Method for adjusting characteristics of voltage control type oscillator

Abstract: A method for adjusting a voltage control type oscillator (10) that can prevent characteristic changes occurring after adjustments and permits the oscillator (10) to be produced at a low cost. The voltage control type oscillator (10) includes a strip electrode (14) formed on a first surface of a dielectric substrate (12) and a ground electrode (16) formed on a second surface of the dielectric substrate (12). These electrodes constitute a microstrip line resonator. Besides the resonator, electric components (18) are mounted on the first surface of the dielectric substrate (12). A case (20) is attached to the dielectric substrate (12) in a manner that the case (20) covers the strip electrode (14) and the electronic components (18). After attaching the case (20), the strip electrode (14) is trimmed by irradiating a laser beam from the second surface side of the dielectric substrate (12).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to methods for adjusting voltage control type oscillators. More particularly, the invention relates to methods for adjusting the frequencies and control-voltage sensitivities of voltage control type oscillators using microstrip line resonators. 2. Description of the Related Art For example, as shown in Fig. 2, in a conventional voltage control type oscillator 1 using a microstrip line resonator, a strip electrode 3 is formed on a first surface of a dielectric substrate 2, and a ground electrode 4 is formed on a second surface of the dielectric substrate 2. In the voltage control type oscillator 1, besides a resonator formed by a microstrip line, electronic components 5 are mounted on the first surface of the dielectric substrate 2. In order to adjust the frequency and control voltage of the voltage control type oscillator 1, the strip electrode 3 is trimmed. In this case, trimming is performed by irradiating a laser beam on the strip electrode 3. In this manner, after trimming the strip electrode 3, a case for covering the strip electrode 3 and the electronic components 5 is attached to the dielectric substrate 2. In addition, in Fig. 3, there is shown another conventional voltage control type oscillator using a microstrip line resonator formed on a multi-layer substrate. In a voltage control type oscillator 1, a strip electrode 3 is formed inside a dielectric substrate 2. Then, two ground electrodes 4 and 6 are formed sandwiching the strip electrode 3 therebetween. Like the ground electrode shown in Fig. 2, the ground electrode 4 is formed on the second surface of the dielectric substrate 2. The ground electrode 6 is formed inside the dielectric substrate 2. Electronic components 5 are mounted on the first surface of the dielectric substrate 2, and a case 7 is attached to the dielectric substrate 2 such that the case 7 covers the electronic components 5. In this voltage control type oscillator 1, after attaching the case 7, trimming of the strip electrode 3 is performed. In this case, a laser beam is irradiated from the second surface side of the dielectric substrate 2 to trim the strip electrode 3. However, as shown in Fig. 2, when trimming the strip electrode from above, since the case 7 is attached after the trimming, a magnetic-field change occurs, thereby causing changes in various characteristics including frequency characteristics. In addition, depending on the state in which the case 7 is attached, there are generated variations between the characteristic changes, which increases variations in the characteristics between produced voltage control type oscillators. In addition, as shown in Fig. 3, when attaching the cover on the first surface of the multi-layer substrate having a circuit formed thereon and trimming the strip electrode from the second surface side of the multi-layer substrate, the distances between the strip electrode formed inside the multi-layer substrate and the ground electrodes sandwiching the strip electrode therebetween are narrow. Thus, noise characteristics such as C/N characteristics (carrier/noise ratio) are deteriorated. Furthermore, in the case of the multi-layer substrate, a substrate material cost is higher than the case using the dielectric substrate having the strip electrode formed thereon. US-A-4,110,640 describes a transparent substrate having a plurality of standard signal generating circuits. Each signal generating circuit comprises a quartz crystal vibrator and an integrated circuit element encapsulated within a vacuum by means of a cover. The integrated circuit element includes a divider wherein adjustment terminal pads are provided for adjusting a desired dividing ratio of the divider. By means of cutting respective connecting leads to the adjustment terminal pads either the positive or negative voltage is provided to the respective pad so as to vary the dividing ratio of the divider of the integrated circuit. This cutting of the connection leads is done by irradiating same by means of a laser from the back side of the surface on which the respective elements are formed. It is the object of the present invention to provide an improvement method for adjusting a voltage control type oscillator preventing characteristic changes occurring after adjustments and permitting the voltage control type oscillator preproduced at a low cost. This object is achieved by a method according to claim 1. The present invention provides a method for adjusting a voltage control type oscillator. The method includes steps of forming a strip electrode on a first surface of a dielectric substrate, forming a ground electrode on a second surface of the dielectric substrate, providing a case which covers the strip electrode on the first surface of the dielectric substrate, and trimming the strip electrode from the second surface side of the dielectric substrate after the case is provided, where in the strip electrode is trimmed by a laser. By using a microstrip line resonator composed of the strip electrode formed on the first surface of the dielectric substrate and the ground electrode formed on the second surface thereof, the substrate material cost can be lower than the case of the multi-layer substrate. In addition, since the method can widen the distance between the strip electrode and the ground electrode, the voltage control type oscillator can have satisfactory characteristics. Furthermore, trimming is performed from the second surface side of the dielectric substrate after the case is provided on the first surface of the dielectric substrate. That is, since the cover is not attached after adjustments, this arrangement can prevent characteristic changes occurring after adjustments. The object of the invention, other objects thereof, the characteristics and advantages of the invention, will be further clarified by the detailed explanation of embodiments shown below with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows an illustration for explaining a method for adjusting a voltage control type oscillator according to the present invention; Fig. 2 shows an illustration for explaining a conventional method for adjusting a voltage control type oscillator; and Fig. 3 shows an illustration for explaining another conventional method for adjusting a voltage control type oscillator. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 illustrates an example of a voltage control type oscillator used in an adjustment method according to the present invention. A voltage control type oscillator 10 includes a dielectric substrate 12. On a first surface of the dielectric substrate 12, for example, a line-shaped strip electrode 14 is formed. On a second surface of the dielectric substrate 12, a ground electrode 16 is formed on its entire surface. The dielectric substrate 12, the strip electrode 14, and the ground electrode 16 constitute a microstrip line resonator. Besides the microstrip line resonator, electronic components 18 are formed on the first surface of the dielectric substrate 12. The microstrip line resonator and the electronic components 18 constitute the voltage control type oscillator 10. A metal case 20 is attached to the first surface of the dielectric substrate 12 such that the case 20 covers the strip electrode 14 and the electronic components 18. In the voltage control type oscillator 10, the frequency and control-voltage sensitivity of the oscillator are adjusted by trimming the strip electrode 14 by irradiating a laser beam from the second surface side of the dielectric substrate 12. The laser-trimming is performed after the case 20 is attached to the first surface of the dielectric substrate 12. When the laser beam is irradiated, slits are formed both in the dielectric substrate 12 and the ground electrode 16. However, as long as the widths of the slits are narrow, there is almost no influence upon the characteristics of the oscillator 10. In the above method, after the case 20 is attached, the strip electrode 14 is trimmed. Thus, the method can prevent characteristic changes occurring when the case 20 is attached after adjustments. For example, it is assumed that in a voltage control type oscillator of 2 GHz band, the case is attached after trimming the strip electrode 14 formed on the first surface of the dielectric substrate 12. In this case, the frequency change is approximately 10% (200 MHz). Furthermore, depending on the state of covering with the case, there are generated variations of approximately 0.5% (± 10 MHz). In other words, in the conventional method, the frequency change amounts to 200 ± 10 MHz, whereas in the present invention, the occurrence of frequency change can be made 0 MHz when the case 20 is attached. Furthermore, since the method of the present invention uses the microstrip line resonator composed of the strip electrode 14 and the ground electrode 16 formed on the surfaces of the dielectric substrate 12, the distance between the strip electrode 14 and the ground electrode 16 can be made greater than the distance between both electrodes in an oscillator using a multi-layer substrate. As a result, noise characteristics such as C/N (carrier to noise) characteristics can be improved. For example, in order to check a C/N ratio at a detuning frequency of 60 kHz, a product comparison was made between the voltage control type oscillator using the resonator composed of the strip electrode 14 and the ground electrode 16 formed on the main surfaces of the dielectric substrate 12 and the voltage control type oscillator using the multi-layer substrate. In this comparison, the C/N ratio of the latter oscillator was 124.6 dBc/Hz, whereas the C/N ratio of the former oscillator was 125.9 dBc/Hz. Therefore, the noise characteristics could be improved by 1.3 dBc. Furthermore, the oscillator having the electrodes 14 and 16 formed on the main surfaces of the dielectric substrate can be produced more cheaply than the oscillator using the multi-layer substrate. Thus, since the substrate material cost can be reduced, the voltage control type oscillator 10 can be produced at a low cost. As described above, in this invention, since the strip electrode is trimmed after attaching the case, the characteristic changes of the oscillator caused by attaching the case can be prevented. In addition, the oscillator of the invention uses the microstrip line resonator composed of the strip electrode and the ground electrode formed on the main surfaces of the dielectric substrate. With this arrangement, as compared with the oscillator using a multi-layer substrate, in the oscillator of the invention, noise characteristics such as C/N characteristics can be improved, and furthermore, the voltage control type oscillator can be produced at a lower cost. While the preferred embodiments of the present invention have been described above, it should be understood that the implementation of other variations and modifications of the invention and its various aspects will be apparent to those skilled in the art, and that the invention is not limited by the specific embodiments described above.

Claims: A method for adjusting a voltage control type oscillator (10), the method comprising the steps of: forming a strip electrode (14) on a first surface of a dielectric substrate (12), and forming a ground electrode (16) on a second surface of the dielectric substrate (12), the strip electrode (14), the ground electrode (16), and the dielectric substrate (12) constituting a microstrip resonator; providing a case (20) which covers the strip electrode (14) on the first surface of the dielectric substrate (12); and characterised by laser trimming the strip electrode (14) of the microstrip resonator from the second surface side of the dielectric substrate (12) after the case (20) is provided.

Inventors: HAYASHI YASUHIRO, HAYASHI, YASUHIRO, Hayashi, Yasuhiro, (A170) Intelectual Prop. Dept.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 2001
Main classification: H03B5
IPC codes: H03B5, H01P7