Active balun

Abstract

An active balun is disclosed. In one aspect, a relatively small single-ended to differential active balun is used in place of a relatively large passive balun. In particular, the active balun may include a shunt inductor at a splitting node that splits a single-ended signal onto an inverting path and a non-inverting path that are provided to a differential amplifier in the amplifier chain. A harmonic rejection circuit may be used to improve performance. The space savings afforded by using an active balun are substantial. Further, the Q factor of the elements used in the active balun may be comparatively low, resulting in cost savings.

Description

ACTIVE BALUNPRIORITY APPLICATION

[0001] The present application is related to U.S. Provisional Patent Application Serial No. 63 / 562,301 filed on March 7, 2024, and entitled “ACTIVE BALUN,” the contents of which are incorporated herein by reference in its entirety.BACKGROUNDI. Field of the Disclosure

[0002] The technology of the disclosure relates generally to single-ended to differential baluns and, more particularly, to an active balun that performs single-ended to differential conversion.II. Background

[0003] Computing devices abound in modern society, and more particularly, mobile communication devices have become increasingly common. The prevalence of these mobile communication devices is driven in part by the many functions that are now enabled on such devices. Increased processing capabilities in such devices means that mobile communication devices have evolved from pure communication tools into sophisticated mobile entertainment centers, thus enabling enhanced user experiences. With the advent of the myriad functions available to such devices, there has been increased pressure to find ways to increase available bandwidth through which data may be sent and received. This pressure has resulted in the continued evolution of wireless standards that control how wireless signals are sent and processed. Commercial pressure to decrease the size of any and all components in a wireless communication device, coupled with the changing wireless standards, has put increased pressure on power amplifiers used to boost signal levels to desired levels to be both small and efficient. Finding ways to improve the performance of such power amplifiers leaves room for innovation.SUMMARY

[0004] Aspects disclosed in the detailed description include an active balun. Specifically, a relatively small single-ended to differential active balun is used in place ofa relatively large passive balun. In particular, the active balun may include a shunt inductor at a splitting node that splits a single-ended signal onto an inverting path and a non-inverting path that are provided to a differential amplifier in the amplifier chain. A harmonic rejection circuit may be used to improve performance. The space savings afforded by using an active balun are substantial. Further, the Q factor of the elements used in the active balun may be comparatively low, resulting in cost savings.

[0005] In this regard, in one aspect, an amplifier chain is disclosed. The amplifier chain includes a single-ended input node and a differential amplifier stage. The amplifier chain also includes an active balun configured to take a single-ended input signal and generate a differential output signal, the active balun serially positioned between the single-ended input node and the differential amplifier stage, and a shunt inductor coupling an input of the active balun to ground.

[0006] In another aspect, a method for transforming a single-ended signal to a differential signal in an amplifier chain is disclosed. The method includes receiving the single-ended signal at a single-ended input node and shunting the single-ended signal to ground at the single-ended input node through an inductor. The method also includes using an active balun coupled to the single-ended input node to create a differential signal and providing the differential signal to a differential amplifier stage.

[0007] In another aspect, a mobile terminal is disclosed. The mobile terminal includes a baseband processor configured to generate a signal to be transmitted and an amplifier chain coupled to a baseband processor and configured to receive a single-ended version of the signal to be transmitted. The amplifier chain of the mobile terminal comprises a single-ended input node, a differential amplifier stage, an active balun configured to take a single-ended input signal and generate a differential output signal, the active balun serially positioned between the single-ended input node and the differential amplifier stage and a shunt inductor coupling the single-ended input node to ground.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 A is a block diagram of a conventional approach to switching between single-ended signals and differential signals in an amplifier chain;

[0009] Figure IB is a top-plan view of a die having the amplifier chain of Figure 1A thereon showing approximate relative size between a passive balun and actual power amplifiers;

[0010] Figure 2 is a block diagram of an amplifier chain with an active balun and shunt inductor according to aspects of the present disclosure;

[0011] Figure 3 is a block diagram of some additional details for the active balun of Figure 2;

[0012] Figure 4 is a block diagram with further additional details for the active balun of Figure 2;

[0013] Figure 5A is a top-plan view of a die using the balun of Figure 2;

[0014] Figure 5B is a side-elevational view of the die of Figure 5A;

[0015] Figure 6 is a hybrid block and circuit diagram of cascoded transistors used to form the amplifiers used in Figure 2;

[0016] Figure 7 is a flowchart illustrating an exemplary process for using an active balun to provide single-ended to differential-ended signaling in an amplifier chain according to aspects of the present disclosure; and

[0017] Figure 8 is a block diagram of a mobile terminal, which may include the amplifier chain of Figures 2-6 according to the present disclosure.DETAILED DESCRIPTION

[0018] The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0019] It will be understood that although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element without departing from the scope of the present disclosure. Asused herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0020] It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element, or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, no intervening elements are present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, no intervening elements are present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, no intervening elements are present.

[0021] Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

[0022] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a," “an,” and “the” are intended to include the plural forms as well unless the context clearly indicates otherwise. It will be further understood that the terms “comprises," “comprising," “includes,” and / or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0023] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms usedherein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0024] In keeping with the above admonition about definitions, the present disclosure uses transceiver in a broad manner. Current industry literature uses “transceiver” in two ways. The first way uses transceiver broadly to refer to a plurality of circuits that send and receive signals. Exemplary circuits may include a baseband processor, an up / down conversion circuit, filters, amplifiers, couplers, and the like coupled to one or more antennas. A second way, used by some authors in the industry literature, refers to a circuit positioned between a baseband processor and a power amplifier circuit as a transceiver. This intermediate circuit may include the up / down conversion circuits, mixers, oscillators, filters, and the like but generally does not include the power amplifiers. As used herein, the term transceiver is used in the first sense. Where relevant to distinguish between the two definitions, the terms “transceiver chain” and “transceiver circuit” are used respectively.

[0025] Aspects disclosed in the detailed description include an active balun. Specifically, a relatively small single-ended to differential active balun is used in place of a relatively large passive balun. In particular, the active balun may include a shunt inductor at a splitting node that splits a single-ended signal onto an inverting path and a non-inverting path that are provided to a differential amplifier in the amplifier chain. A harmonic rejection circuit may be used to improve performance. The space savings afforded by using an active balun are substantial. Further, the Q factor of the elements used in the active balun may be comparatively low, resulting in cost savings.

[0026] Before addressing particular aspects of the present disclosure, a brief overview of the use of baluns in amplifier chains is discussed with reference to Figures 1A and IB. Against this backdrop, a discussion of the active balun of the present disclosure begins below with reference to Figure 2.

[0027] In this regard, Figure 1A is a block diagram of an amplifier chain 100 that has a single-ended input node 102 and a single-ended output node 104. For many reasons, including harmonic performance and higher maximum output power, it may be desirable to use differential elements to condition signals as they pass from the input node 102 to the output node 104. The traditional way to change single-ended signals to differentialsignals is through the use of a passive balun 106. In most implementations of a passive balun, the passive balun 106 is a transformer with two inductors 108A, 108B. To assist in performance, the passive balun 106 will have a high-Q to provide a low insertion loss.

[0028] With continued reference to Figure 1 A, the passive balun 106 may be coupled to a driver amplifier stage 110. The driver amplifier stage 110 may be a differential amplifier stage with a differential input and differential output. The driver amplifier stage 110 may provide an initial signal boost to incoming signals and provide these initially boosted signals to an inter-stage match circuit 112. The inter-stage match circuit 112 may be differential at input and output.

[0029] With continued reference to Figure 1A, the inter-stage match circuit 112 may be coupled to an output amplifier stage 114. Note that there may be other stages (not shown) in some implementations. Likewise, there may be additional filtering or matching circuits that are not shown. The output amplifier stage 114 may likewise be differential at the input and output. A second passive balun 116 may be used to convert the differential signal to a single-ended signal at the output node 104.

[0030] While not shown, note that there are also existing implementations that place the passive balun 106 between the driver amplifier stage 110 and the output amplifier stage 114, leaving the driver amplifier stage 110 as a single-ended device.

[0031] Regardless of actual position, the passive balun 106 is comparatively large and may consume an amount of space loosely equal to the output amplifier stage 114. Thus, as better seen in Figure IB, the passive balun 106 may use approximately twenty-five percent of the die for the amplifier chain 100. The output amplifier stage 114 may use another approximately twenty-five percent, leaving about half of the die for other portions 120, 122. Currently, as of this writing, market trends indicate that continued reliance on such large baluns is becoming commercially impractical. One approach is to move the transformer off the die into a surface-mounted device, but in many cases, these structures are also impractical due to parasitic capacitance. Thus, there is room for innovation that improves the amplifier chain 100.

[0032] Aspects of the present disclosure contemplate replacing the passive balun 106 with an active balun and a shunt inductor, as better seen in Figure 2. Specifically, an amplifier chain 200, according to the present disclosure, includes an input node 202 and an output node 204. The input node 202 and the output node 204 are single-ended. Anactive balun 206 is coupled to the input node 202. The active balun 206 changes a single- ended signal to a differential signal, as better explained below. A shunt inductor 208 is also coupled to the input node 202. The shunt inductor 208 improves the insertion loss and acts as a radio frequency (RF) choke while also providing some bias for the active balun 206. Likewise, because it is a shunt inductor 208, the inductor may be lower Q and may cost less than a series inductor. The shunt inductor 208 may be a printed laminate inductor or a surface-mounted device as needed or desired by design criteria. For example, at low-band and mid-band frequency ranges, the shunt inductor 208 may need to have a relatively large inductance value and be large for a die but more readily accommodated as a surface-mounted device. Other bias solutions, including current sources and / or resistors, are also possible but contribute noise more directly to the input node 202, thereby degrading the noise figure of the amplifier chain that uses such a bias.

[0033] A driver amplifier stage 210 may be coupled to the active balun 206. The driver amplifier stage 210 is, as illustrated, differential on both its input side and its output side.

[0034] With continued reference to Figure 2, an inter-stage match circuit 212 is coupled to the driver amplifier stage 210 and an output amplifier stage 214. The interstage match circuit 212 and the output amplifier stage 214 are both differential devices. To get the differential signal back to a single-ended signal, a second balun 216 couples the output amplifier stage 214 to the output node 204.

[0035] Note that the active balun 206 may move to a position between the driver amplifier stage 210 and the output amplifier stage 214 without departing from the present disclosure. Note also that input stages of an amplifier chain 200 may be inverting or noninverting, and the present disclosure applies to both with a relatively simple swapping of the signal processing polarity, as should be well understood.

[0036] By way of further explanation, Figure 3 provides additional details for the active balun 206. More specifically, the active balun 206 begins at a first node 300 that is coupled to a main path 302 (or non-inverting path) with a first amplifier 304. The first node 300 is also coupled to an inverting path 306 with a capacitor 308 and an inverting amplifier 310. The capacitor 308 acts as an alternating current (AC) coupling capacitor to isolate direct current (DC) biases, although the main path 302 and the inverting path 306 may have different DC biases. The main path 302 and the inverting path 306 areconnected to inputs of an amplifier stage, which, as illustrated, is the driver amplifier stage 210. It should be appreciated that noise in the main path 302 is the opposite of the noise in the inverting path 306 by virtue of the inversion. Thus, the noise will cancel at the amplifier through common mode rejection. Note further, by using amplifiers 304, 310, there is some gain in the signal paths to offset any insertion loss, while reducing the noise contribution of later stages.

[0037] The active balun 206 may be implemented in a relatively small area and using little supply current. Further, the active balun 206 may be implemented in silicon or other semiconductor technology (e.g., silicon germanium (SiGe), gallium arsenide (GaAs), indium phosphorus (InP), gallium nitride (GaN), GaN on silicon, or the like). Most active devices are of the transconductance type. In such cases, a single device stage (e.g., inverting amplifier 310) that has a relatively high impedance is an inverting type (Ginv). An active match stage can also be implemented with a single stage (e.g., first amplifier 304) of a non-inverting type (Zamp). It is generally relatively easy to match Zamp to the input impedance (e.g., 50 ohms), while it may be harder to match Ginv The two stages can be designed to have the same voltage gain.

[0038] The nature of the first amplifier 304 and the inverting amplifier 310 creates harmonics that negatively impact the signals provided to the amplifier. In particular, the second harmonic has proven to be the most significant. Because the inverting harmonic is not equal to the non-inverting harmonic (i.e., they have different distortion characteristics), these harmonics do not cancel like the noise. Accordingly, a load 312 may be placed between the paths 302, 306. This load 312 is designed to provide a second harmonic rejection and provides low impedance at the second harmonic frequency. More details on one possible implementation are provided below with reference to Figure 4. The load 312 may also be coupled to a supply voltage 314.

[0039] Again, further details are provided with reference to Figure 4. Specifically, the load 312 may be a transformer 400 in parallel with a capacitor 402. The supply voltage 314 balances the transformer 400. Because the transformer 400 is effectively a shunt balun (i.e., from supply voltage 314 to both paths 302, 306), the transformer 400 may be formed from low Q factor inductors.

[0040] It should be appreciated that it is possible to implement the inverting amplifier 310 with one or more cascoded N-type field effect transistors (FETs) (NFETs) 404. TheNFETs 404 may be done in a bulk complementary metal oxide semiconductor (CMOS) or silicon on insulator (SOI) CMOS technology, bipolar CMOS, or the like. The NFETs 404 may have a relatively high input impedance when a source 404S is coupled to ground. A fifty ohm input impedance (or other matched impedance) is provided by a commongate stage, implemented, for example, with a matching NFET 406 in the first amplifier 304 (i.e., gates 404G and 406G are coupled). The shunt inductor 208 offers a DC bias to the NFET 406. However, the shunt inductor 208 also couples the source 406S to ground, meaning that both sources 404S and 406S are grounded. A shared bias circuit 408 may be coupled to the gates 404G, 406G. The shared bias means that there is a well-matched gain for the two paths 302, 306. Furthermore, the noise of the bias stage will be rejected as a common-mode signal at an input of the next differential stage.

[0041] While NFETs are specifically contemplated, other FETs may be used (e.g., NPN, PFETs, or the like).

[0042] Normally, semiconductor devices are relatively small compared to passive magnetic devices. If magnetic devices cannot be eliminated from the die, the magnetic devices may be configured to take a minimum amount of area and cost the least possible. The proposed low Q inductors of the transformer 400 mean that the transformer 400 may be implemented on top of active stage components (e.g., the NFETs 404, 406), as better seen in Figures 5A and 5B, where the transformer 400 sits on top of the die 500 having active components therein. The transformer 400 may be separated from the die 500 by a metal shield 502, which prevents output-to-input parasitic coupling. The metal shield 502 may be patterned and / or coupled to ground to prevent eddy currents. This vertical arrangement (along the z-axis) allows the transformer 400 to avoid consuming additional semiconductor circuit area. The net result allows the package to be approximately five to six times smaller than the die for amplifier chain 100 of Figure IB.

[0043] As alluded to above, there may be one or more FETs cascoded in the amplifiers 304, 310. This cascoding is more explicitly illustrated in Figure 6. Specifically, the one or more FETs 404, 406 are instantiated as FETs 604(l)-604(P), 606(1 )-606(N), respectively.

[0044] A process 700 for using the amplifier chain 200 of the present disclosure is discussed with reference to Figure 7. Specifically, the process 700 begins when a signal to be amplified is received at the single-ended input node 202 (block 702). The signal issplit (block 704). The input node 202 is shunted to ground (block 706) through the shunt inductor 208. One signal path 306 is inverted (block 708). Both signal paths 302, 306 are amplified (block 710), and second harmonics are canceled (block 712). The signal is then provided to a differential stage at two outputs (block 714).

[0045] The active baluns, according to aspects disclosed herein, may be provided in or integrated into any processor-based device that has a relevant amplifier chain, such as may occur in a wireless transceiver. Examples, without limitation, include a set-top box, an entertainment unit, a navigation device, a communications device, a fixed location data unit, a mobile location data unit, a global positioning system (GPS) device, a mobile phone, a cellular phone, a smartphone, a session initiation protocol (SIP) phone, a tablet, a phablet, a server, a computer, a portable computer, a mobile computing device, a wearable computing device (e.g., a smartwatch, a health or fitness tracker, eyewear, etc.), a desktop computer, a personal digital assistant (PDA), a monitor, a computer monitor, a television, a tuner, a radio, a satellite radio, a music player, a digital music player, a portable music player, a digital video player, a video player, a digital video disc (DVD) player, a portable digital video player, an automobile, a vehicle component, avionics systems, a drone, and a multicopter.

[0046] More specifically, to provide general details for such wireless devices, reference is made to Figure 8, where the concepts described above may be implemented in various types of user elements 800 (i.e., wireless communication devices). The user elements 800 will generally include a control system 802, a baseband processor 804, transmit circuitry 806, receive circuitry 808, antenna switching circuitry 810, multiple antennas 812, and user interface circuitry 814. In a non- limiting example, the control system 802 can be a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), as an example. In this regard, the control system 802 can include at least a microprocessor(s), an embedded memory circuit(s), and a communication bus interface(s). The receive circuitry 808 receives radio frequency signals via the antennas 812 and through the antenna switching circuitry 810 from one or more base stations. A low noise amplifier and a filter of the receive circuitry 808 cooperate to amplify and remove broadband interference from the received signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal,which is then digitized into one or more digital streams using an analog-to-digital converter(s) (ADC).

[0047] The baseband processor 804 processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. The baseband processor 804 is generally implemented in one or more digital signal processors (DSPs) and ASICs.

[0048] For transmission, the baseband processor 804 receives digitized data, which may represent voice, data, or control information, from the control system 802, which it encodes for transmission. The encoded data is output to the transmit circuitry 806, where a digital-to-analog converter(s) (DAC) converts the digitally encoded data into an analog signal, and a modulator modulates the analog signal onto a carrier signal that is at a desired transmit frequency or frequencies. A power amplifier will amplify the modulated carrier signal to a level appropriate for transmission and deliver the modulated carrier signal to the antennas 812 through the antenna switching circuitry 810 to the antennas 812. The multiple antennas 812 and the replicated transmit and receive circuitries 806, 808 may provide spatial diversity. Modulation and processing details will be understood by those skilled in the art.

[0049] It is also noted that the operational steps described in any of the exemplary aspects herein are described to provide examples and discussion. The operations described may be performed in numerous different sequences other than the illustrated sequences. Furthermore, operations described in a single operational step may actually be performed in a number of different steps. Additionally, one or more operational steps discussed in the exemplary aspects may be combined. It is to be understood that the operational steps illustrated in the flowchart diagrams may be subject to numerous different modifications, as will be readily apparent to one of skill in the art. Those of skill in the art will also understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0050] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

AMENDED CLAIMS received by the International Bureau on 03 July 2025 (03.07.2025)1. (Previously Presented) An amplifier chain contained within a die, the amplifier chain comprising: a single-ended input node; a differential amplifier stage; an active balun configured to take a single-ended input signal and generate a differential output signal, the active balun serially positioned between the single-ended input node and the differential amplifier stage; a harmonic cancelation circuit coupled to the active balun, the harmonic cancelation circuit comprising a transformer, the transformer positioned on a top surface of the die; and a shunt inductor coupling an input of the active balun to ground.

2. (Original) The amplifier chain of claim 1 , wherein the shunt inductor directly couples the single-ended input node to ground and the active balun.

3. (Original) The amplifier chain of claim 1, wherein the active balun comprises an inverting path and a non-inverting path to generate the differential output signal.

4. (Previously Presented) The amplifier chain of claim 3, wherein the harmonic cancelation circuit couples the inverting path and the non-inverting path.

5. Canceled.

6. (Original) The amplifier chain of claim 3, wherein the non-inverting path comprises at least one transistor, an emitter, or a source of the at least one transistor coupled directly to the single-ended input node.

7. (Original) The amplifier chain of claim 3, wherein the inverting path comprises at least one transistor, a base or gate of the at least one transistor coupled to the single-ended input node through a serial capacitor.

8. (Original) The amplifier chain of claim 3, further comprising a common bias circuit configured to apply a bias signal for the inverting path and the non-inverting path.

9. (Original) The amplifier chain of claim 3, wherein the inverting path comprises a plurality of cascoded field effect transistors (FETs).

10. (Original) The amplifier chain of claim 3, wherein noise at the single-ended input node is destructively summed between the inverting path and the non-inverting path.

11. Canceled12. (Original) The amplifier chain of claim 1, wherein the shunt inductor comprises a surfacemounted device.

13. (Previously Presented) A method for transforming a single-ended signal to a differential signal in an amplifier chain housed within a die, comprising: receiving the single-ended signal at a single-ended input node; shunting the single-ended signal to ground at the single-ended input node through an inductor; using an active balun coupled to the single-ended input node to create a differential signal; canceling second-order harmonics using a transformer, where the transformer is positioned on a top surface of the die; and providing the differential signal to a differential amplifier stage.

14. (Original) The method of claim 13, wherein using the active balun comprises splitting the single-ended signal onto two paths wherein a first path of the two paths comprises an inverting amplifier and a second path of the two paths comprises a non-inverting amplifier.

15. (Previously Presented) The method of claim 14, wherein canceling second-order harmonics comprises coupling the transformer to the two paths.

16. Canceled.

17. (Original) The method of claim 14, wherein providing the differential signal to the differential amplifier stage comprises providing the differential signal to a driver amplifier stage.

18. (Original) The method of claim 14, wherein shunting the single-ended signal to ground at the single-ended input node comprises using a surface-mounted device.

19. (Previously Presented) A mobile terminal comprising: a baseband processor configured to generate a signal to be transmitted; and a die comprising an amplifier chain coupled to a baseband processor and configured to receive a single-ended version of the signal to be transmitted, the amplifier chain comprising: a single-ended input node; a differential amplifier stage; an active balun configured to take a single-ended input signal and generate a differential output signal, the active balun serially positioned between the single-ended input node and the differential amplifier stage; and a shunt inductor coupling the single-ended input node to ground; and a transformer configured to cancel second-order harmonics in the active balun, the transformer positioned on top of the die.

20. (Original) The mobile terminal of claim 19, wherein the active balun comprises an inverting path and a non-inverting path to generate the differential output signal.

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