JP3523031B2 - Oscillation circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The circuit of the present invention is mainly used for PL.
The present invention relates to an oscillator circuit suitable for use in obtaining a sine wave signal locked to an original signal by L with a simple configuration, particularly in the field of color subcarrier reproduction of a TV receiver.

[0002]

2. Description of the Related Art Conventionally, a VCO or PLL called an injection lock has been known and put into practical use. When the signal you want to synchronize is injected into the oscillator (injection), the oscillation signal is phase-synchronized with the injection signal.
It is common to use a relaxation oscillator. Since the oscillator is phase-synchronized by itself, a peripheral circuit such as a phase comparator is unnecessary, and it is simple and suitable for incorporating an IC. Although both a PLL and an oscillator can be called, they are hereinafter referred to as an injection type oscillator. As an example of such an oscillator, there is Reference 1: Japanese Patent Application Laid-Open No. 9-93042 "Injection lock FM demodulation circuit". FM demodulation is performed by multiplying the injection oscillator output synchronized with the input signal by the input signal, and the fact that the synchronization phase of the oscillator differs depending on the input frequency (deviation) is used.

Generally, when sine wave oscillation is required, reference 1
In an injection oscillator using such a relaxation oscillator, the oscillation waveform is a rectangular wave, so a sine wave output cannot be obtained unless harmonics are removed by a post filter, which leads to cost increase. Also, T
The chrominance subcarrier processing of the V receiver requires four-phase sine / cosine waves, but the relaxation oscillator cannot obtain a quadrature phase output when the free-running frequency and the input signal frequency are different. In addition, when the filters are used as described above, there arises a problem that the relative phase of the output signal is deviated due to the characteristic variation between the filters and the hue of the image is shifted.

On the other hand, as an example of a sine wave oscillator in which an IC can be incorporated, there is Reference 2: Japanese Patent Laid-Open No. 63-191403 "Oscillation circuit". A so-called gm variable type filter circuit is used and an amplifier circuit is arranged in the feedback path to obtain a sine wave output.

In Reference 2, there is no description about the injection lock, and there is a problem that a sine wave injection type oscillator cannot be put to practical use.

[0006]

When sine wave oscillation is required in the above-mentioned prior art, the sine wave output cannot be obtained by the injection oscillator using the relaxation oscillator in Reference 1, and the sine wave output is not obtained by the color subcarrier processing of the TV receiver. A 4-phase sine / cosine wave is required, but a relaxation oscillator cannot obtain a quadrature phase output when the free-running frequency and the input signal frequency are different. When the filter is used, the problem occurs that the hue of the image is shifted. In addition, there is no description about injection lock in the field of Reference 2,
There is a problem that a sine wave injection type oscillator cannot be put to practical use.

An object of the present invention is to provide an injection type oscillator having a built-in IC, which has a function of tracking an injection signal when the free-running oscillation frequency fluctuates so that an accurate phase relationship with respect to an input signal can be maintained. , And to obtain a sine / cosine wave oscillation signal.

[0008]

In order to solve the above-mentioned problems, the oscillator circuit of the present invention is an oscillator using a gm variable type filter circuit, and an input signal is input to an amplifier of a feedback path or a node inside the gm filter. By adding (injecting) to form an injection type oscillator. Injection signal and 90
Phase comparison with the internal signal of the filter circuit with a degree phase difference,
The phase error is detected to correct the free-running oscillation frequency of the gm filter.

According to this means, an amplifier on the return path and gm
When a signal is injected into any node inside the filter, it acts as a phase shift for the oscillation signal at that node,
The oscillation condition changes depending on the phase characteristics of the filter, and the pull-in operation is performed. Finally, an oscillator can be realized by locking the phase of the oscillation signal at the injected node so that it is in phase with the injection signal.

Further, in the gm filter circuit whose transfer function is a quadratic function, there is a signal node having a 90-degree phase difference from the signal at the injection node. When the free-running oscillation frequency deviates from the injection signal frequency, the signal phase at the injection node deviates from the same phase, and it can be seen from the difference in the two signal phases that the free-running frequency deviates from the injection signal. Phase comparison result is gm
By controlling the free-running oscillation frequency of the filter, the injection signal and the free-running frequency can be finally made equal.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a system diagram for explaining a first embodiment of the present invention. Reference numeral 1 denotes an oscillator, which includes an amplifier 2 and a transconductance variable type gm filter 3. Injection signals Vin and gm from the signal source injected into the input terminal 4
The output signal of the filter 3 is input to the amplifier 2. The amplifier 2 amplifies the difference or the sum of the output of the gm filter 3 and the injection signal Vin. The output of the amplifier 3 is fed back to the input of the gm filter 3 to form an oscillation loop. As the oscillation output, a signal generated at any node in the loop can be taken out as the oscillation output.

The free-running oscillation frequency fo of the gm filter 3 is
It is determined by the control signal input to the frequency control terminal 5. The control signal is, for example, a constant current source or a constant voltage source, and the free-running oscillation frequency fo can be changed by changing these values. When amplifying the difference between the output of the gm filter 3 and the injection signal Vin, both inputs are connected to the positive and negative input terminals of the amplifier 2, and when amplifying the sum, an adder is included in the amplifier 2. In FIG. 1A, the output of the amplifier 2 is taken out from the output terminal 6a, and in FIG. 1B, the output of the gm filter 3 is taken out from the output terminal 6b. In this way, a desired oscillation signal can be obtained from any node in the loop.

Therefore, in the following description of each embodiment, a specific node signal is not referred to. Therefore, the output terminal to which the oscillation output is supplied is shown in a floating state.

A specific circuit configuration example of FIG. 1 is shown in FIG. 2 for further description. The amplifier 2 includes an adder 21 and a limiter amplifier 22, and the injection signal Vin is input to the one of the adders 21 from the input terminal 4. The output of the adder 21 is amplified by the limiter amplifier 22.

The gm filter 3 is, for example, a band pass (B
The circuit connection of the PF) characteristic is shown. This is the same type as the second example shown in the related art, and the description of the correspondence between the transfer function and the circuit parameter is omitted.

In a filter circuit having a quadratic transfer function represented by BPF, only a specific frequency component of an input signal is passed and the phase is rotated by 180 degrees. In case of BPF,
At the frequency where the output amplitude is the largest, the output phase is 0 degree. If an amplifier is provided and a path for amplifying the output signal and returning it to the input is provided, the oscillation condition can be satisfied.
The gain in the oscillation loop, that is, the path from the output of the amplifier 2 to the input to the amplifier 2 via the gm filter 3 is BP.
Although it exceeds 1 times in the vicinity of the maximum gain frequency of F, the phase characteristic is rotating and becomes 0 degree only at the frequency where the amplitude is maximum. Therefore, the frequency at which the phase is 0 degree is the oscillation frequency.

Since the gm filter 3 has the BPF characteristic, even if the oscillation signal of the output of the amplifier 2 is a rectangular wave, the harmonic component is suppressed by the filter, and the gm filter 3
The output of is close to a sine wave. Therefore, an oscillation circuit using a BPF is often used as a sinusoidal oscillation circuit that can be built in an IC.

In FIG. 2, 31 and 32 are gm, respectively.
It is a variable type gm amplifier. The output of the gm amplifier 31 whose positive input is grounded is input to the positive input of the gm amplifier 32 via the buffer amplifier B1 together with the output signal S1 from the limiter amplifier 22 supplied via the capacitor C1. The output of the gm amplifier 32 is input to the output terminal 6 via the capacitor C2 whose one end is grounded and the buffer amplifier B2. The output S2 of the buffer amplifier B2 is the amplifier 2
Is input to the other adder 21 of. Further, the output S2 of the buffer amplifier B2 is input to the negative input of the gm amplifier 32 and the negative input of the gm amplifier 32 via the attenuator m. gm
The amplifiers 31 and 32 are biased by the current from the bias current source 33, have a value of gm according to the current,
The gm is controlled to a desired value by the frequency control terminal 5.

FIG. 3 shows the characteristics of the gm filter 3 which is a BPF.
Shown in. (A) is an amplitude characteristic and (b) is a phase characteristic.
The amplitude becomes maximum at the free-running oscillation frequency fo, and the phase at this time is 0 degree. When the loop gain is set to 1 or more, self-oscillation occurs at the free-running oscillation frequency fo. Limiter amplifier 22
The output signal S1 of 1 contains a harmonic, but since the BPF suppresses the harmonic, a sine wave oscillation output is obtained from the output terminal 6.

In the circuit of FIG. 2, the output signal of the gm filter 3 is phase-locked with the injection signal Vin so that the signal phase becomes 0 degree, that is, the same phase. This will be described with reference to FIG. Taking the phase of the output signal S2 of the gm filter 3 as a reference, and assuming that an injection signal Vin having exactly the same frequency as the free-running oscillation frequency fo is injected, the phase is taken as the b vector. When these two signals are added by the adder 21, the combined vector becomes c, which is equivalent to being advanced and shifted from the a phase during free running. Since the phase shift progresses into the loop and the phase shift is mixed, the oscillation condition changes. As shown in FIG. 3B, the whole shifts toward the upward (upward) direction, and the frequency giving 0 degree becomes high. As a result, the oscillator oscillates at a higher frequency and moves so as to follow the leading phase direction, that is, the b phase. After the transient response ends, all the vectors a, b, and c are locked in the same direction as shown in FIG.

By the way, in the secondary filter circuit, the gm amplifier is cascade-connected in two stages to realize the transfer function.
Even when F is configured, in addition to the output of the BPF characteristic,
A signal between the gm amplifier stages can be output. For example, when the output is taken from between the gm amplifiers 31 and 32 in FIG. 2, the HPF characteristic is obtained. The HPF characteristic is 90 degrees out of phase with the BPF characteristic, and can be used as a signal orthogonal to the BPF characteristic.

Next, a case where the frequency of the injection signal Vin is different from the free-running oscillation frequency fo will be described with reference to FIG. Now, the frequency of the injection signal Vin is the free-running oscillation frequency f.
It is set to fa lower than o. In this case, as shown in FIG. 5A, the b vector of the injection signal Vin is delayed with respect to the a vector of the output signal S2 of the gm filter 3, and the c vector obtained by combining a and b is delayed by φ degrees. . This means that the phase of the output signal S2 of the gm filter 3 is delayed by φ degrees (downward), so that it oscillates at the frequency fa intersecting with 0 degrees as shown in FIG. 5B. Since the oscillation condition is that the phase of the loop becomes 0 degrees at fa, it can be said that the phase is converged in a state in which the phase characteristic of the loop is shifted so that the condition is satisfied. The shift phase is generated by the phase difference between the injection signal Vin and the output signal S2 of the gm filter 3. Free-running oscillation frequency f
In the case of a frequency higher than o, the opposite is true, and φ leads to a phase. Φ increases as the frequency of the injection signal Vin deviates from the free-running oscillation frequency fo.

According to this embodiment, it is possible to realize an injection type oscillator having a sine wave output. Furthermore, in FIG.
Since the point always has a 90-degree phase difference with the output signal S2 of the gm filter 3, a sine / cosine orthogonal signal can be obtained at the same time. When a frequency signal far from the free-running oscillation frequency fo is injected, even if φ is deviated from 0, they are always orthogonal and the relative phase relationship does not change.

Here, the arrangement of the adder 21 will be described. As described with reference to FIG. 4B, the injection signal Vin is g
Since it is locked in phase with the output signal S2 of the m filter 3,
The output of the adder 21 becomes larger than the amplitude during free running. However, φ becomes larger as the injection signal Vin is farther from the free-running oscillation frequency fo, and the increase amount of the amplitude of the combined vector becomes smaller. Therefore, the output amplitude of the adder 21 changes depending on the frequency (maximum at fo). If the adder 21 is arranged in the preceding stage of the limiter amplifier 22, the limiter amplifier 2
Since the output amplitude of 2 is constant, it is possible to avoid the oscillation amplitude change due to the frequency.

In FIG. 2, the amplifier 2 is realized by the sum of the injection signal Vin, but a limiter amplifier 22 is formed by a simple differential amplifier, and the output signal S2 of the gm filter 3 is input to the positive input.
Is connected to the injection signal Vin at the negative input to amplify the difference signal,
It is also possible to simplify the circuit scale. In this case, the b vector in FIG. 4 (b) has a phase opposite to that of a. However, since the DC operating point of the output of the gm filter 3 (which is the same as the positive input potential of gm1) is usually prone to offset, the differential input requires a dynamic range that allows this offset. When taking the sum, the resistor 21 can easily realize the adder 21. Since the injection signal Vin can be input to the DC operating point of the output of the gm filter 3 by C coupling, the problem of offset can be solved. Furthermore, if the adder 21 realizes another advantage, this will be described later.

As for the amplifier 2, the limiter amplifier 22
However, a linear amplifier with an automatic gain control function may be used. If the output amplitude of the amplifier 2 is detected and the gain of the amplifier 2 is controlled so as to have a certain constant amplitude, the loop gain can be maintained exactly at 1, and sine wave oscillation can occur at all nodes in the oscillation loop. can get.

Although the characteristics of the gm filter 3 are based on BPF as an example, they can be realized by low pass (LPF) or all pass (APF). It suffices that consideration is given so that the oscillation condition holds for the output phase of the gm filter 3. BPF
, Φ does not change linearly with frequency, so F
Although not suitable for M demodulation, APF having a linear phase change is suitable. Further, φ depends on the Q of the filter and the magnitude of the injected signal. Since the higher Q is, the larger the differential slope of the phase rotation is, the larger φ is for the same deviation.
Therefore, the slope of the S curve characteristic can be controlled even with Q, and φ becomes larger as the injection signal Vin becomes smaller.

In the embodiment shown in FIG. 1, the amplifier 2 is provided in the return path.
In this example, the injection signal Vin is injected into the amplifier 2, but it is possible to provide an input terminal for injecting the injection signal Vin into the gm filter 3 as shown in FIGS.
FIG. 6 is a system diagram for explaining the second embodiment of the present invention, and FIG. 7 is a system diagram for explaining the third embodiment of the present invention.

That is, in FIG. 6, the output of the gm filter 3a is input to the amplifier 2a, and the output of the amplifier 2a is positively fed back to the gm filter 3a. A concrete example of the amplifier 2a is as described in the description of FIG.

Further, in FIG. 7, a control signal Qc for controlling the Q of the gm filter 3b is supplied from the Q control circuit 71 to the gm filter 3b. The output of the gm filter 3b is supplied to the input terminal of the filter 3b and the Q control circuit 71, and the control signal Qc that satisfies the oscillation condition is supplied to the gm filter 3b to control the Q of the gm filter 3b. In FIG. 3A, the higher the Q, the higher the gain at the free-running oscillation frequency fo. Therefore, if the gain is controlled to be 1, the oscillation condition can be satisfied without the amplifier. . Figure 2
Then, Q can be controlled by changing the value of the attenuator m.

In the configurations of FIGS. 6 and 7, the adder of FIG. 2 can be omitted. This will be described with reference to the circuit configuration diagram of FIG.

FIG. 8 is based on the filter part having the BPF characteristic shown in FIG. 2 as an example, and the same functional parts as those in FIG. In connecting the BPF, the capacitor C2 and the positive input terminal of the gm amplifier 31 are connected to AC ground. These terminals can be directly input terminals for the injection signal without being grounded. For example, nodes NA and N
If B is used as a terminal, it can be injected without adding a circuit. It is also possible to divide the capacitors C1 and C2 to provide an input terminal, and in this case as well, injection can be performed without changing the total capacitance value.

The injection signal Vi is applied to the gm filters 3a and 3b.
In the sense that the input terminal 4 for inputting n is provided, this is an element addition, but adding the gm amplifier 81 is also one means.

No matter which node is injected, as described above,
It locks so that the oscillation phase at the injected node is in phase. When the signal is passed through the gm amplifier, the gm output terminal becomes in-phase locked.

Instead of the AC oscillation loop of the gm filter,
It is also possible to input to a frequency control terminal that normally gives a DC signal. Also in this case, it is not necessary to add an adder. Figure 9
The fourth embodiment of the present invention will be described with reference to the system diagram of FIG. In FIG. 9, a positive feedback loop such as an amplifier is omitted. In this case, the frequency control terminal 5 for controlling the frequency of the gm filter 3c and the input terminal 4 for inputting the injection signal Vin are from the same location. An arbitrary node signal in the oscillation loop is taken out as an oscillation signal.

Since the motion vector of FIG. 9 is different from the above,
This will be described with reference to FIG. The gm filter 3c is assumed to have the BPF characteristic used in FIG. 8, for example. The injection signal Vin passes through the bias current source 33 from the frequency control terminal 5,
The voltage signals are converted by the amplifiers 31 and 32 and the capacitors C1 and C2. At this time, gm amplifiers 31, 32 and capacitors C1, C
If 2 is equal, the injection signals Vin converted by the capacitors C1 and C2 have the same vector.

In FIG. 10, the filter input is the reference vector d.
Then, since the output of the gm amplifier 31 advances by 90 degrees,
e vector. Since the f vector of the injection signal Vin is added to this, the combined vector at point A in FIG. 8 is g. In the gm amplifier 32, the g vector rotates in the direction delayed by 90 degrees, so the h vector is output.
Since the vectors are added, the combined vector becomes i and returns to the same phase as the reference vector d. This circuit uses the injection signal Vin
Based on, the phase is locked at +45 degrees. A signal whose frequency deviates from the free-running oscillation frequency fo is locked at a phase deviated by φ from 45 degrees.

In this case, the oscillation signal having the same phase as the injection signal Vin cannot be obtained, but the adder can be eliminated. On the contrary, it can be used as a π / 4 phase shifter for a sine wave for color tone control of a TV receiver, or for QPSK demodulation. g
The outputs of the m amplifiers 21 and 32 are orthogonal to each other, and the phases of the four-phase outputs do not shift. Π / for injection signal Vin
When two phases are required, they can be combined by adding two adjacent axes from quadrature signals of π / 4 phase.

The injection type oscillator described above is premised on the built-in IC, and the free-running oscillation frequency varies due to the time constant variation in the IC manufacturing process. Injection signal Vi
Even if n deviates from the free-running oscillation frequency fo, the relative quadrature phase of the sine / cosine output does not vary, but the capture range varies. If this is unacceptable, it is necessary to provide a separate tracking function, which will be described with reference to FIG. All of the above-mentioned injection type oscillators are applicable. The oscillator outputs an injection signal and a signal that causes a 90-degree phase difference, and the phase comparator 111 compares the phases. The comparison result is smoothed by the LPF 112 and fed back to the frequency control terminal 5 of the oscillator.

The signal that causes a 90-degree phase difference is a signal that has a 90-degree phase difference with the injection signal Vin at the free-running oscillation frequency fo and that can detect the phase difference φ when Vin deviates from fo. It can be obtained from oscillators other than FIG. In FIG. 2, the signal becomes the point A signal. The phase at point A advances at fo and is 90 degrees, and if the frequency of the injection signal Vin deviates from fo, it shifts from 90 degrees by more than φ. If this is detected by the phase comparator and the gm filter is controlled so that the phase difference is always 90 degrees, the free-running oscillation frequency fo can be made equal to the injection signal. The same can be selected in the example of FIG. 6 and FIG. 7, and in the case of injection from the node NA of FIG.
It is sufficient to extract the 90-degree phase signal from the output of the gm amplifier 31.

There is a large manufacturing variation and the free-running oscillation frequency fo
If the deviation is large, it may not be possible to lock to the injection signal Vin, and tracking adjustment becomes impossible, so means for avoiding this will be described using the circuit configuration diagram of FIG. 12.

If the frequency range (capture range) in which the injection lock can be performed is widened during the tracking adjustment and is returned to the predetermined range when the adjustment is completed, the tracking adjustment can be surely performed. To widen the range, change the injected signal gain,
A gain control circuit may be added. This gain control circuit
It is also possible to use the amplifier 2 of FIG. This will be described below.

FIG. 12 shows an example realized by the amplifier 2 of FIG. The adder 21 is composed of a resistor R and a gm amplifier 121, and inputs the addition signal to the limiter amplifier 22. gm1
21 is provided with a control terminal 122 capable of varying the gm value, and the gain of the injection signal Vin can be changed by inputting, for example, the result of determination of color or black and white to the control terminal 122. Further, in FIG. 2, since it is combined by the adder 21, it is easy to add a means for changing the addition ratio, but in FIG. 6 and FIG. 7, direct injection is performed, so it is necessary to add a gain switching circuit separately. is there. As an example of this, an arrangement like the gm amplifier 81 in FIG. 8 can be considered, and it can be realized by switching gm of the gm amplifier 81.

A pulse for a predetermined time may be used as the range switching control signal. For example, when such an injection type oscillator is used for the color subcarrier of a color TV receiver, the color killer circuit determines that it is black and white. If there is a color, it is possible to set a wide range in the tracking mode, and if the color is determined, the range can be narrowed. By switching the range in this way, it is possible to always obtain stable injection lock performance irrespective of variations in the manufacturing process and reliably perform tracking adjustment.

[0045]

As described above, since the injection type oscillator is capable of incorporating an IC and is capable of obtaining a sine / cosine oscillation signal, the application is not only expanded, but also when the free-running oscillation frequency fluctuates. A tracking function can be added to maintain an accurate phase relationship with the input signal.

[Brief description of drawings]

FIG. 1 is a system diagram for explaining a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram for explaining FIG. 1 as a specific example.

FIG. 3 is a characteristic diagram showing characteristics of the BPF of FIG.

FIG. 4 is a vector diagram for explaining the operation of the phase synchronization process of FIG.

5 is a characteristic diagram for explaining the stationary lock phase of FIG. 2. FIG.

FIG. 6 is a system diagram for explaining a second embodiment of the present invention.

FIG. 7 is a system diagram for explaining a third embodiment of the present invention.

FIG. 8 is a circuit configuration diagram for explaining a specific example of the gm filter in FIGS. 6 and 7.

FIG. 9 is a system diagram for explaining a fourth other embodiment of the present invention.

FIG. 10 is a vector diagram for explaining a lock phase of FIG.

FIG. 11 is a system diagram for explaining an application example in which the free-running oscillation frequency of the injection type oscillator of the present invention is tracked and adjusted.

12 is a circuit configuration diagram for explaining an injection gain switching function of FIG.

[Explanation of symbols]

1 ... Oscillator, 2, 2a ... Amplifier, 3, 3a, 3b ... Gm
Filter, 4 ... Input terminal, 5 ... Frequency control terminal, 6a,
6b ... Output terminal, 21 ... Adder, 22 ... Limiter amplifier, 31, 32, 81, 121 ... Gm amplifier, 33 ... Bias current source, 71 ... Q control circuit, 111 ... Phase comparator, 112 ... LPF, Vin ... Injection signal, B1, B2 ...
Buffer amplifier, m ... Attenuator, C1, C2 ... Capacitor, R ... Resistor.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H03B 5/00-5/28 H03H 11/00-11/54 H03L 7/24

Claims (9)

(57) [Claims] 1. A transconductance (gm) variable type filter circuit having a frequency control terminal, an amplifier circuit for inputting an output of the filter circuit and an injection signal and amplifying a difference or a sum, and an output of the amplifier circuit. oscillating circuit, characterized in that consists of a means constituting an oscillating loop is input to the filter circuit, and means for extracting the oscillation output from any node in the oscillation loop. Wherein said amplifier circuit includes an adder circuit for adding the injection signal and output <br/> force signal of the filter circuit, the summing times
The oscillator circuit according to claim 1, wherein the oscillator circuit is configured by a limiter amplifier that limits-amplifies the addition output of the path . And gm-variable filter circuit 3. A with a frequency control terminal and the injected signal input terminal, and an amplifier circuit for amplifying and receiving an output of said filter circuit, the output of the amplifier circuit is inputted to the filter circuit An oscillating loop, and an oscillating output from an arbitrary node in the oscillating loop. And gm-variable filter circuit wherein with a frequency control terminal and the injected signal input terminal, and a control means for controlling the Q of the filter circuit based on an output of the filter circuit, the output of the filter circuit, oscillating circuit, characterized in that consists of a means constituting an oscillating loop and fed back to the filter input of the filter circuit, and means for extracting the oscillation output from any node in the oscillation loop. Wherein said gm-variable filter circuit oscillator according to any one of claims 3 and 4 inside of the AC ground terminal, characterized in that the injection signal input terminal. And gm-variable filter circuit having a wherein a frequency control terminal, and means constituting a feedback to the oscillation loop to the input terminal to an output terminal of said filter circuit, from any node in the oscillation loop An oscillation circuit in which an oscillation output is taken out and an injection signal is injected into the frequency control terminal. Wherein said gm-variable filter circuit, there is constituted by two gm amplifiers, claim, characterized in that the removal of the oscillation output from the output of the gm amplifier 1 and 3, oscillation circuit according to any one of the 4 and 6. And wherein said injection signal to enter the signal and the injected signal in the oscillation loop showing a 90 degree phase difference the phase comparator for phase comparison, and LPF that smoothes an output of the phase comparator provided, the oscillation circuit according to any one <br/> of claims 1, 3, 4, and 6 an output of the LPF is characterized in that connected to the frequency control terminal. 9. comprises a gain control circuit having a terminal for controlling the injection gain of said injection signal, the control signal from the outside, claims, characterized in that changing the gain of said injection signal 1,3, oscillation circuit according to any one of the 4 and 6.