JPS6113818A - Phase locked oscillator - Google Patents

Abstract

PURPOSE:To keep a stable phase lock state even for a large change in the operating condition by providing a control circuit producing a signal corresponding only to a DC or a low frequency component of a signal filtered by a loop filter and applying an output of the control circuit as a control voltage signal to a limit circuit. CONSTITUTION:When a signal transmitted from the loop filter 4 is inputted to a passing filter 8, a signal extracting a low frequency component and a DC component only from the signal from the filter 4 is formed and the resulting signal is transmitted to a control circuit 7. When the control circuit 7 inputs the signal, the circuit 7 produces a signal of superimposition between a signal reducing the signal voltage into 1/M and a voltage Vr dividing a DC voltage Vcc applied to a terminal 15 by resistors and inputs the said resulting signal to the limit circuit 12. When the limit circuit 12 receives this signal and the signal from the loop filter 4, the circuit 12 superimposes the signal from the control circuit 7 onto a signal reducing a signal voltage from the loop filter 4 into 1/N to form a phase control voltage signal. The phase control voltage signal is transmitted to a VCO1.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a phase-locked oscillator. [Technical Background of the Invention] A conventional phase-locked oscillator has a configuration as shown in the block diagram shown in FIG. In this phase-locked oscillator, a voltage-controlled oscillator (hereinafter referred to as VCO) 11, a reference oscillation circuit 2, a phase comparator circuit 3, and a loop filter 4 constitute a phase-locked loop, and the output from vColl The oscillation signal and the reference signal sent from the reference oscillator 2 are input to a phase comparison circuit 3, which outputs a signal corresponding to the phase difference between these signals, and this signal is converted into an f-wave by a loop filter 4. The P-wave signal is VO
Negative feedback is provided as a phase control voltage signal of OII. and,
When vcoll receives this phase control voltage signal, it forms an oscillation signal at a frequency corresponding to this phase control voltage signal, and transmits this oscillation signal to the phase comparator circuit 3 and the output terminal 14. Note that the oscillation frequency of the oscillation signal during phase synchronization is an integer of the reference frequency of the reference signal.

Synchronization holding range ΔW11 (
angular frequency), the synchronization pull-in range ΔWL (angular frequency) is the phase comparison sensitivity φ, the frequency control sensitivity of vCOl is Kv,
The transfer function and gain of loop filter 4 are each set to 1.
and A, ΔW]II! A@ becomes φ11 K y Δwb=xcy ΔWH. Here, if the oscillation signal frequency of vaoli instantaneously fluctuates outside the synchronization holding range ΔWa due to some influence, that is, the oscillation signal frequency is within a frequency range fO±Δf11 (Δfm
−ΔWH/2π], the oscillation signal becomes out of phase lock.

Therefore, the phase-locked oscillator sweeps the oscillation signal that is different from the phase-locked oscillator, so that the phase-locked oscillator has a frequency range fO±Δfb (Δf 'f, :ΔW x
, /2π).

As a circuit for this sweeping, there is a circuit in which the loop filter 4 is provided with this function. In such a circuit, an active filter is used as the loop filter 4, and when phase synchronization occurs, positive feedback is applied to the active filter to operate as an oscillation circuit to form a signal, and this signal is sent out to generate an oscillation signal. A sweep is being carried out. As another sweeping method, as shown in FIG. 7, there is a method in which a sweep circuit 5 is added to sweep the oscillation signal.

However, when sweeping the oscillation signal to achieve phase synchronization again in this manner, if the sweep speed is too fast, the oscillation signal will not return to the phase synchronization state even if it falls within the synchronization pull-in range ΔW+-. The general sweep speed condition for realizing this phase synchronization is to set the rate of change of the VOO oscillation signal frequency during sweep, that is, the sweep speed, to ΔW (2977
7 seconds), and the natural frequency of the phase-locked loop is W (angular frequency).
Then, 2w<W/・・・・・・・・・(1
). That is, it is known that synchronous pull-in of the oscillation signal will be performed if formula (1) is satisfied. Therefore, the sweep speed is set so as to satisfy the above condition.

By the way, a phase-locked circuit using a VCO having a wide variable oscillation frequency range may be phase-locked to any of the wave numbers of integral multiples of the reference frequency within the variable frequency range. Figure 8 shows a V with a wide oscillation station wave number variable range.
It is a characteristic graph diagram of CO, in which the horizontal axis shows the control voltage of the VCO, and the vertical axis shows the oscillation frequency of VaO. As characteristic curve B shows, the phase locking frequency fO appears at every integer multiple of the reference frequency fR, so within the output frequency range of voo (n
-1) A plurality of phase synchronized wave numbers such as fu, nfi, and (n+t)fR occur.

In this case, the vco corresponding to each phase locking frequency
Phase phase static electricity suppression 1 voltage n-', vn, vn+''. Therefore, a VC with such a wide frequency variable range
In a phase-locked loop using O, the oscillation signal may not be phase-locked to the desired frequency. For this reason, a limiting circuit 6 is inserted between the loop filter 4 and vaol as in other conventional phase-locked oscillators shown in the block diagram in FIG. It is necessary to limit the frequency range of vCO by narrowing the variable frequency range of vCO. Figure 10 is a circuit diagram of this limiting circuit 60. The signal sent out from the loop filter 4 is connected to the terminal 22.
is applied to The signal voltage applied to this terminal 22 is W
VR is the voltage obtained by dividing the DC voltage Vcc applied to the terminal 21 by a resistor, R1e't t Rs t R4 is the value of each resistor, and the voltage is sent from the amplifier 20 and applied to the terminal 23. signal voltage Y
If it is set as outT, then it becomes. Therefore, when the signal voltage VIN changes from 0 to V, the signal voltage VOtlT changes from VR to (Ma・U+V
R). In this way, the change in signal voltage VIM is limited to -0. This signal voltage vOσT is applied to Vool shown in FIG. 9 as a control voltage. Further, the free-running oscillation frequency of vcol is determined by the voltage VR.

Figure 11 shows the V in the phase-locked oscillator shown in Figure 9.
This is a characteristic graph of OO, where the horizontal axis shows the phase control voltage,
The vertical axis shows the oscillation frequency, and line A shows the characteristics of vool. In this phase-locked loop, the phase control voltage is limited to the control voltage range H)K, so the phase-locked oscillation signal has a frequency n
・Limited to fR only.

In addition, when a limiting circuit is provided in the phase-locked loop, when the oscillation signal goes out of the synchronization holding range, the sweep signal sent from the loop filter 4 is also mainly reduced by the limiting circuit 6 and applied to vCOl. Therefore, the rate of change .DELTA.W of the oscillation frequency during sweep is also small, sufficiently satisfying the above-mentioned equation (1), and the pull-in operation during sweep within the synchronous pull-in range is also reliable.

[Problems with background technology]

In the circuit shown in FIG. 9 above, in the phase locked circuit,
By limiting the phase control voltage application range of the VCO, which has a wide frequency variable range, the frequency variable range of the vCO is limited to a specific range. As a single-phase synchronized circuit, when there is a large change due to a change in power supply voltage, a power supply voltage change, a light change, etc., the phase control voltage cannot follow the change beyond this limited range, so phase synchronization may occur. .

In other words, even though a VCO with a wide frequency variable range is used, in order to stabilize the phase synchronization characteristics, va'
Since the frequency variable range of o itself is limited and used,
There is a problem in that phase synchronization tends to occur due to large fluctuations in the free-running frequency of the VO'O, and the VCO's capabilities are not fully utilized.

[Purpose of the invention]

The present invention was made in view of the above-mentioned drawbacks, and takes full advantage of the characteristics of VaO, which has a wide frequency variable range.
An object of the present invention is to provide a phase-locked oscillator that can maintain a stable phase-locked state even under large changes in operating conditions. an oscillation circuit;
a reference oscillation circuit that outputs a reference signal, a phase comparison circuit that outputs a signal corresponding to a phase difference between the oscillation signal and the reference signal, and a loop filter that filters the signal output from the phase comparison circuit; P by the loop filter
In a phase-locked oscillator, the phase-locked oscillator includes at least a limiting circuit that superimposes a signal obtained by reducing the waveformed signal and a control voltage signal and supplies the resulting signal to the voltage-controlled oscillation circuit. A control circuit that generates a signal corresponding only to direct current or low frequency components is provided, and an output signal of this control circuit is supplied to the limiting circuit as the control voltage signal.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. ◎ Figure 1 is a block diagram showing an embodiment of the phase synchronized oscillator of the present invention, and FIG. 2 is a block diagram showing a part of the phase-locked oscillator in more detail.

In this embodiment, the signal sent out from the loop filter 4 is transmitted to the low-pass filter 8 and the limiting circuit 12. When the low-pass filter 8 receives this signal, it extracts only the low frequency component and the DC component from this signal. , and transmits this signal to the control circuit 7. When the control circuit 7 receives this signal, it reduces this signal voltage to i and converts it into a DC voltage VCC applied to the terminal 15. A signal is formed by superimposing the voltage Vr divided by the resistors, and this signal is input to the limiting circuit 12. When the limiting circuit 12 inputs this signal and the signal from the loop filter 4, it superimposes the signal from the control circuit 7 and a signal obtained by reducing the signal voltage from the loop filter 4 to -0 to form a phase control voltage signal. This phase control voltage signal is transmitted to vcol. . vool is phase-locked to the desired frequency by this phase control voltage signal.

The effect of this circuit is that the frequency variable range of VC'o can be automatically controlled by the function of the control circuit 7, following the slow change in the free-running oscillation frequency of va'5.

Next, the characteristics of the phase-locked oscillator circuit of this embodiment will be explained.

FIG. 3 is a graph showing the characteristics of the phase-locked loop of this embodiment, where the vertical axis shows the oscillation frequency of VaO, and the horizontal axis shows the V
The 0 line A indicating the phase control voltage of aO indicates the characteristics of VaO in the initial state, and in order to phase-synchronize ycol, which has a wide frequency variable range, with the desired frequency fO, the phase control voltage is applied by the above-mentioned limiting circuit 12. Range from vl to v! The frequency variable range of vcol is defined as between f and f.

(fz < fo <'*) If K is set, ◎ Also, let vo be the phase control voltage that gives the phase locking frequency fo at this time 0 Here, load fluctuation, temperature change, power supply voltage change, time elapsed If the free-running oscillation frequency of va61 changes slowly due to a change or the like, line A will slowly change to line m accordingly. At this time, the DC component and low frequency component of the signal output from the phase comparator circuit 3 are transmitted to the control circuit 7 via the loop filter 4 and the low pass filter 8.
The circuit 7 forms a signal corresponding to this, and the limiting circuit 12 also forms a phase control voltage signal corresponding to this signal, so that for this purpose the phase control voltage range extends from vl' centered on the voltage vO'. It will change up to y, /.

Therefore, even if the phase control voltage changes significantly, the phase control voltage application range also changes to follow the change, so no phase synchronization occurs. In this way, the phase control voltage is not limited to a specific range, but varies widely enough to take full advantage of the capabilities of vcol.

Further, in the phase-locked oscillator of this embodiment, a desired phase-locked frequency can be easily obtained by changing the reference frequency of the reference oscillator 2 as long as it is within the variable frequency range of Vool. In this case, the voltage Vr of the control circuit 7 is adjusted so that the phase i! Just set the FIJ chamber pressure range (,W
It also has the advantage that there is no need for mechanical adjustment of oo, and that only one type of VaO that can provide a sufficiently wide variable frequency range can be used.

FIG. 4 shows another embodiment of the phase-locked oscillator of the present invention, in which the signal sent out from the loop filter 4 is transmitted to the limiting circuit 12 and the comparator 9, and when the comparator 9 receives this signal, A comparison is made to determine whether the voltages of the DC component and low frequency component of the signal exceed a predetermined comparison voltage value, and a signal corresponding to the comparison result is output.

The relationship between the voltage of the input signal component to be compared and the output voltage in this comparator 9 is shown in the graph of FIG. 5. In this graph, the horizontal axis shows the input signal component voltage, and the vertical axis shows the output voltage. The lines indicate the relationship between the input signal component voltage and the output voltage. In other words, the output voltage becomes 7OU when the input signal component voltage becomes less than the comparison voltage vRIF.
T to vOUTl in a stepwise manner, and when the input signal component voltage exceeds the comparison voltage VR1F, the voltage V
OI) changes from T to VOUT. The signal output from this comparator 9 is transmitted to the smoothing circuit 1o. When the smoothing circuit 10 receives this signal, it forms a signal that suppresses sudden changes in this signal. This is because if a sudden change occurs in the phase control voltage signal applied to vcol, it will cause synchronization. . The signal output from the smoothing circuit 10 is input to the limiting circuit 12. When the limiting circuit 12 receives this signal, it superimposes this signal with a negative voltage signal output from the loop filter 4. to form a phase control voltage signal, and output this phase control voltage signal to vaol. In this case, the phase control voltage range changes stepwise in response to a slow change in the free-running oscillation frequency, and therefore, as in the first embodiment described above, changes in the operating conditions of vcol occur. It is possible to form a phase-locked oscillation signal that widely corresponds to the following. Further, in this embodiment as well, the phase synchronization frequency can be easily changed by changing the reference frequency and the comparison voltage of the comparator 9.

〔Effect of the invention〕

As explained above, according to the present invention, by using the low frequency component signal of the loop voltage signal that controls the sweep frequency as the control voltage signal of the limiting circuit, the voltage application range for phase control of VaO can be changed by changing the characteristics of vOO. A phase-locked type that can maintain a stable phase synchronization state even if the loop voltage signal changes significantly due to load fluctuations, temperature changes, power supply voltage fluctuations, changes over time, etc. An oscillator can be realized.

In addition, since multiple types of phase synchronization frequencies can be set within the frequency variable range of the WOO using only one VaO, it is possible to mass-produce voo and reduce the price.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the phase-locked oscillator of the present invention, FIG. 2 is a block diagram showing in detail an example of a circuit of the embodiment of the present invention shown in FIG. Figure 3 is the first
4 is a block diagram showing another embodiment of the phase-locked oscillator of the present invention, and FIG. 5 is a comparator circuit shown in FIG. 4. Characteristic graph for explaining the operation of No. 9, No. 6
Fig. 7 is a block diagram showing a conventional phase-locked oscillator, Fig. 8 is a characteristic graph of the voltage-controlled oscillator circuit in the conventional phase-locked oscillator shown in Figs. A block diagram of another conventional phase-locked oscillator, FIG. 10 is a partial diagram of the conventional phase-locked oscillator shown in FIG. 9, and FIG. 11 shows the voltage in the conventional phase-locked oscillator shown in FIG. It is a characteristic graph of a controlled oscillation circuit. 1, 11...Voltage controlled oscillation circuit, 2...Reference oscillation circuit, 3...Phase comparison circuit, 4...Loop filter,...Sweep circuit, 6...Limiting circuit, 7...・Open side 1
Circuit, 8...Low pass filter, 9...Comparator, 10...Smoothing circuit, 12...Limiting circuit, 14
, 15...terminal, adder...amplifier, 2], 22
, 23...terminal. Representative Patent Attorney Kensuke Norichika (and others) Figure 3 Figure 4 Figure 4 J □ 〉ha 0 Rator Input Signal Component @ Figure 6 Figure 7 Figure 8. vn-+ l/n vn◆1-
VCOTillmlIff Figure 9 Figure 11 1/n-12/nl/n++

Claims (1)

[Claims] a voltage controlled oscillation circuit that outputs an oscillation signal, a reference oscillation circuit that outputs a reference signal, a phase comparison circuit that outputs a signal corresponding to a phase difference between the oscillation signal and the reference signal, and an output from the phase comparison circuit. and a limiting circuit that superimposes a signal obtained by reducing the signal filtered by the loop filter and a control voltage signal and supplies the superimposed signal to the voltage controlled oscillation circuit. In the phase-locked oscillator, a control circuit is provided that generates a signal corresponding only to the direct current or low frequency component of the signal filtered by the loop filter, and the output of this control circuit is supplied as the control voltage signal to the limiting circuit. A phase-locked production oscillator characterized by: