DE2433376A1 - ADJUSTABLE LC RESONANCE CIRCUIT AND PROCEDURE FOR ADJUSTING IT - Google Patents

Description

Dipl.-Ing. H. Sauenlancl · Dp -Ing. R. König · Dipl.-Ing. K. Bergen

Patent Attorneys ■ 4000 Düsseldorf 3O · Cecilienallee 7G · Telephone 43273s

July 10, 1974 29 429 B

RCA Corporation, 30 Rockefeiler Plaza, New York , N ₀ Y. 10020 (V.St ₀ A.)

"Resettable LC resonant circuit and method too

whose tuning "

An LC resonance circuit with a conventional chip capacitor, Z ₀ B ₀ a ceramic multilayer capacitor, and an inductor, Z ₀ B ₀ made of a wire coil and a core, which consists either of pressed, sintered iron powder or a pressed, sintered powdery ferrite, can be tuned to a target center frequency either by grinding off part of the capacitor or by adjusting the inductor core or by using both methods in combination. Grinding off a capacitor reduces its capacitance and increases the resonance frequency of the circuit. It is difficult, however, to stop the grinding operation at the precise moment when the resonance frequency of a circuit has reached the correct target value. There is this always the danger that the target value is exceeded ₀ If the grinding at such a low speed that sufficient accuracy can be achieved, this process usually takes a economic point of view for too long time.

In a conventional circuit, the location of the inductor core can be changed to either increase

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6 fu

or reducing the resonance frequency of an LC circuit to reach. Therefore, fine-tuning the resonance frequency is not just a matter of setting the capacitor However, the positional adjustment of the core can also become uneconomical when used for adjustment too much time is needed.

Microminiature hybrid circuits often have a printed capacitor and almost all of them have printed ones Resistors on “The inductors can be at low Inductance values can also be printed. Heretofore, printed inductors have usually been flat Spiral made of metal deposited in the vapor phase with or without an associated layer of a magnetic Material to increase the inductance to «However, if the required inductance is large, it is according to the previous one Prior art did not allow to use a printed inductor. Instead, a coil or applied an inductor of more conventional design. When the hybrid circuit is used as an LC resonance circuit practically the same problems arise when tuning the circuit to a desired center frequency.

The invention is based on the object of retuning of LC resonance circuits, especially those with a micro-miniature design to simplify and make more economical.

According to the invention, an LC circuit in a hybrid design is provided for this purpose, which is a retunable circuit Capacitor, one conventionally called a coil of wire or has a main inductor designed as a printed component and a printed second inductor, whose inductance value is small compared to that of the main inductor. Under the expression "printed"

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is understood to be a flat conductor, the conductive material of which is screen-printed or another method of application, E.g. a stencil printing process is specified. The inductance of the second inductor can be changed in small steps so that a fine adjustment of the inductance is possible. The second The inductor is also designed so that its inductance can be increased by trimming or retuning. If the nominal inductance is not too large, the printed inductor can even reduce the total inductance of the Form circuit.

The inventive method for retuning the resonance circuit to a target center frequency is characterized in that the capacitor increases the The resonance frequency of the circuit is tuned until the resonance frequency of the circuit is slightly higher Value than the target center frequency has reached, and • that then the tunable, printed inductor below Increase in its inductance is trimmed until the center frequency has dropped to the target value. By the reduction in capacitance when trimming the capacitor is therefore initially carried out in an approximate manner the center frequency to a slightly higher value, followed by increasing the inductance of an inductor Fine adjustment to the target center frequency of the circuit is made.

In the following wildly the invention based on in, the drawing illustrated embodiments explained in more detail. Show it:

1 shows a plan view of an LC hybrid circuit according to an exemplary embodiment of the invention, to be precise before trimming;

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Figure 2 is a similar view of the circuit after trimming; and

FIG. 5 shows a corresponding view of an alternative embodiment of the circuit according to FIG. 1.

The invention can be used in a hybrid circuit on a ceramic substrate. As in Fig. 1 As shown, the base may be a rectangular plate 2 made of 95% aluminum oxide. on a surface 4 of the base can be a capacitor 6 with a lower metal electrode 8, a dielectric Intermediate layer 10uid of upper metal electrodes 8 and 12 can be made, for example, by printing Defined zones can be produced with an ink, the ink consisting of particles of silver, palladium and palladium oxide and a glass frit with enough organic solvent to make a thick one Paste is made. The ink is applied to the base 4 (or the dielectric layer 10) by screen printing. The solvent is removed by heating in an oven and the dried layers are then fired to melt the glass. The dielectric layer 10 can be a glass frit without the metallic Contain particles.

In the embodiment described, the capacitor 6 can also be made by depositing the layers Metal and a dielectric can be produced from the vapor phase. In addition, the capacitor 8 can even be formed by a multilayer chip capacitor, which can be trimmed to reduce its capacitance have to be.

The circuit also has a main inductor 14,

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formed by a conventional wire winding reel suitable size for mounting on the base 2 or as conventional printed inductor can be implemented. The inductor 14 is printed with the capacitor 6 through Conductors 16 and 18 connected in parallel. The attachment of the coil should preferably be done after firing the circuit take place.

Three parallel printed strip conductors 20, 22 and 24 are connected to the conductor 18. The strip conductors 20, 22 and 24 are arranged at right angles to and starting from the conductor 18. Before trimming, the conductor 18 forms a second inductance. By trimming in such a way that the length of the conduction path over the strip conductors is increased, the inductance of the second inductor and accordingly, of course, the total inductance is increased. The resonance frequency of the circuit can be set in this way. In the circuit shown, the dimensions of the strip conductors are chosen so that when they are trimmed, the total inductance of the circuit is preferably increased by about 5 $ in a manner to be explained below? this dimension can be changed considerably depending on the type of circuit to be set. The size of the maximum inductance determined by the strip section depends largely on the available support zone. It is usually not economical, large areas of the substrate with a printed circuit to v © rs © h @ n _o

The strip _{conductors 20 5} , 22 and 24 can consist of the same Zermetmaterials as the conductors 16 and 18, so that when the circuit is fired, problems arise due to different materials. In the embodiment described, each stripline has the dimensions 2 ₉ 54 χ 0.46 cm and a thickness of 0.19 Ω.

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The procedure for retuning the RC circuit is in progress as follows. The resonance center frequency f of an LC circuit can be expressed by the following equation j

^£ o =

2T

where f _{Q is} measured in Hertz, L in Henry and C in Farads. The capacitor is usually designed to have a capacity of 120 to 13096 after being printed and fired of the nominal capacity after trimming. In order to achieve a certain calculated center frequency f _Q , the values of the capacitor 6 and the main inductor 14 can be varied over a considerable range. As indicated above, the dimensions of the strip conductors 20, 22 and 24 in the circuit described are selected so that, regardless of the selected size (inductance) of the inductor 14, retuning the strip conductors can increase the total inductance by about 5%.

The resonance frequency without trimming the holding components is measured and the change in capacitance required to achieve the desired frequency f is calculated. The capacitance of the capacitor 6 is then reduced (FIG. 2) by grinding away part of the upper electrode 12 to form a slot 26 (or cutting it out with the aid of a laser beam). Because of the lack of accuracy in the grinding process when it is carried out at reasonable speeds, the capacitance is preferably reduced slightly beyond the value required _{to set the desired frequency f Q.} For example, the capacity can be reduced to such an extent that an f ₀ of approximately 10,396 of the desired setpoint results.

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In order to bring the resonance frequency back to the nominal value, the strip conductors 20, 22 and 24 (FIG. 2) are then abraded one after the other by removing zones of their central section while the central frequency of the circuit is monitored. This process is continued until the Ms target resonance frequency is reached ₀ Thus one can for example first start 20 and this grind to form a slot or notch 28 with the strip conductor; in this case one starts from the nearest end of the strip conductor and drives the slot 28 in the direction of the distal end of the strip prior to _o In the embodiment described, the slot has a width of 0 _t 152 © m "Due to the slot 28, the effective length of the conductor increases 18, which increases the inductance of the printed conductor by a small amount _β If this amount is not sufficient to bring the resonance frequency to the desired value, a second slot 30 is cut in the strip conductor 22, etc. A larger or smaller number of strip conductors can be provided ^ whereby the strip conductors themselves can also be made longer or shorter to reduce or expand the maximum range of change of the inductance. In the circuit shown, the incisions in all three strip conductors are 0.152 cm wide and cause an increase in inductance by 0.08 ^ H at 1 MHz. The measured inductance of the conductor 18 before trimming was 0.03 JU H _0. After trimming, it was 0.1

The following table shows the changes in resonance frequency, which can be achieved with different capacitance values and a large inductance. In the In the table, L is the inductance of the coil 14, C

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the capacitance of the capacitor 6, f the resonance frequency of the circuit before trimming the inductor, f ^f _o the resonance frequency after trimming the inductor strips 20, 22, 24 to the maximum extent and ^ f the achieved change in the resonance frequency,

ι) C (pF) ^£ o (MHz) ^{£ t} o (MHz) Δ f kHz 15th 70 4, 91 4, 89 12th , 7 kHz 5 20th 15, 91 15, 79 125 , 49 kHz 1 10 50, 32 43 1 , 9

The capacitance and inductance can be adjusted at different times during manufacture. So can For example, the capacitance can be readjusted "before the circuit is encapsulated and before the active components be attached. The tunable printed inductor can be trimmed after switching to the Part is encapsulated. It may be desirable to proceed in the aforementioned manner when encapsulating the resonant frequency the circuit changed

The previously in connection with the setting of the resonance center frequency The invention described in an LC circuit may also find application in other circumstances, where The inductance of an inductor should be increased using a fine tuning process, this process can be carried out with an automatically operating device. A solid one, attached to a pad The inductor can be supplemented by a re-tunable inductor of the type described. The trimming can be done with the help of an air jet grinder or a laser device.

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Referring to Fig. 3, there is shown a modified embodiment in which a printed inductor, unrelated to a fixed coil, can be trimmed to increase its inductance. Such circuits without a fixed coil can be used in those cases in which the inductances required are sufficiently small. In the circuit according to FIG. 3, the only inductance is formed by the conductor 18, the conduction path of which is lengthened in the areas of the strip conductors 20, 22 and 24 after trimming _{or the like}

In the embodiment according to FIG 3 _e? in which both the capacitor and the inductor from Zemet inks can be constructed _s it may be possible, with a single firing approximated the circuit to bring to the desired resonant frequency ^ Mach firing, however, the resonance frequency etros below or above the desired value are "Depending upon which of these conditions prevails _s can either be trimmed DER capacitor or the inductor for adjusting the desired resonant frequency irierd®n _o

Becoming well known, the capacitance of a capacitor of the printed cermet = materials can be prepared by suspension of the peak combustion temperature and / or the Brem.aau.er changed © n _{e 9} It is also known that the conductivity of printed Zermetleitem by jtnaerung diesar two internal parameters are changed

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Claims (1)

RCA Corporation, 30 Rockefeller Plaza, New York . NY 10020 (V.St.A.) Patent claims: (1./Verfahren for retuning a microelectronic, - ' an adjustable printed capacitor and a fixed main inductor having resonance circuit to a target center frequency, the capacitor has a higher value than the Bndwert to be set, characterized in that a tunable printed inductor with a substantially lower inductance than that of the main inductor is connected in series with the main inductor, the tunable inductor being trimmable to a higher inductance, so that the capacitor is tuned by increasing the resonance frequency of the circuit until the resonance frequency of the circuit is slightly higher than the Setpoint center frequency, and that then the tunable inductor is trimmed until the center frequency has dropped to the setpoint. 2. The method according to claim 1, characterized in that g e - ■ indicates that the trimming of the re-tunable inductor is carried out by removing material from the central area of at least one of several series-connected striplines made of Zeraet material and forming the re-tunable printed inductor. 3. Microelectronic LC resonance circuit, characterized by a tunable 509813/0726 Capacitor (8, 10 _s 11), a fixed main inductor (14) and a printed, re-tunable inductor (18, 20, 22, 24) s which is connected to the main inductor (14) <= and whose inductance can be increased by trimming. Circuit according to Claim 3 _S, characterized in that the re-tunable inductor (18) has a series connection of strips (20, 22, 24) made of conductive material «, Method sum re-tuning a LG = resonance _{circuit with an adjustable capacitor and a fixed main inductor 9} which represents a large part of the total _{inductance required in the circuit s} characterized in that a printed inductor of relatively low inductance is connected in series with the fixed inductor, that the capacitance of the printed capacitor is reduced to increase the resonant frequency of the circuit above the nominal value, and that the printed inductor is then trimmed to lower the resonant frequency of the circuit to the nominal value «, A method of re-tuning of an LC resonance circuit with a large part of the total inductance of the circuit performing fixed main inductor, characterized by _g that first the circuit wirdj so constructed that its resonance frequency is higher than the desired resonant frequency that is a printed inductor relatively low inductance is switched to the fixed inductor in series _s and that the printed inductor the circuit is trimmed to the target value for lowering the resonant frequency. 509813/0726 7. Method for increasing the inductance of a fixed inductor in the course of fine-tuning, thereby characterized in that the inductor is assigned a tunable printed inductor whose Inductance can be increased by trimming, and that the tunable inductor by increasing its inductance is trimmed by a predetermined amount. 8. Microelectronic LC circuit, characterized that a re-tunable capacitor (8, 10, 12) and a printed inductor (18, 20, 22, 24) are connected in series, with the inductor consisting of one or more printed strips (20, 22, 24) having conductive material, which extend from a main conductor (18). 9. Circuit according to claim 8, characterized in that the capacitor (8, 10, 12) is a printed capacitor. 10. Inductor for a microelectronic circuit, its Inductance can be increased by trimming, characterized in that on a base (2), a main conductor (18) is constructed, from which several strip conductors (20, 22, 24) extend. 11. Method of tuning an LC printed resonance circuit, characterized in that initially the LC circuit with a re-tunable capacitor and an inductance-increasing capacitor by trimming Inductor is printed, the conditions during printing are set so that the target resonance frequency it is approximately achieved that the actual resonance 509813/0726 frequency of the printed circuit is measured, and that depending on the position of the actual resonance frequency below or above the target resonance frequency, either the capacitor or the inductor is readjusted or trimmed by such a value that the actual value matches the nominal value of the resonance frequency matches » ■ 0 9813 / 072S Blank page