JP4399782B2 - Frequency selective oscillator and electronic device equipped with the same - Google Patents

Description

  The present invention relates to a frequency selective oscillator, and more particularly, to a frequency selective oscillator that outputs signals having a plurality of different oscillation frequencies and an electronic apparatus including the same.

  In communication devices such as mobile phones and optical fiber communication systems, communication data is transmitted and received based on a clock signal from an oscillator. Some optical fiber communication systems use a plurality of frequencies due to differences in data structures to be transmitted and received. For example, in the US SONET optical fiber communication system, four frequencies in the 600 MHz band, specifically, 622.08 MHz, 644.53125 MHz, 666.551429 MHz, and 669.32658 MHz are used. A corresponding high-frequency oscillator is required. For this reason, a voltage controlled oscillator has been invented in which a plurality of piezoelectric elements are provided and a signal having any one of a plurality of different frequencies is output.

Patent Documents 1 and 2 disclose oscillators that output signals having different frequencies. The oscillator disclosed in Patent Document 1 selectively operates a plurality of crystal oscillators having different oscillation frequencies, selects a harmonic component of the crystal oscillator in operation by a surface wave filter, and amplifies the harmonic component. And complementary output. The oscillator disclosed in Patent Document 2 includes a plurality of resonance circuits, oscillation transistors, and a plurality of bias circuits, and one bias circuit is selected according to a required oscillation frequency, and the selected bias is selected. A power source is connected to one of the resonance circuits via a circuit to oscillate this resonance circuit.
JP 2002-335127 A JP 2002-359521 A

  By the way, when a voltage controlled oscillator is configured by providing a plurality of piezoelectric elements in the oscillator and a signal of any one of a plurality of different frequencies is output, the control voltage applied to the piezoelectric element, It is preferable that the frequency control characteristics with the frequency change amount are the same for each piezoelectric element.

  However, when a plurality of piezoelectric elements are provided in an oscillator, if one piezoelectric element and another piezoelectric element are always connected, isolation between the piezoelectric elements is not ensured and the frequency control characteristics are affected. There is a point. Further, when a plurality of piezoelectric elements are provided and these are oscillated by a single oscillation circuit, there is a problem that there is a limit to adjusting the frequency control characteristics for each piezoelectric element because the oscillation circuit is shared. When the frequency control characteristics of each piezoelectric element are different, there is a problem in that a frequency control characteristic different for each piezoelectric element must be adjusted in a circuit connected to a subsequent stage of an oscillator in which these piezoelectric elements are used.

  Further, in Patent Document 1, since a plurality of piezoelectric oscillators, that is, an oscillation amplifier is provided for each piezoelectric vibrator, there is a problem that the circuit configuration of the entire oscillator becomes large and the piezoelectric oscillator becomes expensive. In Patent Document 2, a circuit that oscillates a piezoelectric vibrator, that is, an oscillation transistor, a split capacitor, and the like are shared, and isolation between the piezoelectric vibrators is not secured. There is a problem that cannot be adjusted.

The present invention has been made to solve the above-described problems, and provides a frequency selective oscillator that adjusts the frequency control characteristic for each piezoelectric element and makes the frequency control characteristic of each piezoelectric element similar. Objective.
It is another object of the present invention to provide an electronic device including the frequency selective oscillator described above.

In order to achieve the above object, a frequency selective oscillator according to the present invention includes a tank circuit including a parallel resonant circuit in which a resistor, an inductor, and a capacitor are connected in parallel between one end and the other end, and an inverting input terminal. And one end of the tank circuit is connected to one of the inverting input terminal and the non-inverting input terminal, and the other end of the tank circuit is connected to the other to input a bias voltage. And a voltage-controlled phase shift circuit that outputs the signal output from the amplifier by advancing or delaying the phase by a predetermined amount, and a piezoelectric element between one end and the other end And a plurality of series circuits configured by connecting impedance elements in series, and a signal output from the voltage controlled phase shift circuit is connected to any one of the plurality of series circuits. A first switching unit and supplies the serial one end, the other end of said series circuit signal by the voltage controlled phase shift circuit is output is supplied, a second switching unit that connects to the one end of the tank circuit , Is further provided.
By adjusting the impedance element, the amount of frequency change (frequency control characteristic) with respect to the control voltage of the piezoelectric element can be adjusted by moving up and down. Therefore, by adjusting the impedance element for each piezoelectric element, the characteristics of each piezoelectric element can be made the same. In the subsequent circuit of the frequency selective oscillator, it is not necessary to adjust different frequency control characteristics for each piezoelectric element, so that the circuit can be simplified.

The frequency selective oscillator can output signals having a plurality of different oscillation frequencies. Furthermore, since the piezoelectric element selected by the switching unit and the non-selected piezoelectric element are not connected, isolation between the piezoelectric elements can be secured, and frequency control characteristics may be exerted between the piezoelectric elements. Absent.

An adjustment impedance element is provided between the voltage control phase shift circuit and the first switching unit . By combining this adjustment impedance element and the impedance element provided for each piezoelectric element, the frequency control characteristics can be finely adjusted over a wide range.

The impedance element is an inductor or a capacitor. Thereby, the frequency control characteristic of the piezoelectric element can be moved up and down, that is, the frequency change amount can be adjusted, and the characteristic of each piezoelectric element can be made the same .

An adjustment capacitor is provided, and one end of the adjustment capacitor is connected between the second switching unit and the tank circuit, and the other end of the adjustment capacitor is grounded . When the capacitance is changed by combining this capacitor and a capacitor provided for each piezoelectric element, the frequency control characteristics can be finely adjusted in a wide range.
The piezoelectric element is a surface acoustic wave resonator. As a result, a signal with low jitter characteristics can be obtained.

  An electronic apparatus according to the present invention includes the above-described frequency selective oscillator. Thereby, the electronic device can obtain signals having a plurality of different frequencies. Since there is no need to adjust different frequency control characteristics for each piezoelectric element, the electronic device can be simplified.

  Hereinafter, preferred embodiments of a frequency selective oscillator and an electronic apparatus including the same according to the present invention will be described. FIG. 1 is an explanatory diagram of a frequency selective oscillator. FIG. 1 shows a mode in which a surface acoustic wave (SAW) resonator is used as a piezoelectric element and inductors L1 and L2 are used as impedance elements. The frequency selective oscillator 10 includes a SAW resonator 12, inductors L1 and L2, capacitors C1 and C2, a switching unit 14, a tank circuit 16, an oscillation differential amplifier 18, an output differential amplifier 20, and a feedback buffer differential amplifier. 22 and a voltage controlled phase shift circuit 24, and constitutes a voltage controlled oscillator. The SAW resonator 12, the inductors L1 and L2, the tank circuit 16, the oscillation differential amplifier 18, the feedback buffer differential amplifier 22 and the voltage control phase shift circuit 24 form a positive feedback oscillation loop.

  A plurality of SAW resonators 12 are provided, each having a different oscillation frequency. Since the SAW resonator 12 has no unnecessary vibration other than the main vibration, it has a feature that it does not cause a jitter. An inductor L1 (L1a, L1b) is connected to each of the SAW resonators 12 in series. Switching portions 14 (14a, 14b) are provided at both ends of a circuit in which the SAW resonator 12 and the inductor L1 are connected in series. That is, a plurality of the circuits are connected in parallel, and a switching unit 14 is provided at the parallel connection. A capacitor C1 (C1a, C1b) is connected in series to each of the circuits via one switching unit 14a.

  Although FIG. 1 shows a form using two SAW resonators 12, the present invention is not limited to this form, and three or more SAW resonators 12 having different oscillation frequencies may be provided. In addition, the switching unit 14 connected to both ends of the circuit is configured to select one of the plurality of SAW resonators 12 in conjunction with the control signal CONT input via the switching terminal Tc. Further, an inductor L2 is provided before the switching unit 14b provided on the input side of the SAW resonator 12, that is, between the other switching unit 14b and the voltage control phase shift circuit 24. The inductors L1 and L2 are used to adjust the amount of frequency change (frequency control characteristics) with respect to the control voltage of the SAW resonator 12.

  The tank circuit 16 is constituted by a parallel resonance circuit of a resistor R, an inductor L and a capacitor C, and one end is connected between the SAW resonator 12 and the non-inverting input terminal D1 of the oscillation differential amplifier 18. The other end of the tank circuit 16 is connected to the inverting input terminal D2 of the oscillation differential amplifier 18. One end of a capacitor C2 is connected between the tank circuit 16 and one switching portion 14a, and the other end of the capacitor C2 is grounded. The capacitor C2 and the capacitor C1 connected in series to the SAW resonator 12 selected by the switching unit 14 are connected in parallel with the tank circuit 16 and used to adjust the amount of change in frequency (control sensitivity) with respect to the control voltage. It has been. The tank circuit 16 is connected in parallel with the capacitors C1 and C2, and resonates at a predetermined frequency.

  The oscillation differential amplifier 18, the output differential amplifier 20, and the feedback buffer differential amplifier 22 are integrated and formed as one integrated circuit (IC) chip 26. The IC chip 26 constitutes an oscillation circuit. ing. Since these differential amplifiers 18, 20, and 22 are composed of differential amplifier circuits using an ECL line receiver (emitter coupling theory), it is easy to make an integrated circuit, and the frequency selective oscillator 10 can be downsized. It has become easy.

  The non-inverting input terminal D1 of the oscillation differential amplifier 18 is connected to the switching unit 14, and the output signal of the SAW resonator 12 is input to the non-inverting input terminal D1. The inverting input terminal D2 of the oscillation differential amplifier 18 is connected to the switching unit 14 via the tank circuit 16. Further, the reference bias voltage VBB output from the IC chip 26 is applied to the inverting input terminal D2. The output signal from the SAW resonator 12 may be input to the inverting input terminal D2 of the oscillation differential amplifier 18, and the bias voltage VBB may be input to the non-inverting input terminal D1. The oscillation differential amplifier 18 is configured to output an output signal having a phase difference of 180 degrees from the non-inverting output terminal Q + and the inverting output terminal Q−.

  The non-inverting input terminal of the output differential amplifier 20 is connected to the non-inverting output terminal Q + of the oscillation differential amplifier 18, and the inverting input terminal is connected to the inverting output terminal Q− of the oscillation differential amplifier 18. . The output differential amplifier 20 shapes the output signal from the oscillation differential amplifier 18 and outputs it as a clock signal via the output terminals T + and T−.

  Further, the feedback buffer differential amplifier 22 is a differential amplifier having a buffer function. The inverting input terminal of the feedback buffer differential amplifier 22 is connected to the inverting output terminal Q− of the oscillation differential amplifier 18, and the non-inverting input terminal is connected to the non-inverting output terminal Q + of the oscillation differential amplifier 18. . The signal SQ1 output from the non-inverting output terminal Q1 of the feedback buffer differential amplifier 22 is output to the outside of the frequency selective oscillator 10. The signal SQ2 output from the inverting output terminal Q2 is input to the voltage control phase shift circuit 24 as an output signal for the positive feedback oscillation loop. Note that the output signal SQ1 from the non-inverting output terminal Q1 may be used as the output signal for the positive feedback oscillation loop, and the output signal SQ2 from the inverting output terminal Q2 may be output to the outside of the frequency selective oscillator 10.

  FIG. 2 shows a circuit diagram of the voltage control phase shift circuit 24. The voltage control phase shift circuit 24 is composed of a voltage control type reactance control circuit using a variable capacitance diode Cv, and in order to satisfy the phase condition of the frequency selective oscillator 10, a control voltage input via the voltage control terminal Tv. Based on Vc, the phase of either the output signal SQ1 or SQ2 from the feedback buffer differential amplifier 22 is advanced or delayed by a predetermined amount, and adjusted to a predetermined phase amount.

  Next, adjustment of frequency control characteristics using the inductors L1 and L2 will be described. FIG. 3 is an explanatory diagram for adjusting the frequency change amount in the frequency control characteristic of the SAW resonator 12. FIG. 3A is an explanatory diagram when the amount of change moves up and down, and FIG. 3B is an explanatory diagram when the characteristics of the SAW resonators 12 are the same. When the inductances of the inductors L1 and L2 are changed, the frequency change amount of the frequency control characteristic of the SAW resonator 12 is adjusted. That is, the solid line shown in FIG. 3A changes to the dotted line shown above or below the solid line by changing the inductance, and the frequency change amount changes. Therefore, if the inductors L1 and L2 are not provided in each SAW resonator 12, the frequency control characteristics of each SAW resonator 12 (SAW resonators 1 and 2) are different as shown by the solid line in FIG. 3B. However, when the inductor L1 is provided in each SAW resonator 12 and the inductance is changed together with the inductor L2, the frequency change amount of the frequency control characteristic of each SAW resonator 12 is adjusted and becomes the same, and the dotted line in FIG. It becomes like this.

  When the inductors L1 and L2 are used, the oscillation frequency of all the SAW resonators 12 is adjusted by the inductor L2, and the oscillation frequency of each SAW resonator 12 is adjusted by the inductor L1. That is, if a inductor having a large inductance is used for the inductor L2 and a inductor having a small inductance is used, the amplitude of the inductance can be increased and changed finely. Therefore, the frequency control characteristic also has a wide fluctuation range, and the frequency change amount can be finely adjusted. In some embodiments, the inductor L2 may not be provided. Furthermore, although the present embodiment has been described in the form of using the inductors L1 and L2 as impedance elements, a capacitor may be used instead of the inductor.

  Next, adjustment of frequency control characteristics using the capacitors C1 and C2 will be described. FIG. 4 is an explanatory diagram for adjusting the control sensitivity in the frequency control characteristics of the SAW resonator 12. FIG. 4A is an explanatory diagram when the control sensitivity of the characteristics changes, and FIG. 4B is an explanatory diagram when the characteristics of the SAW resonators 12 are the same. When the capacitances of the capacitors C1 and C2 connected to the SAW resonator 12 are changed, the change amount (control sensitivity) of the frequency change amount with respect to the control voltage of the SAW resonator 12 changes. This is because the solid line shown in FIG. 4A changes as indicated by the dotted line by changing the capacitance and changing the control sensitivity of the characteristic. For this reason, if the capacitors C1 and C2 are not used, the control sensitivity of each SAW resonator 12 (SAW resonators 1 and 2) is different as shown by the solid line in FIG. When the capacitor C1 is connected to the capacitor C2 and the capacitance is changed together with the capacitor C2, the control sensitivity of the frequency control characteristics of each SAW resonator 12 is adjusted and becomes the same as shown by the dotted line in FIG.

  In the case where the capacitors C1 and C2 are used, if a capacitor C2 having a large capacitance is used and a capacitor C1 having a small capacitance is used, the capacitance swing is large and can be finely changed. Therefore, the control sensitivity of the frequency control characteristic has a wide fluctuation range and can be finely adjusted. In some embodiments, the capacitor C2 may not be provided.

  When the frequency control characteristic of each SAW resonator 12 requires both frequency change adjustment and control sensitivity adjustment, the inductances of the inductors L1 and L2 are changed and the capacitances of the capacitors C1 and C2 are changed. Thus, the characteristics of each SAW resonator 12 can be made the same.

  Next, the operation of the frequency selective oscillator 10 will be described. First, the switching unit 14 selects any one SAW resonator 12 from among the plurality of SAW resonators 12 by a control signal CONT input via the switching terminal Tc. The selected SAW resonator 12 forms a positive feedback oscillation loop together with the inductors L2 and L1, the tank circuit 16, the IC chip 26, and the voltage control phase shift circuit 24. The selected SAW resonator 12 receives a signal via the inductors L1 and L2, and oscillates at a predetermined frequency of the SAW resonator 12 to output a signal. The signal output from the SAW resonator 12 is input to the oscillation differential amplifier 18 via the tank circuit 16. The output signals from the oscillation differential amplifier 18 have a phase difference of 180 degrees, and this output signal is input to the output differential amplifier 20 and the feedback buffer differential amplifier 22. The output differential amplifier 20 shapes the output signal from the oscillation differential amplifier 18 and outputs it as a clock signal to the outside of the frequency selective oscillator 10 via the output terminals T + and T−. The output signal is output to the non-inverting output terminal Q1 and the inverting output terminal Q2 via the feedback buffer differential amplifier 22. The voltage control phase shift circuit 24 appropriately sets the phase of the output signal SQ2 output from the inverting output terminal Q2 of the feedback buffer differential amplifier 22 based on the control voltage Vc input via the voltage control terminal Tv. Adjust to phase. The signal SQ1 output from the non-inverting output terminal Q1 is output to the outside of the frequency selective oscillator 10.

  In such a frequency selective oscillator 10, the inductor L <b> 1 is connected to each SAW resonator 12, so that the frequency change amount of the frequency control characteristic can be adjusted for each SAW resonator 12. By adjusting the characteristics for each SAW resonator 12, the characteristics of all the SAW resonators 12 provided in the frequency selective oscillator 10 can be made the same. In addition, since the inductor L2 is provided between the voltage control phase shift circuit 24 and the switching unit 14, the inductance swing is large and finely changed by adjusting the inductance by combining the inductor L2 and the inductor L1. And the characteristics can be finely adjusted. Therefore, a signal having a constant frequency change amount with respect to the control voltage can be output to a circuit connected to the output side of the frequency selective oscillator 10. In addition, since it is not necessary to adjust the frequency control characteristic corresponding to each SAW resonator 12, the circuit connected to the output side of the frequency selective oscillator 10 can be simplified.

  Further, since the capacitor C1 is connected to each SAW resonator 12, the control sensitivity of the frequency control characteristic can be adjusted for each SAW resonator 12. Further, by using the capacitor C2, the control sensitivity of the characteristics can be finely adjusted. By adjusting the characteristics for each SAW resonator 12, the control sensitivity of all the SAW resonators 12 provided in the frequency selective oscillator 10 can be made the same.

  Further, the frequency change amount of the characteristic is adjusted by changing the inductances of the inductors L1 and L2, and the control sensitivity of the characteristic is adjusted by changing the capacitances of the capacitors C1 and C2, so that the frequency selective oscillator 10 is provided. The above-described characteristics of all the SAW resonators 12 can be made the same.

  Further, a switching unit 14 is provided on the input side and the output side of the SAW resonator 12, and any one of the plurality of SAW resonators 12 is selected based on a control signal CONT input from the switching terminal Tc to the switching unit 14. Since it can be selected, only one SAW resonator 12 is connected to the positive feedback oscillation loop. Accordingly, it is possible to ensure isolation between the SAW resonator 12 selected by the switching unit 14 and the other SAW resonators 12 that are not selected, and the frequency control characteristics are not affected. In addition, since a plurality of signals having different frequencies can be output from one frequency selective oscillator 10, a predetermined oscillation frequency corresponding to the specifications of the electronic device can be obtained. One type of frequency selective oscillator 10 can meet individual system specifications in an optical fiber communication system.

  Further, since the capacitors C1 and C2 are connected in parallel with the tank circuit 16, it is not necessary to switch the tank circuit 16 corresponding to each SAW resonator 12, and a plurality of inductor components can be reduced, and voltage control is performed. The size of the type oscillator can be suppressed.

  In the present embodiment, the SAW resonator 12 is used as the piezoelectric element. However, a piezoelectric vibrator such as an AT cut can be used as the piezoelectric element. Since the SAW resonator 12 does not have a secondary vibration unlike a piezoelectric vibrator, the main vibration and the secondary vibration are not coupled and unnecessary spurious does not exist. Further, since a multiplier circuit for obtaining a high frequency is not required, harmonics are not generated. Therefore, since the SAW resonator 12 does not generate jitter due to these, a high-quality signal can be output.

  Next, an example in which the above-described frequency selective oscillator 10 is mounted on an electronic device will be described. FIG. 5 is an explanatory diagram of a schematic configuration of the optical interface module. The optical interface module 30 performs signal conversion between an optical signal and an electrical signal in order to perform data transmission / reception via an optical network. For example, signal conversion between a 10.3125 Gbit / s optical signal and a 3.125 Gbit / s electrical signal (four systems) is performed. The electrical / optical converter 32 converts the electrical signal output from the parallel / serial (P / S) converter 34 into an optical signal and outputs the optical signal to the optical network side. The optical / electrical converter 36 converts the optical signal input from the optical network side into an electrical signal and outputs the electrical signal to the serial / parallel (S / P) converter 38. The voltage controlled oscillator 40 is the frequency selective oscillator 10 described above, and four SAW resonators 12 are provided in this oscillator. The clock signal output from the voltage controlled oscillator 40 is a 3.125 Gbit / s S / P conversion unit 44 and P / S conversion unit 46, 10. It is used for each part of the 3125 Gbit / s P / S converter 34 and S / P converter 38.

  As described above, since the frequency selective oscillator 10 is provided as the voltage-controlled oscillator 40 in the optical interface module 30, the optical interface module 30 can obtain signals of a plurality of different frequencies with one frequency selective oscillator 10. Since the frequency control characteristic of each SAW resonator 12 mounted on the oscillator 10 is a frequency change amount with respect to a similar control voltage, the frequency change amount is adjusted to the circuit side subsequent to the frequency selective oscillator 10. There is no need to provide a circuit, and the configuration of the optical interface module 30 can be simplified.

  In addition, the optical interface module 30 uses a voltage-controlled oscillator 40 that is highly stabilized by forming a tank circuit 16 for each selected SAW resonator 12 and greatly reducing unnecessary jitter. As a result, a timing margin between the transmission / reception data and the clock signal is secured, so that stable data transmission / reception can be performed via the optical network without malfunction. Furthermore, stable operation can be easily ensured in a 10 Gbit / s high-speed network system capable of transmitting a large amount of data such as moving images.

  Since the frequency selective oscillator 10 is a voltage controlled oscillator, it can be applied to a phase locked loop composed of a phase comparator, a loop filter, and a voltage controlled oscillator. Therefore, the frequency selective oscillator 10 can be mounted on an electronic device on which the phase synchronization circuit is mounted.

It is explanatory drawing of a frequency selection type | mold oscillator. It is a circuit diagram of a voltage control phase shift circuit. It is explanatory drawing about adjustment of the amount of frequency changes in the frequency control characteristic of a surface acoustic wave resonator. It is explanatory drawing about adjustment of the control sensitivity in the frequency control characteristic of a surface acoustic wave resonator. It is explanatory drawing of schematic structure of an optical interface module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ......... Frequency selective oscillator, 12 ......... Surface acoustic wave (SAW) resonator, 14 ......... Switching part, 16 ...... Tank circuit, 24 ...... Voltage control phase shift circuit, 30 ......... Optical interface module.

Claims (6)

A tank circuit constituted by a parallel resonant circuit in which a resistor, an inductor and a capacitor are connected in parallel between one end and the other end ;
A bias voltage having an inverting input terminal and a non-inverting input terminal, one end of the tank circuit being connected to one of the inverting input terminal and the non-inverting input terminal, and the other end of the tank circuit being connected to the other An amplifier to which
A voltage-controlled phase shift circuit that advances or delays the phase of the signal output from the amplifier by a predetermined amount; and
A frequency selective oscillator comprising:
A plurality of series circuits formed by connecting the piezoelectric element and the impedance element in series between the one end and the other end,
A first switching unit that supplies a signal output from the voltage controlled phase shift circuit to the one end of any of the plurality of series circuits;
A second switching unit for connecting the other end of the series circuit to which the signal output from the voltage control phase shift circuit is supplied to the one end of the tank circuit;
A frequency selective oscillator, further comprising:   2. The frequency selective oscillator according to claim 1, wherein an adjustment impedance element is provided between the voltage controlled phase shift circuit and the first switching unit.   3. The frequency selective oscillator according to claim 1, wherein the impedance element is an inductor or a capacitor. It has a capacitor for adjustment,
One end of the adjustment capacitor is connected between the second switching unit and the tank circuit ,
4. The frequency selective oscillator according to claim 1, wherein the other end of the adjustment capacitor is grounded .   5. The frequency selective oscillator according to claim 1, wherein the piezoelectric element is a surface acoustic wave resonator.   An electronic device comprising the frequency selective oscillator according to claim 1.

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