JPH11150417A - Oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To add a function for tracking an injected signal, when an self- oscillation frequency fluctuates and to provide oscillation signals of sine/cosine, which have a precise phase relation against an input signal, by injecting the input signal to the amplifier of the feedback path of an oscillator using a transconductance (gm) variable filter circuit and a node in a gm filter. SOLUTION: An injected signal Vin from a signal source, which is injected into an input terminal 4 of an oscillator 1, and the output of a gm filter 3 are inputted to an amplifier 2. The amplifier 2 amplifies a difference between the output of the gm filter 3 and the injected signal Vin or the sum of them. The output of the amplifier 3 is fed back to the input of the gm filter, and an oscillation loop is constituted. The autonomous oscillation frequency of the gm filter is decided by a control signal inputted to a frequency control terminal 5. Thus, a phase is locked, so that the signal phase of the output of the gm filter 3 becomes zero degree, namely, in-phase with respect to the injected signal Vin. Then, the oscillation output of a sine wave can be obtained from an output terminal 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, a VCO or a PLL called an injection lock has been known and put to practical use. When the signal to be synchronized is injected into the oscillator (injection), the oscillation signal is phase-locked to the injected signal.
It is common to use a relaxation oscillator. Since the phase of the oscillator is synchronized by itself, no peripheral circuit such as a phase comparator is required, which is simple and suitable for incorporating an IC. Both the PLL and the oscillator can be said to be called an injection type oscillator. As an example of such an oscillator, reference 1: Japanese Patent Application Laid-Open No. 9-93042, "Injection Lock FM Demodulation Circuit" is known. FM demodulation is performed by multiplying the input signal by the output of the injection oscillator synchronized with the input signal, and utilizes the fact that the synchronous phase of the oscillator differs depending on the input frequency (deviation).

[0003] In general, when sine wave oscillation is required, reference 1
In the injection oscillator using the relaxation oscillator as described above, since the oscillation waveform is a rectangular wave, a sine wave output cannot be obtained unless harmonics are removed by a post filter, resulting in an increase in cost. Also, T
In the chrominance subcarrier processing of the V receiver, a four-phase sine / cosine wave is required, but a quadrature phase output cannot be obtained if the free-running frequency differs from the input signal frequency in the relaxation oscillator. In addition, when the filters are used as described above, there is a problem that the relative phase of the output signal is shifted 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 capable of incorporating an IC, there is Japanese Patent Application Laid-Open No. 63-191403, "Oscillation Circuit". A sine wave output is obtained by using a so-called gm variable filter circuit and arranging an amplifier circuit on the feedback path.

In Reference 2, there is no description about the contents of injection locking, 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, a sine wave output cannot be obtained with the injection oscillator using the relaxation oscillator in Reference 1, and the chromatic subcarrier processing of the TV receiver is not performed. Although a four-phase sine / cosine wave is required, a quadrature-phase output cannot be obtained with a relaxation oscillator if the free-running frequency and the input signal frequency are different. When a filter is used, there is a problem that the hue of an image is shifted. In the field of Reference 2, there is no description about the injection lock.
There is a problem that a sine-wave injection type oscillator cannot be put to practical use.

SUMMARY OF THE INVENTION An object of the present invention is to provide an injection type oscillator capable of incorporating an IC, and to add a function of tracking an injection signal when the free-running oscillation frequency varies, thereby maintaining an accurate phase relationship with an input signal. And to obtain a sine / cosine wave oscillation signal.

[0008]

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

According to this means, the feedback path amplifier and gm
When a signal is injected into any node inside the filter, it has the effect of shifting the phase of the oscillation signal at that node,
The oscillation condition changes depending on the phase characteristic of the filter, and the pull-in operation is performed. Eventually, the oscillator is locked so that the phase of the oscillation signal at the injected node becomes the same as the phase of the injected signal, and an oscillator can be realized.

In a gm filter circuit having a transfer function of a quadratic function, there is a signal node having a phase difference of 90 degrees from the signal of the injection node. If the free-running oscillation frequency deviates from the injection signal frequency, the signal phase of the injection node deviates from the in-phase, and it can be seen from the two signal phase differences that the free-running frequency deviates from the injection signal. Gm in phase comparison result
By controlling the free-running oscillation frequency of the filter, the injection signal and the free-running frequency can be finally equalized.

[0011]

Embodiments of the present invention will be described below in detail 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 comprises an amplifier 2 and a transconductance variable gm filter 3. Injection signal Vin and gm from a signal source injected into input terminal 4
The output signal of the filter 3 is input to the amplifier 2. The amplifier 2 amplifies the difference or sum between 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 extracted as an oscillation output.

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

For this reason, in the following description of each embodiment, it is assumed that no specific node signal is indicated. Therefore, the output terminal to which the oscillation output is supplied is shown in a floating state.

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

The gm filter 3 is, for example, a band pass (B
The circuit connection of (PF) characteristic is shown. This is the same type as the example 2 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 second-order transfer function represented by a BPF, only a specific frequency component of an input signal is passed, and the phase is rotated by 180 degrees. In the 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 providing feedback 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 time in the vicinity of the maximum gain frequency of F, the phase characteristic is rotated and becomes 0 degree only at the frequency at which the amplitude becomes maximum. Therefore, the frequency at which the phase becomes 0 degree is the oscillation frequency.

Since the gm filter 3 has a BPF characteristic, even if the oscillation signal output from the amplifier 2 is a rectangular wave, harmonic components are suppressed by the filter, and the gm filter 3
Output is close to a sine wave. For this reason, an oscillation circuit using a BPF is often used as a sine wave oscillation circuit that can be built in an IC.

In FIG. 2, reference numerals 31 and 32 denote gm, respectively.
This is a variable 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
To the other end of the adder 21. 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,
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 gain of the loop is set to 1 or more, free-running oscillation is performed at the free-running oscillation frequency fo. Limiter amplifier 22
Although the output signal S1 includes a harmonic, the harmonic is suppressed by the BPF, so that a sine wave oscillation output is obtained from the output terminal 6.

In the circuit shown in FIG. 2, the phase is locked so that the signal phase of the output of the gm filter 3 is 0 degree, that is, in-phase with the injection signal Vin. This will be described with reference to FIG. Using the phase of the output signal S2 of the gm filter 3 as a reference, the a vector is used. Assuming that the injection signal Vin having the same frequency as the free-running oscillation frequency fo is injected, the phase is used as the b vector. When these two signals are added by the adder 21, the combined vector becomes c, which is equivalent to being shifted from the phase a during self-running. Oscillation conditions change because the phase shifts into the loop and the phase shift is mixed. As shown in FIG. 3B, the whole shifts in the forward (up) direction, and the frequency giving 0 degree increases. 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 end of the transient response, 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 BP is connected to realize the transfer function by cascading the gm amplifiers in two stages.
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 an output is taken from between the gm amplifiers 31 and 32 in FIG. The HPF characteristic has a phase shifted by 90 degrees from 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 assumed that fa is 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 has been shifted in the direction of delay of φ degrees (downward), so that oscillation occurs at a frequency fa intersecting 0 degrees as shown in FIG. 5B. Since the oscillation condition is that the loop phase becomes 0 degree at fa, it can be said that the condition converges while shifting the phase characteristic of the loop so that the condition is satisfied. The shift phase is generated by a 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 reverse is the case, and φ becomes the leading phase. Φ increases as the frequency of the injection signal Vin departs from the free-running oscillation frequency fo.

According to this embodiment, an injection oscillator having a sine wave output can be realized. Further, FIG.
Since the point always has a phase difference of 90 degrees with the output signal S2 of the gm filter 3, quadrature signals of sine / cosine can be obtained at the same time. When a frequency signal far from the free-running oscillation frequency fo is injected, even if φ deviates from 0, it is 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 the signal is locked in phase with the output signal S2 of the m filter 3,
The output of the adder 21 is larger than the amplitude during self-running. However, as the injection signal Vin becomes farther from the free-running oscillation frequency fo, φ becomes larger, and the amplitude increase amount of the combined vector becomes smaller, so that the output amplitude of the adder 21 changes depending on the frequency (the maximum is fo). If the adder 21 is arranged before the limiter amplifier 22, the limiter amplifier 2
Since the output amplitude of No. 2 is constant, a change in oscillation amplitude due to the frequency can be avoided.

In FIG. 2, although the amplifier 2 is realized by the sum with the injection signal Vin, a limiter amplifier 22 is formed by a simple differential amplifier, and the output signal S2 of the gm filter 3 is applied 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. 4B has an opposite phase to a. However, the DC operating point of the output of the gm filter 3 (which is the same as the positive input potential of the gm1) is likely to be offset normally, and the differential input needs a dynamic range that can tolerate this offset. When the sum is obtained, the adder 21 can be easily realized by a resistor. 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. Further, another advantage derived from the realization by the adder 21 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 to have a certain constant amplitude, the gain of the loop can be accurately maintained at 1, and the sine wave oscillation is generated at all nodes in the oscillation loop. can get.

The characteristics of the gm filter 3 are exemplified by a BPF, but can be realized by a low-pass (LPF) or an all-pass (APF). It is sufficient that the oscillation condition is satisfied with respect to 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 with a linear phase change is suitable. Φ depends on the Q of the filter and the magnitude of the injection signal. Since the differential slope of the phase rotation increases as Q increases, φ for the same deviation increases.
Therefore, even if the slope of the S-curve characteristic is Q, it can be controlled, and φ decreases as the injection signal Vin decreases.

In the embodiment shown in FIG. 1, the amplifier 2 is
This is an example in which the injection signal Vin is injected into the amplifier 2. However, an input terminal for injecting the injection signal Vin into the gm filter 3 can be provided as shown in FIGS.
FIG. 6 is a system diagram for explaining a second embodiment of the present invention, and FIG. 7 is a system diagram for explaining a 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. The specific example of the amplifier 2a is as described in the description of FIG.

In FIG. 7, a control signal Qc for controlling the Q of the 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 a 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 the case of FIG. 3A, the gain at the free-running oscillation frequency fo increases as the Q increases. For example, if the gain is controlled to be 1, the oscillation condition can be satisfied without an amplifier. . FIG.
In, the 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 portion having the BPF characteristic shown in FIG. 2 as an example, and the same functional portions as those in FIG. 2 are denoted by the same reference numerals. In the connection of 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 used as input terminals for the injection signal without being grounded.
If B is used as a terminal, injection can be performed without adding a circuit. The input terminals can be provided by dividing the capacitors C1 and C2. In this case, the input 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 an input terminal 4 for inputting n is provided, an element is added, but adding a gm amplifier 81 is one means.

Regardless of which node is injected, as described above,
Locking is performed so that the oscillation phase at the injected node becomes the same. When the signal is passed through the gm amplifier, the phase is locked at the gm output terminal.

Instead of the AC oscillation loop of the gm filter,
It is also possible to input the signal to a frequency control terminal that normally supplies a DC signal. In this case, no additional adder is required. FIG.
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 assumed to be from the same place. An arbitrary node signal in the oscillation loop is extracted as an oscillation signal.

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

In FIG. 10, the filter input is changed to a 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 composite vector at the point A in FIG. 8 is g. Since the g vector is rotated in the delay direction by 90 degrees in the gm amplifier 32, the h vector is output.
Since the vectors are added, the composite vector becomes i and returns to the same phase as the reference vector d. This circuit uses the injection signal Vin
Is locked at a phase of +45 degrees with respect to. A signal whose frequency is shifted from the free-running oscillation frequency fo is locked with a phase shifted by φ from 45 degrees.

In this case, an oscillation signal having the same phase as the injection signal Vin cannot be obtained, but the adder can be eliminated. Conversely, 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, and there is no phase shift between the four-phase outputs. For the injection signal Vin, π /
When two phases are required, the signals can be synthesized by adding two adjacent axes from a π / 4 phase orthogonal signal.

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 of the sine / cosine output does not vary, but the capture range varies. If this cannot be tolerated, 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. This oscillator outputs an injection signal and a signal that produces 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 produces a 90-degree phase difference is a signal that has a 90-degree phase difference from 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 the oscillators except for FIG. In FIG. 2, the signal is a point A signal. The phase of the point A is fo and advances 90 degrees, and when the frequency of the injection signal Vin deviates from fo, the phase shifts from 90 degrees by more than φ. If this is detected by the phase comparator and the gm filter is controlled so as to always have a phase difference of 90 degrees, the free-running oscillation frequency fo can be made equal to the injection signal. 6 and 7 can be selected in the same way. When the injection is performed from the node NA in FIG. 8,
A 90-degree phase signal may be extracted from the output of the gm amplifier 31.

The self-running oscillation frequency fo has a large manufacturing variation.
If the deviation is large, the injection signal Vin may not be locked, and tracking adjustment may not be possible. Means for avoiding this will be described with reference to the circuit configuration diagram of FIG.

During the tracking adjustment, the frequency range (capture range) in which injection locking can be performed is widened, and when the adjustment is returned to a predetermined range when the adjustment is completed, the tracking adjustment can be surely performed. To widen the range, change the signal gain to be injected.
What is necessary is just to add a gain control circuit. This gain control circuit
It is also possible to use the amplifier 2 of FIG. Hereinafter, this will be described.

FIG. 12 shows an example realized by the amplifier 2 of FIG. The adder 21 includes a resistor R and a gm amplifier 121, and inputs an addition signal to a limiter amplifier 22. gm1
If a control terminal 122 capable of changing the gm value is provided at 21 and a result of, for example, color or monochrome determination is input to the control terminal 122, the gain of the injection signal Vin can be changed. Also, in FIG. 2, since the signals are synthesized by the adder 21, it is easy to add a means for changing the addition ratio, but in FIGS. 6 and 7, since the direct injection is performed, it is necessary to add a separate gain switching circuit. is there. As an example of this, an arrangement like the gm amplifier 81 in FIG. 8 can be considered, and this can be realized by switching the gm of the gm amplifier 81.

The range switching control signal may be a pulse of a predetermined time. For example, when such an injection type oscillator is used for a color subcarrier of a color TV receiver, the color killer circuit determines that it is monochrome. If so, a wide range can be set in the tracking mode, and if it is determined that the color is selected, the range can be narrowed. If the range is switched in this manner, a stable injection lock performance can be always obtained irrespective of the variation in the manufacturing process, and the tracking adjustment can be reliably performed.

[0045]

As described above, the injection type oscillator which can incorporate a IC and can obtain a sine / cosine oscillation signal can be used. Therefore, not only can the application be expanded, but also if the free-running oscillation frequency varies, the injection signal can be increased. , A correct tracking relationship can be maintained with respect to the input signal.

[Brief description of the 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 a specific example of FIG. 1;

FIG. 3 is a characteristic diagram showing characteristics of the BPF of FIG. 2;

FIG. 4 is a vector diagram for explaining the operation of the phase synchronization process of FIG. 2;

FIG. 5 is a characteristic diagram for explaining a stationary lock phase in FIG. 2;

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 of 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 in FIG. 9;

FIG. 11 is a system diagram for explaining an example in which tracking adjustment of the free-running oscillation frequency of the injection type oscillator of the present invention is applied.

FIG. 12 is a circuit configuration diagram for explaining an injection gain switching function in FIG. 11;

[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 signals, B1, B2 ...
Buffer amplifier, m: attenuator, C1, C2: capacitor, R: resistor.

Claims (10)

[Claims] A variable transconductance (gm) filter circuit having a frequency control terminal; an amplifier circuit for receiving an output of the filter circuit and an injection signal and amplifying a difference or a sum; and an output of the amplifier circuit An oscillation circuit configured to input an oscillation output to the filter circuit, and an oscillation output from an arbitrary node in the oscillation loop. 2. The oscillation circuit according to claim 1, wherein the amplifier circuit includes an addition circuit that adds the filter output signal and the injection signal, and a limiter amplifier that limits and amplifies the addition output. 3. A gm variable filter circuit having a frequency control terminal and an injection signal input terminal, an amplifier circuit for receiving and amplifying an output of the filter circuit, and an output of the amplifier circuit being input to the filter circuit. An oscillation circuit comprising: a means for forming an oscillation loop by means of a circuit; and means for extracting an oscillation output from an arbitrary node in the oscillation loop. 4. A gm variable filter circuit having a frequency control terminal and an injection signal input terminal; a detection circuit for detecting whether or not an output amplitude of the filter circuit is a predetermined amplitude, and detecting the detection amplitude; Control means for controlling Q of the filter circuit based on a detection result of the circuit; means for forming an oscillation loop by feeding back an output of the filter circuit to a filter input of the filter circuit; Means for taking out an oscillation output from the node. 5. The oscillation circuit according to claim 3, wherein an AC ground terminal inside the gm variable filter is used as an injection signal input terminal. 6. A signal input from an injection signal input terminal to an internal node of a gm variable filter circuit via a gm amplifier or an addition circuit of a passive element. The oscillation circuit according to any of the above. 7. A gm variable type filter circuit having a frequency control terminal, and means for forming an oscillation loop by feeding back an output terminal of the filter circuit to an input terminal, wherein an arbitrary node in the oscillation loop is provided. An oscillation circuit wherein an oscillation output is taken out and an injection signal is injected into the frequency control terminal. 8. The gm variable filter circuit comprises two gm filters.
8. The oscillation circuit according to claim 1, wherein the oscillation circuit is constituted by m amplifiers, and an oscillation output is extracted from an output of each of the gm amplifiers. 9. A phase comparator for inputting a signal in an oscillation loop having a phase difference of 90 degrees with respect to an injection signal and an injection signal and comparing the phases, and an LPF for smoothing the phase comparison output, wherein the LPF is provided. 8. The oscillation circuit according to claim 1, wherein said output is connected to a frequency control terminal. 10. A gain control circuit having a terminal for controlling an injection gain of an injection signal, wherein the gain of the injection signal is changed by an external control signal. 8. The oscillation circuit according to any one of 7.