JPH11112232A - Oscillation circuit - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When used in a wireless device by reducing the level of excessively low frequency noise and suppressing the sideband noise of the oscillation frequency without using an expensive coaxial resonator having a large volume. Of the adjacent channel selectivity characteristic or the like is suppressed. SOLUTION: An amplifier circuit including a transistor Q1 and resistors R1 to R3 of a bias circuit of the transistor,
Capacitors C1 to C of a feedback circuit connected to this amplifier circuit
3 and an inductor L1, and an oscillation circuit that oscillates at a predetermined oscillation frequency absorbs a noise component from a low-frequency excessive noise source existing in the transistor Q1 while maintaining a normal oscillation operation at the oscillation frequency. An impedance circuit 1 for suppressing the level of the lever noise component is provided. The impedance circuit 1 includes an inductor L1 and a capacitor C1 connected in series between the base and the emitter of the transistor Q1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation circuit, and more particularly to an oscillation circuit used for a frequency synthesizer of a radio equipment having a frequency division multiple access structure.

[0002]

2. Description of the Related Art As a typical example of a conventional oscillation circuit used for a synthesizer or the like of a radio equipment, FIG. 8 shows a grounded collector / modified Colpitts oscillation circuit using bipolar transistors as active elements. In FIG. 8, R1,
R2 and R3 are resistors, C1, C2 and C3 are capacitors, L
1 is an inductor, Q1 is a bipolar transistor, V1
Is a DC voltage source. This oscillation circuit comprises resistors R1, R
2, R3, bipolar transistor Q1, DC voltage source V
1 and a Colpitts-type amplifier comprising a grounded-collector-type amplifier circuit constituted by 1 and a feedback circuit constituted by capacitors C1, C2, C3 and an inductor L1. Resistance R
Reference numerals 1 and R2 divide the voltage of the DC voltage source V1 to determine the DC bias voltage at the base of the bipolar transistor Q1. The resistor R3 is a DC bias feedback resistor that determines the collector current and the emitter current, and also serves as the load resistance of a common-collector type amplifier circuit. Since the impedance of the DC voltage source V1 connected to the collector of the bipolar transistor Q1 is ideally zero in AC, the collector is grounded.

Since the DC voltage source V1 and its wiring actually have impedance, a bypass capacitor whose impedance is sufficiently reduced at the oscillation frequency is often inserted between the collector and the ground potential point. Capacitor C
Reference numeral 1 also functions as a DC cut capacitor for preventing the base voltage of the bipolar transistor Q1 from being short-circuited to the ground potential point by the inductor L1. Capacitor C1
In the frequency range in which the series connection impedance of the inductor L1 and the inductor L1 is inductive, the series connection impedance can be regarded as one inductor, and the circuit of FIG. 8 can be regarded as a Colpitts oscillation circuit.

If the phase of the signal returned to the input by the above-described feedback circuit is the same as the phase of the original signal and the amplification degree is 1 or more, oscillation starts. After the start of oscillation, the amplitude of the signal increases, and the above-described amplifier circuit (of the common-collector type) reaches saturation and its gain decreases. Eventually, a steady state is reached where the gain of this amplifier circuit compensates for the loss of the feedback circuit and the loss taken out as a signal.

[0005]

In a transistor circuit such as an oscillation circuit, a transistor or a certain resistor is almost independent of frequency such as thermal noise (shot noise) or shot noise at a frequency lower than about 100 kHz. , A noise much larger than the level of the white noise is generated. This is called low frequency excessive noise. As the types of the excessively low frequency noise, 1 / f noise (also called flicker noise or the like), burst noise (also called popcorn noise, random telegraph signal noise, or the like), and generation / recombination noise are known.

FIG. 9 shows an example of excessive low frequency noise.
FIG. 3 is a characteristic diagram of a measured equivalent base noise current spectrum density of a bipolar transistor. In FIG. 9, 1
The / f noise has a spectrum that is literally inversely proportional to the frequency, while the burst noise and the generated and recombined noise both have a spectrum like the frequency response of a low-pass filter and have a hump on the 1 / f noise. Observed. As shown in FIG. 9, these low frequency excessive noises are much larger than the white noise level.

[0007] These excessively low-frequency noises usually cause a problem in a low-frequency amplifier circuit or the like, but also cause a significant deterioration in the sideband noise characteristics of the oscillation circuit. The reason is that, as described above, the amplifier circuit used in the oscillation circuit is saturated and nonlinear operation is performed, so that the same operation as the frequency conversion circuit is performed, and excessive low frequency noise is up-converted to both sides of the oscillation frequency. Because it is done. FIG. 10 shows a frequency characteristic diagram of the level of the power spectrum of the oscillation signal exhibiting the phenomenon of up-conversion of excessive low-frequency noise.

[0008] Sideband noise in an actual oscillation circuit is:
The upconverted low-frequency excessive noise is further emphasized near the oscillation frequency. That is, the oscillation circuit forms a resonance circuit with the transistors, capacitors, inductors, and resistors that are this component,
This is because the resonance circuit is affected in a region where the offset frequency from the carrier (oscillation frequency) is lower than the one half-width frequency determined by the load Q (quality factor) of the resonance circuit (region close to the oscillation frequency). FIG. 11 shows a characteristic diagram of the sideband noise power spectrum level of the oscillation circuit exhibiting this phenomenon. In FIG.
f ₀ is the oscillation frequency, Q _L is the load Q of the resonant circuit.

When the level of sideband noise generated as described above is high, when this oscillation circuit is used as a local signal generator or a transmission signal generator (synthesizer, etc.) of a frequency division multiple access wireless device, an adjacent circuit may be used. There is a problem that the channel selectivity characteristic or the adjacent channel leakage power characteristic deteriorates. Further, since the sideband noise is substantially equivalent to the fluctuation of the phase of the oscillation signal, the digital modulation radio using the phase of the carrier has a problem that the modulation accuracy and the error rate are deteriorated.

One method of reducing the sideband noise is to increase the load Q of the resonance circuit in the above-described oscillation circuit and narrow the half-width frequency thereof. In order to realize this, it is necessary to increase the Q of the inductor used for the oscillation circuit or the resonance element or capacitor as a substitute for the inductor. However, at a high frequency used in a radio, it is difficult to realize a high Q element. In particular, it is difficult to realize a high-Q inductor at a high frequency. For example, a coaxial resonator may be used instead of the inductor, but there is a disadvantage that the volume of the element is large and the cost is high.

On the other hand, the excessively low frequency noise of the oscillation circuit is mainly the excessively low frequency noise of active elements such as transistors.
Bipolar transistors having relatively low low-frequency excessive noise are often used in oscillation circuits up to a frequency band having sufficiently high-frequency characteristics. However, the dominant low-frequency excessive noise source during normal operation of this bipolar transistor is often the base noise current source, and the oscillation circuit usually has a circuit configuration in which the influence of this current source is very large. .

FIG. 12 is an equivalent circuit diagram of the oscillation circuit shown in FIG. 8 at a low frequency, which will be described below with reference to FIG. At low frequencies, capacitors C1,
Assuming that the impedances of C2 and C3 are sufficiently large, FIG.
Then they are all open. In FIG, R _B the resistance R1
And R2 in parallel. Further, the voltage source v _RB may express thermal noise voltage of the resistance R _B. Similarly, the resistance value of R _E is the resistor R3, the voltage source v _RE is intended to represent the thermal noise voltage of the resistance R _E. Current source i
_be represents the base noise current of the bipolar transistor Q1, and often includes the most dominant low frequency excessive noise source of the bipolar transistor together with the shot noise. r _i is the base input resistance, which is the reciprocal of the conductance value determined by the DC voltage-current characteristics of the base-emitter junction of the intrinsic transistor (bipolar transistor Q1). Voltage _V be the voltage applied to the base input resistance r _i, that is, the base-emitter voltage of the intrinsic transistor. The dependent current source g _m V _be expresses the amplifying action of the transistor, and is represented by the product of the transconductance g _m and the voltage V _be . In FIG. 12, the parasitic resistance and the parasitic capacitance are ignored. The output conductance due to the base width modulation effect was also ignored. The root-mean-square value of the voltage sources v _RB and v _RE (the average value is represented by a superscript bar) is represented by Expressions 1 and 2, respectively. Here, k is the Boltzmann constant, T is the absolute temperature, and Δf is the frequency width. Current source i
root mean square _be is generally expressed as Equation 3.

[0013]

(Equation 1)

[0014]

(Equation 2)

[0015]

(Equation 3)

[0016] In Equation 3, q is the electron charge, I _B is the DC base current, f is the frequency, K _f is 1 / f noise constant, the DC base current dependence exponent of gamma _f 1 / f noise, K
_b is burst noise or generation / recombination noise constant,
gamma _b is a burst noise or DC base current dependence exponent generation and recombination noise, f _c is the frequency corresponding to the developmental process of the burst noise or generation-recombination noise. In the right side of Expression 3, the first term represents shot noise, the second term represents 1 / f noise, and the third term represents burst noise or generated / recombination noise.

As described above, 1/2 of the second and third terms is used.
f noise, burst noise or generated / recombination noise greatly exceeds the level of white noise (shot noise) at low frequencies. Then, the base input resistance r _i is expressed by Equation 4, and the transconductance g _m
Is given by Expression 5. In Equation 5, I _C is a DC collector current.

[0018]

## EQU4 ## r _i = kT / qI _B

[0019]

## EQU5 ## g _m = qI _C / kT

In FIG. 12, the voltage V due to each noise source
The fluctuation of _be is up-converted to both sides of the oscillation frequency by the nonlinear operation of the oscillation circuit. In the oscillation circuit, in order to reduce the DC bias current and not to lower the Q of the resonance circuit, the resistance value R _B is several k.
About several tens kΩ from Omega, the value of several kΩ several hundred Omega for the same reason as the resistance value R _E are common. Thus the resistance value R _B, when R _E is large, fluctuation of the voltage V _be is a noise current source i _BE component contributing is dominant. That is, the configuration is such that the influence of the low frequency excessive noise source is large. This will be described below. When the mean square value of the fluctuation of the voltage V _be is expressed by each noise source, Equation 6 is obtained. In Expression 6, β is the current amplification factor, which is a low frequency in this case, and therefore, Expression 7 is almost equal to the DC current amplification factor β ₀ .

[0021]

(Equation 6)

[0022]

## EQU7 ## β = β ₀ = I _C / I _B

The first term on the right side of Equation 6 is the thermal noise source v of the resistor.
_RB and v _RE are components that contribute to the fluctuation of the voltage V _be ,
The second term is a component contributed by a noise current source _ibe including excessive low-frequency noise. Therefore, the first term and the second term are represented as the following equations, and when transformed, the equations become the following equations (8) and (9).

[0024]

(Equation 8)

[0025]

(Equation 9)

When these are compared, the denominator of both equations is the same, and the numerator of Equation 8 includes R _B + R _E and the numerator of Equation 9 includes (R _B + R _E ) ² , so that R _B + R _E Increases, the second term becomes dominant. That is, as the resistance values R _B and R _E increase, the influence of the noise current source _ibe including excessively low frequency noise becomes dominant. FIG. 13 is a graph showing this, in which the calculated values of the level of the white noise (shot noise) component in the first term and the second term shown in the following Expression 10 are plotted.

[0027]

(Equation 10)

[0028] In FIG. 13, the horizontal axis is the vertical axis by the value of the resistance R _B is the noise voltage root mean square value per unit frequency. The solid line indicates the part of the formula 10 is a component that contributes to wander white noise component of the current source i _BE including low frequency excessive noise voltage V _BE, the dotted line resistance R _B, R _E
Thermal noise indicates part of the formula 8 is a component that contributes to the fluctuation of the voltage V _be of. These calculations give a resistance value R _E of 100
And Omega, DC base current I _B is 50 .mu.A, the current amplification factor β
100, frequency width Δf is 1 Hz, Boltzmann constant k is 1.38
× 10 ^-23 J / K, absolute temperature T is 300K, electron charge q is
The test was performed at 1.6 × 10 ⁻¹⁹ C. 13, when the resistance value R _B is greater than about 1 k [Omega, part of the formula 10 is larger than the part of the formula 8, it is seen that the dominant noise.

As described above, the conventional oscillator circuit, when used in a wireless device, is a source of excessively low-frequency noise of a transistor, which is one of the causes of deteriorating sideband noise which is an important characteristic of the oscillator circuit. The impact is significant.

An object of the present invention is to reduce the level of excessively low-frequency noise and reduce the oscillation frequency without using a coaxial resonator whose volume and cost increase, in view of the above-mentioned problems of the prior art. The present invention provides an oscillation circuit that can suppress sideband noise at the time of use and can suppress deterioration of adjacent channel selectivity characteristics, adjacent channel leakage power characteristics, and deterioration of modulation accuracy and error rate when used in a wireless device. It is in.

[0031]

The present invention has the following means in order to achieve the above object. That is, the oscillation circuit of the present invention is an oscillation circuit that includes a transistor, an amplification circuit including a bias circuit for the transistor, and a feedback circuit connected to the amplification circuit, and oscillates at a predetermined oscillation frequency. While maintaining a normal oscillation operation at the oscillation frequency by the amplifying circuit and the feedback circuit, a noise component from a low-frequency excessive noise source existing in a transistor of the amplifying circuit is absorbed to output the noise component to the outside. It is configured by providing an impedance circuit for reduction.

Further, the transistor of the amplifier circuit is a bipolar transistor, and the low frequency excessive noise source exists between the base and the emitter of the transistor.
The impedance circuit has an impedance sufficiently smaller than a combined impedance of the amplifier circuit and the feedback circuit viewed from the low frequency excessive noise source in a low frequency region where noise components from the low frequency excessive noise source are concentrated, and In terms of frequency, the circuit is connected between the base and the emitter of the transistor as a circuit having an impedance sufficiently larger than the combined impedance of the amplifier circuit and the feedback circuit viewed from the connection point of the impedance circuit.

Further, the transistor of the amplifier circuit is a bipolar transistor, and the low frequency excessive noise source exists between the base and the emitter of the transistor.
And an emitter resistor for feedback and load between the emitter and the ground potential point of the transistor, wherein the impedance circuit is provided in the low frequency region where noise components from the low frequency excessive noise source are concentrated. Has a sufficiently smaller impedance than the combined impedance of the amplifier circuit and the feedback circuit as viewed from above, and at the oscillation frequency, a circuit having an impedance sufficiently larger than the combined impedance of the amplifier circuit and the feedback circuit as viewed from the connection point of the impedance circuit. The transistor is connected between a base and a ground potential point of the transistor.

Further, the impedance circuit is a series connection circuit of a capacitor and an inductor, and the inductor of the impedance circuit and the inductor included in the feedback circuit are shared by one inductor.

The function of the bias circuit of the transistor included in the amplifier circuit is transferred to the impedance circuit, and the impedance circuit having the function of the bias circuit is used as an impedance bias circuit. And a circuit provided with at least one of an inductor and a capacitor.

Further, in parallel with the emitter resistor, an impedance circuit for an emitter resistor having an impedance sufficiently smaller than the emitter resistor in the low frequency region and having an impedance sufficiently larger than the emitter resistor at the oscillation frequency is provided. Is done.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention has an amplifier circuit provided with a transistor and a bias circuit for the transistor, and a feedback circuit connected to the amplifier circuit, and oscillates at a predetermined oscillation frequency. Added an impedance circuit to the oscillation circuit that absorbs the noise component from the low frequency excessive noise source existing in the transistor and suppresses the output level of this noise component to the outside, without hindering the oscillation operation at the above oscillation frequency. It is composed.

By adding such an impedance circuit, even if the noise level increases due to the up-conversion based on the nonlinearity of the active element (transistor) or the resonance circuit in the vicinity of the oscillation frequency, the low-frequency source serving as the source is provided. Since the output level of excessive noise to the outside is kept low, the sideband noise level of the oscillation signal (at the oscillation frequency) also becomes low, and when used in a wireless device, its adjacent channel selectivity characteristics, adjacent channel It is possible to suppress the deterioration of the leakage power characteristic, the modulation accuracy, the error rate, and the like. In addition, it is not necessary to use an expensive coaxial resonator having a large volume.

[0039]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of the present invention. This embodiment differs from the conventional oscillation circuit shown in FIG. 8 in that the conventional oscillation circuit (hereinafter referred to as a conventional example) is used.
On the other hand, while maintaining the oscillation operation at the oscillation frequency normally, the noise component from the low frequency excessive noise source existing between the base and the emitter of the transistor Q1 is absorbed and the output level of this noise component to the outside is suppressed. , Transistor Q
Inductor L connected in series between one base and emitter
2 and a capacitor C4. In the low-frequency region, the low-frequency excessive noise source has an impedance sufficiently smaller than that of the conventional example (as viewed from between the base and the emitter). The point is that an impedance circuit 1 having an impedance sufficiently larger than the combined impedance of the conventional example viewed from the middle is provided.

FIG. 2 is an equivalent circuit of this embodiment. FIG.
2, the capacitors C1, C2, and C3 are ignored as being open at low frequencies in FIG. 2, as in the equivalent circuit of the conventional example shown in FIG. _{Also, R B, r i, R} E is the resistance value, v _RB and v _RE is the thermal noise voltage source, i _BE is the base noise current source including a low frequency excessive noise, V _BE is the base-emitter voltage clogging resistance r _The voltage applied to _i , g _m V _be, is a dependent current source, which corresponds to the equivalent circuit of the conventional example. The inductance value of L _BE inductor L2 2,
C _be is the capacitance value of the capacitor C4, and R _be is the inductor L
2 and an equivalent resistance value representing the loss of the capacitor C4.
Here, the value of L _be is selected so that its impedance can be almost ignored at low frequencies and sufficiently high at high frequencies, which are oscillation frequencies. The value of C _be is chosen so that the impedance is sufficiently small at low frequencies. R _BE varies depending on the type and the value of the inductors L2 and capacitor C4, but the resistance value R _B, usually much smaller than R _E. Therefore,
The series connection impedance of L _be , C _be , and R _be is negligibly small at low frequencies and sufficiently high at high frequencies.

[0041] As an example, in FIG. 3, 200 nH and L _BE, C
L for the frequency when _be is 1 mF and R _be is 5Ω
_be, shows C _be, the absolute value of the series connection impedance R _BE (impedance of the impedance circuit 1). In this low frequency of about 10MHz from FIG. 3, several tens Hz is the absolute value of about 5Ω series connected impedances, resistance R _B, sufficiently negligible in comparison with R _E. And 1GH
At high frequencies above z, the absolute value of the series connection impedance is greater than 1 kΩ. Therefore, when the oscillation frequency is used this configuration to the oscillating circuit is at least 1 GHz, the base noise current source i _BE and L _BE including low frequency excessive noise, C _BE, and the impedance circuit 1 of the series connection of R _BE parallel At low frequencies, the base noise current source _ibe is almost short-circuited, so that the noise current (noise component) from the base noise current source _ibe is absorbed by this impedance circuit, and its influence is greatly reduced. Can be reduced. In other words, the up-conversion on both sides of the oscillation frequency and the low-frequency excessive noise of the voltage V _be emphasized by the resonance circuit are reduced from the source,
The noise level near the oscillation frequency can be suppressed.

On the other hand, at a high frequency which is the oscillation frequency, the impedance of the impedance circuit 1 is high, and the oscillation operation at the oscillation frequency can be maintained normally without deteriorating the load Q of the resonance circuit of the oscillation circuit. it can. Therefore, when the oscillation circuit according to this embodiment is used in a wireless device, it is possible to suppress the deterioration of the adjacent channel selectivity characteristic, the adjacent channel leakage power characteristic, the modulation accuracy, the error rate, and the like. Moreover, it is not necessary to use an expensive coaxial resonator having a large volume.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention. In this embodiment, the impedance circuit 1a
It is provided between the emitter of the transistor Q1 and the ground potential point. Therefore, unlike the first embodiment, the impedance circuit cannot be said to be completely parallel to the base noise source, but the series circuit with the resistor R3 is connected in parallel, and the resistors R1 and R2 are connected in parallel. Since the short circuit is caused by the impedance circuit 1a, a sufficient effect can be expected when the value of the resistor R3 is not so large. Also,
Although not shown in FIG. 4, when the value of the resistor R3 is large, the impedance is low by connecting an impedance circuit for an emitter resistor having a low impedance at a low frequency and a high impedance at an oscillation frequency in parallel with R3. A short circuit at the frequency can eliminate the influence of low frequency excessive noise.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention. This embodiment is different from the impedance circuit 1a of the second embodiment shown in FIG.
An impedance / bias circuit 2 having an inductor L2 and a low noise DC constant voltage circuit 21 instead of R2, and having the same function as the impedance circuit 1a of the second embodiment and the function of a bias circuit for the transistor Q1. Is provided. In this embodiment, the DC constant voltage circuit 21 has a function of applying a DC bias voltage to the base of the transistor Q1 and has a small output impedance. Therefore, the circuit connected in series with the inductor L2 includes a capacitor and an inductor L2. As in the case of the series-connected impedance circuit, a circuit having low impedance in the low frequency region and high impedance in the high frequency (oscillation frequency) can be realized without deteriorating the load Q of the resonance circuit of the oscillation circuit at the oscillation frequency. The oscillation operation can be kept normal, and the influence of a noise current source including excessively low frequency noise can be reduced.

FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention. In the fourth embodiment, one inductor L1 shares the inductor L2 of the impedance circuit 1a of the second embodiment shown in FIG. 4 and the inductor L1 included in the feedback circuit. An impedance circuit 1b in which a parallel circuit of capacitors C4 and C5 (corresponding to C1) are connected in series is connected between the base of the transistor Q1 and the ground potential point.

In this embodiment, if the value of the capacitor C4 is selected so that the impedance becomes sufficiently small at a low frequency, the impedance of the base of the transistor Q1 with respect to the ground potential in the low frequency region becomes low, and excessive low frequency noise is reduced. The influence of the noise current source can be reduced. The capacitor C4 whose impedance is sufficiently low in a low frequency region usually has an impedance at a high frequency that is not negligibly small due to its internal loss and parasitic inductance. Therefore, the capacitor C
Reference numeral 5 denotes a high-frequency-dedicated bypass capacitor inserted to ensure that the impedance at the high frequency at the connection point with the inductor L1 is reduced. This embodiment has the same effect as the second embodiment, and also has the advantage of reducing the number of circuit elements.

FIG. 7 is a circuit diagram showing a fifth embodiment of the present invention. The fifth embodiment is a combination of the third embodiment and the fourth embodiment. The impedance bias circuit 2a includes an inductor L1 having both a feedback circuit function and an impedance circuit function. Feedback circuit C
Capacitor C5 with 1 function (high frequency exclusive bypass)
And a low-noise DC constant voltage circuit 21a having a function of a bias circuit for the transistor Q1 and a function of a capacitor C4 of an impedance circuit. In the third to fifth embodiments, when the value of the resistor R3 is large, an impedance circuit for an emitter resistor can be provided in parallel with the resistor R3 as described above.

[0048]

As described above, according to the present invention, an impedance circuit for absorbing a noise component from a low-frequency excessive noise source existing in a transistor without hindering an oscillation operation at an oscillation frequency to suppress the level of the noise component. Is provided, even if the noise level is increased by an up-conversion or resonance circuit based on the nonlinearity of the active element near the oscillation frequency, the level of the excessive low-frequency noise that is the source of the noise can be suppressed to a low level. Signal) sideband noise level can be suppressed to a low level, and when used in wireless equipment, the degradation of adjacent channel selection characteristics and adjacent channel leakage power characteristics, and the degradation of modulation accuracy and error rate can be suppressed. There is no need to use an expensive coaxial resonator having a large volume and an expensive effect.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the embodiment shown in FIG.

FIG. 3 is a characteristic diagram of the absolute value of frequency versus impedance of the impedance circuit of the embodiment shown in FIG.

FIG. 4 is a circuit diagram showing a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 8 is a circuit diagram showing an example of a conventional oscillation circuit.

FIG. 9 is a characteristic diagram of frequency versus noise current spectrum density of the oscillation circuit shown in FIG. 8;

10 is a characteristic diagram of a power spectrum level for explaining up-conversion of excessively low frequency noise in the oscillation circuit shown in FIG. 8;

11 is a characteristic diagram of noise power spectrum level for explaining sideband noise in the oscillation circuit shown in FIG. 8;

FIG. 12 is an equivalent circuit diagram of the oscillation circuit shown in FIG.

13 is a characteristic diagram for resistance R _B of the dominant component of the noise source present in the transistor of the oscillation circuit shown in FIG.

[Explanation of symbols]

 1, 1a, 1b Impedance circuit 2, 2a Impedance bias circuit C1 to C5 Capacitor L1, L2 Inductor Q1 Transistor R1 to R3 Resistance V1 DC voltage source

Claims (7)

[Claims] 1. An oscillation circuit having a transistor and an amplifier circuit including a bias circuit for the transistor, and a feedback circuit connected to the amplifier circuit, wherein the oscillation circuit oscillates at a predetermined oscillation frequency. And an impedance circuit that absorbs a noise component from a low-frequency excessive noise source existing in a transistor of the amplifier circuit and reduces the output of the noise component to the outside while maintaining a normal oscillation operation at the oscillation frequency by the feedback circuit. An oscillation circuit, comprising: 2. The transistor of the amplifying circuit is a bipolar transistor, the low-frequency excessive noise source exists between a base and an emitter of the transistor, and the impedance circuit includes a noise from the low-frequency excessive noise source. In the low frequency region where the components are concentrated, the amplifier circuit has an impedance sufficiently smaller than the combined impedance of the amplifier circuit and the feedback circuit viewed from the low frequency excessive noise source, and the amplifier circuit viewed from the connection point of the impedance circuit at the oscillation frequency. 2. The oscillation circuit according to claim 1, wherein the oscillation circuit is connected between the base and the emitter of the transistor as a circuit having an impedance sufficiently larger than the combined impedance of the feedback circuit. 3. The transistor of the amplifying circuit is a bipolar transistor, the low-frequency excessive noise source exists between the base and the emitter of the transistor, and the source for feedback acts between the emitter and the ground potential point of the transistor. In the low frequency region where the noise component from the low frequency excessive noise source is concentrated, the impedance circuit is more than the combined impedance of the amplifier circuit and the feedback circuit viewed from the low frequency excessive noise source. A circuit having a low impedance and having an impedance sufficiently larger than the combined impedance of the amplifier circuit and the feedback circuit viewed from the connection point of the impedance circuit at the oscillation frequency, connected between the base and the ground potential point of the transistor. Item 2. The oscillation circuit according to Item 1. 4. The oscillation circuit according to claim 2, wherein said impedance circuit is a series connection circuit of a capacitor and an inductor. 5. The oscillation circuit according to claim 4, wherein the inductor of the impedance circuit and the inductor included in the feedback circuit are shared by one inductor. 6. The function of a bias circuit of a transistor included in the amplifier circuit is transferred to the impedance circuit, and an impedance circuit having the function of the bias circuit is used as an impedance bias circuit, and the impedance bias circuit is replaced with the bias circuit. 2. The oscillation circuit according to claim 1, wherein the oscillation circuit comprises a low-noise DC constant voltage circuit having the function of (1), and a circuit including at least one of an inductor and a capacitor. 7. An emitter resistor having an impedance sufficiently smaller than the emitter resistance in the low frequency region and having an impedance sufficiently larger than the emitter resistance at the oscillation frequency in parallel with the emitter resistance of the oscillation circuit according to claim 3. Oscillator circuit with an impedance circuit.