GB2118392A

GB2118392A - Voltage-controlled oscillator mounted on a thick-film printed substrate

Info

Publication number: GB2118392A
Application number: GB08307555A
Authority: GB
Inventors: Yukio Fukumura; Masayuki Matsukura
Original assignee: Nippon Electric Co Ltd
Current assignee: NEC Corp
Priority date: 1982-03-19
Filing date: 1983-03-18
Publication date: 1983-10-26
Also published as: GB8307555D0; AU1257983A; JPS58161504A

Abstract

A voltage-controlled oscillator includes an electrically insulating ceramic substrate 1 on which there is mounted an oscillator 101, 23, a resonator 11 for determining the frequency of oscillation of the oscillator and an oscillation frequency control 41, 21, 22 for changing the frequency of the oscillation, the resonator comprising a thick-film conductive layer forming a quarter- wavelength microstrip line 311a. Conductive connection patterns, e.g. 312a and a grounding pattern 2a on the reverse of the substrate are also thick- film printed. In order to increase the oscillator Q-factor, the pattern 311a for the resonator 11 and preferably also the connecting and grounding patterns are metal-plated (with copper or silver) 311b, 312b, 2b. <IMAGE>

Description

SPECIFICATION Voltage controlled oscillator mounted on a thickfilm printed substrate Background of the invention The present invention relates to a voltage controlled oscillator for use in digital frequency synthesizers, etc.

Digital frequency synthesizers have recently been used as the receiving or transmitting oscillator of a mobile radio equipment for VHF and UHF bands.

High immunity to mechanical vibration and an excellent spectrum purity are required of a digital frequency synthesizer for use in such fields. This is because a mobile radio transmitter is susceptible to vibration and shock, and its oscillator is required to have a high frequency spectrum purity. If a digital frequency synthesizer does not fulfill said requirements, an undesirable modulation tends to be caused at the radio transmitter by vibration to deteriorate the spectrum purity or interfere with adjacent radio channels. Heretofore, to increase the vibration immunity, the voltage controlled oscillator is formed and mounted on a substrate of a ceramic made of a ceramic such as alumina. More specifically, the ceramic substrate is printed with conductive and resistive patterns in thick film and mounted with a chip capacitor, a transistor and a varactor, etc.

Moreover, it is printed in thick film with a resonator which determines the oscillation frequency of the voltage controlled oscillator. An oscillator of this construction may be less expensive and superior in vibration inmunity. However, the quality factor Q of the resonator is decreased because the conductive patterns of the thick film comprise silver-pa radium which has a resistance 10 times greater than that of silver or copper, thereby deteriorating spectrum purity of the oscillator.

Use of a gold evaporated thin film conductive pattern having smaller resistance has been proposed to solve the above problem, but this would make a mobile radio transmitter more costly to manufacture.

Summary of the invention An object of the present invention is, therefore, to provide a voltage controlled oscillator which has a high frequency spectrum purity and high vibration immunity.

In one embodiment a voltage controlled oscillator is obtained by printing the resonator in thick film and then electroplating a metal film over the thick-film printed resonator.

Brief description of drawings The objects and features of the present invention will now be described with reference to the accompanying drawings.

Figure 1 shows a circuit diagram of a voltage controlled oscillator according to the present invention.

Figure 2 is a plan view of the ceramic substrate according to the present invention, on which the voltage controlled oscillator shown in Figure 1 is formed and mounted.

Figures 3A, 3B and 3C are a plan view, a left-side view, and a right-side view of the ceramic substrate, respectively.

Figure 4A is a plan view showing the plated portion of the conductor patterns of Figure 3A.

Figure 4B is a sectional view of Figure 4A along the line X - X'.

Figure 5 is a graph showing the change in the carrier to noise ratio (C/N) with respect to the deviation from the desired oscillation frequency of the voltage controlled oscillator wherein the curve a represents the case where the thick-film printed conductor pattern is not plated; and b in the case where the thick-film printed conductor pattern is plated.

Preferred embodiment of the invention Referring to Figure 1, the voltage controlled oscillator is essentially comprised of an oscillator section, a resonator section and an oscillation frequency control section. The oscillator section comprises a transistor 101, coupling capacitors 22 and 25, a feedback capacitor 23, bypass capacitors 24, 26 and 27, biassing resistors 31 through 33 and a choke coil 13. The resonator section comprises a microstrip line 11 whose length is 1/4 the wavelength of the oscillation frequency in the oscillator section. The oscillation frequency control section comprises a varactor diode 41, a coupling capacitor 21 and a choke coil 12. A terminal 202 is connected to a DC power source. A biassing voltage is supplied to the transistor 101 through the resistors 31 to 33 and the choke coil 13. The oscillator section provides an oscillation signal to a terminal 201.The resonator section stabilizes the oscillation frequency of the oscillator section. The oscillation frequency can be varied by changing the capacitance of the diode 41 by the voltage supplied from a terminal 203. Thus, the oscillation at a constant frequency can be obtained by supplying a constant voltage to the terminal 203. For generating the oscillation at a given frequency, the oscillation frequency control section may be substituted with a capacitor of a fixed capacitance.

Referring now to Figure 2, the voltage controlled oscillator of Figure 1 is formed and mounted on the ceramic substrate 1. Electrical components such as the transistor 101, diode 41, capacitors 21 through 27, choke coils 12, 13 and resistors 31 to 32 are mounted in predetermined arrangement as shown.

Conductive connecting patterns for connecting the electrical components and a pattern for the resonator 11 are printed in a thick film as shown in Figures 3A, 3B and 3C. In Figures 3A and 3B, silver-paradium paste is thick-film printed on the top, sides and bottom surfaces of the ceramic substrate 1 and sintered at a temperature between 7000C and 900 C, to form patterns 2a and 311 a to 324a of approximately 100 microns in thickness. It is noted that the whole bottom surface of the ceramic substrate 1 is printed in thick film to form the grounding pattern 2a.The resonator 11,which is indicated by 311 a in Figures 3A and 3B, is a microstrip line of 1/4 wavelength; one end thereof is connected to the grounding pattern 2a via the pattern printed on the side of the ceramic substrate 1, as shown in Figure 3B. The electrical components 24,26,27,31,32 and 41 shown in Figure 1 are also connected to the grounding pattern 2a via the conductive patterns 320a, 321 a, 323a, 319a, 322a and 312a, and the patterns on the side surfaces, respectively.Among the thick-film printed patterns, those capable of increasing the factor Q of the oscillator, i.e., the pattern 31 1a for the resonator 11, the conductive connecting patterns 312a and 319a to 323a and the grounding pattern 2a, are plated with metal such as copper or silver to form plated layers 311 b, 31 2b, 319b to 323b and 2b 3 of about 2 microns in thickness, as shown in Figures 4A and 4B. Any conventional electroplating may be employed to plate the pattern for the resonator 11, the conductive connecting patterns and the grounding pattern, using the grounding pattern of the ceramic substrate 1 as an electrode. Since one end of the resonator pattern is connected to the grounding pattern, both the grounding pattern and the resonator pattern can be easily plated simultaneously.

The use of the plating can decrease the resistance of the thick-film printed resonator pattern, thereby increasing the factor Q of the reasonator.

It should be noted that the only resonator pattern 31 1a may be metal-plated and the resistors 31 through 33 of Figure 1 can be thick-film printed.

Figure 5 shows the comparison, with respect to the CIN vs. oscillation frequency deviation (Af) characteristics, between the conventional voltage controlled oscillator and the voltage controlled oscillator of the present invention in which the resonator is plated to increase its Q. In Figure 5, the symbol f, represents the oscillation frequency; Af, the frequency deviation from the oscillation frequency; a, C/N vs. Af characteristics of the conventional voltage controlled oscillator; and bC/N vs. Af characteristics of the voltage controlled oscillator according to the present invention. As is evident from the Figure, the voltage controlled oscillator of the present invention is superior in C/N vs. Af characteristics, or in the frequency spectrum purity of the oscillator.

As has been described in the foregoing, a voltage controlled oscillator of an excellent C/N vs. Af characteristics and a high vibration immunity can be obtained by printing the resonator in thick film and then electro plating a metal film over the thick-film printed resonator.

Claims

1. A voltage controlled oscillator comprising an oscillator, a resonator for determining the frequency of oscillation of the oscillator, an oscillation frequency control for changing the frequency of the oscillation and an electrically insulating substrate for mounting the oscillator and the oscillation frequency control thereon, in which the resonator comprises a thick film conductive layer having a length equal to one fourth (1/4) of the wavelength of the oscillation on a surface of said substrate, and a metal layer on a surface of said conductive layer.

2. A voltage controlled oscillator as claimed in claim 1, including a second thin film conductive layer on a rear surface of said substrate, a third thin film conductive layer on the side of said substrate to connect said first and second conductive layers, and second and third metal layers on the surfaces of said second and third conductive layers respectively.

3. A voltage controlled oscillator substantially as described herein with reference to the accompanying drawings.

4. A method of making a voltage controlled oscillator having a resonator for determining the frequency of oscillation of the oscillator, an oscillation frequency control for changing the oscillation frequency and an electrically insulating substrate for mounting the oscillator and the oscillation frequency control thereon, including the steps of printing a thick film conductive layer having a length equal to one fourth (1/4) of the wavelength of the oscillation on a surface of the substrate and plating a metal layer on a surface of the said conductive layer.

5. A method of making a voltage controlled oscillator as claimed in claim 4 substantially as described herein with reference to the accompanying drawings.