B has a greater negative polarity than the circuit shown in this example.
[0117]
FIG. 9C is a graph showing the relationship between frequency and phase noise. At 10 kHz, the phase noise is -95 dBc / Hz.
[0118]
FIG. 10 is a graph showing a simulation result of data when the bias circuit B is not used in the resonance circuit of FIG.
[0119]
FIG. 10A is a graph showing the relationship between frequency and impedance (| Z |: Ω). C ₁ = 6 pF. Also in this resonance circuit, three peaks appear.
[0120]
FIG. 10B is a graph showing the relationship between the total admittance conductance (real part) and frequency. Comparing the negative value of the present invention with a comparative example described later, the negative value of the present invention is larger.
[0121]
FIG. 10C is a graph showing the relationship between frequency and phase noise. At 10 kHz, the phase noise is -86 dBc / Hz.
[0122]
FIG. 11 is a graph showing a simulation result of data according to the resonance circuit of FIG. 5 (comparative example).
[0123]
FIG. 11A is a graph showing the relationship between frequency and impedance (| Z |: Ω). C ₁ = 0.65 pF. In this resonance circuit, two peaks appear.
[0124]
FIG. 11B is a graph showing the relationship between the total admittance conductance (real part) and frequency. Negative values are smaller.
[0125]
FIG. 11C is a graph showing the relationship between frequency and phase noise. At 10 kHz, the phase noise is -86 dBc / Hz.
[0126]
FIG. 12 is a graph showing a simulation result of data according to the resonance circuit of FIG. 5 (comparative example).
[0127]
FIG. 12A is a graph showing the relationship between frequency and impedance (| Z |: Ω). C ₁ = 6 pF. In this resonance circuit, two peaks appear.
[0128]
FIG. 12B is a graph showing the relationship between the total admittance conductance (real part) and frequency. Negative values are smaller.
[0129]
FIG. 12C is a graph showing the relationship between frequency and phase noise. At 10 kHz, the phase noise is -84 dBc / Hz.
[0130]
FIG. 13 is a graph showing a simulation result of data on a resonance circuit (comparative example) in which a bias circuit B is provided in the resonance circuit of FIG.
[0131]
FIG. 13A is a graph showing the relationship between frequency and impedance (| Z |: Ω). C ₁ = 0.65 pF, L ₀ = 3.3 nH, f ₀ = 2.77 GHz, C ₀ = 0.5 pF. In this resonance circuit, two peaks appear.
[0132]
FIG. 13B is a graph showing the relationship between the total admittance conductance (real part) and frequency.
[0133]
FIG. 13C is a graph showing the relationship between frequency and phase noise. At 10 kHz, the phase noise is -90 dBc / Hz.
[0134]
【The invention's effect】
As described above, according to the oscillation circuit of the present invention, phase noise can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an oscillation circuit according to an embodiment.
FIG. 2 is a circuit diagram showing a preferred example of the resonance circuit shown in FIG.
FIG. 3 is a circuit diagram showing another preferred example of the resonance circuit shown in FIG. 1;
FIG. 4 is a circuit diagram showing another preferred example of the parallel resonance circuit shown in FIG. 1;
FIG. 5 is a circuit diagram of a parallel resonance circuit according to a comparative example.
FIG. 6 is a circuit diagram showing a preferred example of the oscillation circuit shown in FIG. 1;
FIG. 7 is a graph showing a simulation result of data according to the resonance circuit (the present invention) of FIG. 6;
FIG. 8 is a graph showing a simulation result of data relating to the resonance circuit (the present invention) of FIG. 6;
9 is a graph showing a simulation result of data when the bias circuit B is not used in the resonance circuit of FIG. 6;
FIG. 10 is a graph showing a simulation result of data when the bias circuit B is not used in the resonance circuit of FIG. 6;
FIG. 11
6 is a graph showing a simulation result of data according to the resonance circuit of FIG. 5 (comparative example).
FIG. 12 is a graph showing a simulation result of data according to the resonance circuit of FIG. 5 (comparative example).
13 is a graph showing a simulation result of data of a resonance circuit (comparative example) in which a bias circuit B is provided in the resonance circuit of FIG.
FIG. 14 is a table showing mathematical expressions.
FIG. 15 is a graph showing the relationship between frequency and reactance.
[Explanation of symbols]
S: parallel resonance circuit, X ₁ ... First reactance element row, X ₂ … Additional reactance element row, X ₃ ... Reference reactance element row.

Claims (11)

In an oscillation circuit having a resonance circuit coupled to a negative resistance circuit,
The resonance circuit includes a parallel resonance circuit including a first reactance element row and a reference reactance element row connected in parallel to each other,
The first reactance element row and the reference reactance element row each have a series resonance frequency,
At least the first reactance element row has a variable capacitance capacitor,
The movable range of the variable capacitance is set so that the series resonance frequency of the first reactance element row and the reference reactance element row can be relatively close to the parallel resonance frequency in the parallel resonance circuit. Characteristic oscillation circuit. 2. The oscillation circuit according to claim 1, wherein one of the reactances of the first reactance element row and the reference reactance element example near the parallel resonance frequency is inductive, and the other is capacitive. The oscillation circuit according to claim 1, further comprising an additional reactance element array provided in parallel with the reference reactance element array. The movable range of the variable capacitance is set such that the sum of the reciprocals of the reactances of the reactance element rows connected in parallel can be zero. The oscillation circuit described in the section. The oscillation circuit according to any one of claims 1 to 4, wherein the reference reactance element row includes a capacitor having a variable capacitance. The capacitances of the capacitors in the first reactance element row and the capacitances of the capacitors in the reference reactance element row can be changed while keeping the capacities substantially equal, and the coils of the first reactance element row can be changed. 6. The oscillation circuit according to claim 5, wherein the inductance of the reference reactance element row and the inductance of the coil of the reference reactance element row are close to each other so as not to coincide with each other. A resistor, a capacitor and a coil are connected in parallel to the reference reactance element row, and a bias circuit having a parallel resonance frequency is provided;
There are at least two parallel resonance frequencies of the parallel resonance circuit that give a solution in which the sum becomes zero,
7. The oscillation circuit according to claim 1, wherein a parallel resonance frequency of the bias circuit and a target parallel resonance frequency of the parallel resonance circuit are substantially matched. The oscillation circuit according to claim 7, further comprising a coil that connects between the bias circuit and the reference reactance element row. 9. The oscillation circuit according to claim 7, further comprising a substrate on which the parallel resonance circuit is formed, and a package accommodating the substrate, wherein the coil is an inductance of the substrate and the package. 10. The negative resistance circuit has a transistor,
A predetermined element row is connected between a current path of the transistor and a ground potential,
The predetermined element row includes a coil and a capacitor,
The parallel resonance circuit has at least two parallel resonance frequencies,
The total conductance of the oscillation circuit at the target parallel resonance frequency becomes negative,
In order that the total conductance of the oscillation circuit at the parallel resonance frequency not intended is positive,
The oscillation circuit according to claim 1, wherein values of a coil and a capacitor of the predetermined element row are set. The oscillation circuit according to claim 1, further comprising a coil connected in parallel to a capacitor included in the first reactance element row or the reference reactance element row.

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