JP2009177522A - Method of adjusting frequency of crystal oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of adjusting frequency of a crystal oscillator which facilitates frequency adjustment. <P>SOLUTION: In the method of adjusting frequency of the crystal oscillator, the crystal oscillator having a frequency adjusting circuit comprising a parallel circuit of first and second capacitors is provided, a frequency obtained when the second capacitor is made variable together with a frequency obtained when a circuit pattern to be connected with the second capacitor is opened to make the capacitance value zero are measured with the first capacitor used as fixed value, a frequency change standard to the second capacitor is formed from the frequencies, and the frequency of each crystal oscillator is adjusted based on the frequency change standard. The frequency change standard has a frequency obtained when the circuit pattern to be connected with the second capacitor is short-circuited to make the capacitance infinite, the frequency change standard is compensated by these frequencies of the crystal oscillator, and the crystal oscillator is formed so that the value of the second capacitor is set based on the compensated frequency change standard. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a frequency adjustment method for a crystal oscillator, and more particularly to an adjustment method that facilitates frequency adjustment and increases productivity.

(Background of the Invention)
Since the crystal oscillator has high frequency stability due to the crystal resonator, it is applied as a frequency source to various electronic devices, particularly to communication devices. In such a case, the frequency deviation standard of the oscillation frequency with respect to the nominal frequency (reference oscillation frequency) is strict, and it becomes difficult to satisfy the standard at the oscillation frequency as designed. Therefore, in general, a frequency adjustment circuit is provided in a crystal oscillator (oscillation circuit) to satisfy the oscillation frequency within the standard.

(Example of conventional technology)
FIG. 3 is a diagram of a crystal oscillator for explaining a conventional example. FIG. 3A is a basic oscillation circuit of the crystal oscillator, and FIG. 3B is a diagram of an oscillation circuit to which a frequency adjustment circuit is added.

  The crystal oscillator includes, for example, a Colpitts type oscillation circuit having a crystal resonator 1, a dividing capacitor C (ab), and an oscillation amplifier 2. The crystal unit 1 forms a resonance circuit with the dividing capacitor C (ab). The oscillation amplifier 2 amplifies the resonance frequency of the resonance circuit, feeds back a part thereof, and continues oscillation by the resonance circuit. In the figure, reference symbols R1 and R2 are base bias resistors, R3 is a load resistor, Vcc is a power source, and Vout is an oscillation output.

  In this case, the oscillation frequency largely depends on the resonance frequency due to the dividing capacitor C (ab) in which the crystal resonator 1 is dominant, and strictly speaking, a series equivalent capacitance including the oscillation amplifier 2 viewed from the crystal resonator 1 ( Load capacity). However, when the frequency deviation example Δ (f0−fx) / f0 as a standard for limiting the change from the nominal frequency becomes strict to about ± 50 ppm or less, the standard oscillation circuit alone does not satisfy the standard. However, f0 is a nominal frequency and fx is an actual oscillation frequency.

  Therefore, normally, the frequency adjustment circuit 3 is connected in series to the crystal resonator 1 in the oscillation closed loop. The frequency adjustment circuit 3 is composed of, for example, a parallel circuit of first and second capacitors C1 and C2. The first capacitor C1 is for coarse adjustment with a fixed capacitance value, and the second capacitor C2 is a fine adjustment with variable capacitance value. For use. The first and second capacitors C2 are both chip capacitors.

  In such a case, the oscillation frequency of the basic oscillation circuit is set in advance lower than the nominal frequency f0, and a large number of crystal oscillators are formed. Then, a frequency change characteristic, that is, a frequency change standard that becomes a standard of the crystal oscillator with respect to the capacitance value of the second capacitor C2 of the frequency adjusting circuit 3 is formed. In this case, first, only the first capacitor C1 (for coarse adjustment) is connected to the crystal oscillator for data creation, and the terminal pq of the second capacitor C2 is opened to form an oscillation circuit (oscillation closed loop). Figure (a) ".

  However, the capacitance value of the first capacitor C1 is a fixed value, and the oscillation frequency fx is higher than the nominal frequency (reference oscillation frequency) f0. The oscillation frequency fx when the terminal of the second capacitor C2 is opened (opened) and the capacitance value is 0 is defined as the open oscillation frequency fxo. Next, the capacitance value of the second capacitor C2 is changed from 0 to a larger direction (infinite direction) and connected in sequence, and the variable oscillation frequency with respect to the capacitance value of the second capacitor C2 is measured.

  Then, a frequency change standard of the crystal oscillator for the capacitance value Cx of 0 to the maximum value of the second capacitor C2 is created (FIG. 4 (b)). The vertical axis of the graph indicates that the frequency deviation of the nominal frequency f0 is 0. For example, the oscillation frequency fx indicates that the frequency deviation (f0−fx) / f0 is x (ppm). Thereby, in the crystal oscillator for data creation, the optimum capacitance value Cc of the second capacitor C2 for obtaining the oscillation frequency fx as the nominal frequency f0 is obtained from the frequency change standard.

Finally, a first capacitor C1 having a fixed capacity is connected to a number of crystal oscillators to be adjusted. Then, the open oscillation frequency fxo ′ (≠ fxo) of each crystal oscillator in which the first capacitor C1 is connected and the terminals of the second capacitor C2 are opened and the capacitance value is 0 is measured. Next, based on the relationship between the open oscillation frequency fxo (frequency deviation x) according to the frequency change standard and the optimum capacitance value Cc, the optimum capacitance is determined from the open oscillation frequency fxo ′ (frequency deviation x ′) of the crystal oscillator to be adjusted. The value Cc ′ (≠ Cc) is obtained. Then, a second capacitor C2 having an optimum capacitance value Cc ′ is connected.
Japanese Patent Laid-Open No. 2-9207

(Problems of conventional technology)
However, in the crystal oscillator configured as described above, the second constant is caused by variations in the constants of the circuit elements that affect the oscillation frequency, in particular, C1 (series capacitance) and C0 (same parallel capacitance) that are constants of the equivalent circuit of the crystal unit 1. The frequency change characteristic with respect to the capacitor C2 also varies. Therefore, the frequency change characteristic of each crystal oscillator to be adjusted is different from the frequency change standard of the crystal oscillator used for data creation.

  Therefore, the optimum capacitance value Cc ′ obtained from the oscillation frequency fx∞ ′ of the crystal oscillator to be adjusted based on the frequency change standard is not satisfied as the deviation standard of the nominal frequency f0 becomes stricter. There is a problem that the oscillation frequency fH (frequency deviation is Hppm) or fL (Lppm) is higher or lower than the nominal frequency f0.

  In this case, the second capacitor C2 having the optimum capacitance value Cc ′ may be removed and the second capacitor C2 may be attached as a new capacitance value Cx having the nominal frequency f0. However, this takes time and adversely affects the circuit pattern. This causes a problem of lowering productivity.

(Object of invention)
SUMMARY OF THE INVENTION An object of the present invention is to provide a frequency adjustment method for a crystal oscillator that facilitates frequency adjustment and increases productivity.

  The present invention provides a crystal oscillator in which a frequency adjustment circuit comprising a parallel circuit of a first capacitor and a second capacitor is connected in series to a crystal resonator in an oscillation closed loop, as indicated in the claims (claim 1). The capacitance value of the second capacitor together with the oscillation frequency at the time of opening when the capacitance value of the first capacitor is a fixed value, the circuit pattern connected to the second capacitor is opened and the capacitance value Cx is 0 The variable oscillation frequency when the value is varied is measured, and the frequency change standard of the crystal oscillator with respect to the capacitance value of the second capacitor is formed from the open oscillation frequency and the variable oscillation frequency, and the oscillation frequency is adjusted. The target crystal oscillator is a frequency adjustment method of a crystal oscillator in which a capacitance value of the second capacitor is set based on the frequency change standard, and the frequency change The standard has an oscillation frequency at the time of short circuit when the circuit pattern connected to the second capacitor is short-circuited to make the capacitance value infinite, and the frequency change standard is the oscillation at the time of opening of the crystal oscillator to be adjusted The crystal oscillator, which is corrected by the frequency and the oscillation frequency at the time of short circuit, is configured to set the capacitance value of the second capacitor based on the corrected frequency change standard.

  With such a configuration, the frequency variable standard has both an oscillation frequency when the circuit pattern to which the second capacitor is connected is opened (capacity of the second capacitor is 0) and short-circuited (the capacitance is infinite). And the change characteristic between the time of an open time and the time of a short circuit is grasped | ascertained by the oscillation frequency at the time of variable when the capacitance value of a 2nd capacitor | condenser is varied.

  Therefore, even when the frequency change characteristics of each crystal oscillator to be adjusted differ from the frequency change standard due to variations in the circuit constants of each element, particularly the equivalent constants (C1, C0) of the crystal oscillator, And the change characteristic of the frequency change standard can be corrected relatively easily from the oscillation frequency at the time of short circuit.

  Based on the corrected frequency change standard, the appropriate capacitance value of the second capacitor can be easily obtained from, for example, the open oscillation frequency or short circuit oscillation frequency of the crystal oscillator to be adjusted. Therefore, the frequency adjustment of the crystal oscillator can be facilitated and the productivity can be increased.

(Embodiment section)
According to a second aspect of the present invention, in the first aspect, each of the oscillation frequencies is indicated by a frequency deviation from a reference oscillation frequency. Thereby, the frequency change characteristic with respect to the capacitance value of the second capacitor in the frequency change standard is clarified.

  In the third aspect of the present invention, in the crystal oscillator to be adjusted according to the first aspect, the circuit pattern to which the second capacitor is connected is formed by previously short-circuiting the circuit board, and the oscillation frequency at the time of the short-circuit is measured. Thereafter, the circuit pattern is opened and the oscillation frequency at the time of opening is measured.

  Thereby, since the circuit pattern to which the second capacitor is connected is short-circuited in advance, it is possible to easily measure the short-circuit oscillation frequency when the capacitance value of the second capacitor is infinite. Then, since the circuit pattern is opened after that, the open oscillation frequency when the capacitance value of the second capacitor is 0 and the variable oscillation frequency when the capacitance value is changed by connecting the second capacitor C2 are easily measured. it can.

  In these cases, the second capacitor C2 having the same capacitance value as that when the frequency change standard is formed can be connected to the crystal oscillator to be adjusted and compared with the frequency change standard. However, in this case, the second capacitor must be removed, and the productivity is lowered as described above.

  According to claim 4 (independent claim), in an oscillator circuit board in which an oscillation circuit is formed in which a frequency adjustment circuit composed of a parallel circuit of a first capacitor and a second capacitor is connected in series to a crystal resonator in an oscillation closed loop. The circuit pattern to which the second capacitor is connected has a configuration in which opposing sides are previously short-circuited by a straight path.

  As a result, the line length between the circuit patterns is made the shortest, the influence on the oscillation frequency due to the stray capacitance or the like is reduced, and the oscillation frequency when the crystal oscillator is short-circuited can be easily measured. And the frequency adjustment of Claim 3 mentioned above can be implemented.

  FIG. 1 is a diagram for explaining an embodiment of the present invention. FIG. 1 (a) is an oscillation circuit for explaining frequency adjustment of a crystal oscillator, and FIG. 1 (b) is a diagram of a circuit pattern provided on an oscillator circuit board. It is. In addition, the same number is attached | subjected to the same part as a prior art example, and the description is simplified or abbreviate | omitted.

  As described above, the crystal oscillator includes a Colpitts type oscillation circuit having the crystal resonator 1, the dividing capacitor C (ab), and the oscillation amplifier 3, and the frequency adjustment circuit 3 is connected to the crystal resonator 1 in series. The frequency adjustment circuit 3 is also composed of a parallel circuit of a first capacitor C1 and a second capacitor C2 in this example.

  In this embodiment, the circuit pattern shown by coloring the oscillator circuit board 4 on which the oscillation circuit and the frequency adjustment circuit 3 are formed is as follows. That is, the circuit pattern to which the first capacitor C1 of the frequency adjusting circuit 3 is connected, that is, each terminal is formed open, but each terminal pq of the circuit pattern to which the second capacitor C2 is connected is a straight path between opposite sides. It is formed by short-circuiting in advance.

  In such a case, as described above, after the frequency change standard is created by the crystal oscillator for data creation, the frequency of each of the crystal oscillators to be adjusted is individually adjusted. In the frequency change standard working process, first, each element (not shown) constituting the oscillation circuit is mounted on the circuit board 4 except at least the second capacitor C2 for fine adjustment of the frequency adjustment circuit 3.

  In this case, since the circuit pattern to which the second capacitor C2 of the frequency adjusting circuit 3 is connected is short-circuited, the capacitance value Cx of the second capacitor C2 is infinite. Therefore, the crystal oscillator forms an oscillation closed loop in which the capacitance value of the frequency adjustment circuit 3 is infinite regardless of the presence or absence of the first capacitor C1. In this example, the capacitance value of the first capacitor C1 is connected in advance to the circuit pattern as a fixed value.

  Next, the short-circuit oscillation frequency fx∞ is measured with the capacitance value Cx of the second capacitor C2 being infinite while the circuit pattern connected to the second capacitor C2 is short-circuited. Next, the circuit pattern to which the second capacitor C2 is connected is cut to open the circuit pattern (between the terminals pq). Then, as described above, the open-circuit oscillation frequency fxo with the capacitance value set to 0 by opening the circuit patterns is measured.

  Next, the capacitance value Cx of the second capacitor C2 is varied and connected between circuit patterns (between the terminals pq), and the variable oscillation frequency corresponding to the change of the capacitance value Cx is measured. As a result, the frequency change standard here changes the capacitance value Cx of the second capacitor C2 from 0 at the time of opening to infinity (∞) at the time of short circuit, as shown by the curve (b) in FIG. It becomes the frequency change characteristic at the time. Even in this case, the oscillation frequency fx is represented by a frequency deviation x “= (f0−fx) / f0” from the nominal frequency f0. Thereby, in the crystal oscillator for data creation, the optimum capacitance value Cc of the second variable capacitor C2 having the oscillation frequency of the nominal frequency f0 can be obtained.

  In the frequency adjustment of each crystal oscillator to be adjusted, the circuit pattern to which the second capacitor C2 is connected is first short-circuited and the capacitance value Cx of the second capacitor C2 is infinite, similarly to the crystal oscillator for data creation. The oscillation frequency fx∞ ′ (≠ fx∞) at the time of short circuit of the crystal oscillator is measured. Next, the circuit pattern is cut, and the open oscillation frequency fxo ′ (≠ fxo) is measured in which the circuit pattern is opened and the capacitance value Cx of the second capacitor C2 is zero.

  Next, based on the frequency change standard “curve (A)” by the crystal oscillator for data creation and the oscillation frequency fxo ′ at the time of opening and the oscillation frequency fx∞ ′ at the time of short circuit of the crystal oscillator to be adjusted. Correct the frequency change characteristics of. In this case, the open oscillation frequency fxo ′ of the crystal oscillator to be adjusted is converted to the open oscillation frequency fxo of the frequency change standard and matched.

  Thus, the frequency change characteristic from the open oscillation frequency fxo (fxo ′) to the short-circuit oscillation frequency fx∞ ′ is different from the frequency change standard “curve (A)” and is suitable for the crystal oscillator to be adjusted. A corrected frequency change standard “curve (b) or (c)” is obtained.

  Then, an appropriate capacitance Cc ′ of the second capacitor C2 is obtained based on the frequency standard “curve (b) or (c)” corrected in conformity with the crystal oscillator for adjustment. A variable capacitor C2 having an appropriate capacitance value Cc 'is connected between the circuit patterns. These are sequentially processed for a large number of crystal oscillators to be adjusted.

  With such a configuration (frequency adjustment method), the frequency change standard by the crystal oscillator for data creation and the frequency change characteristic by the crystal oscillator to be adjusted are not only the oscillation frequency at open and variable frequency, but also the oscillation at short circuit It becomes the frequency change characteristic that takes in the frequency.

  Therefore, even if the frequency change characteristic of the crystal oscillator to be adjusted differs from the frequency change standard due to variations in the constants (C1 and C0) of the crystal resonator 1, the frequency change standard is set based on the oscillation frequency at the time of short circuit and open. Can be easily corrected. Thereby, the variable capacitor of each crystal oscillator to be adjusted is set to an appropriate capacitance Cc ′, and the oscillation frequency fx can be satisfied within the specification of the nominal frequency f0.

  In this example, the circuit pattern to which the second capacitor C2 of the oscillation circuit board 4 is connected is previously short-circuited by a straight path. Therefore, the line length between the circuit patterns (terminals pq) is shortened to minimize the influence on the oscillation frequency due to the stray capacitance, and the oscillation frequency when the crystal oscillator is short-circuited can be easily measured. However, this does not exclude measuring the oscillation frequency at the time of short circuit using a probe or the like.

1A and 1B are diagrams illustrating an embodiment of the present invention, in which FIG. 1A is an oscillation circuit illustrating frequency adjustment of a crystal oscillator, and FIG. 1B is a diagram of a circuit pattern provided on an oscillator circuit board. It is a graph of the frequency change standard (frequency change characteristic) with respect to the 2nd capacitor | condenser explaining the effect | action by one Embodiment of this invention. FIG. 4A is a circuit diagram of a crystal oscillator for explaining a conventional example, in which FIG. 1A is a basic oscillation circuit of the crystal oscillator, and FIG. It is a figure explaining the frequency adjustment of a prior art example, the figure (a) is a circuit diagram of a crystal oscillator, and the figure (b) is a graph of the frequency change standard with respect to a 2nd capacitor | condenser.

Explanation of symbols

  1 crystal oscillator, 2 oscillation amplifier, 3 frequency adjustment circuit.

Claims (4)

A crystal oscillator in which a frequency adjustment circuit including a parallel circuit of a first capacitor and a second capacitor is connected in series to a crystal resonator in an oscillation closed loop;
The capacitance value of the first capacitor was varied along with the oscillation frequency at the time of opening when the capacitance value was set to 0 by opening the circuit pattern to which the second capacitor was connected by setting the capacitance value of the first capacitor to a fixed value. Measure the oscillation frequency when variable,
From the oscillation frequency at the time of opening and the oscillation frequency at the time of variable, forming a frequency change standard of the crystal oscillator with respect to the capacitance value of the second capacitor,
The crystal oscillator to be adjusted for oscillation frequency is a frequency adjustment method for a crystal oscillator in which a capacitance value of the second capacitor is set based on the frequency change standard,
The frequency change standard has a short-circuit oscillation frequency when the circuit pattern connected to the second capacitor is short-circuited to make the capacitance value infinite, and the frequency change standard is the crystal oscillator to be adjusted. It is corrected by the oscillation frequency at the time of opening and the oscillation frequency at the time of the short circuit,
The crystal oscillator frequency adjustment method, wherein the crystal oscillator to be adjusted has a capacitance value of the second capacitor set based on the corrected frequency change standard.   2. The frequency adjustment method for a crystal oscillator according to claim 1, wherein each oscillation frequency is indicated by a frequency deviation from a reference oscillation frequency.   2. The crystal oscillator to be adjusted according to claim 1, wherein the circuit pattern to which the second capacitor is connected is formed by short-circuiting to a circuit board in advance, and the oscillation frequency at the time of short-circuit is measured, and then the circuit pattern is A method of adjusting a frequency of a crystal oscillator in which the oscillation frequency when open is measured.   A circuit to which the second capacitor is connected in an oscillator circuit board formed with an oscillation circuit in which a frequency adjusting circuit composed of a parallel circuit of a first capacitor and a second capacitor is connected in series to a crystal resonator in an oscillation closed loop The oscillator circuit board, wherein the pattern is formed by short-circuiting opposite sides in advance by a straight path.