Patent Publication Number: US-10790789-B2

Title: Injection lock power amplifier with back-gate bias

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. § 120 as a continuation of U.S. patent application Ser. No. 15/933,542 filed on Mar. 23, 2018, the entire teachings of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to amplifiers, and, more specifically, to power amplifiers using injection lock that is controlled by back-gate bias. 
     Current wireless technology trends towards increasing numbers of wireless standards and radio frequency (RF) bands to support wireless communications have led to the development of multi-standard, multi-band cellular systems. Such efforts have produced well-performing wideband receivers and frequency synthesizers. However, power amplifiers having the desired performance, output power, etc., across multiple frequency bands remains a challenge for such cellular systems. 
     Due to the fast-growing demand of wireless communication, a CMOS transceiver has been developed and has become available for the commercial market. However, there are still technical obstacles to achieve widespread application of millimeter-wave (mmWave) CMOS applications, especially in the design of Power Amplifier (PA). For example, the gain of a CMOS transistor at 60 GHz is typically small, so multiple-stage design is usually employed in order to obtain higher gain. In addition, power combining technology can be a solution to CMOS&#39;s low output power. However, the efficiency of a CMOS PA is usually low due to the poor RF performance of the transistor. Techniques, such as multi-stage design would further reduce the overall efficiency. An Injection Locking Power Amplifier (ILPA) can achieve high efficiency at 60 GHz in addition to providing high gain with a compact size. However, there are some major drawbacks of the ILPA. 
     Using current sources to tune the injection current and oscillator core current increases the headroom required and possibility of noise up-conversion. AC-coupling with resistor bias to de-coupled the DC biases in the oscillator core increases the loss, especially for mmWave applications. 
     SUMMARY 
     According to devices and methods herein, back-gate bias available from fully-depleted semiconductor-on-insulator (FDSOI) technology is used to tune the injection current and oscillator core current independently. The back-gate voltages of both differential pairs can be tuned independently as well to obtain symmetric outputs. Small devices can be used for mmWave application, which reduces the input load and thus lowers the power consumption and maximizes the operating frequency. 
     According to an exemplary structure herein, a transformer has a primary side and a secondary side. Output from the primary side is coupled to the secondary side. A first power supply is connected to a center tap of the primary side of the transformer. An oscillator includes a first transistor and a second transistor. The front-gate of the first transistor is connected to the drain of the second transistor and the primary side of the transformer. The front-gate of the second transistor is connected to the drain of the first transistor and the primary side of the transformer. A third transistor is connected to the first transistor and a fourth transistor is connected to the second transistor. The third and fourth transistors inject a desired frequency to the oscillator. A voltage source is connected to the back-gate of the first transistor and the back-gate of the second transistor. 
     According to other exemplary structures herein, a transformer has a primary side and a secondary side. Output from the primary side is coupled to the secondary side. A first power supply is connected to a center-tap of the primary side of the transformer. The structure includes a pair of switching transistors. Each transistor of the pair of switching transistors includes a source node, a front-gate node, a back-gate node, and a drain node. The pair of switching transistors are cross-coupled such that the drain node of each one of the switching transistors is connected to the front-gate node of the other switching transistor, and the drain nodes are connected to the primary side of the transformer. The structure also includes a pair of injection transistors. Each transistor of the pair of injection transistors includes a source node, a front-gate node, a back-gate node, and a drain node. The drain node of each one of the injection transistors is connected to the drain node of one of the switching transistors and the source node of each of the injection transistors is connected to the source node of each of the switching transistors. An injection signal is connected to the front-gate of each transistor of the pair of injection transistors, and a bias voltage source is connected to the back-gate of each transistor of the pair of switching transistors. 
     According to exemplary methods herein, a pair of switching transistors is cross coupled such that the drain node of each one of the switching transistors is connected to the front-gate node of the other switching transistor. The drain nodes of each one of the switching transistors are connected to the primary side of a transformer. An injection current is provided to the pair of switching transistors to oscillate the transformer. Output power from the secondary side of the transformer is measured. It is determined if output power from both sides of the transformer are approximately equal. Responsive to the output power from both sides of the transformer not being approximately equal, output power of the switching transistors is controlled by adjusting voltage to the back-gate of the switching transistors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The devices and methods herein will be better understood from the following detailed description with reference to the drawings, which are not necessarily drawn to scale and in which: 
         FIG. 1  is a schematic diagram of an exemplary power amplifier according to devices and methods herein; 
         FIG. 2  is a schematic diagram of an exemplary power amplifier with a single-ended output according to devices and methods herein; 
         FIG. 3  is a schematic diagram of an exemplary power amplifier with a single-ended input according to devices and methods herein; and 
         FIG. 4  is a schematic diagram of an exemplary power amplifier and an adjustment flowchart according to devices and methods herein. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure will now be described with reference to an injection locked power amplifier that uses back-gate bias of fully-depleted semiconductor-on-insulator (FDSOI) transistors to tune the injection current and oscillator core current independently during operation of the power amplifier. While the disclosure will be described hereinafter in connection with specific devices and methods thereof, it will be understood that limiting the disclosure to such specific devices and methods is not intended. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the disclosure as defined by the appended claims. 
     For a general understanding of the features of the disclosure, reference is made to the drawings. The drawings are not to scale; however, in the drawings, like reference numerals have been used throughout to identify identical elements. 
     It will be readily understood that the devices and methods of the present disclosure, as generally described and illustrated in the drawings herein, may be arranged and designed in a wide variety of different configurations in addition to the devices and methods described herein. Thus, the following detailed description of the devices and methods, as represented in the drawings, is not intended to limit the scope defined by the appended claims but is merely representative of selected devices and methods. The following description is intended only by way of example, and simply illustrates certain concepts of the devices and methods, as disclosed and claimed herein. 
     According to devices and methods herein, a structure includes a cross-coupled pair of transistors, referred to herein as switching transistors, that provides the negative resistance loaded to the primary of a transformer. The center-tap of the primary of the transformer is connected to the power supply. The output from the primary is coupled to the secondary of the transformer. The secondary of the transformer can have either differential or single-ended outputs. An injection current is provided from injection transistors. The primary inductance of the transformer is designed such that the oscillator core is oscillating close to the desired operating frequency. In operation, the injection transistors inject the desire frequency and the oscillator will finally lock to the injected frequency. The back-gate of the cross-coupled switching transistors is used to change the oscillator core current and subsequently the output power. The lock-in range is proportional to the injection current. This can be accomplished by changing the back-gate bias of the injection transistors. Any transistor mismatches between the cross-coupled switching transistors and the injection transistors can be tuned out by applying different back-gate biases in each of the transistors and thus minimum transistor size can be used. For single-ended output, the transformer can be configured as a balun where one of the secondaries is connected to ground. Due to this configuration, the input impedance seen on each input of the primary can have some difference and thus create asymmetry output swings in the primary outputs. The back-gate bias to the cross-coupled transistors can be used to calibrate out this asymmetry as well. 
     The cross-coupled pair of switching transistors with the inductances from the transformer can oscillate with a well-defined oscillating frequency (f osc ). Using the injection current through the injection transistors, the injection locked power amplifier (ILPA) can be tuned to the input frequency (f in ). The tuning range can be controlled through the back-gate voltage to the injection transistors. The oscillating frequency (f osc ) may be approximately in the mid-range of locked input frequency (f in ). Back-gate bias to the cross-coupled pair of switching transistors controls the output power. Note that the ratio of injection current to the current in the oscillator can be kept to a desired constant number since the back-gate bias to the switching transistors and the injection transistors are controlled independently. Each back-gate control can be either common or independent to the differential pair. 
     Referring now to the drawings,  FIG. 1  is a schematic diagram of an exemplary power amplifier, indicated generally as  101 . The power amplifier  101  may include an oscillator  104  that includes a pair of switching transistors. Within a transistor, the semiconductor (or channel region) is positioned between a conductive “source” region and a similarly conductive “drain” region and when the semiconductor is in a conductive state, the semiconductor allows electrical current to flow between the source and drain. A “gate” is a conductive element that is electrically separated from the semiconductor by a “gate oxide” (which is an insulator) and current/voltage within the gate changes the conductivity of the channel region of the transistor. Each transistor  107 ,  108  of the pair of switching transistors is a fully-depleted semiconductor-on-insulator (FDSOI) transistor. FDSOI is a planar process technology that uses an ultra-thin layer of insulator, called a buried oxide, positioned on top of the base silicon. A very thin un-doped silicon film implements the transistor channel. The details of FDSOI transistors are omitted herefrom to allow the reader to focus on the salient aspects of the systems and methods described herein. 
     Each transistor  107 ,  108  of the pair of switching transistors includes a source node  110 ,  111 , a front-gate node  114 ,  115 , a back-gate node  118 ,  119 , and a drain node  121 ,  122 . The pair of switching transistors are cross-coupled such that the drain node of each one of the switching transistors is connected to the front-gate node of the other switching transistor. For example, the drain node  121  of switching transistor  107  is connected to the front-gate node  115  of switching transistor  108  and the drain node  122  of switching transistor  108  is connected to the front-gate node  114  of switching transistor  107 . As used herein, the switching transistors  107 ,  108  may sometimes be referred to as M 1  and M 2 . 
     The power amplifier  101  may include a pair of injection transistors. Each transistor  125 ,  126  of the pair of injection transistors is a FDSOI transistor that includes a source node  129 ,  130 , a front-gate node  133 ,  134 , a back-gate node  137 ,  138 , and a drain node  141 ,  142 . The drain node of each one of the injection transistors is connected to the drain node of one of the switching transistors and the source node of each of the injection transistors is connected to the source node of each of the switching transistors. That is, the drain node  121  of switching transistor  107  is connected to the drain node  141  of injection transistor  125  and the drain node  122  of switching transistor  108  is connected to the drain node  142  of injection transistor  126 . Further, the source node  110  of switching transistor  107  is connected to the source node  129  of injection transistor  125  and the source node  111  of switching transistor  108  is connected to the source node  130  of injection transistor  126 , all of which are connected to ground  145 . As used herein, the injection transistors  125 ,  126  may sometimes be referred to as M 1 INJ and M 2 INJ. 
     The oscillator  104  provides a signal output at a selected frequency to a pair of transformers. Each transformer  148 ,  149  of the pair of transformers includes windings on a primary side  152 ,  153  and windings on a secondary side  156 ,  157 . The ratio K of windings between the primary side  152 ,  153  and the secondary side  156 ,  157  for each of transformer  148 ,  149  should be the same. A first power supply  160  is connected to a center tap  163  on the primary side between transformer  148  and transformer  149 . RF output  166 ,  167  from the secondary side  156 ,  157  of each transformer  148 ,  149  can be used, for example, in RADAR or wireless cellular communication applications, or other applications as would be known to one of ordinary skill in the art. A DC bias voltage for the RF output  166 ,  167  can be provided at  170  on the secondary side between transformer  148  and transformer  149 . 
     An injection signal source is connected to the front-gate node  133 ,  134  of each transistor  125 ,  126  of the pair of injection transistors. Input to the back-gate nodes  137 ,  138  of the injection transistors  125 ,  126  can change the injection current and minimize the input load. A bias voltage source is connected to the back-gate node  118 ,  119  of each transistor  107 ,  108  of the pair of switching transistors. In operation, the injection transistors  125 ,  126  inject the desired frequency and the oscillator  104  will lock to the injected frequency. The bias voltage input to the back-gate nodes  118 ,  119  of the switching transistors  107 ,  108  can be used to change the oscillator core current and subsequently the output power. The bias voltage input to the back-gate nodes  118 ,  119  of the switching transistors  107 ,  108  can also be used to compensate any current fluctuation due to process and/or temperature. The lock-in range is proportional to the injection current. This can be accomplished by changing the back-gate bias of the injection transistors  125 ,  126 . In order to get fast lock-in time during start-up, the input to the back-gate nodes  137 ,  138  of the injection transistors  125 ,  126  can be initially increased; then, once the oscillator  104  is close to being locked, the injection input can be reduced to nominal to save power. 
     The injection current can be used to balance the amplitudes of the RF output  166 ,  167 . For example, the input to the back-gate node  137  of injection transistor  125  is not necessarily the same as the input to the back-gate node  138  of injection transistor  126 . In addition, the bias voltage input to the back-gate node  118  of switching transistor  107  is not necessarily the same as the bias voltage input to the back-gate node  119  of switching transistor  108 . Both the inputs to the back-gate nodes  137 ,  138  of the injection transistors  125 ,  126  and the bias voltage inputs to the back-gate nodes  118 ,  119  of the switching transistors  107 ,  108  can be either differential or independent. In other words, each back-gate control can be either common or independent to the differential pair. Any transistor mismatches between the cross-coupled switching transistors  107 ,  108  and the injection transistors  125 ,  126  can be tuned out by applying different back-gate biases in each of the transistors and thus minimum transistor size can be used. 
     In  FIG. 2 , the injection locked power amplifier  202  has a single RF output  205 . The output from the secondary side  157  of transformer  149  is sent to ground  208 . For single-ended output, the transformer can be configured as a balun where one of the secondaries is connected to ground. Due to this configuration, the input impedance seen on each input of the primary side of the transformer can have some difference and thus create asymmetry output swings in the primary outputs. The back-gate bias to the cross-coupled transistors  107 ,  108  can be used to calibrate out this asymmetry. 
     In  FIG. 3 , the injection locked power amplifier  303  has a single-ended input  306  for the injection transistors  125 ,  126 . In the exemplary embodiment of  FIG. 3 , a pair of input transformers may have an RF input at  309  and a connection to ground  312  at the opposite end. Each input transformer  315 ,  316  of the pair of input transformers includes windings on a primary side  319 ,  320  and windings on a secondary side  323 ,  324 . The ratio K of windings between the primary side  319 ,  320  and the secondary side  323 ,  324  for each of input transformer  315 ,  316  should be the same, although not necessarily the same as for transformer  148 ,  149 . A second power supply  327  is connected between input transformer  315  and input transformer  316  on the secondary side. The second power supply  327  provides DC voltage for the injection transistors  125 ,  126 . The output of the input transformer  315  is connected to the front-gate node  133  of injection transistor  125  and the output of the input transformer  316  is connected to the front-gate node  134  of injection transistor  126 . The amount of DC voltage for the second power supply  327  can be adjusted to change the injection current for the injection transistors  125 ,  126 ; however, according to devices and methods herein, changing the back-gate bias of the injection transistors  125 ,  126  provides better control. 
       FIG. 4  shows the power amplifier  101  of  FIG. 1  having differential back-gate bias for the switching transistors  107 ,  108  (M 1 /M 2 ) and includes a flow diagram illustrating the processing flow of an exemplary method to adjust power imbalance in the output from an injection locked power amplifier (ILPA), such as described above. At  410 , the RF outputs  166 ,  167  are received by a power detector. A single power detector can be used to measure both RF outputs  166 ,  167  of power. At  415 , the power detector measures the output power. The power detector is used for relative measurement only and not absolute measurement, so the design is much simpler. According to devices and methods herein, the power detector is used to detect leakage only. no direct connection is made to the RF outputs  166 ,  167 , indicated as RFOUTP/RFOUTM so the outputs will not be loaded once the calibration is complete. At  420 , the difference between the RF outputs  166 ,  167 , indicated as RFOUTP/RFOUTM, is determined. If the difference is less than approximately 0.1 dB there is no need for adjustment, so the process stops, at  425 . Otherwise, at  430 , the back-gate voltage (VBGN 2 ) at the back-gate node  119  of switching transistor  108  (M 2 ) is adjusted. At  435 , a check is made to see if the back-gate voltage (VBGN 2 ) is at the maximum allowable limit. If so, at  440 , the back-gate voltage (VBGN 2 ) at the back-gate node  119  of switching transistor  108  (M 2 ) is set to a default value. At  445 , the power detector again measures the output power. As before, the power detector is used for relative measurement only and not absolute measurement. At  450 , the difference between the RF outputs  166 ,  167 , indicated as RFOUTP and RFOUTM, is determined. If the difference is less than approximately 0.1 dB there is no further adjustment, so the process stops, at  455 . Otherwise, at  460 , the back-gate voltage (VBGN 1 ) at the back-gate node  118  of switching transistor  107  (M 1 ) is adjusted. The process reverts to  445  to again measure the output power. If, at  435 , after adjusting the back-gate voltage (VBGN 2 ), it is not at the maximum allowable limit, the power detector again measures the output power, at  470 . As before, the power detector is used for relative measurement only and not absolute measurement. The process reverts to  420  to again determine if the difference between the RF outputs  166 ,  167 , indicated as RFOUTP/RFOUTM, is less than approximately 0.1 dB. While the above process begins by first adjusting the back-gate voltage (VBGN 2 ) at the back-gate node  119  of switching transistor  108  (M 2 ) before adjusting the back-gate voltage (VBGN 1 ) at the back-gate node  118  of switching transistor  107  (M 1 ), the order can be reversed. Moreover, adjusting of the back-gate voltages (VBGN 1 /VBGN 2 ) can be done in any order or combination. 
     For electronic applications, semiconducting substrates, such as silicon wafers, can be used. The substrate enables easy handling of the micro device through the many fabrication steps. Often, many individual devices are made together on one substrate and then singulated into separated devices toward the end of fabrication. In order to fabricate a microdevice, many processes are performed, one after the other, many times repeatedly. These processes typically include depositing a film, patterning the film with the desired micro features, and removing (or etching) portions of the film. For example, in memory chip fabrication, there may be several lithography steps, oxidation steps, etching steps, doping steps, and many others are performed. The complexity of microfabrication processes can be described by their mask count. 
     The methods as described above may be used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (that is, as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case, the chip is mounted in a single chip package (such as a plastic carrier, with leads that are affixed to a motherboard or other higher-level carrier) or in a multichip package (such as a ceramic carrier that has either or both surface interconnections or buried interconnections). In any case, the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor. 
     While only one or a limited number of transistors are illustrated in the drawings, those ordinarily skilled in the art would understand that many different types transistor could be simultaneously formed with the embodiment herein and the drawings are intended to show simultaneous formation of multiple different types of transistors; however, the drawings have been simplified to only show a limited number of transistors for clarity and to allow the reader to more easily recognize the different features illustrated. This is not intended to limit this disclosure because, as would be understood by those ordinarily skilled in the art, this disclosure is applicable to structures that include many of each type of transistor shown in the drawings. 
     The terminology used herein is for the purpose of describing particular devices and methods only and is not intended to be limiting of this 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 “including”, when used in this specification, 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. 
     In addition, terms such as “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”, “over”, “overlying”, “parallel”, “perpendicular”, etc., used herein are understood to be relative locations as they are oriented and illustrated in the drawings (unless otherwise indicated). Terms such as “touching”, “on”, “in direct contact”, “abutting”, “directly adjacent to”, etc., mean that at least one element physically contacts another element (without other elements separating the described elements). 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The descriptions of the various devices and methods herein have been presented for purposes of illustration but are not intended to be exhaustive or limited to the devices and methods disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described devices and methods. The terminology used herein was chosen to best explain the principles of the devices and methods, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the devices and methods disclosed herein. 
     While various examples are described herein, it will be appreciated from the specification that various combinations of elements, variations, or improvements therein may be made by those skilled in the art and are within the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosed concepts without departing from the essential scope thereof. Therefore, it is intended that the concepts not be limited to the particular examples disclosed as the best mode contemplated for carrying out the devices and methods herein, but that the devices and methods will include all features falling within the scope of the appended claims.