VARIABLE ATTENUATOR

Abstract

 The invention discloses a variable attenuator, comprising: a base, a first film resistor located on the base, an input terminal and an output terminal connected to the two ends of the first film resistor; the two ends of the first film resistor are further electrically connected to one end of a third film resistor and one end of a fourth film resistor; the other ends of the third film resistor and fourth film resistor are further electrically connected to one end of a second film resistor, the other end of the second film resistor is electrically connected to a ground terminal; the variable attenuator of the invention further comprises a first conductive sheet and a second conductive sheet that can be electrically contacted by the first film resistor and the second film resistor respectively and are used to change the resistance values of the first film resistor and second film resistor, respectively; the variable attenuator of the invention further comprises an insulator, wherein the first conductive sheet and the second conductive sheet are fixed thereon. The variable attenuator of the invention is suitable for use in various high frequency and microwave circuits and systems, and has the features of a wide frequency band, small size, easy fabrication, low cost, and so on.

Description

FIELD OF THE INVENTION

[0001] This invention relates to variable attenuators in the electronics and communication fields, and more particularly, to variable attenuators suitable for use in various high frequency and/or microwave circuits and systems.

BACKGROUND OF THE INVENTION

[0002] In the family of electronic components, the variable attenuator is one of the common and basic components in electrical circuits and systems. The existence of a variable inductor makes the fabrication of electrical circuits and the debugging of systems more flexible and convenient. Currently, the variable attenuator is being widely used in circuits and systems with operating frequencies below a few hundred megahertz (MHz). For example, in CATV (Community Antenna Television) systems and microwave circuits, the variable attenuator is used for testing, regulating power levels, increasing isolation, etc. However, as the operation frequency is in a comparatively high frequency band, the current three-dimensional variable attenuator which is made of a contact spring, a slide block, a guide screw, and so on, has the drawbacks of large parasitic parameters and comparatively poor high frequency characteristics.

DESCRIPTION OF THE INVENTION

[0003] In view of the above-described problems, it is one objective of the invention to provide a variable attenuator with a good wide band characteristics that is suitable for use in high frequency and/or microwave circuits and systems.

[0004] In accordance with one objective of the invention, provided is a variable attenuator comprising: a base 11, a first film resistor 1 located on the base 11, and an input terminal 9 and an output terminal 10 connected to the two ends of the first film resistor 1, respectively; the two ends of the first film resistor 1 are also electrically connected to one end of a third film resistor 6 and one end of a fourth film resistor 7, respectively; the other ends 14 of the third film resistor 6 and fourth film resistor 7 are electrically connected to one end of the second film resistor 2, and the other end of the second film resistor 2 is electrically connected to a ground terminal 13; the variable attenuator further comprises a first conductive sheet 3 or path and a second conductive sheet 4 or path that can be electrically connected or is connectable to the first film resistor 1 and the second film resistor 2 for changing the resistance values thereof; the variable attenuator further comprises an insulator 12 for fixing the first conductive sheet 3 and the second conductive sheet 4 disposed thereon.

[0005] In accordance with the invention, the film resistors are printed on a planar structured base suitable for use in high frequency and/or microwave devices, with the assistance of the insulator and the conductive sheets, so as to change the contact area between the conductive sheets and the film resistors to change the resistance values of the film resistors, and thereby, to realize the purpose of the variable attenuator.

[0006] Therefore, the variable attenuator according to the invention provides the following advantages:

(a) since a microstrip base structure is adopted, the range of useful frequencies for the variable attenuator is very wide; the continuous variable attenuation of a signal in the high frequency and microwave frequency range can be realized;

(b) it has a small size, is easy to adjust, and is suitable for use in various miniaturized circuits and communication circuits;

(c) it has a simple structure, and a low fabrication cost;

(d) it is suitable for various equalization circuits;

(e) it is suitable for various isolation circuits;

(f) it is suitable for various regulating circuits, controlling circuits, stabilizing circuits, and circuits for adjusting the amount of coupling;

(g) it is suitable for circuits where high attenuation is required, systematic error of an actual circuit is large, and regulation of all parts are is needed to satisfy characteristics of overall circuits;

(h) it has a low insertion loss; and

(i) it can serve in adjusting and testing instruments for research and development work in laboratories.

DISCRIPTION OF THE DRAWINGS

[0007] Fig. 1 is a structural diagram of the variable attenuator in accordance with the invention;

[0008] Fig. 2 is an exploded view of the variable attenuator in accordance with the invention;

[0009] Fig. 3 is an electric diagram of the variable attenuator in accordance with the invention;

[0010] Fig. 4 shows a theoretical characteristic variation curve of the resistance value of the first film resistor 1 and the second film resistor 2, when the insulator drives the conductive sheet to rotate clockwise as the variable attenuator is adjusted by an external force, in accordance with the invention; and

[0011] Fig. 5 shows an attenuation variation curve of the variable attenuator when the insulator drives the conductive sheet to rotate clockwise as the variable attenuator is adjusted by an external force, in accordance with the invention.

DESCRIPTION OF THE INVENTION

[0012] With reference to Figs. 1-2, a variable attenuator of the invention comprises a base 11, an input terminal 9 located on the base 11, an arc shaped first microstrip signal line 5 with one end connected to the input terminal 9, an arc shaped first film resistor 1 with one end connected to the other end of the first microstrip signal line 5, and an output terminal 10 connected to the other end of the first film resistor 1. In addition, the two ends of the first film resistor 1 are electrically connected to one end of a third film resistor 6 and one end of a fourth film resistor 7, respectively; the other ends 14 of the third film resistor 6 and fourth film resistor 7 are both electrically connected to one end of the second film resistor 2, the other end of the second film resistor 2 is connected to a ground terminal 13, or is connected to the ground terminal 13 via a second microstrip signal line 8. In certain embodiments of the invention, the first film resistor 1, the second film resistor 2, the third film resistor6, and the fourth film resistor 7 are all printed film resistors with the bottom side or surface connected to the base 11 and the top side or surface made of conductive and non-insulated resistance material.

[0013] Particularly, the resistance value of the third film resistor 6 is equal to that of the fourth film resistor 7. Generally, the third film resistor 6 and the fourth film resistor 7 are film resistors having the same resistance value, Zo, at the input and output terminals, for example, 50 Ohms. A first conductive sheet 3 or path for contact short-circuiting, and having the same shape as the first microstrip signal line, is located above the top side of the first microstrip signal line, and is fixed on the insulator 12. The insulator 12 is a forced displacement board, and is further fixed with a second conductive sheet 4 or path. The first conductive sheet 3 and the second conductive sheet 4 are fixed at the bottom side of the insulator 12 (namely the forced displacement board), respectively. The function of the first conductive sheet 3 is to adjust the resistance value of the first film resistor 1, while that of the second conductive sheet 4 is to adjust the resistance value of the second film resistor 2. The first conductive sheet 3 does not contact with the second conductive sheet 4. The first conductive sheet 3 and the second conductive sheet 4 rotate with the rotation of the insulator 12. For example, when the insulator 12 (the forced displacement board) rotates clockwise, the first conductive sheet 3 rotates on and in contact with the first microstrip signal line 5 and the first film resistor 1 simultaneously. The contact area between the first conductive sheet 3 and the first film resistor 1 increases so that the resistance value of the first film resistor 1 decreases. The second conductive sheet 4 rotates on the second microstrip signal line 8 and the second film resistor 2 simultaneously. The contact area between the second conductive sheet 4 and the second film resistor 2 decreases so that the resistance value of the second film resistor 2 increases. Through the change in the geometric area, namely the change in the contact area between the conductive sheet and the film resistor, the virtual resistance value of the first film resistor 1 and the second film resistor 2 can be changed, namely, the actual effective resistance value of the first film resistor 1 and the second film resistor 2 is changed.

[0014] When the insulator 12 (forced displacement board) rotates clockwise, it is preferred that the maximum rotation angle of the insulator 12 be maintained so as to make the first conductive sheet 3 nearly or totally short-circuit the first film resistor 1; the length (arc length) of the first conductive sheet 3 should cover or nearly cover the first film resistor 1, and should be avoided from contacting the second film resistor 2. When the second conductive sheet 4 rotates clockwise, the conductive sheet 4 needs to be designed not to contact the first microstrip signal line 5 and the input terminal 9.

[0015] Similarly, when the insulator 12 (forced displacement board) rotates counter-clockwise, the maximum rotation angle of the second conductive sheet 4 needs to be maintained so as to avoid the second conductive sheet 4 from contacting the output terminal 10; when the first conductive sheet 3 rotates counter-clockwise, the first conductive sheet 3 needs to be designed not to contact the ground terminal 13.

[0016] The first conductive sheet 3 and the second conductive sheet 4 can also be film resistors, which overlap and are electrically connected, and can be regarded as two resistors in parallel. Similarly, the resistance value of the film resistor can be changed and the same effect can be achieved. However, it is required that the first conductive sheet 3 can only be used to electrically contact the first film resistor 1 to change the resistance value thereof, and cannot directly contact other microstrip signal lines or film resistors; it is required that the second conductive sheet 4 can only be used to electrically contact the second film resistor 2 to change the resistance value thereof, and cannot directly contact other microstrip signal lines or film resistors. Therefore, the first film resistor 1 and the second film resistor 2 can be fabricated on the base 11 in different layers from other microstrip signal lines, the input and output terminals, and other film resistors so as to keep the basic principle and structure of the variable attenuator.

[0017] The co-plane of the first film resistor 1 and the first conductive sheet 3 is, without limitation, in the same plane as that of the second film resistor 2 and the second conductive sheet 4.

[0018] Fig. 3 illustrates the basic principle diagram of the variable attenuator of the invention. The operation principle of the variable attenuator is equivalent to a continuous variable bridge T-shaped attenuator, which is a symmetric wide band network with interchangeable input and output terminals.

[0019] Fig. 4 illustrates an ideal theoretical variation curve of the first film resistor 1 and the second film resistor 2 when the insulator 12 (forced displacement board) rotates clockwise. The variation trend of the resistance value of the first film resistor 1 is opposite to that of the second film resistor 2.

[0020] Fig. 5 illustrates a curve showing the attenuation amount of the variable attenuator fabricated according to the curve of Fig. 4 when the insulator 12 (forced displacement board) rotates clockwise. During designing and fabricating, the first film resistor 1 and the second film resistor 2 are chosen according to the curve of Fig. 4 so as to realize variation in the attenuation amount, which is required when the displacement of the variable attenuator is changed.

[0021] When the resistance value of one of the film resistors increases, the resistance value of the other film resistor decreases, and vice versa. Based on the variation trend of Fig. 3, a continuous variable attenuator can be fabricated.

[0022] The variable attenuator can be made into various package types, such as a surface mount type, a pin leg lead type, or a patch cord type.

[0023] In addition, in accordance with the invention, a silicon rubber film that is conductive in the vertical direction can be added between the base 11 and the insulator 12 so as to stabilize the contact between the film resistor and the conductive sheet, and thereby, to avoid wear between the film resistor and the conductive sheet.

[0024] Besides, in accordance with the invention, a groove can also be processed on the insulator 12, and the first conductive sheet 3 and the second conductive sheet 4 are located inside of the groove. An elastic substance having a negligible influence on the high frequency and microwave characteristics is added between the first conductive sheet 3 and the second conductive sheet 4 acting for contact short-circuiting within the groove so as to stabilize the contact between the film resistor and the conductive sheet, and thereby, to avoid wear between the film resistor and the conductive sheet.

[0025] The main feature of the variable attenuator of the invention is that in one plane (it can be multi layered), through the short-circuiting function of the conductive sheets, the resistance value of the first film resistor and the second film resistor can be simultaneously and flexibly changed in opposite directions. The first conductive sheet 3, the second conductive sheet 4, the first film resistor 1, and the second film resistor 2 can be in the geometric shape of an arc, rectangular, or other shape. The variable attenuator of the invention is miniaturized and cost-effective, and is suitable for use in the upper microwave frequency band.

Claims

1. A variable attenuator, comprising: a base (11), a first film resistor (1) located on the base (11), an input terminal (9) and an output terminal (10) connected to the two ends of the first film resistor (1); the two ends of the first film resistor (1) are further electrically connected to one end of a third film resistor (6) and one end of a fourth film resistor (7); the other ends of the third film resistor (6) and fourth film resistor (7) are further electrically connected to one end of a second film resistor (2), the other end of the second film resistor (2) is electrically connected to a ground terminal (13); a first conductive sheet (3) and a second conductive sheet (4) that can be electrically contacted by the first film resistor (1) and the second film resistor (2), respectively and are used to change the resistance values of the first film resistor (1) and second film resistor (2), respectively; and an insulator (12) with the first conductive sheet (3) and the second conductive sheet (4) fixed thereon.

2. The variable attenuator of claim 1, wherein the resistance value of said third film resistor is equal to that of said fourth film resistor.

3. The variable attenuator of claim 1 or claim 2, wherein the position of said first conductive sheet (3) and said second conductive sheet (4) can be changed when moving said insulator (12) so as to change the contact area between said first conductive sheet (3) and said first film resistor (1) and that between said second conductive sheet (4) and said second film resistor (2).

4. The variable attenuator of claim 1 or claim 2, wherein said first conductive sheet (3), said second conductive sheet (4), said first film resistor (1), and said second film resistor (2) can be in the shape of an arc or rectangular; and said first conductive sheet (3) and said second conductive sheet (4) can also be film resistors.

5. The variable attenuator of claim 1 or claim 2, wherein the common plane of said first film resistor (1) and said first conductive sheet (3) is without limitation in the same plane as that of said second film resistor (2) and said second conductive sheet (4); and the base (11) can be a multi-layered base.

6. The variable attenuator of claim 3, wherein the force to change the geometrical position of said first conductive sheet (3) and said second conductive sheet (4) can be a mechanical manual force, an automatic controlled mechanical force, an electromagnetic force, a force produced by heat or temperature, a force produced by the flow, expansion, or contraction of a liquid, or a force initiated by an optoelectronic excitation process.

7. The variable attenuator of claim 1, wherein the configuration of said variable attenuator is of a surface mount type, a pin leg lead type, or a patch cord type.

8. The variable attenuator of claim 7, wherein a silicon rubber film conductive in the vertical direction is added between said base (11) and said insulator (12).

9. The variable attenuator of claim 7, wherein a groove is disposed on said insulator (12); said first conductive sheet (3) and said second conductive sheet (4) are located inside of said groove; and an elastic substance is added between said first conductive sheet (3) and said second conductive sheet (4) within said groove.

Drawing