JP2000269739A - Quartz oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a side band f0±nΔf (f0 is the oscillation frequency and Δf is the external oscillation frequency and n=1, 2, to ∞) sandwiching to due to external oscillation. SOLUTION: The output signal of a quartz oscillator 2 is subjected to FM detection by an FM detection part 3, the polarity of this signal is inverted by an inverter 4, and the signal level is adjusted by a level adjustment part 5, it is applied to the control voltage terminal of a voltage controlled quartz oscillator 1 to cancel the side band generated in the quartz oscillator 1 by external oscillation, and only the signal of the oscillation frequency f0 is outputted to suppress the degradation of phase noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal oscillator,
The present invention relates to a device for preventing deterioration of phase noise due to a sideband generated by external vibration (mechanical vibration).

[0002]

2. Description of the Related Art An oscillator using a crystal unit has a very high frequency stability against a temperature change and a change over time.
It is well known that it is excellent also in the vicinity of phase noise. For example, it is used for an LNB (Low Noise Frequency Converter) for receiving satellite radio waves. However, when mechanical vibration is applied from the outside during operation of the crystal oscillator and the crystal oscillator vibrates, as shown in FIG.
A side band of fo ± nΔf (n = 1, 2,...) Is generated at a frequency interval equal to the frequency f1 of the external vibration f1 = Δf, and shows a spectrum just like FM modulation (frequency modulation). There is a problem that the phase noise of the output deteriorates, and as a result, the performance of the crystal oscillator deteriorates.

[0003]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention provides two crystal oscillators, and performs FM detection on the output of one crystal oscillator, inverts the output, and inverts the other crystal oscillator (voltage-controlled crystal oscillator). The purpose of the present invention is to suppress the deterioration of the phase noise by canceling the sideband generated by the oscillation of the quartz oscillator due to the external vibration.

[0004]

In order to achieve the above object, a crystal oscillator according to the present invention comprises a first crystal oscillator using a first crystal oscillator and a second crystal oscillator having the same structure as the first crystal oscillator. A second crystal oscillator configured using a crystal oscillator,
An FM detector for FM-detecting the output signal of the second crystal oscillator, and an inverter for inverting the polarity of the signal from the FM detector are provided. The signal from the inverter is applied to the first crystal oscillator, A configuration is made such that a sideband generated by the first crystal oscillator due to vibration is canceled by a sideband generated by the second crystal oscillator due to external vibration.

For this reason, at least the first crystal oscillator is configured using a voltage-controlled crystal oscillator, and a signal from an inverter is applied to a control voltage terminal.

Further, a level adjuster for adjusting a level of a signal from the inverter is provided at a subsequent stage of the inverter, and a level of a signal applied to the first crystal oscillator is adjusted according to a control sensitivity of the first crystal oscillator. A side band wave generated by one crystal oscillator is canceled well.

The first crystal oscillator and the second crystal oscillator are set under such conditions that mechanical vibration of each crystal resonator due to external vibration is similarly generated in both.

In addition, the first crystal oscillator is connected to a PLL (Phase Locator).
ked Loop) circuit.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings. FIG. 1 is a block diagram of a main part of an embodiment of a crystal oscillator according to the present invention. In the figure,
Reference numeral 1 denotes a first crystal oscillator, which is constituted by a voltage controlled crystal oscillator using a first crystal resonator. Reference numeral 2 denotes a second crystal oscillator (for compensation), which is configured using a second crystal oscillator having the same structure as the first crystal oscillator. Reference numeral 3 denotes an FM detection unit, and a second crystal oscillator 2
Of the second crystal oscillator 2 generated by the second crystal oscillator vibrating due to external vibration. Reference numeral 4 denotes an inverter for inverting the polarity of the signal from the FM detector 3. Reference numeral 5 denotes a level adjuster for adjusting the level of the signal from the inverter 4 and applying the signal to the control voltage terminal of the first crystal oscillator 1.

Next, the operation of the crystal oscillator according to the present invention will be described. When an external vibration (periodic or random in period) is applied, the first crystal oscillator forming the first crystal oscillator 1 and the second crystal forming the second crystal oscillator 2
The first crystal oscillator 1 and the second crystal oscillator 2 are arranged so that the crystal oscillator receives the same vibration. When no external vibration is applied, the first crystal oscillator 1 and the second crystal oscillator 2 oscillate at the frequency fo as shown in FIG. 3A, respectively, but the vibration of the frequency f1 (= Δf) is applied from the outside. In this case, the frequency fo ± nΔf (n = 1, 2,...) Around the frequency fo as shown in FIG.
, Fo ± 2Δf, fo ± 3Δf,..., Generate a spectrum as if the frequency fo was FM-modulated.

The signals of the frequency fo and the frequency fo ± nΔf (n = 1, 2,...) Output from the crystal oscillator 2 are input to the FM detection unit 3, and the signal of the frequency fo ± nΔf is subjected to FM detection. This signal is input to the inverter 4 to invert the polarity. The signal of the frequency fo ± nΔf whose polarity is inverted is adjusted to an appropriate signal level by the level adjusting unit 5 and applied to the first crystal oscillator 1. At least the first crystal oscillator 1 is composed of a voltage controlled crystal oscillator (VCXO),
Is applied to the control voltage terminal. This allows
The sideband of the frequency fo ± nΔf generated in the first crystal oscillator 1 is canceled out, and only the signal of the frequency fo is output from the first crystal oscillator 1, whereby the deterioration of the phase noise of the oscillation output can be suppressed. The cause of the performance degradation of the crystal oscillator can be eliminated. The level adjuster 5 adjusts the level of the signal applied to the control voltage terminal of the first crystal oscillator 1,
This is to completely cancel the sideband wave.

FIG. 2 is a block diagram showing a main part of an example in which the crystal oscillator according to the present invention is used as a reference oscillator of a PLL circuit. The phase comparator 11, LPF 12, VCO 13 and frequency divider 14 are shown in FIG.
Constitutes a PLL circuit. 11 is a phase comparison unit that compares the phase of the reference signal from the first crystal oscillator with the comparison signal from the frequency divider 14 and outputs a signal corresponding to the phase difference. LPF for extracting DC component
(Low-pass filter), 13 is a VCO (voltage controlled oscillator) that oscillates a signal (clock) having a frequency controlled by the signal from the LPF 12, and 14 is a frequency divider that divides the signal from the VCO 13 to the frequency of the reference signal. It is.

The second crystal oscillator 2 is for canceling a sideband generated by the first crystal oscillator 1 when an external vibration is applied, and is for extracting the same sideband as this sideband. 1, the first constituting the second crystal oscillators 1 and 2,
The second crystal resonator has the same structure, and the first and second crystal oscillators 1 and 2 are simultaneously vibrated by external vibration. However, since the second crystal oscillator 2 is only for extracting a sideband by FM detection, it may have an oscillation frequency different from that of the first crystal oscillator 1. Note that the second crystal oscillator 2 may also be constituted by a voltage controlled crystal oscillator.

[0014]

As described above, according to the crystal oscillator of the present invention, when a mechanical vibration is applied from the outside, the sideband generated by this vibration is converted into the sideband generated by another crystal oscillator. Thus, a signal from which the sideband is removed is output from the crystal oscillator, and a crystal oscillator having good phase noise can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of an embodiment of a crystal oscillator according to the present invention.

FIG. 2 is a main block diagram of an example in which a crystal oscillator according to the present invention is applied to a PLL circuit.

FIG. 3 is an explanatory diagram of an oscillation spectrum of a crystal oscillator.

[Explanation of symbols]

 Reference Signs List 1 crystal oscillator (voltage controlled crystal oscillator) 2 crystal oscillator 3 FM detector 4 inverter 5 level adjuster 11 phase comparator 12 LPF 13 VCO 14 frequency divider

Claims (5)

[Claims] 1. A first crystal oscillator configured using a first crystal resonator, a second crystal oscillator configured using a second crystal resonator having the same structure as the first crystal resonator, and a second crystal oscillator And an inverter for inverting the polarity of the signal from the FM detector. The signal from the inverter is applied to the first crystal oscillator, and the first oscillator is applied to the first crystal oscillator by external vibration. A crystal oscillator in which a sideband generated by a crystal oscillator is canceled by a sideband generated by a second crystal oscillator by external vibration. 2. The crystal oscillator according to claim 1, wherein at least said first crystal oscillator comprises a voltage-controlled crystal oscillator, and a signal from said inverter is applied to a control voltage terminal. 3. A level adjuster for adjusting a level of a signal from the inverter is provided at a subsequent stage of the inverter, and adjusts a level of a signal applied to the first crystal oscillator according to a control sensitivity of the first crystal oscillator. 3. The crystal oscillator according to claim 1, wherein the sideband generated in the first crystal oscillator is canceled out well. 4. The first crystal oscillator and the second crystal oscillator are arranged under such a condition that mechanical vibrations of the respective crystal units due to external vibrations are similarly generated on both sides. Or the crystal oscillator according to 3. 5. The method according to claim 1, wherein the first crystal oscillator is a PLL (Phase Locator).
5. The crystal oscillator according to claim 1, wherein the crystal oscillator is used as a reference oscillator of a ked Loop circuit.