JP2697361B2 - Phase locked oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase locked oscillator,
In particular, it relates to starting a high-precision phase-locked oscillator using an ultra-high stability variable oscillator.

[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, and
The frequency divider 3 converts the frequency of the input signal to the same frequency as that of the input signal applied to the input terminal 100, and compares the phase of the output signal of the frequency divider 3 with the phase of the input signal applied from the input terminal 100. Phase comparator 1 for generating a phase difference signal, and variable oscillator 2 for generating an output signal having a frequency corresponding to the phase difference signal
It is composed of

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

[0004] In the ultra-high stability variable oscillator, various stabilizing means are used to improve the stability of the variable oscillator. For example, in the case of a crystal variable oscillator, the entire oscillator is housed in a thermostat to minimize the effects of environmental temperature changes, and the temperature inside the thermostat is kept at a constant high temperature, making it less susceptible to environmental temperature changes and changing characteristics with temperature changes. Is used to minimize stabilization.

[0005] Such a variable oscillator exhibits design performance when the temperature in the thermostat is kept at a predetermined high temperature. If the temperature has not been reached, the characteristics are generally significantly different from the design values. For this reason, if a phase-locked oscillator is configured using such a variable oscillator, it cannot be synchronized with an input signal immediately after power-on because the center frequency of the variable oscillator is significantly shifted.
However, after a while, the temperature in the thermostat becomes a predetermined value, and the various characteristics of the variable oscillator become initial values, and can be synchronized with the input signal. Therefore, the phase difference between the two signals provided to the phase comparator of such a phase locked oscillator is not synchronized with the input signal immediately after the power is turned on, and thus changes continuously. After a while, when the temperature in the constant temperature bath of the variable oscillator reaches a predetermined value, pulling in is started from that point in time, and finally the phase difference becomes approximately 1/2 of the phase comparison range and becomes stable.

[0006] In a network synchronizer, which is a main application of a phase locked oscillator using an ultra-high stable variable oscillator, it is desirable that the output phase of the phase locked oscillator does not fluctuate as much as possible. For this reason,
Normally, the output is not used immediately after turning on the power,
In general, the temperature in the thermostat becomes a predetermined value, the drawing operation is completed, and the temperature is properly synchronized with the input signal, and then the thermostat is put to practical use.

[0007]

Therefore, after the conventional phase-locked oscillator is turned on, the time required until the temperature in the thermostat reaches a predetermined value after the power is turned on is calculated by the following formula. ) Is required. In the above equation, the time required for the pull-in of the second term is determined by the phase difference between the two signals applied to the phase comparator at the time of starting the pull-in, and this phase difference is obtained when the temperature of the thermostat becomes a predetermined value. Is the phase difference between the two signals at that time, and is an arbitrary value within the phase comparison range since it is in an asynchronous state before that. Therefore, the phase difference at the start of the pull-in may be at the end of the phase comparison range.
Generally, in a high-precision phase-locked oscillator, the pull-in speed is extremely slow, and when the phase difference at the start of pull-in is at the end of the phase comparison range as described above, it takes about 30 minutes.

As described above, in the conventional phase-locked oscillator, even after the power supply is turned on and the variable oscillator enters a normal state, a long time is required for pulling in the variable oscillator, and a long time is required until the variable oscillator is actually used. It had disadvantages that were needed.

An object of the present invention is to provide a phase locked oscillator which eliminates such disadvantages.

[0010]

According to the present invention, there is provided a frequency divider for dividing an output signal to the same frequency as an input signal, a phase of an output signal of the frequency divider and a phase of an input signal are compared, and a phase difference is determined. and a phase comparator for generating a phase difference signal, the variable oscillator and a phase locked oscillator configured by for generating a frequency corresponding to the phase difference signal, the operation state of said variable oscillator
Condition monitoring means for monitoring the condition, wherein the frequency divider
Phase initial to control the output phase according to the output of the state monitoring means
A frequency divider with a functionalization function, wherein the state monitoring means
When detecting that the oscillator is not in the normal state,
The input signal applied to the phase comparator and the phase
The phase difference between the output signal of the divider with initialization function and the
Be equal to the phase difference that occurs when the writing is completed
And when the variable oscillator becomes normal, immediately
The control is completed .

[0011]

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, the elements denoted by reference numerals 100, 200, 1, and 2 are the same as those in the conventional phase locked oscillator shown in FIG. Reference numeral 40 denotes state monitoring means for monitoring the operation state of the variable oscillator 3. For example, if the variable oscillator 3 is a crystal oscillator having a constant-temperature bath, a temperature detector for monitoring the temperature of the constant-temperature bath corresponds. 30 is the state monitoring means 4
0 is a frequency divider with a phase initialization function in which the output signal phase is controlled in accordance with the output of 0, and if the state monitoring means 40 detects that the variable oscillator is not in the normal state, The output phase of the frequency divider 30 with the initialization function is controlled to be exactly 180 ° with respect to the input signal, that is, the phase difference between the input signal and the output signal of the frequency divider becomes a half of the phase comparison range. You. When the temperature of the thermostat in the variable oscillator reaches a predetermined value and the variable oscillator becomes normal, the above-described 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.

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

In the phase-locked oscillator having such a configuration, immediately after the power is turned on, the variable oscillator 3 cannot initially synchronize with the input signal as described above because the temperature in the thermostat does not reach the predetermined value. . However, in this case, since the state monitoring means 40 detects that the variable oscillator 3 is not in a normal state, that is, that the temperature in the internal thermostat has not reached a predetermined value, the output phase of the frequency divider 30 Is always kept at a phase that is exactly 180 ° different from the input signal. Therefore, at this point, the phase difference between the two signals input to the phase comparator 1 is always different by 180 °, and the pull-in is completed, and the phase relationship is maintained equal to that of the normal synchronization.

After a while after the power is turned on, the temperature in the thermostat reaches a predetermined value, and the phase-locked oscillator is ready to synchronize with the input signal and starts the pull-in operation. As described above, since 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 of the completion of the pull-in, the pull-in operation is immediately completed.

In the above embodiment, a crystal oscillator with a thermostat is described as an example of the variable oscillator. However, various suitable state monitoring means can be used according to the type of the variable oscillator, and the same as this embodiment. Needless to say, the operation described above can be realized.

[0017]

As described above, the phase-locked oscillator of the present invention has 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 so as to be equal to the phase difference generated when the pull-in is completed normally. For this reason, as soon as the variable oscillator becomes normal, the pull-in is completed, so that not only the time required for the pull-in operation after the variable oscillator becomes normal can be significantly shortened, but also after the variable oscillator becomes normal. Has the effect that the output phase fluctuation is small.

[Brief description of the drawings]

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Phase comparator 2 Variable oscillator 3 Divider 30 Divider with phase initialization function 40 Variable oscillator status monitor 100 Input terminal 200 Output terminal

Claims (2)

(57) [Claims] A frequency divider for dividing an output signal to a frequency equal to that of an input signal, a phase comparing an output signal of the frequency divider with an input signal, and generating a phase difference signal corresponding to a phase difference. A phase-locked oscillator configured by a comparator and a variable oscillator that generates a frequency corresponding to the phase difference signal, comprising: a state monitoring unit that monitors an operation state of the variable oscillator; A frequency divider with a phase initialization function for controlling an output phase according to the output of the monitoring means, wherein the state monitoring means detects that the variable oscillator is not in a normal state; The phase difference between the input signal applied to the comparator and the output signal of the frequency divider with phase initialization function is controlled so as to be equal to the phase difference generated when the pull-in operation is completed normally, and the variable oscillator operates normally. The place that became A phase locked oscillator, characterized in that immediately complete the control. 2. The phase-locked oscillator according to claim 1, wherein said variable oscillator is a crystal oscillator having a constant temperature bath, and said condition monitoring means is a temperature detector for monitoring a temperature of said constant temperature bath. .