JP2004096449A - Oscillation circuit and electronic equipment using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an oscillation circuit, which is adaptive to clock frequencies over a wide range by varying a voltage within a fixed rangeand which has small jitters and is made small-sized and low-cost, comprising electronic equipment using the same. <P>SOLUTION: Provided are a SAW resonator which resonates at a specified resonance frequency, a voltage-controlled phase shifting circuit which outputs an output signal by shifting the phase of an input signal by a specified quantity with an external control voltage and is composed of a circuit element, an inductance element which adjusts a variation range of a specified phase shift quantity, and an amplifier which inputs the resonance frequency from the SAW resonator and amplifies and outputs it. A positive feedback oscillation loop is formed of the SAW resonator, voltage-controlled phase shifting circuit, inductance element, and amplifier and the SAW resonator is connected in series with the inductance element through the circuit element constituting the voltage-controlled phase shifting circuit. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an oscillation circuit and an electronic device using the same. The present invention relates to an electronic device using the same.
[0002]
[Prior art]
In a communication device such as a mobile phone, transmission and reception of communication data are performed based on a clock signal from an oscillator. Broadband communication networks have advanced, and the frequency band of clock signals required for the communication equipment has shifted to a high-frequency band exceeding 400 MHz, and data is transmitted and received at high speed in this high-frequency band. 2. Description of the Related Art In electronic devices typified by communication devices in recent years, the following points have been desired for a high-frequency oscillation circuit due to a demand for higher communication speed.
[0003]
That is, (1) stable oscillation in a high frequency band (high frequency stability), (2) stable oscillation in a practical temperature range of communication equipment (temperature compensation), (3) It is desired that the jitter of the clock signal output from the oscillation circuit is sufficiently small.
[0004]
FIG. 12 is a block diagram showing a configuration of a conventional high-frequency oscillation circuit using an AT-cut type crystal resonator. This high-frequency oscillation circuit 1C includes an oscillation unit 100 using an AT-cut type crystal oscillator vibrating at several tens of MHz, a multiplying unit 101 for generating this oscillation output as a high-frequency signal of several hundreds of MHz, and one input. It comprises a differential converter 102 that can extract a differential signal as an output signal from a signal. The oscillating unit 100 receives an external control voltage Vc and can vary the oscillating frequency within a certain range.
[0005]
[Problems to be solved by the invention]
As shown in FIG. 13, such a high-frequency oscillation circuit 1C is used as one component of a clock conversion circuit, that is, a voltage-controlled oscillation circuit (Voltage Controlled Crystal Oscillator) 113.
[0006]
The clock conversion circuit 110 employs a configuration applying a PLL circuit, and includes a phase comparison unit 111, a loop filter 112, a voltage control type oscillation circuit (VCXO) 113, frequency division circuits 114 and 115, and a buffer circuit 116. Used for clock frequency conversion and jitter reduction. This is an example in which the above-described high-frequency oscillation circuit 1C is used as the voltage-controlled oscillation circuit (VCXO) 113 and applied as one configuration of a PLL circuit.
[0007]
A clock signal F1 having jitter is externally divided by M by a frequency divider 114 and input to one input terminal of the phase comparator 111, and is generated by a voltage controlled oscillator (VCXO) 113 to the other input terminal. The divided clock signal F2 is frequency-divided by N by the frequency dividing circuit 115 and input, and phase comparison is performed. Then, the loop filter 112 generates a predetermined control voltage Vc according to the result of the phase comparison, and outputs the control voltage Vc to the voltage-controlled oscillation circuit (VCXO) 113. In the voltage-controlled oscillation circuit (VCXO) 113, a desired high-frequency clock signal F2 corresponding to a predetermined control voltage Vc is obtained.
[0008]
In the clock conversion circuit 110, in order to be able to synchronize with the clock signal F1 containing a lot of jitter inputted from the outside, in recent years, a wide specification range is required for a frequency variable range. I have. The specification must be satisfied especially by the voltage controlled oscillator (VCXO) 113. For example, consider a case where a low-speed network system is connected to a 10 gigabit optical network system. In this case, it is assumed that the frequency accuracy of the low-speed network system is initially within ± 20 ppm of the specification (specification), and thereafter, the frequency accuracy is reduced to about 50 ppm due to a loss or the like in the transmission path. In the US SONET (Synchronous Optical NETwork) system, even if the initial frequency accuracy is within ± 20 ppm, the frequency fluctuation of the deteriorated input signal is suppressed to within ± 20 ppm specified for the 50 ppm frequency fluctuation of the degraded input signal. Is required.
[0009]
Note that the precision used here is conceptually shown for the sake of explanation, and the precision actually used is expressed on the basis of jitter, so that it is often defined by time.
[0010]
When designing the frequency variable range of the voltage controlled oscillator (VCXO) 113, it is necessary to consider its own frequency deviation, frequency temperature characteristics, and aging. For example, in an optical network system to which the US SONET system is applied, if the respective fluctuation values of the frequency deviation, the frequency temperature characteristic, and the aging are added to the specification of ± 20 ppm, the frequency control can be performed at least within a range of ± 100 ppm. Required.
[0011]
In the case of the low-speed network system described above, the standard specifies a frequency accuracy wider than ± 20 ppm of the SONET system. Therefore, when connecting to this low-speed network system, a frequency variable range wider than ± 100 ppm is required.
[0012]
For the reasons described above, the voltage controlled oscillation circuit (VCXO) has a problem that frequency control must be performed over a wide range within a fixed control voltage variable range.
[0013]
Contrary to the general countermeasures against the above-mentioned problem, the power supply voltage supplied to the oscillation circuit has been reduced in response to the recent reduction in power consumption. Specifically, 3.3V is currently the mainstream, but there is a problem that the control voltage cannot be widened in the future because the movement to a lower power supply voltage (2.5V) is increasing in the future.
[0014]
The above-mentioned AT-cut type crystal resonator is easy to be coupled to the main vibration more closely when the temperature condition changes, when the sub-vibration other than the main vibration exists close to the main vibration. There are also unwanted spurs. Further, the frequency multiplier employs a method of multiplying the frequency based on the main vibration of the AT-cut crystal resonator, that is, a method of generating harmonics and obtaining only necessary harmonics as high-frequency signals. Unnecessary spurious due to the coupling of the main vibration and sub-vibration of the AT-cut crystal unit, and unnecessary spurious due to the vibration, and other than the high-frequency signal generated by the multiplication circuit based on the main vibration of the AT-cut crystal unit Unnecessary harmonics cause jitter and increase the jitter.
[0015]
Furthermore, the conventional high-frequency oscillation circuit is composed of an oscillation circuit, a multiplication circuit, and a differential conversion circuit, and requires a large number of components, so that it is large-sized, which is contrary to recent demands for ultra-small size and low cost. there were.
[0016]
The present invention has been made in order to solve the above-described problems, and has been widely applied to a clock signal having much jitter that has been deteriorated due to factors such as transmission line loss in a network within a certain control voltage range. It is an object of the present invention to obtain an oscillation circuit capable of performing crossover frequency control. At the same time, even when the range of control voltage cannot be widened due to the recent reduction in power supply voltage, the frequency control range can be easily maintained and expanded without adding a dedicated circuit for expanding the frequency variable range. An object of the present invention is to obtain an oscillation circuit that can be used. It is another object of the present invention to provide an oscillation circuit with reduced jitter and reduced size and cost without using an AT-cut type crystal resonator, a frequency multiplier, or a differential converter.
[0017]
Furthermore, the present invention provides an electronic device using an oscillation circuit capable of performing frequency control over a wide range within a certain control voltage range and having a small size and low cost with little jitter, for example, optical network communication. The purpose is to obtain equipment.
[0018]
[Means for Solving the Problems]
The oscillation circuit according to claim 1, wherein in the oscillation circuit, a SAW resonator that resonates at a predetermined resonance frequency and an output signal in which the phase of an input signal is shifted by a predetermined phase shift amount by an external control voltage. A voltage-controlled phase shift circuit composed of circuit elements, an inductance element that sets a variable range of the predetermined phase shift amount, and an amplifier that receives, amplifies, and outputs a resonance signal from the SAW resonator, The SAW resonator, the voltage controlled phase shift circuit, the inductance element, and the amplifier form a positive feedback oscillation loop, and the SAW resonator is connected to the SAW resonator via the circuit element forming the voltage controlled phase shift circuit. And connected in series with the inductance element.
[0019]
According to the above configuration, a positive feedback oscillation loop is formed by the SAW resonator, the voltage control phase shift circuit, the inductance element, and the amplifier, and the inductance element is connected to the inductance element through the circuit element that configures the voltage control phase shift circuit. SAW resonators are connected in series.
With such a connection, it is possible to prevent a series resonance circuit from being formed by the inductance element and the parallel capacitance when the SAW resonator is represented by an equivalent circuit. For this reason, the effect of the series resonance circuit is reduced, and there is an effect that the frequency can be easily controlled over a wide range within a predetermined control voltage variable range by increasing the value of the inductance element.
[0020]
In the oscillation circuit according to claim 2, in the configuration according to claim 1, the amplifier has an inverted output terminal and a non-inverted output terminal, and one of the inverted output terminal and the non-inverted output terminal is the positive output terminal. It is a differential amplifier that functions as an output terminal of a feedback oscillation loop.
[0021]
According to the above configuration, since the differential amplifier used here has an inverting output terminal and a non-inverting output terminal, any one of the output terminals can be selected to function as the output terminal of the positive feedback loop. It has the effect of being able to.
[0022]
According to a third aspect of the present invention, in the oscillator circuit according to the second aspect, the differential amplifier is a differential amplifier circuit using an ECL line receiver.
[0023]
Since a differential amplifier circuit using the ECL line receiver can operate at low power and operate at high speed, it is preferably used for a circuit that needs to operate at high speed, such as a high-frequency oscillator circuit. Further, it is preferable to use the ECL line receiver in a case where the resistance value of the external emitter terminating resistor of the ECL line receiver is changed and a load circuit that needs to be driven by the current value is connected.
[0024]
According to a fourth aspect of the present invention, in the oscillation circuit according to the first aspect, the circuit element is a passive element.
[0025]
It is preferable that the circuit element constituting the voltage control phase shift circuit is a passive element which does not take up a space for mounting and can be easily used alone as one electronic component.
[0026]
According to a fifth aspect of the invention, there is provided an electronic apparatus including the oscillation circuit according to any one of the first to fourth aspects.
[0027]
According to the above configuration, using the SAW resonator, there is no coupling or spurious of main vibration and sub-vibration, and no frequency multiplying circuit is required, so that an oscillation circuit free of jitter due to these is obtained. Then, in a clock conversion circuit to which this oscillation circuit which has no jitter and has a wide frequency variable range is applied, the clock signal is converted into a high-frequency clock signal with reduced jitter. Thereby, a timing margin between a plurality of transmission data and the clock signal is secured, and multiplexed data is transmitted and received, so that an effect of preventing a malfunction in an electronic device, for example, an optical transceiver module can be obtained.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
(1) First embodiment
(1-1) Configuration of First Embodiment
A. Oscillation circuit configuration
FIG. 1 is a block diagram showing the configuration of the oscillation circuit according to the first embodiment of the present invention.
[0029]
In FIG. 1, an oscillation circuit 1A includes an IC chip 2a containing an oscillation amplifier 10, output amplifiers 11a and 11b, and a feedback buffer amplifier 12, a SAW resonator X that resonates at a predetermined resonance frequency, and a positive feedback oscillation. It is composed of a voltage control phase shift circuit 13 for controlling the amount of phase shift in the loop, an extension coil Lv (inductance element), and an impedance circuit 14. A positive feedback oscillation loop is formed by at least the oscillation amplifier 10, the feedback buffer amplifier 12, the voltage control phase shift circuit 13, the SAW resonator X, and the extension coil Lv.
[0030]
In the oscillation circuit 1A, the SAW resonator X, the voltage control phase shift circuit 13,
The extension coils Lv are connected in series in this order. The reason for this configuration will be described in detail in (1-2) Principle of the First Embodiment.
[0031]
A resonance signal of a desired frequency f0 from the SAW resonator X is input to the oscillation amplifier 10 via the input terminal D of the IC chip 2a. Then, the input signal having the desired frequency f0 is amplified by the oscillation amplifier 10 and output to its output terminal.
[0032]
The output amplifier 11a is an output circuit for preventing the influence from a load circuit (not shown) connected via the output terminal OUT and shaping the waveform of the oscillation signal output from the output terminal of the oscillation amplifier 10. The output amplifier 11b can be used, for example, as an output circuit for outputting an output signal for a PLL feedback loop of an oscillation circuit 1A used for a clock conversion circuit described later.
[0033]
The feedback buffer amplifier 12 is a feedback amplifier circuit having a buffer function.
The voltage control phase shift circuit 13 performs phase adjustment for satisfying the phase condition of the oscillation circuit 1A. The voltage control phase shift circuit 13 controls the amount of phase shift according to the phase of the output signal SQ output from the feedback buffer amplifier 12 via the output terminal Q of the IC chip 2a.
[0034]
The impedance circuit (Zd) 14 is a passive circuit for supplying a predetermined voltage to the input terminal D of the oscillation amplifier 10.
[0035]
B. SAW resonator
The SAW resonator X has an interdigitated excitation electrode and a ladder-shaped reflector arranged on a piezoelectric substrate, and generates a standing wave by reflecting a surface wave excited by the excitation electrode with a reflector. It functions as. Since the SAW resonator X has vibration energy localized on the surface of the SAW resonator and is hardly coupled to sub-vibrations other than the main vibration, the resonance point of the SAW resonator X at a frequency other than a predetermined frequency is lower than that of the AT-cut crystal resonator. It has the great advantage of not being present. The resonance frequency of the SAW resonator is several hundred MHz to several GHz, and is used for a high-frequency oscillation circuit.
[0036]
C. Voltage control phase shift circuit and extension coil
FIG. 2 is a circuit diagram showing a configuration of the voltage control phase shift circuit 13.
[0037]
2, a voltage control phase shift circuit 13 includes a variable capacitance diode (circuit element: passive element) Cv having a cathode connected to a voltage control terminal Tv via an input resistor Rv, and an anode connected to a bias resistor R1. Is grounded through the ground. A DC cut capacitor (circuit element: passive element) C1 is connected between the cathode of the variable capacitance diode Cv and the SAW resonator X, and an elongation coil Lv is connected to its anode.
[0038]
In such a configuration, the phase of the voltage-controlled oscillation circuit 1A using the SAW resonator is controlled by changing the capacitance value of the variable capacitance diode Cv according to the magnitude of the control voltage Vc. When the phase is changed by changing the capacitance value of the variable capacitance diode Cv by the control voltage Vc, the phase of the SAW resonator also changes due to the oscillation condition of the oscillation circuit, and as a result, the resonance frequency changes. That is, the oscillation frequency of the oscillation circuit 1A changes.
[0039]
The extension coil Lv is an inductance element for setting a variable range of a predetermined phase shift amount for shifting the phase of the resonance signal of the SAW resonator by the voltage control phase shift circuit 13, that is, a variable range of the frequency. The variable range of the frequency can be widened by increasing the value of the extension coil Lv.
[0040]
Note that the voltage control phase shift circuit 13 is not limited to the above-described circuit configuration, and can adopt various configurations.
[0041]
(1-2) Principle of the first embodiment
Next, the principle of the first embodiment will be described with reference to FIGS.
[0042]
The principle of the first embodiment is that the SAW resonator X and the extension coil Lv are connected in series via the voltage control phase circuit 13 in the positive feedback oscillation loop formed by the oscillation circuit 1A shown in FIG. That is the point. That is, it is based on the finding that the oscillation circuit 1A employing such a configuration secures a constant frequency variable range even in a narrow control voltage variable range.
[0043]
A. Frequency variable range by SAW resonator, extension coil and voltage control phase circuit
Before describing the above findings, a description will be given of the SAW resonator X, the extension coil Lv, the voltage control phase circuit 13, and the frequency variable range when connected in this order with reference to FIGS.
[0044]
FIG. 3 is an equivalent circuit diagram when the SAW resonator X, the extension coil Lv, and the variable capacitance diode Cv forming the voltage control phase circuit 13 are connected in series. 3, an equivalent circuit of the SAW resonator X, the extension coil Lv, and the variable capacitance diode Cv are shown from the left side. The equivalent circuit of the SAW resonator X is composed of a parallel circuit combining two series circuits, one of which is composed of a series resistor R, a series capacitance C and a series inductance L connected in series. The other is that since the SAW resonator X is placed between the two electrodes, the parallel capacitance (mainly the capacitance between the electrodes) C0 connected in parallel with the element, which is unrelated to vibration, is there.
[0045]
FIG. 4 is a diagram showing the equivalent circuit of the SAW resonator X shown in FIG. 3, and the reactance characteristics of the circuit when the extension coil Lv and the variable capacitance diode Cv are connected in series.
[0046]
Although not shown, the capacitance value of the variable capacitance diode Cv shown in FIG. 3 is varied by a control voltage Vc from outside.
[0047]
First, the variable range of the frequency when the extension coil Lv is not connected will be described. As shown in FIG. 4, there is a series resonance frequency fs due to the variable capacitance diode Cv, the series capacitance C, and the series inductance L. At a frequency higher than the series resonance frequency fs, the characteristic shows inductive. On the other hand, since the parallel capacitance C0 exists, there is a parallel resonance frequency fp due to the parallel capacitance C0 and the series inductance L. At a frequency higher than the parallel resonance frequency fp, the characteristic shows capacitive.
[0048]
In the case of an oscillation circuit without the extension coil Lv, the operating point is determined in the range (a) between the series resonance frequency fs and the parallel resonance frequency fp shown in FIG. That is, the variable capacitance diode Cv changes the reactance (inductivity) in the range shown in FIG. 4B by varying the control voltage Vc from the outside, and the range shown in FIG. It becomes.
[0049]
Next, as shown in FIG. 3, when the extension coil Lv is further connected in series to a series circuit of the SAW resonator X and the variable capacitance diode Cv, as shown in FIG. 4, a frequency region lower than the series resonance frequency fs ( The operating point moves to d). That is, the variable capacitance diode Cv changes the reactance (capacitance) shown in FIG. 4E by changing the control voltage Vc from the outside, and the range shown in FIG. Become. In this case, the control range of the control voltage Vc from the outside is the same range as when there is no extension coil Lv. The frequency variable range (f) can be further increased by increasing the value of the extension coil Lv connected in series.
[0050]
By the way, when the voltage controlled phase shift circuit 13 composed of the SAW resonator X, the extension coil Lv, and the variable capacitance diode Cv is connected in series in this order, as shown in FIG. It can be seen that a series resonance circuit is formed.
[0051]
B. Influence of series resonance circuit by extension coil and parallel capacitance
Next, the effect of the series resonance circuit formed by the extension coil Lv and the parallel capacitance C0 will be described with reference to FIG.
[0052]
FIG. 5 shows resonance characteristics of a series resonance circuit formed by an equivalent circuit of the SAW resonator X excluding the extension coil Lv and the electrode capacitance C0, and a series resonance circuit formed by the extension coil Lv and the electrode capacitance C0. FIG.
[0053]
In FIG. 5, the characteristic indicated by (a) is a resonance characteristic of a series resonance circuit formed by an equivalent circuit of the SAW resonator X excluding the extension coil Lv and the electrode capacitance C0. The characteristic shown in FIG. 5B is a resonance characteristic of a series resonance circuit formed by the extension coil Lv and the electrode capacitance C0.
[0054]
The first condition for obtaining a variable range of the resonance frequency in the oscillation circuit 1A is to lower the Q of the oscillation circuit, that is, to increase the value of the extension coil Lv. The second condition is that the resonance frequency fs0 of the series resonance circuit composed of the series inductance L and the series capacitance C, and the characteristic shown in FIG. 5A is composed of the extension coil Lv and the parallel capacitance C0. The resonance frequency fs1 of the series resonance circuit is different from the characteristic shown in FIG.
[0055]
In a circuit configuration in which the SAW resonator X, the extension coil Lv, and the variable capacitance diode Cv are connected in series in this order, the SAW resonator X and the extension coil Lv form a series resonance circuit. In this case, to secure a variable range of the resonance frequency over a wide range, it is necessary to increase the inductance of the extension coil Lv and decrease Q as described above. However, when the inductance of the extension coil Lv is increased, the difference between the two resonance frequencies fs0 and fs1 is reduced as shown by the arrow in FIG. 5, and the two resonances are overlapped with each other, so that abnormal oscillation is likely to occur. Therefore, it is not easy to increase the inductance of the extension coil Lv.
[0056]
Therefore, it is necessary to reduce the influence of the series resonance circuit formed by the extension coil Lv and the parallel capacitance C0. The configuration is as shown in FIG.
[0057]
C. Effect of moving the extension coil away from the SAW resonator
Next, by employing a configuration in which the SAW resonator X shown in FIG. 2 is connected in series with the extension coil Lv via the voltage control phase shift circuit 13, the SAW resonator X is formed by the extension coil Lv and the parallel capacitance C0. The effect of reducing the influence of the resonance circuit will be described.
[0058]
FIG. 6 is a diagram illustrating resonance characteristics when a configuration in which the SAW resonator X and the extension coil Lv are connected in series via the voltage control phase shift circuit 13 is employed.
[0059]
According to FIG. 6, the resonance frequency fs1 moves as shown by the arrow in the figure with respect to the resonance frequency fs0 of the series resonance circuit formed by the equivalent circuit of the SAW resonator X excluding the extension coil Lv and the electrode capacitance C0. . That is, it can be seen that the resonance frequency fs1 of the series resonance circuit formed by the extension coil Lv and the electrode capacitance C0 moves to the resonance frequency fs2, and the difference between the resonance frequencies fs0 and fs2 increases.
[0060]
A characteristic (a) shown in FIG. 7 shows a frequency characteristic obtained when the SAW resonator X and the extension coil Lv are directly connected in a variable control voltage range. The characteristic (b) shown in FIG. 7 is a frequency characteristic obtained when the SAW resonator X and the extension coil Lv are connected via the voltage control phase shift circuit 13.
[0061]
According to FIG. 7, in the case of the characteristic (a), the frequency variable range is ± 50 ppm around the resonance frequency at the intersection (c) with the characteristic (b), for example, 310 MHz. On the other hand, within the same variable control voltage range, the frequency range in the case where the SAW resonator X and the extension coil Lv are connected via the voltage-controlled phase shift circuit 13 in the characteristic (b) of FIG. Is approximately 150 ppm. As a result, it is understood that the range is expanded by 50 ppm or more.
[0062]
(1-3) Effects obtained from the first embodiment
Next, effects obtained from the first embodiment of the present invention will be described.
[0063]
As described above, by connecting the SAW resonator and the extension coil via the voltage control phase shift circuit, the influence of the series resonance circuit formed by the extension coil Lv and the parallel capacitance C0 can be reduced, so that the extension is easily performed. The effect of increasing the value of the coil and expanding the frequency variable range is obtained.
[0064]
Similarly, even if the control voltage variable range is reduced due to the recent decrease in the power supply voltage, the frequency variable range can be easily maintained and expanded without adding a dedicated circuit for expanding the frequency variable range. The effect that it can be obtained can be obtained.
[0065]
Although the first embodiment according to the present invention has been described in the example in which the feedback buffer amplifier 12 is connected to the output section of the oscillation amplifier 10, even if the feedback buffer amplifier 12 is omitted, the above-described configuration is applied. The same effect as described above can be obtained.
[0066]
When the feedback buffer amplifier 12 is omitted (however, when the oscillation circuit 1A is entirely composed of discrete components), the number of components can be reduced, but this affects the output side of the positive feedback oscillation loop. On the other hand, when the feedback buffer amplifier 12 is provided, the number of components is not reduced, but the influence on the output side of the positive feedback oscillation loop can be reduced.
[0067]
In addition, by using the SAW resonator X that resonates at a high frequency of several hundred MHz or more and has no sub-vibration, an effect that a conventional multiplying circuit can be omitted can be obtained.
[0068]
Further, the SAW resonator X has no coupling between the main vibration and the sub-vibration of the AT-cut type crystal resonator and no unnecessary spurious as described in "Problems to be Solved by the Invention". Since no circuit is required, unnecessary harmonics are not generated. As a result, it is possible to obtain an effect that an oscillation circuit having no jitter generated due to coupling of the main vibration and the sub-vibration and unnecessary spurious and harmonics can be obtained.
[0069]
Further, as described above, it is possible to eliminate the need for the conventional frequency multiplier circuit and to obtain an oscillator circuit that is reduced in size and cost without adding a dedicated circuit for extending the frequency variable range. The effect that can be obtained is obtained.
[0070]
(2) Second embodiment
(2-1) Configuration of Second Embodiment
FIG. 8 is a block diagram showing the configuration of the oscillation circuit according to the second embodiment of the present invention. Note that the same blocks as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0071]
The oscillation circuit 1B includes an IC chip 2b having a built-in oscillation differential amplifier 21, an output differential amplifier 22, and a feedback buffer differential amplifier 23, a SAW resonator X having a predetermined resonance frequency, and an external circuit. The control circuit includes a voltage control phase shift circuit 13 for adjusting the phase shift amount to a predetermined amount based on the control voltage Vc, an extension coil Lv, and an impedance circuit (Zd) 14. Further, the reference bias voltage VBB output from the IC chip 2b is supplied to the inverting input terminal D2 of the oscillation differential amplifier 21 from outside. A positive feedback oscillation loop is formed by at least the oscillation differential amplifier 21, the feedback buffer differential amplifier 23, the SAW resonator X, the voltage control phase shift circuit 13, and the extension coil Lv. It is to be noted that the SAW resonator X and the extension coil Lv are connected in series via the voltage control phase shift circuit 13 as in the first embodiment.
[0072]
The above-mentioned three differential amplifiers 21 to 23 are differential amplifier circuits using an ECL line receiver (Emitter-Coupled Logic) shown in FIG.
[0073]
In the oscillation differential amplifier 21, a signal having a predetermined resonance frequency f0 passing through the SAW resonator X is input to the non-inverting input terminal D1 of the oscillation differential amplifier 21. Then, an output signal having a mutual phase difference of 180 degrees is output from the non-inverted output terminal Q + and the inverted output terminal Q-.
[0074]
The output differential amplifier 22 shapes the waveform of the output signal from the oscillation differential amplifier 21 and outputs it as a clock signal F having a predetermined oscillation frequency, for example, 622.08 MHz.
[0075]
The feedback buffer differential amplifier 23 is a differential amplifier having a buffer function, and its output is output to output terminals Q1 and Q2. An emitter termination resistor (not shown) is connected to each output terminal Q1 and Q2 of the feedback buffer differential amplifier 23 using the ECL line receiver for external connection of the IC chip 2b.
[0076]
FIG. 9 shows a state in which the emitter terminating resistors R7 and R8 are connected to the respective output terminals of OUT− and OUT +.
[0077]
The voltage-controlled phase shift circuit 13 converts one of the output signals SQ1 and SQ2 from the feedback buffer differential amplifier 23 into a predetermined phase amount in order to satisfy the phase condition of the oscillation circuit 1B based on the external control voltage Vc. Adjust to
[0078]
By using the voltage control type phase shift circuit 13, the same circuit pattern can be used for a plurality of SAW resonators X having different predetermined resonance frequencies, and the design can be simplified.
[0079]
The impedance circuit (Zd) 14 is connected between the non-inverted and inverted input terminals of the oscillation differential amplifier 21 so that a potential difference occurs between the inverted and non-inverted input terminals of the oscillation differential amplifier 21. .
[0080]
(2-2) Principle of the second embodiment
Since the principle of the second embodiment is the same as that of the first embodiment, a detailed description thereof will be omitted. When a feedback buffer differential amplifier 23 is used instead of the feedback buffer amplifier 12 as shown in FIG. 1, the SAW resonance is applied to either the non-inverted output terminal Q1 or the inverted output terminal Q2 of the differential amplifier 23. The slave X, the voltage control phase shift circuit 13, and the extension coil Lv are connected in this order. In this embodiment, it is connected to the inverted output terminal Q2. The other non-inverting output terminal Q1 can be used as an output terminal of an output signal for a PLL feedback loop of the oscillation circuit 1B used in a clock conversion circuit described later.
[0081]
(2-3) Effects obtained from the second embodiment
As described above, according to the second embodiment, the same effects as those of the first embodiment can be obtained, and the following effects can be obtained.
[0082]
Since the above-mentioned amplifier is a differential amplifier circuit using an ECL line receiver, it is possible to configure an oscillation circuit that needs to operate at high speed with low power consumption, and to use a level conversion circuit in this differential amplifier circuit. The effect that it can be easily constructed is obtained.
[0083]
(3) Third embodiment
Next, a third embodiment of the present invention will be described.
[0084]
FIG. 10 is a diagram showing a schematic configuration of an optical transceiver module 90 for a 10.3125 Gigabit optical network using the clock conversion circuit 93 to which the oscillation circuit 1A according to the first embodiment described above is applied. .
[0085]
The optical transceiver module 90 realizes an interface function for optical / electrical conversion and electric / optical conversion, and multiplexing and demultiplexing, for example, between a server computer and an optical network.
[0086]
As shown in FIG. 10, for example, the low frequency clock signal RLCK having a large amount of jitter extracted by the demultiplexing unit 94 is selected by the selection unit 96 by an external control signal CONT. The selected low-frequency clock signal RLCK having a large amount of jitter is converted into a high-frequency clock signal RHCK with reduced jitter in a clock conversion circuit 93 to which the voltage-controlled SAW oscillation circuit (VCSO) 93-1 of the present invention is applied. Is done. The clock signal RHCK is used as a reference clock signal for multiplexing the N pieces of transmission data TxDATA as one piece of transmission data in the multiplexing unit MUX91.
[0087]
Here, the operation of the optical transceiver module 90 will be described with reference to FIG.
[0088]
The clock conversion circuit 93 to which the voltage control type SAW oscillation circuit (VCSO) 93-1 having a wide variable range according to the present invention is applied converts the low frequency external clock signal (TxREF) selected by the selection unit 96 into a high frequency clock. Convert to a signal. For example, the selection unit 96 selects an external clock signal (TxREF) having a low frequency of 64 KHz to 155.52 MHz and supplies it to the clock conversion circuit 93. The clock conversion circuit 93 converts the clock signal into a high frequency clock signal of 622.08 MHz in the 600 MHz band and supplies the clock signal to the multiplexing unit 91. As a result, the optical signal in the 10 GHz band (OC-192) is sent out to the optical transmission line in the electrical / optical converter 92.
[0089]
Further, the demultiplexing unit 94 extracts a high-frequency clock signal from the data of the optical signal (OPIN) received by the optical / electrical conversion unit 95 by a CDR (Clock and Data Recovery) function. When the selection unit 96 selects the clock signal (RCLK), a high-frequency clock signal with little jitter is supplied from the clock conversion circuit 93 to the multiplexing unit 91.
[0090]
That is, the clock conversion circuit 93 to which the voltage control type SAW oscillation circuit (VCSO) 93-1 having a wide variable range according to the present invention is applied is used for the optical transceiver module 90 to input a clock signal containing much jitter. Also, the clock conversion circuit 93 can generate a high-frequency clock signal with very little jitter and supply it to the multiplexing unit 91. As a result, a timing margin between the transmission data (TxDATA × N) to be multiplexed in the multiplexing section 91 and the clock signal is secured, so that malfunction of the transmission data of the multiplexing section 91 can be prevented. Is obtained.
[0091]
Further, in a high-speed network system represented by 10 gigabits capable of transmitting a large amount of data such as a moving image, a stable operation can be easily secured.
[0092]
In the third embodiment, the example using the oscillation circuit 1A according to the above-described first embodiment has been described. However, regardless of this, the same applies to the case where the oscillation circuit 1B according to the second embodiment is used. The effect of can be obtained.
[0093]
(4) Modified example
The present invention is not limited to the embodiments described above, and can be implemented in various modes. For example, the following modified embodiments are possible.
[0094]
(First Modification)
In the above, the configuration in which the SAW resonator X and the extension coil Lv are connected via the voltage control phase shift circuit 13 has been described. However, the same effect as described above can be obtained with the configuration shown in FIG.
[0095]
11 is that the extension coil Lv is arranged in the voltage control phase shift circuit 13, and the SAW resonator X and the extension coil Lv are connected via the passive components (elements) constituting the voltage control phase shift circuit 13. This is to prevent the connection from forming a series resonance circuit.
[0096]
For example, FIG. 11A shows a configuration in which the SAW resonator X and the extension coil Lv are connected via the DC cut capacitor C1. FIG. 11B shows a configuration in which the SAW resonator X and the extension coil Lv are connected via the variable capacitance diode Cv. FIG. 11 (3) shows a configuration in which the DC cut capacitor C1 is divided into two, that is, the SAW resonator X and the extension coil Lv are connected via the capacitor C12 among the capacitors C11 and C12. Since the capacitances of C11 and C12 of the capacitor shown in FIG. 11 (3) are divided, each capacitance needs to be twice as large as the original capacitor C1.
[0097]
(Second Modification)
Although the amplifier according to the above-described embodiment has been described by way of the example in which the transistor is configured using the bipolar transistor, the amplifier may be configured with a MOS transistor having a different transistor type.
[0098]
(Third Modification)
Also, the case where the oscillation circuit is used for an optical interface module for a network has been described, but the invention can be applied to various electronic devices such as a wireless communication device such as a mobile phone that requires an oscillation circuit, particularly a high-frequency oscillation circuit.
[0099]
(Fourth modification)
As for the piezoelectric material constituting the piezoelectric vibrator such as a quartz oscillator, a ceramic oscillator, or a SAW resonator, a configuration using langasite or lithium tetraborate as another piezoelectric material in addition to quartz crystal may be used.
[0100]
【The invention's effect】
As described above, by connecting the SAW resonator and the extension coil via the voltage control phase shift circuit, the influence of the series resonance circuit formed by the extension coil and the parallel capacitance can be reduced, so that the extension coil can be easily connected. There is an effect that the frequency variable range can be expanded by increasing the value. Similarly, even if the control voltage variable range is reduced due to the recent decrease in the power supply voltage, the frequency variable range can be easily maintained and expanded without adding a dedicated circuit for expanding the frequency variable range. effective.
[0101]
In addition, since a configuration that does not require a frequency multiplier circuit can be adopted by using the SAW resonator X, an oscillation circuit that does not require a dedicated circuit for extending the frequency variable range and that is reduced in size and cost with less jitter is provided. Is obtained.
[0102]
Further, the received clock signal with much jitter is converted into a high-frequency clock signal with reduced jitter by a clock conversion circuit to which the oscillation circuit having a wide frequency variable range according to the present invention is applied. Accordingly, a timing margin between a plurality of transmission data and the clock signal is secured, and multiplexed data is transmitted and received. This has an effect of preventing a malfunction in an electronic device, for example, an optical transceiver module.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an oscillation circuit according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram showing a configuration of a voltage control phase shift circuit.
FIG. 3 is a circuit diagram in a case where an equivalent circuit of a SAW resonator, an extension coil, and a variable capacitance diode constituting a voltage control phase circuit are connected in series.
4 is a diagram showing a reactance characteristic of a circuit when an equivalent circuit of the SAW resonator shown in FIG. 3, an extension coil, and a variable capacitance diode are connected in series.
FIG. 5 is a diagram showing resonance characteristics of a series resonance circuit formed by an equivalent circuit of the SAW resonator excluding the extension coil and the electrode capacitance, and a series resonance circuit formed by the extension coil and the electrode capacitance.
FIG. 6 is a diagram illustrating resonance characteristics of a series resonance circuit in a case where a configuration in which an extension coil and a SAW resonator are connected in series via a voltage-controlled phase shift circuit is employed.
FIG. 7 is a graph showing a control voltage-frequency characteristic of the oscillation circuit according to the first embodiment.
FIG. 8 is a block diagram illustrating a configuration of an oscillation circuit according to a second embodiment of the present invention.
FIG. 9 is a circuit diagram showing a circuit configuration of an ECL line receiver.
FIG. 10 is a diagram illustrating a schematic configuration of an optical transceiver module for an optical network of 10.3125 Gigabits using a clock conversion circuit to which the oscillation circuit according to the first or second embodiment is applied;
FIG. 11 is a circuit diagram showing a configuration of a modified example of the SAW resonator, the voltage control phase shift circuit, and the extension coil in the first embodiment.
FIG. 12 is a block diagram showing a configuration of a conventional high-frequency oscillation circuit using an AT-cut type crystal resonator.
FIG. 13 is a block diagram illustrating a configuration of a clock conversion circuit when a conventional high-frequency oscillation circuit is used as a component of the clock conversion circuit.
[Explanation of symbols]
1A, 1B ... voltage control type SAW oscillation circuit
2a ... IC chip
10 ... Amplifier for oscillation
11a, 11b ... output amplifier
12 ... Amplifier for feedback buffer
2b ... IC chip
21 ・ ・ ・ Oscillation differential amplifier
22 ... Output differential amplifier
23 ... Differential amplifier for feedback buffer
13 ... Voltage control phase shift circuit
Cv: Variable capacitance diode
C1, C11, C12 ... DC cut capacitor
Rv, R1 ... resistance
Lv: Extension coil
14 ... Impedance circuit
X: SAW resonator
R: Series resistance
C: Series capacity
L: Series inductance
C0: Parallel capacity
90 ・ ・ ・ Optical transceiver module for optical network
91: Multiplexer
92 ··· Electric / optical conversion unit
93 clock conversion circuit
94 ··· Demultiplexing unit
95 ・ ・ ・ Optical / electrical converter
96 ・ ・ ・ Selector

Claims (5)

In the oscillation circuit,
A SAW resonator that resonates at a predetermined resonance frequency;
A voltage control phase shift circuit comprising circuit elements, which outputs an output signal in which the phase of the input signal is shifted by a predetermined phase shift amount by an external control voltage,
An inductance element for setting a variable range of the predetermined phase shift amount;
An amplifier for receiving, amplifying and outputting a resonance signal from the SAW resonator,
A positive feedback oscillation loop is formed by the SAW resonator, the voltage control phase shift circuit, the inductance element, and the amplifier;
The oscillation circuit, wherein the SAW resonator is connected in series with the inductance element via the circuit element constituting the voltage control phase shift circuit. The amplifier is
10. A differential amplifier having an inverting output terminal and a non-inverting output terminal, wherein one of the inverting output terminal and the non-inverting output terminal is a differential amplifier functioning as an output terminal of the positive feedback oscillation loop. Item 2. The oscillation circuit according to item 1. The differential amplifier,
3. The oscillation circuit according to claim 2, wherein the oscillation circuit is a differential amplifier circuit using an ECL line receiver. The circuit element includes:
The oscillation circuit according to claim 1, wherein the oscillation circuit is a passive element. An electronic apparatus comprising the oscillation circuit according to claim 1.

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