JPS59193607A - Reference signal oscillator - Google Patents

Abstract

PURPOSE:To attain minute adjustment of an oscillating frequency by connecting in time division an impedance element adjustable via an electronic switch controlled by a pulse train having a prescribed impulse coefficient to a resonance circuit. CONSTITUTION:The impedance element 5 whose impedance value is adjusted optionally is provided to a part of an electric resonance circuit including a crystal oscillator 2. Then, the element 5 is connected in time division to a resonance circuit via an electronic switch circuit 6 controlled by the pulse train having the prescribed impulsive coefficient. As a result, the effective impedance value of the element 5 becomes a value multiplying a specific reducing factor to the impedance value of the element 5, and the minute adjustment is attained without decreasing the element 5 especially, allowing to attain minute adjustment of a frequency continuously.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reference signal oscillator whose frequency can be finely adjusted.

Reference signal oscillators are used as basic clock sources in watches, communication equipment, computers, and the like. As a reference signal oscillator, an LC oscillator is insufficient in terms of stability, and a crystal oscillator is usually used. A reference signal oscillator is required to have not only long-term frequency stability but also absolute accuracy. For example, in short-range communication, 800 MHz to 90
For a fixed frequency within 0M1-1z, 32768 on a wristwatch
Tune to the frequency of Hz (2151-Iz). Therefore, the oscillation frequency is adjusted by selecting a crystal resonator, giving it an inductance characteristic with extremely low loss near a specific frequency, and resonating with the external capacitance. FIG. 1 shows a typical circuit of a crystal oscillator. Here, 1 is an amplification element, 2 is a crystal oscillator, C is a fixed capacitor, C2 is a capacitor for coarse frequency adjustment, and C3 is a capacitor for fine frequency adjustment. C3 is a trimmer capacitor used for final frequency adjustment. However, adjustment using a trimmer capacitor is difficult when frequency accuracy requirements are strict.

In particular, changes in stray capacitance around the frequency adjustment circuit and instability of the adjustment circuit itself are problematic. FIG. 2 is a diagram showing the change in capacitance C with respect to the angle θ of the rotation axis of the trimmer capacitor. Although A is a designed adjustment curve, in reality it changes irregularly between the curves B1 and B2 due to backlash between the electrodes, nonuniform dielectric constant, or moisture adsorption.

This error range ΔC is quite large within the range of change of the angle θ.

In particular, in the case of a capacitor in which the change in capacitance C with respect to the angle θ is small in design in order to finely adjust the frequency, the error rate becomes significantly large. The A curve is expressed by the following formula.

C-co ten to θ (1) ko\de k
is the slope of the A curve, and co is the residual capacity.

Since k is set small for fine adjustment, the maximum rotation angle θma
The design maximum capacitance change ΔCd- with respect to x is θ. 1aX
and the error range ΔC are approximately the same size. Therefore, it is difficult to manually adjust the frequency by changing the rotation angle.
It is also complicated.

This difficulty in adjustment can be avoided by not using a trimmer capacitor but by connecting fixed capacitors in a time-division manner by turning transmission gates on and off.

That is, by minutely changing the on-off impact coefficient, the effective capacity can be finely adjusted.

However, in this method, the frequency of the oscillator is divided and the output signals of each stage of the frequency dividing circuit are combined using a logic gate and applied to the transmission gate, so the frequency can only be adjusted within the combined range.

Moreover, the combinational circuit becomes complicated.

Next, from the point of view of vehicle power consumption, the residual capacity C8 of the trimmer capacitor is
There is a desire to make the size as small as possible. In order to lower the power of the crystal oscillator, the current of the amplifier element 1 must be lowered and its impedance increased.In order to increase the impedance of the reactance element accordingly, a capacitor is connected externally to the crystal oscillator. It becomes necessary to reduce the capacitance value. The above requirement is difficult to meet because the trimmer capacitor has a mechanically rotating part, so the residual capacitance C6 does not become small.

Since wristwatches are required to extremely reduce power consumption, the residual capacity C6 must be reduced in some way.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks, to provide a reference signal oscillator that allows fine frequency adjustment and has low power loss.

The reference signal oscillator according to the present invention includes an impedance element whose impedance value can be arbitrarily adjusted as part of an electric resonant circuit including a crystal resonator, and an electronic switch controlled by a pulse train having a constant impulse coefficient. The present invention is characterized in that the impedance element is connected to the resonant circuit in a time-division manner via a circuit.

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 3 is a circuit diagram of one embodiment of the present invention.

1 is an amplification element, 2 is a crystal oscillator, 3 to 5 are capacitors,
6 is a field effect transistor used as an electronic switch circuit element. Capacitor 4 is a capacitor for coarse frequency adjustment, and capacitor 5 is a trimmer capacitor for fine frequency adjustment.

This trimmer capacitor 5 is connected to the field effect transistor 6'
When the f-ton voltage is applied, it is directly connected to one end of the crystal oscillator 2, and when the voltage is No or 11, it is not connected.The signal applied to the gate of the field effect transistor 6 is a constant alternating current. The pulse train CLK has an impact coefficient of are connected in parallel. This R has a high resistance and does not affect the capacitance change due to the pulse train CLK seen from one end of the crystal resonator 2."As described in 2, in this embodiment, the electric field The effect transistor 6 and Rp form an electronic switch circuit SW.

Since the capacitance of the trimmer capacitor 5 is connected to the crystal oscillator 2 in a time-sharing manner by the electronic switch circuit SW, the effective capacitance value is equal to 50 rotations of the trimmer capacitor 11al.
+Angle θ multiplied by a specific reduction coefficient. This reduction coefficient is determined by the impact coefficient of the pulse train CLK. For example, if the impact coefficient is small and is 0.05, the value becomes 0.05. In the characteristics of the rotating shaft angle θ versus the capacitance C shown in FIG. 2, the residual capacitance C6 and the variation ΔC are reduced, and the slope is also reduced. Therefore, in order to perform fine adjustment, there is no need to specially reduce k in the above-mentioned relational expression (1), and there is no need to forcefully reduce co. FIG. 4 shows the improvement effect achieved by the present invention. Here, the m curve is the conventional example, and k = J71 was made small for the purpose of fine adjustment, but the error range Δc due to variation
As mentioned above, adjustment is extremely difficult due to m. 1 curve is the characteristic of the capacitor used in the embodiment of the present invention, k
= k A should be larger than km. It is assumed that the error range ΔC and the residual capacity C8 are the same. The n curve is an effective capacitance characteristic when operated in a time-division manner according to the present invention. The residual volume ff1co decreases to CO2, and k decreases to 11, which is about the same as km. The error range ΔCn is ΔC,
, 20m. As a result, the design maximum capacitance change ΔC,1=k. θmax crab 41-.

The fine adjustment is about the same as θmax, but the error range ΔC1
can be made much smaller than 20m and can be adjusted reliably.゛Also, the maximum capacity change ratio to the residual capacity is θmax/
Co', which can be larger than kmθmax/Co of the conventional example.

As mentioned above, the frequency adjustment is large (1), and fine adjustment is possible using a trimmer capacitor with high mechanical reliability.Also, the residual capacitance is effectively reduced, which reduces the power loss of the crystal oscillator. Therefore, the oscillation output does not decrease even if the current is decreased.

In the above embodiment, the field effect transistor 6 is used as the electronic switch circuit element, but if a transmission gate is used, the amplitude range of the signal to be handled is expanded and the degree of freedom of the DC level is also expanded. Other diode switches and semiconductor variable capacitance diode switches can also be used. 1. In the above embodiment, the trimmer capacitor 5 is used as the impedance element, but a semiconductor variable diode or a variable resistance element may be used. 5(a) shows the case where the above-mentioned trimmer capacitor 5 is used, FIG. 5(1)) shows the case where a 1' conductor variable capacitance diode C type is used, and FIG. 5(C) shows the case where the variable resistance element R type is used.

(1)) In (C), capacitor C12 and variable impedance element C31 are connected in parallel to capacitor C1.
A series circuit with 3 is connected. electronic switch circuit S
When W is controlled by pulse train CLK (b) (C)
Because the capacitive impedance of the circuit changes (a)
can give a similar effect. This is ■. N
T is a bias voltage that changes the capacitance value of the semiconductor variable capacitance diode C13. (b) The circuit of (C), especially (C
) has a resistance component, which lowers the Q value at resonance, but there are other advantages that will be described later.

Note that in the circuit of (C), C12 may be short-circuited and m variable resistance elements may be used.

As explained above, the reference signal oscillator according to the present invention solves the difficulty of adjustment by using a trimmer capacitor with small capacitance change for fine frequency adjustment, and uses a trimmer capacitor with high mechanical reliability and large capacitance change. Using this method, we were able to continuously and reliably fine-tune the frequency. Furthermore, since the residual capacity is reduced, it is possible to reduce the power loss of the crystal oscillator. By using a semiconductor variable diode or a variable resistance element as an impedance element, if a slight reduction in Q value during resonance is allowed, an oscillator that is not affected by humidity and dust and stable against mechanical shock can be obtained. be able to. In the present invention, the pulse train that controls the electronic switch circuit only needs to have a constant spitting coefficient, so it is extremely easy to form this pulse train from the frequency dividing circuit of the crystal oscillator to the gate circuit compared to the conventional example. It is.

In the crystal oscillator according to the present invention, there is an incidental phenomenon in which the oscillation frequency varies minutely in response to the on/off of the electronic switch circuit within a time period shorter than the repetition period of the pulse train of time division control. This is a general phenomenon that occurs when time-division control is used, but it poses no problem for purposes that require stability of the average frequency averaged over a long period of time, such as in a reference signal oscillator for a watch. However, if it is intended as a reference signal oscillator for communication, it cannot be used as is because it is frequency modulated by a control pulse train. For the latter purpose, the output of the time-sharing controlled crystal oscillator of the present invention is frequency-divided until its period is an integer multiple of the period of the pulse train controlling the electronic switch circuit, and the divided output is used to generate a voltage-controlled oscillator. The configuration may be such that the voltage controlled oscillator performs phase lock control and outputs a signal from the voltage controlled oscillator.

This will be explained below with reference to FIG. 602 in Figure 6
is the aforementioned crystal oscillator with time division control according to the present invention, 604
is a frequency divider, 606 is a phase comparator, 608 is a low-pass P wave filter,
610 is a voltage controlled oscillator, 614 is a gate circuit that synthesizes a pulse train (hereinafter referred to as a control pulse train) for controlling the electronic switch circuit of the crystal oscillator 602 from the signal of the frequency divider 6Q4, and 612 is a variable capacitance diode. 6th
In the figure, the output signal of the crystal oscillator 602 is frequency-divided until its period is an integral multiple of the period of the control pulse train.
4 is applied to the phase comparator 606.

Further, an output signal from a voltage controlled oscillator 610 is applied to this phase comparator 606 . In the figure, this output signal is obtained by dividing the output of the crystal oscillator by a frequency divider, but depending on the frequency, the frequency may not be divided. Voltage controlled oscillator 610
A semiconductor variable capacitor u, i diode 612 is connected to the resonant circuit of a crystal oscillator, and the frequency is changed by a bias voltage applied thereto. A phase difference signal between the two input signals is obtained from the phase comparator 606. This phase difference signal passes through the low-pass p-wave generator 608 and applies a DC voltage to the semiconductor variable capacitance diode 612 to finely adjust the oscillation frequency of the voltage controlled oscillator 610. Since the crystal oscillator 602 is time-divisionally controlled, the frequency varies minutely within the repetition period of the control pulse, but the output signal is frequency-divided and the average frequency is divided by the time that is an integer multiple of the repetition period. This signal is used as a frequency signal to control the oscillation frequency of the voltage controlled oscillator 610 in a phase lock manner.

As explained above, the frequency fluctuation within the repetition period of the control pulse train of the time-division controlled crystal oscillator is canceled by frequency division, and the voltage-controlled oscillator can be used for jitter-free communication from the phase-locked voltage-controlled oscillator. A frequency reference signal can be obtained.

Although the voltage controlled oscillator is a crystal oscillator whose frequency is adjusted by a semiconductor variable capacitance diode, it goes without saying that an LC oscillator can be used in this configuration.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a circuit of a conventional crystal oscillator, Fig. 2 is a diagram showing the rotation axis angle versus capacitance characteristic of a trimmer capacitor for frequency adjustment of the circuit of Fig. 1, and Fig. 3 is a diagram showing an example of the circuit of the present invention. FIG. 4 is a diagram illustrating the improvement of the rotation axis angle versus capacitance characteristic of the trimmer capacitor in FIG. 3, and FIG. 5 is a diagram illustrating examples in which various variable impedance elements are used in the present invention. , FIG. 6 is a diagram showing another embodiment in which a crystal oscillator is incorporated into a phase locked circuit. DESCRIPTION OF SYMBOLS 1... Amplification element, 2... Crystal resonator, 3-5... Capacitor, 6... Field effect transistor, 602... Crystal oscillator, 60
4... Frequency divider, 606... Phase comparator, 6
08...Low frequency p-wave generator, 610...Voltage controlled oscillator, 612...Semiconductor variable capacitance diode, 614...
Gate circuit, CLK...control pulse train, S
W...Electronic switch circuit, C engineering 0. C... Capacitor, C... Semiconductor diode, ■
oNT...bias voltage of C13, R...variable resistance element. Patent Applicant Citizen Watch Co., Ltd. Agent Patent Attorney Akihiko Sato Figure 1 Figure 2 0, 6mCl. Procedural amendment (voluntary) June 20, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi 1 Indication of the case 1988 Patent Application No. 067816 2 Title of the invention Reference signal oscillator 3 Relationship with the person making the amendment Patent application Person (1 location: 2-1-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name) (196) Citizen Watch Co., Ltd. Address: 1-17-7 Akasaka, Minato-ku, Tokyo Target of amendment (1) Details Column for detailed explanation of the invention (2) Column for brief explanation of the drawings in the specification (3) Column for the brief explanation of drawings in Figure 6 of the drawings Contents of the amendments (1) Column for detailed explanation of the invention Specification No. 13 On the 8th line of the page, add the following between the period and the water in "...Adjust. Crystal...". "The Komata capacitor 615 is a DC cut capacitor for ensuring the application of bias voltage to the semiconductor variable capacitor diode 612." (2) Brief description of the drawing section Specification 1, Page 15, No. 1 Add the following between the comma and CLK in the line "...Gate circuit, CLK.""615...DC power capacitor," (3) Corrected to the attached drawing in Figure 6 of the drawings.

Claims (6)

[Claims] (1) A part of the electric resonant circuit including the crystal resonator is equipped with an impedance element whose impedance value can be arbitrarily adjusted, and the electric resonant circuit is connected to the A reference signal oscillator characterized in that an impedance element is connected to a resonant circuit in a time-sharing manner. (2) The reference signal oscillator according to claim 1, wherein the impedance element is a variable capacitor. (3) The reference signal oscillator according to claim 2, wherein the impedance element is a mechanically adjusted trimmer capacitor. . (4) The reference signal oscillator according to claim 2, wherein the impedance element is an electrically controlled semiconductor variable capacitance diode. (5) The reference signal oscillator according to claim 1, wherein the impedance element is a mechanically adjusted variable resistance element. (6) A part of the electrical resonant circuit including the crystal resonator is equipped with an impedance element whose impedance value can be arbitrarily adjusted, and the electrical resonant circuit is connected via an electronic switch circuit controlled by a pulse train having a constant impulse coefficient. The output of a crystal oscillator, which connects impedance elements to a resonant circuit in a time-divisional manner, is frequency-divided until its period becomes an integral multiple of the period of the pulse train that controls the electronic switch circuit, and the divided output produces a voltage. A reference signal oscillator characterized in that a controlled oscillator is controlled in phase lock and a signal is output from the voltage controlled oscillator.