JPH04326817A - Phase locked oscillator - Google Patents

Abstract

PURPOSE:To immediately complete pull-in when the oscillator is made normal by providing a means to monitor the normality of the variable oscillator. CONSTITUTION:Since the inside temperature of a constant temperature tank does not reach a prescribed value just after a power source is turned on, the variable oscillator is not synchronized with an input signal. In this case, however, a state monitor means 40 detects the variable oscillator 2 is not in a normal state namely, detects the temperature in the inside constant temperature tank does not reach the prescribed value and therefore, the output phase of a frequency divider 30 is kept at a phase different from that of the input signal at 180 deg. at all times. Accordingly, the phases of two signals inputted to a phase comparator 1 at such a time point are different at 180 deg. at all time and kept in the phase relation of completing pull-in and regularly synchronizing the oscillator. Thus, the pull-in is completed as soon as the variable oscillator is turned to the normal state.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a phase-locked oscillator.
In particular, it concerns the startup of high-precision phase-locked oscillators using ultra-high stability variable oscillators.

0002

2. Description of the Related Art As shown in FIG. 2, a conventional phase-locked oscillator divides the frequency of a signal at an output terminal 200,
A frequency divider 3 converts the frequency to the same frequency as the input signal applied to the frequency divider 3, and compares the phase of the output signal of this frequency divider 3 with the input signal applied from the input terminal 100, and calculates the frequency according to the phase difference between the two signals. A phase comparator 1 that generates a phase difference signal, and a variable oscillator 2 that generates an output signal with a frequency corresponding to this phase difference signal.
It consists of

Normally, the center frequency of the variable oscillator 2 is adjusted to be equal to the frequency that this phase-locked oscillator outputs when it is synchronized with an input signal. Therefore, in the phase synchronized oscillator using the variable oscillator adjusted in this way, the phase difference between the two signals given to the phase comparator 1 is half the phase comparison range.

[0004]Various stabilizing means are used in the ultra-high stability variable oscillator to improve the stability of the variable oscillator. For example, in order to minimize the effects of environmental temperature changes on a variable crystal oscillator, the entire oscillator is housed in a constant temperature oven, and by keeping the inside of the oven at a constant high temperature, it is less susceptible to environmental temperature changes, and the characteristics change due to temperature changes. Stabilization measures are used to minimize the

[0005] Such a variable oscillator exhibits its designed performance when the temperature inside the thermostatic oven is maintained at a predetermined high temperature. If the temperature has not been reached, the characteristics generally differ significantly from the designed values. Therefore, if such a variable oscillator is used to configure a phase-locked oscillator, the center frequency of the variable oscillator will be significantly shifted immediately after power is turned on, and it will not be possible to synchronize with the input signal. However, after a while, the temperature in the thermostatic oven reaches a predetermined value, and the various characteristics of the variable oscillator return to their initial values, allowing synchronization with the input signal. Therefore, the phase difference between the two signals applied to the phase comparator of such a phase synchronized oscillator is not synchronized with the input signal immediately after the power is turned on, and therefore continuously changes. After a while, when the temperature in the constant temperature oven of the variable oscillator reaches a predetermined value, the pull-in starts from that point, and the phase difference is finally stabilized to approximately 1/2 of the phase comparison range.

In a network synchronization device, which is the main application of a phase-locked oscillator using an ultra-highly stable variable oscillator, it is desirable that the output phase of the phase-locked oscillator fluctuates as little as possible. For this reason,
Normally, the output is not used immediately after the power is turned on.
Generally, the device is put into practical use after the temperature in the thermostatic chamber reaches a predetermined value, the pull-in operation is completed, and the device is properly synchronized with the input signal.

[0007]

[Problem to be solved by the invention] Therefore, after the power is turned on, until a conventional phase-locked oscillator can actually be used, it takes (time for the temperature in the thermostatic chamber to reach a predetermined value) + (draw-in time). ) Is required. In the above equation, the time required for the second term to be pulled in is determined by the phase difference between the two signals applied to the phase comparator at the time the pull-in starts, but this phase difference is determined when the temperature of the thermostatic oven reaches a predetermined value. This is the phase difference between the two signals at the time when the two signals are in an asynchronous state before that, so it is an arbitrary value within the phase comparison range. Therefore, the phase difference at the start of the pull-in may be at the extreme end of the phase comparison range. In general, a high-precision phase-locked oscillator has an extremely slow pull-in speed, and it takes about 30 minutes if the phase difference at the start of the pull-in is at the end of the phase comparison range, as described above.

As described above, in conventional phase-locked oscillators, even after the power is turned on and the variable oscillator is in a normal state, it takes a long time to pull in the oscillator, and it takes a long time to reach a state where it can actually be used. It had the disadvantage of requiring a lot of effort.

An object of the present invention is to provide a phase-locked oscillator that eliminates such drawbacks.

0010

[Means for Solving the Problems] The present invention provides a frequency divider that divides an output signal to a frequency equal to that of an input signal, and a frequency divider that compares the phases of the output signal of this frequency divider and the input signal, and responds according to the phase difference. A phase synchronized oscillator comprising a phase comparator that generates a phase difference signal, and a variable oscillator that generates a frequency according to the phase difference signal, comprising: a state monitoring means for monitoring the operating state of the variable oscillator; It has a phase initialization means for setting the output phase of the frequency generator to a constant phase difference from the input signal, and until the variable oscillator returns to a normal state, the phase difference between the two signals applied to the phase comparator is adjusted. It is characterized in that it is maintained at a predetermined value.

[0011]

Embodiments Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, each element numbered 100, 200, 1, and 2 is the same as each element in the conventional phase-locked oscillator shown in FIG. Reference numeral 40 denotes a state monitoring means for monitoring the operating state of the variable oscillator 3. For example, if the variable oscillator 3 is a crystal oscillator having a thermostatic oven, it corresponds to a temperature detector for monitoring the temperature of the thermostatic oven. 30 is condition monitoring means 4
This is a frequency divider with a phase initialization function whose output signal phase is controlled according to the output of The output phase of the frequency divider 30 with initialization function is controlled to be exactly 180 degrees with respect to the input signal, that is, the phase difference between the input signal and the output signal of the frequency divider is 1/2 of the phase comparison range. Ru. Further, when the temperature of the constant temperature bath in the variable oscillator reaches a predetermined value and the variable oscillator becomes normal, the above-mentioned phase control operation is not performed. Therefore, in this case, the frequency divider 30 operates as a frequency divider that divides the output signal and converts it to the same frequency as the input signal, and has the same function as the frequency divider 3 shown in FIG. 2.

As described above, in this embodiment, when the variable oscillator 2 is abnormal, it is sufficient that it always has a constant phase relationship with the input signal, so this variable phase oscillator is realized by a frequency divider with an initialization function. be done.

In the phase synchronized oscillator having such a configuration, immediately after the power is turned on, the variable oscillator 3 cannot synchronize with the input signal as described above because the temperature inside the thermostatic chamber has not reached the predetermined value. . However, in this case, the state monitoring means 40 detects that the variable oscillator 3 is not in a normal state;
That is, since it is detected that the temperature in the internal thermostat has not reached the predetermined value, the output phase of the frequency divider 30 is always maintained at a phase exactly 180 degrees different from the input signal. Therefore,
At this point, the phase difference between the two signals input to the phase comparator 1 is always 180° different, and the pull-in is completed, and the phase relationship is maintained equal to that of a normally synchronized state.

[0015] After a while after the power is turned on, the temperature inside the thermostatic oven reaches a predetermined value, and the phase-locked oscillator becomes able to synchronize with the input signal and starts the pull-in operation. As described above, the phase difference between the two signals applied to the phase comparator 1 at the start of the pull-in is equal to the phase difference at the time the pull-in is completed, so the pull-in operation is immediately completed.

[0016] In the above embodiment, a crystal oscillator with a constant temperature oven was used as an example of the variable oscillator, but various appropriate condition monitoring means can be used depending on the type of variable oscillator, and the same as in this embodiment can be used. It goes without saying that this operation can be realized.

[0017]

As explained above, the phase-locked oscillator of the present invention has a means for monitoring the normality of the variable oscillator constituting the phase-locked oscillator. The phase difference between the two signals applied to the comparator is controlled to be equal to the phase difference that would occur if the pull-in was completed normally. Therefore, as soon as the variable oscillator becomes normal, the pull-in is completed, which not only greatly reduces the time required for the pull-in operation after the variable oscillator becomes normal, but also after the variable oscillator becomes normal. This has the effect of reducing output phase fluctuations.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a phase-locked oscillator of the present invention.

FIG. 2 is a block diagram of a conventional phase-locked oscillator.

[Explanation of symbols]

1 Phase comparator 2 Variable oscillator 3 Frequency divider 30 Frequency divider with phase initialization function 40 Variable oscillator status monitor 100 Input terminal 200 Output terminal

Claims (2)

[Claims] 1. A frequency divider that divides an output signal to a frequency equal to that of an input signal, and a phase divider that compares the phase of the output signal of this frequency divider and the input signal and generates a phase difference signal according to the phase difference. In a phase synchronized oscillator comprising a comparator and a variable oscillator that generates a frequency according to the phase difference signal, a state monitoring means monitors the operating state of the variable oscillator, and the output phase of the frequency divider is input as an input signal. and a phase initialization means for making a constant phase difference, and the phase difference between the two signals applied to the phase comparator is maintained at a predetermined value until the variable oscillator returns to a normal state. A phase-locked oscillator featuring: 2. A phase synchronized oscillator, wherein the predetermined value is 180°.