WO1996013101A1

WO1996013101A1 - Multi-function radio frequency circuit

Info

Publication number: WO1996013101A1
Application number: PCT/US1995/012825
Authority: WO
Inventors: Richard S. Kommrusch; Rong-Fong Huang
Original assignee: Motorola Inc.
Priority date: 1994-10-24
Filing date: 1995-09-29
Publication date: 1996-05-02

Abstract

A circuit (100) includes an antenna switch having desired components (106) and stray components (104, 108) associated therewith. The circuit (100) also includes a filter combined with the antenna switch circuitry. The filter circuit uses the stray capacitance (104, 108) of the switch circuit to realize its intended function. Such an efficient use of the stray components of one circuit by another provides for a spatially efficient substrate.

Description

MULTI-FUNCTION RADIO FREQUENCY CIRCUIT

Technical Field

This invention is generally related to radio frequency circuits and more particularly to those used in communication devices.

Background Miniaturization of radio communication devices has made significant leaps in the last several years with new developments in multi-layer integrated ceramic technologies . These developments have assisted in the miniaturization of many components such as chip capacitors and inductors. In general, as the number of components shrinks so does the size of the product. To reduce part count designers are generally inclined to combine a number of functionalities on a single module. However, the combination of functionalities on a single module results in many unexpected couplings such as stray capacitance which tend to increase signal loss. This additional loss degrades circuit and device performance. In addition to the increased loss, the combination of radio frequency functionalities on a single module generally produces additional undesired spurious signals. Attempts to improve the performance of the module by minimizing the stray effect often result in an increase in the size of modules hence defeating the initial impetus. It is therefore desired to reduce component counts of a radio frequency communication module with minimum adverse effects.

Brief Description of the Drawings

FIG. 1 shows a schematic diagram of a radio frequency circuit in accordance with the present invention.

FIG. 2 shows a top view of the middle layer lay out of a multi-layer structure in accordance with the present invention of the schematic diagram of FIG. 1.

FIG. 3 shows a cross sectional view of the multi-layer structure in accordance with the present invention of the schematic diagram of FIG. 1.

FIG. 4 shows a multi-layer ceramic structure in accordance with one embodiment of the present invention. Detailed Description of the Preferred Embodiment

In order to control radiation of harmonic frequencies and reduce component count the present invention combines the functions of a filter and an antenna switch on a single module. An objective with combining the functions of these two components on a signal module was to reduce component count. This objective is met by the efficient use of the stray capacitance of one circuit for the benefit of the other. The technique used in the accomplishment of this objective will be better understood by referring to the drawings and the description that follows.

Referring to FIG. 1, a schematic diagram of a radio frequency circuit, specifically an antenna switch/filter circuit 100 in accordance with the present invention is shown. The circuit 100 includes a first circuit that performs the function of switching an antenna 116 between a transmit port 102 and a receive port 140. A second circuit provides DC blocking and harmonic filtering. The switching of the antenna port 116 to the transmit port 102 or the receive port 140 is controlled via a control signal applied to B+, port 131. Diodes 112 and 130 along with components 110 ,124, 120, 128, and 132 form the antenna switch portion of the circuit 100. DC blocking is provided by Capacitors 106,118, and 136. When in the transmit mode, circuit elements 104, 108, 124, 126, 120, 122, and 114 form a harmonic filter in the transmitter to antenna path. When in the receive mode, circuit elements 114, 122, 120,126, 128, 134, and 138 form a harmonic filter in the receiver to antenna path. As is known in the art, the fabrication of a Multi- Layer Ceramic (MLC) circuit with outside ground plans inevitably results in the formation of stray capacitance. As an example in FIG 3, the plates of the series, DC blocking, capacitor 106 have stray capacitance to ground represented by capacitors 104 and 108 schematic. Similar stray capacitors can be found on blocking capacitors 118 and 136. In a traditional antenna switch design these stray capacitance are undesirable. However, when a harmonic filter is added to the traditional antenna switch, a use for the stray capacitors is found.

Thus, the utilization of the stray capacitance associated with the antenna switch circuit provides for a more spatially efficient module. These stray capacitances are used in place of discrete components normally required for the construction of a harmonic filter. This substitution reduces the component count, hence a smaller module. Referring to FIG. 2, the top view of the 11th layer lay out of the module 100 in accordance with the present invention is shown. Transmission lines and capacitors are realized via metallized lines and pads and/or inter-layer runners. Both three dimensional and two dimensional zigzag structures could be used in order to save space occupied by the transmission Unes. As can be seen from the top view depicted in FIG. 2, the preferred embodiment includes one 3 turn helical line and three conventional zigzag lines. This layout is aimed at providing the best combination of performance and size compactness. The construction of these components will be described in more detail in association with FIG. 4. In short, the module 100 is realized utilizing a twenty layer MLC structure, with a size of 360 mils x 300 and a thickness of 80 mils. As stated, this construction allows the stray reactances to be effectively used in order to reduce the number of discrete components. FIG. 4 shows several layers of a multi-layer substrate arrangement

400 that, when assembled, provides a device having transmission lines and multi-layer capacitors with desired characteristics. These layers are selectively metallized in accordance with known procedures. One such procedure is explained in a pending application titled "Transmission Line Device Using Stacked Conductive Layers" having a serial number

08/187951, an attorney docket number 736/738F/I and assigned to Motorola Inc.

In accordance with the present invention, a first ground plane 410 is deposited on a first dielectric substrate 402. A first conductive layer 430 partially enclosing a first area on a second dielectric substrate 406 is positioned substantially adjacent to the first dielectric substrate 402. A second conductive layer 440 that at least partially encloses an area on a third substrate 408 and corresponding to the first area 430 is positioned substantially adjacent to the second dielectric substrate 406. This process is continued until all the transmission lines and capacitors of device 100 are formed. The last layer 404 includes a ground plane 420 on one of its major surfaces. This ground layer 420 in conjunction with the ground layer 410 on substrate 402 provides for the shielding of the components formed via the selective metallization of the inner layers. The capacitor 106 is formed on substrates 406, 408, ... of layers 2-20 via plates 430 and 440 which at least partially enclose first and second areas on subsequent layers.. In other words, the staking of the layers 2-20 allows the plates 430 and 440 to provide their intended function of forming the blocking capacitor 106. The coupling of plate 430 to two ground planes 410 and 420 results in the formation of stray capacitances that would normally be unwanted and steps must be taken to offset their undesired effects. This stray capacitance is symbolically shown by 108 in the schematic diagram of FIG. 1. In accordance with the present invention, the capacitor 108 is used as an effective component of the filter portion of the circuit 100. Similarly, a stray capacitance is formed between ground planes 410 and 420 and the plate 440. This capacitor is symbolically shown as 104 and functions as part of the filter circuit. It is noted that although the 20 layers of the device 100 are used to realize the capacitors in the preferred embodiment, only two layers are necessary. Modifications to the layout of the components on the substrates will allow a designer to use limited layers to realize these capacitors. Such modifications do not constitute a departure from the spirits of the present invention which is concerned with the efficient utilization of substrate space.

Conductive vias, such as 422 are used to carry signals from one substrate to another. These vias provide the conductive means for connecting the first and second conductive runners on several layers. In other words, the vias could be used to provide conductive means for connecting a first plurality of conductive strips to a second plurality of conductive strips, wherein a multiple- turn coil is formed using the first plurality of conductive strips and the second plurality of conductive strips.

In addition to the capacitors, the transmission lines of the circuit 100 are realized on the substrate of FIG. 4. These transmission lines are fabricated in a fashion similar to the fabrication of the capacitor 106. In general, a first plurality of conductive strips are disposed on one of the dielectric substrates. These strips are then coupled to capacitors 104, 106, 108, ... in accordance with the schematic diagram of circuit 100. In a preferred embodiment, the dielectric substrates 402, 404, 406, ... are formed using ceramic materials that can be co-fired with a co-fireable metal composition. Further, the conductive layers 412, 430, and 440 are preferably deposited on the dielectric substrates as provided by, for example, DuPont's Green Tape™, Systems, thereby producing conductive layers having relatively high conductance values. Similarly, the conductive vias, for example 422, are made by at least partially filling the volume of spatially arranged, pre-punched holes in the ceramic using the co-fireable metal composition.

It can be seen that stray capacitors formed on a substrate by one circuit may be effectively used by another circuit residing on the same substrate. The strategic location of components increases the efficient utilization of otherwise undesired components. It should be noted that although FIG 4 illustrates the use of vertically stacked conductive layers, the present invention further anticipates the use of conductive layers that are horizontally stacked. Referring to FIG. 3, a side view of the various layers of the substrate of

FIG. 400 is shown. As can be seen, the capacitors and inductors are formed using the multi-layer structure described above. Diode 112 is placed on the top surface and is connected according to the schematic diagram.

In summary, a novel fabrication technique is employed to utilize the area of a circuit board efficiently. As part of this technique, stray capacitances associated with the fabrication of the circuit are used advantageously by others circuit in order to reduce component count. In other words, the reactive components of one portion of a radio frequency circuit are strategically situated in order to allow their associated stray reactances to operate as functional components of another portion of the circuit. This avoids attempts to offset the effects of stray reactances while simultaneously reducing component count. What is claimed is:

Claims

CJajms

1. A radio frequency circuit, comprising: a first circuit having a first intended function and stray capacitance associated therewith; and a second circuit having a second intended function and coupled to the first circuit, the second circuit using the stray capacitance of the first circuit to perform the second intended function

2. The radio frequency circuit of claim 1, wherein the first circuit includes an antenna switch.

3. The radio frequency circuit of claim 1, wherein the second circuit includes a filter.

4. The radio frequency circuit of claim 1, further including a transmission line device.

5. The radio frequency circuit of claim 4, wherein the transmission line device comprises: a first ground plane disposed on a first dielectric substrate; a first conductive layer that at least partially encloses a first area on a second dielectric substrate, wherein the second dielectric substrate is positioned substantially adjacent to the first dielectric substrate; and a second conductive layer that at least partially encloses a second area corresponding to the first area on a first major surface of a third dielectric substrate, wherein the third dielectric substrate is positioned substantially adjacent to the second dielectric substrate.

6. A spatially efficient radio frequency circuit, comprising: a multi-layer substrate assembly; an antenna switch having stray capacitance associated therewith and formed on a portion of the multi-layer substrate assembly; a filter having at least one capacitor and combined with the antenna switch on the substrate assembly in order to allow the stray capacitance of the antenna switch to function as the at least one capacitor..

7. The radio frequency circuit of claim 6, further including a transmission line device.

8. A communication device, comprising: a radio f equency circuit, including: an antenna switch having a stray capacitance associated therewith; and a filter combined with the antenna switch and having at least one capacitor formed via the stray capacitance of the antenna switch.

9. The communication device of claim 7, further including a transmission line device.