Compact radio frequency harmonic filter using integrated passive device technology

The present invention relates generally to electronic components. More particularly, the present invention relates to radio frequency (“RF”) harmonic filters fabricated using integrated passive device (“IPD”) technology.

The prior art is replete with electronic devices and components designed for high frequency data communication applications. A common practical application for such devices and components is cellular telephony systems. In this regard, the need for component integration will increase as module sizes decrease for high performance cellular phones with advanced features. Cellular phone radio transmitters use several passive components for functions such as filtering, impedance matching, and switching. For example, a harmonic filter is used for signal selectivity over radio bands, such as the 824-915 MHz AMPS/GSM band or the 1.71-1.91 GHz DCS/PCS band. Practical harmonic filters for use in these bands are specifically designed to reject the second, third, and fourth harmonic frequencies from an RF input signal.

In conventional IPD implementations, an RF harmonic filter includes at least two loop inductors, which represent the bulk of the physical space of the device, which is typically on the order of approximately 1 mm 2 . In addition, conventional RF harmonic filter designs employ distinct input impedance matching and output impedance matching circuit elements, which inherently contribute to the overall size of the device. In accordance with the current trend toward miniaturization, a smaller device footprint is desirable, especially if such a smaller footprint can be achieved without a significant increase in manufacturing cost or complexity.

Accordingly, it is desirable to have a compact, low cost, RF harmonic filter that can be fabricated as an IPD. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

An RF harmonic filter device configured in accordance with an embodiment of the invention is implemented as an IPD using only one IPD loop inductor. The RF harmonic filter employs at least one circuit that functions as a combined harmonic resonance and impedance matching circuit. The elimination of an IPD loop inductor results in a reduction in the footprint of the device, thus reducing the overall size and packaging requirements of the RF harmonic filter device.

The above and other aspects of the invention may be carried out in one form by an RF harmonic filter circuit fabricated using IPD. The RF harmonic filter circuit includes a substrate, only one IPD loop inductance formed on the substrate, and a harmonic resonance circuit formed on the substrate, where the harmonic resonance circuit includes the IPD loop inductance.

A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures.

FIG. 1 is a schematic diagram of a prior art harmonic filter circuit topology;

FIG. 2 is a perspective view of an example device layout for a high band harmonic filter having the topology shown in FIG. 1 ;

FIG. 3 is a perspective view of an example device layout for a low band harmonic filter having the topology shown in FIG. 1 ;

FIG. 4 is a schematic diagram of a high band harmonic filter circuit topology according to an example embodiment of the invention;

FIG. 5 is a perspective view of an example device layout for a high band harmonic filter having the topology shown in FIG. 4 ;

FIG. 6 is a graph showing simulated insertion loss characteristics for the high band harmonic filter shown in FIG. 5 ;

FIG. 7 is a schematic diagram of a low band harmonic filter circuit topology according to an example embodiment of the invention;

FIG. 8 is a perspective view of an example device layout for a low band harmonic filter having the topology shown in FIG. 7 ; and

FIG. 9 is a graph showing simulated insertion loss characteristics for the low band harmonic filter shown in FIG. 8 .

The following detailed description is merely illustrative in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

The invention may be described herein in terms of functional and/or schematic components. It should be appreciated that such components may be realized in any number of practical ways. For example, an embodiment of the invention may employ various elements, e.g., conductive traces, wire bonds, integrated passive devices, semiconductor substrate materials, dielectric materials, or the like, which may have characteristics or properties known to those skilled in the art. In addition, those skilled in the art will appreciate that the present invention may be practiced in conjunction with any number of practical RF circuit topologies and applications and that the harmonic filter circuits described herein are merely example applications for the invention.

For the sake of brevity, conventional techniques related to RF circuit design, RF signal propagation, RF impedance matching, semiconductor process technology, integrated passive device fabrication, and other aspects of the circuits (and the individual operating components of the circuits) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical embodiment.

The following description refers to elements or features being “connected” together. As used herein, unless expressly stated otherwise, “connected” means that one element/feature is directly or indirectly connected to another element/feature, and not necessarily mechanically. For example, although the various schematics depict example arrangements of elements, additional intervening elements, devices, features, or components may be present in actual embodiments (assuming that the functionality of the circuits are not adversely affected).

As used herein, a “node” means any internal or external reference point, connection point, junction, signal line, conductive element, or the like, at which a given signal, logic level, voltage, data pattern, current, or quantity is present. Furthermore, two or more nodes may be realized by one physical element (and two or more signals can be multiplexed, modulated, or otherwise distinguished even though received or output at a common mode).

FIG. 1 is a schematic diagram showing the general circuit topology of an RF harmonic filter 100 , FIG. 2 is a perspective view of an example IPD layout for a high band RF harmonic filter 200 having the circuit topology shown in FIG. 1 , and FIG. 3 is a perspective view of an example IPD layout for a low band RF harmonic filter 300 having the circuit topology shown in FIG. 1 . RF harmonic filters 100 / 200 / 300 share a number of features and, where applicable, the following description of common features is intended to apply to RF harmonic filters 100 / 200 / 300 individually and collectively.

An RF signal enters harmonic filter 100 at an input port 102 (corresponding to a conductive RF input pad), and a filtered RF signal within the desired RF band is provided at an output port 104 (corresponding to a conductive RF output pad). In the practical layouts shown in FIG. 2 and FIG. 3 , the RF energy propagates over conductive traces formed on an insulating (semiconducting) substrate. Harmonic content associated with the RF input signal is rejected by three harmonic resonance circuits: a second harmonic resonance circuit 106 / 206 / 306 ; a third harmonic resonance circuit 108 / 208 / 308 ; and a fourth harmonic resonance circuit 110 . Second harmonic resonance circuit 106 / 206 / 306 is realized as an LC tank circuit (inductor L 1 in parallel with capacitor C 1 ), third harmonic resonance circuit 108 / 208 / 308 is realized as an LC tank circuit (inductor L 7 in parallel with capacitor C 5 ), and fourth harmonic resonance circuit 110 is realized as an LC series combination (capacitor C 3 in series with inductor L 5 ). Harmonic filter 100 also includes an input impedance matching circuit 112 and an output impedance matching circuit 114 . Input impedance matching circuit 112 is realized as an LC series combination (capacitor C 2 in series with inductor L 4 ), and output impedance matching circuit 114 is realized as an LC series combination (capacitor C 4 in series with inductor L 6 ). The specific inductor and capacitor values of the harmonic filters are selected according to the desired filtering characteristics and the desired output frequency band. For example, harmonic filter 300 may be suitably configured for operation with AMPS/GSM applications (824-915 MHz), while harmonic filter 200 may be suitably configured for operation with DCS/PCS applications (1710-1910 MHz).

In practice, IPDs can be used to effectively reduce component and module sizes. As used herein, an IPD is a passive electronic device or a passive electronic component that can be fabricated using semiconductor process technology. An IPD can be produced with very high precision, excellent reproducibility, and low cost in high quantities by utilizing semiconductor wafer processing technologies. The layouts of harmonic filter 200 and harmonic filter 300 represent IPD realizations, where all of the depicted elements are formed on the same substrate (e.g., a semiconductor or insulating substrate such as GaAs, glass, or ceramic) using the same semiconductor process technology (i.e., the fabrication or manufacturing process by which the IPD is formed). In harmonic filters 200 / 300 , inductors L 1 and L 7 are realized as conductive RF signal line loops (bridges are employed at the respective “intersections” of each inductor to insulate the inductor loops from the respective C 1 and C 5 transmission lines), and the C 1 , C 2 , C 3 , C 4 , and C 5 capacitors are formed as IPDs on the substrate in the desired locations. The L 1 and L 7 inductors in harmonic filter 200 are smaller in size, include less loops, and have lower inductances than the L 1 and L 7 inductors in harmonic filter 300 . Notably, inductors L 4 , L 5 , and L 6 (not shown in FIGS. 2 and 3 ) are realized as wire bonds or other inductance elements connected between respective contact pads (numbered 210 , 212 , and 214 in FIG. 2 ; numbered 310 , 312 , and 314 in FIG. 3 ) and ground pads, which may be off-chip. Thus, inductors L 4 , L 5 , and L 6 are not actually part of the IPD itself, and harmonic filters 100 / 200 / 300 may be referred to as “two inductor” IPDs.

FIG. 4 is a schematic circuit diagram of a high band RF harmonic filter 400 configured in accordance with an embodiment of the invention, and FIG. 5 is a perspective view of an example IPD layout for RF harmonic filter 400 . Referring to FIG. 4 , harmonic filter 400 generally includes an RF input node 402 , an RF output node 404 , a second harmonic resonance circuit 406 connected between RF input node 402 and RF output node 404 , a combined third harmonic resonance and input matching circuit 408 connected to RF input node 402 , and a combined fourth harmonic resonance and output matching circuit 410 connected to RF output node 404 . In operation, RF input node 402 may be connected, via an inductance L 2 , to a component, device, circuit, or termination 412 that provides an input impedance (typically 50 ohms) for harmonic filter 400 , and RF output node 404 may be connected, via an inductance L 3 , to a component, device, circuit, or termination 414 that provides an output impedance (typically 50 ohms) for harmonic filter 400 .

Second harmonic resonance circuit 406 includes an inductor L 1 connected in parallel with a capacitor C 1 , where inductor L 1 and capacitor C 1 are each connected between RF input node 402 and RF output node 404 . Second harmonic resonance circuit 406 is suitably configured to reject the second harmonic component of the RF input signal. Combined third harmonic resonance and input matching circuit 408 includes a capacitor C 2 connected in series with an inductor L 4 . As shown in FIG. 4 , combined third harmonic resonance and input matching circuit 408 is connected between RF input node 402 and ground. Combined third harmonic and input matching circuit 408 is suitably configured to reject the third harmonic component of the RF input signal while establishing a desired input impedance for harmonic filter 400 . Combined fourth harmonic resonance and output matching circuit 410 includes a capacitor C 3 connected in series with an inductor L 5 . As shown in FIG. 4 , combined fourth harmonic resonance and output matching circuit 410 is connected between RF output node 404 and ground. Combined fourth harmonic and output matching circuit 410 is suitably configured to reject the fourth harmonic component of the RF input signal while establishing a desired output impedance for harmonic filter 400 .

In an alternate embodiment, harmonic filter 400 may employ a combined fourth harmonic resonance and input matching circuit (in lieu of combined third harmonic resonance and input matching circuit 408 ), and a combined third harmonic resonance and output matching circuit (in lieu of combined fourth harmonic resonance and output matching circuit 410 ). Of course, such an alternate embodiment would require appropriate design and optimization to accommodate the combined functions. Furthermore, although the preferred embodiment maintains the position of the second harmonic resonance circuit as shown in FIG. 4 , an alternate embodiment may utilize that position for the third or fourth harmonic resonance circuit, with the second harmonic resonance circuit being combined with the input or output matching circuit as described herein.

Referring to FIG. 5 , an RF signal enters harmonic filter 400 at an RF input pad 416 (which corresponds to RF input node 402 in FIG. 4 ), and a filtered RF signal within the desired RF band is provided at an RF output pad 418 (which corresponds to RF output node 404 in FIG. 4 ). In the practical layout shown in FIG. 5 , the RF energy propagates over conductive traces formed on an insulating (semiconducting) substrate 419 . The IPD layout shown in FIG. 5 depicts elements formed on the same substrate 419 (e.g., a semiconductor or insulating substrate such as GaAs, glass, or ceramic) using the same semiconductor process technology (i.e., the fabrication or manufacturing process by which the IPD is formed). In this regard, inductor L 1 is realized as a conductive RF signal line loop inductor (air or dielectric bridges are employed at the respective “intersections” of inductor L 1 to insulate the inductor loops from the transmission lines utilized for the C 1 capacitor).

In practice, the C 1 , C 2 , and C 3 capacitors are each realized as an IPD capacitance formed on substrate 419 in the desired locations. IPD capacitance C 1 is connected between RF input pad 416 and RF output pad 418 (in the example embodiment, inductance L 1 forms bridges over the transmission line associated with IPD capacitance C 1 ). In this regard, the input end of capacitor C 1 corresponds to its RF input node and the output end of capacitor C 1 corresponds to its RF output node. IPD inductance L 1 is also connected between RF input pad 416 and RF output pad 418 . Thus, IPD capacitance C 1 is connected in parallel with IPD inductance L 1 . IPD capacitance C 2 is connected between RF input pad 416 and a ground pad 420 , and IPD capacitance C 3 is connected between RF output pad 418 and a ground pad 422 .

Notably, inductors L 4 and L 5 (not shown in FIG. 5 ) are realized as wire bonds, conductive traces, or other inductance elements connected between respective ground pads 420 / 422 and grounding pads or other ground potential locations, which may be off-chip. In other words, these inductance elements establish ground connections to ground pads 420 / 422 . Thus, inductors L 2 , L 3 , L 4 , and L 5 need not actually be part of the IPD substrate itself, and harmonic filter 400 may be referred to as a “single inductor” IPD. In practical embodiments, harmonic filter 400 includes only one IPD loop inductor. As mentioned above, IPD capacitance C 2 and the L 4 inductance element connected to ground pad 420 form the combined third harmonic resonance and input matching circuit, which is connected to RF input pad 416 , while IPD capacitance C 3 and the L 5 inductance element connected to ground pad 422 form the combined fourth harmonic resonance and output matching circuit, which is connected to RF output pad 418 .

In accordance with one practical embodiment of harmonic filter 400 , IPD inductance L 1 , IPD capacitance C 1 , IPD capacitance C 2 , IPD capacitance C 3 , the L 4 inductance element, and the L 5 inductance element are suitably configured to provide a filter response that rejects harmonic frequencies corresponding to a pass band of 1.71 GHz to 1.91 GHz. To accomplish this objective, the input and output matching circuit component values are tuned to make the combined circuits resonate at the desired third and fourth harmonic frequencies while still providing good input and output impedance matching. Typical component values for such an example embodiment are contained in Table 1.

In accordance with known semiconductor fabrication techniques, harmonic filter 400 , including IPD inductance L 1 , IPD capacitances C 1 , C 2 , and C 3 , RF input pad 416 , RF output pad 418 , ground pads 420 / 422 , and other elements shown in FIG. 5 may be formed on a common semiconductor substrate 419 using a plurality of metal layers and a number of dielectric layers. The metal layers are deposited and the desired conductive traces are etched or otherwise formed from the metal layers. The metal layers are typically referred to as “metal 1,” “metal 2,” “metal 3,” and so on to indicate the order in which they are deposited or formed onto the substrate during the fabrication process. In accordance with one practical embodiment, at least portions of the IPD capacitances are formed from the metal 2 layer and the loops of IPD inductance L 1 are formed from the metal 3 layer. In accordance with one practical semiconductor process technology, metal 1 elements are approximately 0.6 μm to 2.0 μm thick; metal 2 elements are approximately 2.5 μm thick, and metal 3 elements are approximately 10 μm thick.

Harmonic filter 400 can be fabricated using IPD process technology in a manner that results in a smaller footprint relative to harmonic filter 200 shown in FIG. 2 . Notably, harmonic filter 400 eliminates one of the two IPD loop inductors employed by harmonic filter 200 , eliminates one of the LC tank circuits employed by harmonic filter 200 , combines an input matching circuit functionality with a harmonic resonance circuit functionality, and combines an output matching circuit functionality with a harmonic resonance circuit functionality. Even though the overall die size is considerably smaller, the operation of harmonic filter 400 does not suffer. In this regard, FIG. 6 is a graph showing simulated insertion loss (S 21 ) characteristics for harmonic filter 400 . FIG. 6 illustrates the frequency rejection at the second, third, and fourth harmonics.

FIG. 7 is a schematic circuit diagram of a low band RF harmonic filter 500 configured in accordance with an embodiment of the invention, and FIG. 8 is a perspective view of an example IPD layout for RF harmonic filter 500 . Referring to FIG. 7 , harmonic filter 500 generally includes an RF input node 502 , an RF output node 504 , a second harmonic resonance circuit 506 connected between RF input node 502 and RF output node 504 , and a combined third harmonic resonance, input matching, and output matching circuit 508 connected between RF input node 502 and RF output node 504 (circuit 508 is also connected to ground at one node). In accordance with a practical embodiment, the combined circuit may also be configured to function as a fourth harmonic resonance circuit. In operation, RF input node 502 may be connected, via an inductance L 2 , to a component, device, circuit, or termination 510 that provides an input impedance (typically 50 ohms) for harmonic filter 500 , and RF output node 504 may be connected, via an inductance L 3 , to a component, device, circuit, or termination 512 that provides an output impedance (typically 50 ohms) for harmonic filter 500 .

Second harmonic resonance circuit 506 includes an inductor L 1 connected in parallel with a capacitor C 1 , where inductor L 1 and capacitor C 1 are each connected between RF input node 502 and RF output node 504 . Second harmonic resonance circuit 506 is suitably configured to reject the second harmonic component of the RF input signal. Combined third harmonic resonance, input matching, and output matching circuit 508 includes a capacitor C 2 connected at one end to RF input node 502 and connected at the other end to an inductor L 6 . The other end of inductor L 6 is connected to a node 514 . In other words, the C 2 /L 6 series combination is connected between RF input node 502 and node 514 . Combined third harmonic resonance, input matching, and output matching circuit 508 also includes a capacitor C 3 connected between RF output node 504 and node 514 , and an inductor L 5 connected between node 514 and ground. Combined third harmonic resonance, input matching, and output matching circuit 508 is suitably configured to reject the third harmonic component of the RF input signal while establishing a desired input impedance and a desired output impedance for harmonic filter 500 . Optionally (or inherently), combined third harmonic resonance, input matching, and output matching circuit 508 may also perform rejection of the fourth harmonic component of the RF input signal.

Although the preferred embodiment maintains the position of the second harmonic resonance circuit as shown in FIG. 7 , an alternate embodiment may utilize that position for the third or fourth harmonic resonance circuit, with the second harmonic resonance circuit being combined with the input/output matching circuit as described herein. Furthermore, the L 6 inductance need not be located as shown in FIG. 7 . For example, the L 6 inductance may be located in series with the C 3 capacitor, the L 6 inductance may be “divided” into two or more inductors, or the like.

Referring to FIG. 8 , an RF signal enters harmonic filter 500 at an RF input pad 516 (which corresponds to RF input node 502 in FIG. 7 ), and a filtered RF signal within the desired RF band is provided at an RF output pad 518 (which corresponds to RF output node 504 in FIG. 7 ). In the practical layout shown in FIG. 8 , the RF energy propagates over conductive traces formed on an insulating (semiconducting) substrate 520 . The IPD layout shown in FIG. 8 depicts elements formed on the same substrate 520 (e.g., a semiconductor or insulating substrate such as GaAs, glass, or ceramic) using the same semiconductor process technology (i.e., the fabrication or manufacturing process by which the IPD is formed). In this regard, inductor L 1 is realized as a conductive RF signal line loop inductor (air or dielectric bridges are employed at the respective “intersections” of inductor L 1 to insulate the inductor loops from the transmission lines utilized for the C 1 capacitor).

In practice, the C 1 , C 2 , and C 3 capacitors are each realized as an IPD capacitance formed on substrate 520 in the desired locations. IPD capacitance C 1 is connected between RF input pad 516 and RF output pad 518 (in the example embodiment, inductance L 1 forms bridges over the transmission line associated with IPD capacitance C 1 ). IPD inductance L 1 is also connected between RF input pad 516 and RF output pad 518 . Thus, IPD capacitance C 1 is connected in parallel with IPD inductance L 1 . IPD capacitance C 2 is connected between RF input pad 516 and a ground pad 522 (which may be realized as a portion of a conductive trace 524 ), and IPD capacitance C 3 is connected between RF output pad 518 and a ground pad 526 (which may be realized as a portion of a conductive trace 524 ). In the example embodiment shown in FIG. 8 , ground pad 522 and ground pad 526 are connected together, and integrated with, conductive trace 524 . Conductive trace 524 functions as another IPD inductance (corresponding to inductance L 6 in FIG. 7 ) for harmonic filter 500 . This second IPD inductance is connected between the “ground” ends of IPD capacitance C 2 and IPD capacitance C 3 . As shown in FIG. 8 , conductive trace 524 may be configured as a non-looped inductor, in contrast to IPD inductance L 1 .

Notably, inductor L 5 (not shown in FIG. 8 ) is realized as a wire bond, conductive trace, or other inductance element connected between ground pads 526 (or any suitable area of conductive trace 524 ) and a grounding pad or other ground potential location, which may be off-chip. In other words, this inductance element establishes a ground connection to ground pad 526 and, in turn, to IPD capacitance C 3 . Furthermore, the small amount of inductance needed for inductor L 6 can be realized with conductive trace 524 connected between IPD capacitances C 2 and C 3 , rather than a loop inductor. Thus, inductors L 2 , L 3 , and L 5 need not be part of the IPD substrate itself, and harmonic filter 500 may be referred to as a “single inductor” IPD. In practical embodiments, harmonic filter 500 includes only one IPD loop inductor. As mentioned above, IPD capacitance C 2 , IPD capacitance C 3 , IPD inductance L 6 , and the L 5 inductance element connected to ground pad 526 form the combined third harmonic resonance, fourth harmonic resonance, input matching, and output matching circuit 508 , which is connected between RF input pad 516 and RF output pad 518 .

In accordance with one practical embodiment of harmonic filter 500 , IPD inductance L 1 , IPD capacitance C 1 , IPD capacitance C 2 , IPD capacitance C 3 , IPD inductance L 6 , and the L 5 inductance element are suitably configured to provide a filter response that rejects harmonic frequencies corresponding to a pass band of 824 MHz to 915 MHz. To accomplish this objective, the matching circuit component values are tuned to make the combined circuit resonate at the desired third harmonic frequency, while still providing good input and output impedance matching. In practice, tuning for resonance at the third harmonic frequency will also provide some rejection at the fourth harmonic frequency. Typical component values for such an example embodiment are contained in Table 2.

Harmonic filter 500 can be fabricated using IPD process technology in a manner described above, which results in a smaller footprint relative to harmonic filter 300 shown in FIG. 3 . Notably, harmonic filter 500 eliminates one of the two IPD loop inductors employed by harmonic filter 300 , eliminates one of the LC tank circuits employed by harmonic filter 300 , and combines the functionality of an input matching circuit, a harmonic resonance circuit, and an output matching circuit into a single sub-circuit. Even though the overall die size is considerably smaller, the operation of harmonic filter 500 does not suffer. In this regard, FIG. 9 is a graph showing simulated insertion loss (S 21 ) characteristics for harmonic filter 500 . FIG. 9 illustrates the frequency rejection at the second, third, and fourth harmonics.

While at least one example embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the example embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.