JPS63142906A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To make the oscillation output level stable by detecting the oscillating state of an oscillated level or phase or harmonics so as to control the loop gain in response to the oscillating state. CONSTITUTION:An output of an amplifier 1 with a gain K is fed back positively to the amplifier 1 via a phase shifter 2 having a feedback rate of beta. The feedback rate beta is controlled in response to the control input to a control terminal 4 of the phase shifter 2 to change the phase characteristic thereby varying the oscillating frequency. The gain of the amplifier 1 varies with the change in a current of a variable current source 5 as the gain control means. The current of the current source 5 is controlled by a detected output from a level detection circuit 6 and the detection circuit 6 controls the variable current source 5 in response to the output of the detection circuit 6 detecting an output level of the amplifier 1 so as to make the output level stable.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an oscillation circuit, and particularly to a variable frequency oscillation circuit in which the oscillation frequency is changed by controlling the phase characteristics of a feedback path.

80 Summary of the Invention The present invention provides an oscillation circuit that positively feeds back an output from an amplifier to the amplifier via a phase shifter and controls the oscillation frequency by controlling the phase characteristics of the phase shifter. The oscillation output level is stabilized by detecting the oscillation state such as harmonics or oscillation level and controlling the loop gain according to this oscillation state.

C0 Prior Art Figure 4 shows the basic configuration of a so-called phase control type variable frequency oscillation circuit.
The output of the K amplifier 11 is positively fed back to the input terminal of the amplifier 11 via a phase shifter 12 with a feedback factor β. The output from amplifier 11 is taken out via output terminal 13. The oscillation condition of this oscillation circuit is Kβ≧1. Here, as the phase shifter 12, an LC (coil and capacitor) circuit, a CR (capacitor and resistor) circuit, a crystal, etc. are used. The feedback factor β is controlled in accordance with the control input to the control terminal 14 of the phase shifter 12 to change the phase characteristics and the like, and the oscillation frequency changes due to the change in the phase characteristics.

As a specific example of such a variable frequency oscillation circuit, a VCO (voltage controlled oscillation circuit) described in Japanese Patent Publication No. 61-14684 is known.

D. Problems to be Solved by the Invention By the way, when changing the oscillation frequency by changing the phase characteristics of the phase shifter 12 in accordance with the control signal of the control terminal 14, it is generally not possible to change only the phase. As shown in FIG. 5, the loop gain also changes when the oscillation frequency changes. In this Fig. 5, the horizontal axis is the frequency,
The vertical axis shows the phase and loop gain. Here, even if the loop gain when the oscillation frequency is rA is more than OdB, for example to the point in the figure, if the oscillation frequency changes to f or rc, the loop gain will change to point B in the figure.
Alternatively, as at point C, the voltage may fall below OdB and oscillation may stop. Conversely, if the loop gain significantly exceeds OdB when the oscillation frequency changes,
The output waveform may be distorted. Even if these oscillations do not stop or waveform distortion occurs, the oscillation level fluctuates as the oscillation frequency changes.

The present invention has been made in view of these circumstances, and provides an oscillation circuit that can minimize or prevent level changes and oscillation stoppages caused by changes in the phase characteristics of the phase shifter in the feedback path. The purpose is to provide.

Means for Solving the E0 Problem In order to solve the above-mentioned problem, the oscillation circuit according to the present invention provides positive feedback of the output from the amplifier to the amplifier via the phase shifter, and In a variable frequency oscillation circuit that controls the oscillation frequency by controlling the phase characteristics of the amplifier, there is provided an oscillation state detection means for detecting the oscillation state according to the output from the amplifier, and a gain of a loop consisting of the amplifier and the phase shifter. and a gain control means for controlling the oscillation state detection means, and is characterized in that the gain control means is controlled in accordance with the output from the oscillation state detection means to stabilize the output level.

Even when the output level changes due to variable control of the F1 action oscillation frequency, the oscillation state detection means controls the gain control means to control the gain of the loop, so the output level is kept constant. A stable oscillation state can always be obtained.

G. Embodiment FIG. 1 is a block circuit diagram showing an oscillation circuit according to an embodiment of the present invention.

In FIG. 1, the output of an amplifier 1 with a gain (amplification) K is positively fed back to the input terminal of the amplifier 1 via a phase shifter 2 with a feedback factor β. The oscillation output from the amplifier 1 is taken out via the output terminal 3. The oscillation condition of this oscillation circuit is Kβ≧1.The phase shifter 2 is composed of an LC (coil and capacitor) circuit, a CR (capacitor and resistor) circuit, or a crystal. The feedback factor β is controlled in accordance with the control input to the control terminal 4, so that the phase characteristics change.

This change in phase characteristics causes the oscillation frequency to change.

A variable Ti current source 5 as gain control means is connected to the amplifier 1, and the gain of the amplifier 1 changes in accordance with changes in the current value of the variable current source 5. The current value of the variable current source 5 is controlled by a detection output from a level detection circuit 6, and this level detection circuit 6 is adapted to detect the output level from the amplifier 1. That is, a level detection circuit 6 serves as an oscillation state detection means for detecting an oscillation state according to the output from the amplifier 1, and a variable current tA5 serves as a gain control means for controlling the gain of the loop made up of the amplifier 1 and the phase shifter 2. and
The variable current a5 as the gain control means is controlled in accordance with the output from the level detection circuit 6 as the oscillation state detection means to stabilize the output level.

For example, FIG. 2 is a frequency characteristic diagram for explaining an example of a control operation for stabilizing the output level.

In FIG. 2, a curve GA represents the frequency characteristic of the loop gain when the gain K of the amplifier 1 does not change, as in the case of FIGS. 4 and 5 described above. As is clear from this frequency characteristic curve G, at frequency r, the loop gain is OdB or more as shown at point A in the figure, and normal oscillation occurs, but the phase characteristic of the phase shifter 20 is not controlled. If the oscillation frequency is changed to, for example, f or fc, the loop gain will drop below OdB as shown at point B or C in the figure, and normal oscillation will no longer occur and abnormalities such as oscillation stop will occur. There is a possibility that this may occur. Therefore, the change in the output level when the oscillation frequency is changed is detected by the level detection circuit 6, and the current value of the variable current source 5 as the gain control means is controlled according to this detection level. Control gain. This and the profit system +
For example, as shown in Fig. 3, when the output level is low, the control amount (current value of the variable electric power source 5, etc.) is increased to increase the gain of the amplifier 1, and when the output level is high, the control amount is increased. Reduce the amount to reduce the gain. Specifically, for example, when the output level is reduced by controlling the oscillation frequency to rll or f, the gain of amplifier I is increased to change the frequency characteristics to curve G in FIG. The loop gain at the frequency r or f is controlled so as to be the same as that at the point A (OdB or more) as shown at point B'' or point C° in the figure, respectively.

Here, the variable voltage /Jta serving as the gain control means of the amplifier 1 is
The current value of 5, generally the control amount of the loop gain, is determined by the level detection circuit 6 which serves as the oscillation state detection means.
Depending on the output level of the phase shifter 2, it may be changed linearly as shown in curve a in Fig. 3, or depending on the characteristics of the phase shifter 2, the application of the oscillation circuit, etc. It may be changed in a stepwise manner as shown in the curve, or in a curve expressed by a quadratic function or other high-order function.In short, any type of change that works to keep the output level constant may be used. .

Therefore, even when the output level changes due to variable control of the oscillation frequency, the level detection circuit 6, which is the oscillation state detection means, controls the gain of the amplifier 1 via the variable current source 5, which is the gain control means. Since the output level is controlled to be kept constant, abnormalities such as oscillation stoppage and waveform distortion are prevented, output level fluctuations are suppressed to a small level, and stable oscillation can be achieved, and the oscillation frequency can be varied. The range can be apparently widened.

Note that the present invention is not limited to the above-mentioned embodiments, and for example, the gain control means may include a variable current source 5.
The configuration is not limited to, but may be one that performs gain control using voltage.Also, a configuration that controls the characteristics of the phase shifter 2, the gain of a variable gain circuit separately provided in the loop, etc. according to the oscillation state. may be adopted. Further, the oscillation state detection means is not limited to the level detector 6, and may be any device that can detect the state of the output, such as a detection circuit for harmonic components and phase of the oscillation output. ,
Other changes may be made within the scope of the invention.

H1 Effects of the Invention According to the oscillation circuit of the present invention, the gain of the loop consisting of the amplifier and the phase shifter is controlled by the oscillation state detection means and the gain control means so that the output level is kept constant. Therefore, abnormalities such as oscillation stoppage and waveform distortion are prevented, output level fluctuations are suppressed to a small level, and not only a stable oscillation state can be obtained at all times, but also the variable range of the oscillation frequency can be apparently widened.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram showing an oscillation circuit as an embodiment of the present invention, Fig. 2 is a graph showing frequency characteristics of loop gain and phase to explain control operation, and Fig. 3 shows control characteristics. 4 is a block circuit diagram showing an example of a normal phase-controlled oscillation circuit, and FIG. 5 is a graph showing frequency characteristics of loop gain and phase of the circuit shown in FIG. 4. l...Amplifier 2...Phase shifter 3...Output terminal 4...Frequency control terminal 5...Variable current source 6...Level detection circuit

Claims (1)

[Claims] An oscillation circuit that positively feeds back an output from an amplifier to the amplifier via a phase shifter and controls the oscillation frequency by controlling the phase characteristics of the phase shifter, comprising: oscillation state detection means for detecting an oscillation state according to the output; and gain control means for controlling the gain of a loop consisting of an amplifier and a phase shifter; An oscillation circuit characterized by controlling means to stabilize an output level.