JP2018182525A - Frequency synthesizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output an output signal having a satisfactory frequency characteristic, if an external vibration is added thereto, with a reduced lockup time.SOLUTION: A frequency synthesizer 1 includes: a reference oscillator 10 which outputs a reference signal; a first PLL circuit 20 which outputs a first oscillation signal of a first frequency; a frequency divider 30 which divides the first oscillation signal; and a second PLL circuit 40 which outputs a second oscillation signal of a second frequency higher than the first frequency. The first PLL circuit 20 includes a first loop filter 22 which causes to pass a first band signal included in a signal being output from a first phase comparator 212, to output the passed signal to a first voltage controlled oscillator 23 as a first control voltage. The second PLL circuit 40 includes a second loop filter 42 which causes to pass a signal of a second band wider than the first band, the signal being included in a signal output from a second phase comparator 412, to output the passed signal to a second voltage controlled oscillator 43 as a second control voltage.SELECTED DRAWING: Figure 1

Description

  The present invention relates to frequency synthesizers.

  Conventionally, a frequency synthesizer using a PLL (Phase Locked Loop) circuit is known as a circuit for outputting an oscillation signal of a desired frequency (see, for example, Patent Document 1).

JP, 2009-44215, A

  Generally, a crystal oscillator with high frequency stability and little phase noise is used as an output source of a reference signal input to the PLL circuit. However, since the crystal oscillator utilizes the piezoelectric phenomenon, noise is included in the reference signal due to the application of external vibration or shock. Then, the frequency characteristic of the output signal of the PLL circuit is degraded, and the frequency characteristic of the output signal of the frequency synthesizer is also degraded.

  On the other hand, it is conceivable to narrow the pass band of the loop filter provided in the PLL circuit to remove noise contained in the reference signal. However, narrowing the pass band of the loop filter has a problem that the lockup time in the PLL circuit becomes long.

  Therefore, the present invention has been made in view of these points, and it is an object of the present invention to provide a frequency synthesizer that outputs an output signal having good frequency characteristics even when external vibration is given, and has a short lockup time. To aim.

  A frequency synthesizer according to a first aspect of the present invention comprises an oscillator for outputting a reference signal, a first phase control oscillator for outputting a first oscillation signal of a first frequency, and a divider for dividing the first oscillation signal. And a second phase control oscillator for outputting a second oscillation signal having a second frequency higher than the first frequency, wherein the first phase control oscillator is based on a first control voltage. A first voltage controlled oscillator for outputting the first oscillation signal, a first phase comparator for outputting a first phase difference signal indicating a phase difference between the reference signal and the first oscillation signal, and the first phase difference A first loop filter for passing a signal of a first band included in the signal and outputting the passed signal as the first control voltage to the first voltage controlled oscillator; the second phase controlled oscillator includes 2 based on the control voltage A second voltage controlled oscillator that outputs two oscillation signals; and a second phase comparator that outputs a second phase difference signal indicating a phase difference between the signal divided by the divider and the second oscillation signal; A second loop filter that passes a signal in a second band wider than the first band, which is included in the second phase difference signal, and outputs the passed signal as the second control voltage to the second voltage control oscillator; Have.

  The first phase control oscillator further includes a first divider for outputting a first divided signal obtained by dividing the first oscillation signal by a first dividing ratio, and the first phase comparator is configured to The second phase control oscillator outputs the first phase difference signal indicating the phase difference between the reference signal and the first divided signal, and the second phase control oscillator divides the second oscillation signal by a second dividing ratio. The second phase comparator may further include a second frequency divider that outputs a frequency divided signal, and the second phase comparator may indicate the phase difference between the signal divided by the frequency divider and the second frequency divided signal. Two phase difference signals may be output.

  The frequency synthesizer may further include a detection unit that detects a frequency of vibration given to the frequency synthesizer, and a setting unit that sets the first band of the first loop filter based on the detected frequency. Good.

  The first phase comparator outputs the first phase difference signal indicating a phase difference between the reference signal and the first divided signal by a charge pump, and the setting unit is configured to output the first signal. The first band may be set by changing the amount of current to be output according to the phase difference between the first divided signal and the first divided signal.

  According to the present invention, it is possible to output an output signal having good frequency characteristics even when external vibration is given, and to shorten the lockup time.

It is a figure showing composition of a frequency synthesizer concerning a 1st embodiment. It is a figure which shows the structure of the conventional frequency synthesizer. It is a figure which shows the measurement result of the phase noise characteristic of the conventional frequency synthesizer. It is a figure which shows the measurement result of the phase noise characteristic at the time of taking anti-vibration measures by providing a damping material in the reference | standard oscillator of the conventional frequency synthesizer. It is a figure which shows the measurement result of the phase noise characteristic of the frequency synthesizer which concerns on 1st Embodiment. It is a figure which shows the structure of 1st PLL-IC which concerns on 2nd Embodiment.

First Embodiment
[Configuration of frequency synthesizer 1]
FIG. 1 is a diagram showing the configuration of the frequency synthesizer 1 according to the first embodiment. The frequency synthesizer 1 includes a reference oscillator 10, a first PLL circuit 20 as a first phase control oscillator, a frequency divider 30, and a second PLL circuit 40 as a second phase control oscillator.

  The first PLL circuit 20 includes a first loop filter 22 that removes noise of a frequency corresponding to the vibration given to the frequency synthesizer 1, and outputs a first oscillation signal from which the noise is removed. The first loop filter 22 is a low pass filter that uses a frequency lower than the frequency assumed as the frequency of the vibration applied to the frequency synthesizer 1 as a cutoff frequency. Thereby, even when vibration is applied to the frequency synthesizer 1, noise applied by the vibration, which is included in the oscillation signal output from the first PLL circuit 20, is reduced.

  The second PLL circuit 40 includes a second loop filter 42 having a wider signal passband than the first loop filter 22 and outputs a second oscillation signal. The cut-off frequency of the second loop filter 42 is higher than the cut-off frequency of the first loop filter 22, and the pass band width of the signal in the second loop filter 42 is wide, so the second PLL circuit 40 locks up at high speed. Thus, the frequency synthesizer 1 can maintain good frequency characteristics even when vibration is applied, and can output an output signal in a short lockup time.

Then, each structure with which the frequency synthesizer 1 is provided is demonstrated.
The reference oscillator 10 is, for example, a crystal oscillator such as an oven-controlled crystal oscillator (OCXO), and generates a reference signal of a predetermined frequency. The reference oscillator 10 of the present embodiment generates a 50 MHz reference signal. The reference oscillator 10 outputs the generated reference signal to the first PLL circuit 20.

  The first PLL circuit 20 includes a first PLL-IC (Integrated Circuit) 21, a first loop filter 22, and a first voltage control oscillator 23. The first PLL-IC 21 is an integrated circuit that functions as a first frequency divider 211 and a first phase comparator 212.

  The first frequency divider 211 generates a first divided signal by dividing the first oscillation signal of the first frequency output from the first voltage control oscillator 23 by a first division ratio. The first frequency divider 211 outputs the first frequency divided signal to the first phase comparator 212.

  The first phase comparator 212 outputs a first phase difference signal based on the phase difference between the reference signal output from the reference oscillator 10 and the first oscillation signal output from the first voltage control oscillator 23. The first phase comparator 212 outputs a first phase difference signal indicating a phase difference between the reference signal and the first divided signal to the first loop filter 22.

  The first loop filter 22 is, for example, a low pass filter. The first loop filter 22 passes the signal of the first band frequency included in the signal output from the first phase comparator 212. The first band is preset based on the vibration given to the frequency synthesizer 1. Here, it is assumed that the frequency of vibration given to the frequency synthesizer 1 is 5 Hz to 500 Hz, and the first band is 0 to 5 Hz. Thereby, the first loop filter 22 can reduce the noise generated by the vibration applied to the frequency synthesizer 1. The first loop filter 22 outputs the passed signal to the first voltage control oscillator 23 as a first control voltage.

  The first voltage control oscillator 23 outputs a first oscillation signal of a first frequency based on the first control voltage. The first frequency is, for example, 2 GHz. The first voltage control oscillator 23 outputs the first oscillation signal to the first PLL IC 21 and the frequency divider 30.

  Here, it is preferable that the first voltage control oscillator 23 be configured by a substrate pattern, a chip inductor, and a capacitor that are not easily affected by external vibration. In addition, the first voltage control oscillator 23 has a narrow band and good phase noise characteristics so that deterioration of the phase noise is reduced when the first oscillation signal is multiplied to the frequency output by the second voltage control oscillator 43. It is preferable that it is an oscillator which has Preferably, the frequency of the first oscillation signal is a predetermined frequency. That is, in the first PLL circuit 20, it is preferable that the first division ratio be a fixed value.

  The frequency divider 30 divides the first oscillation signal at a predetermined division ratio. The divider 30 outputs the divided signal to the second PLL circuit 40.

The second PLL circuit 40 includes a second PLL-IC 41, a second loop filter 42, and a second voltage control oscillator 43.
The second PLL-IC 41 is an integrated circuit that functions as a second frequency divider 411 and a second phase comparator 412.

  The second frequency divider 411 divides the second oscillation signal of the second frequency output from the second voltage control oscillator 43 by a second division ratio to generate a second divided signal. The second frequency divider 411 outputs the second frequency divided signal to the second phase comparator 412. When changing the frequency of the output signal of the frequency synthesizer 1 in the present embodiment, the second division ratio is changed.

  The second phase comparator 412 outputs a second phase difference signal based on the phase difference between the signal divided by the frequency divider 30 and the second oscillation signal output from the second voltage control oscillator 43. The second phase comparator 412 outputs a second phase difference signal indicating the phase difference between the reference signal and the second divided signal to the second loop filter 42.

  The second loop filter 42 is, for example, a low pass filter. The second loop filter 42 passes the signal of the frequency of the second band which is included in the signal output from the second phase comparator 412 and has a wider bandwidth than the first band. The second band is preset based on the lockup time required of the frequency synthesizer 1. In the present embodiment, the second band is set to 0 to 20 kHz. The second loop filter 42 outputs the passed signal to the second voltage control oscillator 43 as a second control voltage.

  The second voltage control oscillator 43 outputs a second oscillation signal of the second frequency based on the second control voltage. The second frequency is higher than the first frequency, for example, 9 GHz. The second voltage control oscillator 43 outputs the second oscillation signal to the second PLL-IC 41 and also outputs it as the output signal fout of the frequency synthesizer 1 to the outside.

[Result of measurement of phase noise characteristic]
Subsequently, the measurement result of the phase noise characteristic of the frequency synthesizer 1 will be described in comparison with the measurement result of the conventional frequency synthesizer. First, measurement results of the conventional frequency synthesizer 100 to be compared will be described. FIG. 2 is a diagram showing the configuration of a conventional frequency synthesizer 100. As shown in FIG.

  As shown in FIG. 2, the conventional frequency synthesizer 100 includes a reference oscillator, a PLL-IC, a loop filter, and a voltage controlled oscillator. The reference oscillator of the conventional frequency synthesizer 100 is a crystal oscillator like the reference oscillator 10 of the frequency synthesizer 1 and outputs a 50 MHz reference signal. Further, it is assumed that the voltage controlled oscillator of the conventional frequency synthesizer 100 outputs an output signal of 9 GHz as the frequency synthesizer 1 does.

  FIG. 3 is a view showing measurement results of phase noise characteristics of the conventional frequency synthesizer 100. As shown in FIG. The characteristic shown by the solid line in FIG. 3 shows the phase noise characteristic when the conventional frequency synthesizer 100 is not vibrated. Further, the characteristic shown by the broken line shows the phase noise characteristic when the conventional frequency synthesizer 100 is vibrated at 5 Hz to 500 Hz.

  In the conventional frequency synthesizer 100, noise is added to the output signal at a frequency corresponding to the vibration, when the vibration is applied. As shown in FIG. 3, it can be confirmed that the phase noise characteristic when the vibration is applied is deteriorated as compared to the phase noise characteristic when the vibration is not applied.

  FIG. 4 is a diagram showing measurement results of phase noise characteristics in the case where the vibration damping measures are taken by providing a damping material in the reference oscillator of the conventional frequency synthesizer 100. In FIG. The characteristic shown by the solid line in FIG. 4 shows the measurement result of the phase noise characteristic in the case where vibration is applied in a state in which the reference oscillator of the conventional frequency synthesizer 100 is subjected to the vibration isolation. Further, the characteristic shown by the broken line is a diagram showing the measurement result of the phase noise characteristic in the case where vibration is applied to the reference oscillator of the conventional frequency synthesizer 100 without taking anti-vibration measures. As shown in FIG. 4, although it can be confirmed that the phase noise characteristic is improved between 50 Hz and 500 Hz by applying the vibration isolation measures to the reference oscillator, the phase noise characteristic at a frequency of 50 Hz or less It can also be confirmed that there was little improvement.

  FIG. 5 is a view showing measurement results of phase noise characteristics of the frequency synthesizer 1 according to the present embodiment. The characteristic shown by the solid line in FIG. 5 indicates the measurement result of the phase noise characteristic when the frequency synthesizer 1 is vibrated at 5 Hz to 500 Hz. Further, the characteristic shown by the broken line shows the measurement result of the phase noise characteristic in the case where vibration is applied in the state where the vibration isolation measures are applied to the reference oscillator of the conventional frequency synthesizer 100.

  The phase noise characteristic of the frequency synthesizer 1 is degraded in the vicinity of 2 Hz to 5 Hz and 400 Hz to 800 Hz as compared with the phase noise characteristic when the reference oscillator of the conventional frequency synthesizer 100 is subjected to the vibration reduction measures. However, it can be confirmed that the phase noise characteristic of the frequency synthesizer 1 is significantly improved at 5 Hz to 400 Hz as compared with the phase noise characteristic when the vibration control is applied to the reference oscillator of the conventional frequency synthesizer 100.

  The deterioration of the phase noise characteristic in the vicinity of 2 Hz to 5 Hz and 400 Hz to 800 Hz is obtained by multiplying the first oscillation signal output from the first voltage control oscillator 23 to amplify the phase noise included in the first oscillation signal. Degradation caused by Therefore, as described above, it is preferable that the first voltage control oscillator 23 be an oscillator having a narrow band and good phase noise characteristics so as to reduce the deterioration.

[Effect of First Embodiment]
As described above, the frequency synthesizer 1 according to the first embodiment includes the first PLL circuit 20 having the first loop filter 22 and the second PLL circuit 40 having the second loop filter 42. The first loop filter 22 passes the signal of the first band included in the signal output from the first phase comparator 212, and outputs the passed signal to the first voltage control oscillator 23 as a first control voltage. The second loop filter 42 passes the signal of the second band wider than the first band included in the signal output from the second phase comparator 412, and controls the second voltage as the second control voltage. Output to the oscillator 43.

  The first PLL circuit 20 attenuates the noise superimposed on the reference signal by the external vibration by the first loop filter 22, so that the anti-vibration performance can be improved. As a result of narrowing the bandwidth of the first PLL circuit 20, the lockup time is delayed when the frequency of the first oscillation signal output from the first PLL circuit 20 is changed. However, when changing the frequency of the output signal, the frequency synthesizer 1 according to the present embodiment does not change the frequency of the first oscillation signal output from the first PLL circuit 20, and the second PLL circuit has a short lockup time. By changing the second division ratio at 40, the frequency of the output signal can be changed. Thereby, the lockup time when changing the frequency of the output signal of the frequency synthesizer 1 can be shortened. Therefore, the frequency synthesizer 1 can maintain good frequency characteristics even when external vibration is applied, and can output an output signal of a desired frequency with a short lockup time.

Second Embodiment
[Setting the passband of the first loop filter 22 based on the frequency of vibration]
Subsequently, a second embodiment will be described. The second embodiment is different from the first embodiment in that the frequency of vibration given to the frequency synthesizer 1 is detected, and the pass band of the first loop filter 22 is set based on the frequency. The frequency synthesizer 1 according to the second embodiment will be described below. Description of the same parts as those of the first embodiment will be omitted as appropriate.

  FIG. 6 is a diagram showing the configuration of the first PLL-IC 21 according to the second embodiment. As shown in FIG. 6, the first PLL-IC 21 includes a detection unit 213 and a setting unit 214.

  The detection unit 213 detects the frequency of the vibration given to the frequency synthesizer 1. For example, the detection unit 213 measures the waveform of the vibration given to the frequency synthesizer 1. Then, the detection unit 213 performs Fourier transform of the measured waveform, and detects the frequency of the vibration having a predetermined level or more by specifying the frequency of the vibration included in the measured waveform. The detection unit 213 detects the lowest frequency among the one or more frequencies lower than the cut-off frequency in the second loop filter 42. The detection unit 213 outputs information indicating the detected frequency to the setting unit 214.

  The setting unit 214 sets a first band of the first loop filter 22 based on the detected frequency. For example, the first phase comparator 212 is configured by a charge pump, and outputs a current proportional to the phase difference as a signal indicating the phase difference. The setting unit 214 sets the first band by changing the amount of current output from the charge pump according to the phase difference.

  For example, the setting unit 214 sets the first phase comparator 212 such that the amount of current output from the charge pump according to the phase difference decreases as the detected frequency decreases. When the amount of current output from the charge pump decreases, the amount of current flowing into or out of the capacitor constituting the first loop filter 22 decreases. As a result, the temporal change of the control voltage output from the first loop filter 22 becomes gentle, and the first band of the first loop filter 22 becomes narrow. In addition, when the amount of current output from the charge pump increases, the amount of current flowing into or out of the capacitor constituting the first loop filter 22 increases. As a result, the temporal change of the control voltage output from the first loop filter 22 becomes sharp, and the first band of the first loop filter 22 becomes wide.

[Effect of Second Embodiment]
As described above, the frequency synthesizer 1 according to the second embodiment detects the frequency of the vibration given to itself, and sets the first band of the first loop filter 22 based on the frequency. By doing this, the frequency synthesizer 1 can automatically set the first band suitable for the installation environment, and improve the vibration resistance performance in the installation environment.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It is apparent to those skilled in the art that various changes or modifications can be added to the above embodiment. For example, in the second embodiment, the first PLL-IC 21 includes the detection unit 213 and the setting unit 214. However, the present invention is not limited to this. The detection unit 213 and the setting unit 214 are provided separately from the first PLL-IC 21. It may be done. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the present invention.

1 ... frequency synthesizer, 10 ... reference oscillator, 20 ... first PLL circuit, 21 ... first PLL-IC, 211 ... first divider, 212 ... first phase comparator , 213: detection unit, 214: setting unit, 22: first loop filter, 23: first voltage control oscillator, 30: frequency divider, 40: second PLL circuit, 41 second PLL-IC 411 second frequency divider 412 second phase comparator 42 second loop filter 43 second voltage controlled oscillator

Claims (4)

An oscillator that outputs a reference signal, a first phase control oscillator that outputs a first oscillation signal of a first frequency, a divider that divides the first oscillation signal, and a second frequency higher than the first frequency And a second phase control oscillator for outputting a second oscillation signal of
The first phase controlled oscillator is
A first voltage controlled oscillator that outputs the first oscillation signal based on a first control voltage;
A first phase comparator that outputs a first phase difference signal indicating a phase difference between the reference signal and the first oscillation signal;
And a first loop filter that passes a signal of a first band included in the first phase difference signal and outputs the passed signal as the first control voltage to the first voltage control oscillator.
The second phase control oscillator is
A second voltage controlled oscillator that outputs the second oscillation signal based on a second control voltage;
A second phase comparator that outputs a second phase difference signal indicating a phase difference between the signal divided by the divider and the second oscillation signal;
A second loop filter that passes a signal in a second band wider than the first band, which is included in the second phase difference signal, and outputs the passed signal as the second control voltage to the second voltage control oscillator; Have
Frequency synthesizer. The first phase control oscillator further includes a first divider that outputs a first divided signal obtained by dividing the first oscillation signal by a first dividing ratio.
The first phase comparator outputs the first phase difference signal indicating a phase difference between the reference signal and the first divided signal.
The second phase control oscillator further includes a second divider that outputs a second divided signal obtained by dividing the second oscillation signal by a second dividing ratio,
The second phase comparator outputs the second phase difference signal indicating a phase difference between the signal divided by the divider and the second divided signal.
A frequency synthesizer as claimed in claim 1. A detection unit that detects the frequency of vibration given to the frequency synthesizer;
And a setting unit configured to set the first band of the first loop filter based on the detected frequency.
A frequency synthesizer as claimed in claim 2. The first phase comparator outputs the first phase difference signal indicating a phase difference between the reference signal and the first divided signal by a charge pump.
The setting unit sets the first band by changing an amount of current output by the charge pump in accordance with a phase difference between the reference signal and the first divided signal.
A frequency synthesizer as claimed in claim 3.

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