Patent Publication Number: US-2023163734-A1

Title: Power amplifier system

Description:
RELATED APPLICATIONS 
     This application claims the benefit of provisional patent application serial number 63/281,366, filed Nov. 19, 2021, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to a power amplifier system in a front-end transmit architecture that eliminates a typically used series switch from the output signal path. 
     BACKGROUND 
     Traditional front-end modules use a physical switch component in the transmit path from the power amplifier to the antenna. Such component disconnects the power amplifier when not in transmit mode. During the transmit mode the switch is in series with the power amplifier output, resulting in an unwanted insertion loss and thus a loss in efficiency for the module. In most cases the power amplifier and the switch are implemented with different technologies, often on different integrated circuits, for example, a gallium arsenide (GaAs) power amplifier and silicon-on-insulator complementary metal oxide semiconductor (SOI-CMOS) switch. 
     SUMMARY 
     A power amplifier system is disclosed having an N number of transistors coupled together drain-to-source between a supply node and a fixed voltage node, wherein a first one of the N number of transistors coupled nearest to the fixed voltage node is configured to operate as an amplifying device in an ON-mode, and remaining ones of the N number of transistors are configured to operate as cascode devices in the ON-mode and to operate as turned-off switches in an OFF-mode. A controller is configured to place the N number of transistors in the ON-mode when a radio frequency (RF) signal is to be amplified by the first one of the N number of transistors and to place the N number of transistors in the OFF-mode when the RF signal is not to be amplified by the first one of the N number of transistors. 
     In another aspect, any of the foregoing aspects individually or together, and/or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various features and elements as disclosed herein may be combined with one or more other disclosed features and elements unless indicated to the contrary herein. 
     Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG.  1    is a general diagram of a power amplifier system having transconductance and cascode devices that are configured to selectively operate as an amplifier in an ON-mode or as switch in an OFF-mode. 
         FIG.  2    is a diagram showing an embodiment of the power amplifier system that includes selectable gate resistors. 
         FIG.  3    is a diagram showing an embodiment the power amplifier system in a reconfigurable complementary amplifier configuration. 
         FIG.  4    is a diagram showing an embodiment of the power amplifier system further including selectable bias switches. 
         FIG.  5    is a diagram showing an embodiment of the power amplifier system having bypass capacitors selectably coupled to gates of the cascode devices. 
         FIG.  6    is a diagram showing an alternate embodiment in which the transconductance device is reconfigured as a parallel switch while the cascode devices are reconfigured as a series switch. 
         FIG.  7    is a diagram showing how the disclosed power amplifier system may interact with user elements such as wireless communication devices. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     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. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     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, there are no intervening elements 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, there are no intervening elements 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, there are no intervening elements present. 
     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. 
     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. 
     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 used herein 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. 
     Embodiments are described herein with reference to schematic illustrations of embodiments of the disclosure. As such, the actual dimensions of the layers and elements can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are expected. For example, a region illustrated or described as square or rectangular can have rounded or curved features, and regions shown as straight lines may have some irregularity. Thus, the regions illustrated in the figures are schematic and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the disclosure. Additionally, sizes of structures or regions may be exaggerated relative to other structures or regions for illustrative purposes and, thus, are provided to illustrate the general structures of the present subject matter and may or may not be drawn to scale. Common elements between figures may be shown herein with common element numbers and may not be subsequently re-described. 
       FIG.  1    is a general diagram of a power amplifier system  10 . A transmit path is turned off when not transmitting a radio frequency signal to avoid unwanted leakages into a load such as an antenna. A series switch or a combination of series and parallel switches are used for this action. 
     In this regard, the power amplifier system  10  has an N number of transistors Q 1  and Q 2  through QN that are configured to selectively operate as an amplifier in an ON-mode or as a switch in an OFF-mode. In the ON-mode, a substantial current is allowed to flow through the transistors Q 2  through QN. In the OFF-mode, practically no current flows through the transistors Q 2  through QN. 
     The amplifier system  10 , which is typically integrated within a front-end module&#39;s (FEM) transmit architecture, eliminates a traditional series switch from an output signal path and thus results in lower insertion loss and thus better efficiency. A radio frequency (RF) output terminal  12  that is labeled RF_OUT is included in the output signal path. In the exemplary embodiment depicted in  FIG.  1   , the RF output terminal  12  is coupled to a drain of the transistor QN. An RF input terminal  14  labeled RF_IN is coupled to a gate of the transistor Q 1 . In the ON-mode, an RF signal received at the RF input terminal  14  is amplified by the transistor Q 1  and is output at the RF output terminal  12 . In this case, in the ON-mode the transistor Q 1  functions as a transconductance device. 
     The power amplifier system  10  also includes bias circuitry  16  and a controller  18 . The bias circuitry  16  is configured to generate selectable bias levels for the N number of transistors Q 1  and Q 2  through QN under control of the controller  18  by way of a bias control terminal  20 , which is labeled BIAS_CTRL in  FIG.  1   . 
     In the exemplary embodiment depicted in  FIG.  1   , the power amplifier system  10  also includes an N number of gate switches SW 1  and SW 2  through SWN, one of each being coupled between a respective gate of the transistors Q 1  and Q 2  through QN and an ON/OFF voltage output terminal  22 , which is labeled ON/OFF in  FIG.  1   . The controller  18  further includes a switch control bus  24 , labeled CTRL and depicted in dashed line. The switch control bus  24  may be used to control the opening and closing of each of the switches SW 1  through SWN individually or simultaneously in various embodiments. The controller  18  is also configured to generate a voltage signal at the ON/OFF output terminal that is applied to the gates of the switches SW 1  through SWN when the switches SW 1  through SWN are closed to place the transistors Q 2  through QN in the 
     OFF-mode. Transistors Q 2  through QN are configured to function as cascode devices and voltage protection devices in the ON-mode or as a series switch in the OFF-mode. 
     The amplifier system  10  may be realized with complementary metal oxide semiconductor (CMOS) power amplifiers but may also be realized in other configurations, such as junction field-effect transistors, pseudomorphic high electron mobility transistors (pHEMTs), and other types of amplifiers in which several transistors are cascaded to sustain the large output voltage swing. The amplifier system  10  according to the present disclosure may be fabricated using bulk and silicon-on-insulator (SOI)/silicon-on-sapphire fabrication processes. In the case of a SOI, a more even distribution of the radio frequency (RF) voltage over the cascoded transistors Q 2  through QN operated as switches can be achieved, resulting usually in a higher maximum operating power. In at least some embodiments, the N number of transistors are of the partially depleted SOI complementary metal oxide semiconductor (CMOS) type. In other embodiments, the N number of transistors are of the fully depleted SOI CMOS type. 
     Each of the transistors Q 1  through QN needs to handle properly the RF signal when operating as an amplifier. The transconductance device that is transistor Q 1  needs minimum series resistance in the gate. For this reason, in some embodiments, a series switch in the gate of the transconductance device may be omitted as depicted in  FIG.  1   . 
     There are many ways in which the switches may be configured. In  FIG.  2   , the Nth transistor is Q 3  and the Nth switch is SW 3 . The exemplary embodiment of  FIG.  2    includes gate resistors RG 1 , RG 2 , and RG 3  coupled between the gates of transistors Q 1 , Q 2 , and Q 3  and the switches SW 1 , SW 2 , and SW 3 , respectively. Note that  FIG.  2    depicts a double-pole single-throw reconfigurable switch configuration. Other connections are also possible. For example, the transconductance device may be re-routed as a series device from the signal path perspective. 
     This and other reconfigurable switch configurations are realizable for both N-type cascaded amplifiers and P-type cascaded amplifiers. Furthermore, the reconfigurable switch configuration can be generalized for the complementary N-type and P-type amplifiers as shown in  FIG.  3   . In this case there are two sets of cascode transistors in which Q 2 , Q 3 , and Q 4  are N-type devices and transistors Q 5 , Q 6 , and Q 7  are P-type devices. In this exemplary embodiment, there are two transconductance devices, which are the transistor Q 1  and a transistor Q 8 . The transistor Q 1  is an N-type device and the transistor Q 8  is a P-type device. Also, in this exemplary embodiment, the controller  18  is further configured to reconfigure all of the transistors Q 1  through Q 8  as switches in the OFF mode, or only a subset of the transistors Q 1  through Q 8  may be reconfigured to operate as switches. Gate resistors RG 4 , RG 5 , RG 6 , RG 7 , and RG 8  are coupled between the gates of the transistors Q 4 , Q 5 , Q 6 , Q 7 , and Q 8  and switches SW 5 , SW 6 , SW 7 , and SW 8 , respectively. 
     A reason for the disclosed reconfigurable switch configurations is to have protection in both ON-mode and the OFF-mode. One advantage is that the same ones of the transistors Q 1  through Q 8  may be used to provide protection in both the ON-mode and the OFF-mode. Another advantage is that the power amplifier system  10  reuses the same ones of the transistors Q 1  through Q 8  to implement both an amplifier function in the ON-mode and a switch function in the OFF-mode and thus takes significantly less footprint for the amplifier system  10 , which results in a smaller and lower cost solution. 
     Furthermore, in most cases the amplifier and the switch components are realized with different processes and often are integrated in different integrated circuits. The power amplifier can often be a bipolar or heterojunction bipolar transistor (HBT) process—silicon germanium (SiGe), gallium arsenide (GaAs), indium phosphide (InP), and gallium nitride (GaN), for example—while the switch is done in SOI-CMOS. The main drawback of this configuration is the extra insertion loss brought by the physical dedicated series switch. 
     In many FEMs, the power amplifier is built with high-voltage devices—HBT, pHEMT, and laterally diffused metal oxide semiconductor (LD-MOS), for example—that can handle the entire large output signal swing in a single device. 
     For the switch, the MOS processes have much lower breakdown voltage and require a number of MOS—field-effect transistors (FETs) to be stacked in order to handle the maximum signal level. The insertion loss of the switch is further increased if a higher linearity is needed (larger number of stacked devices) or multiple branches are switched together. 
     In the case of CMOS power amplifiers, the output stage needs to be cascaded anyway since the breakdown voltage of each individual MOSFET is much lower than the maximum signal that is handled. This is true for both bulk and SOI CMOS implementations. 
       FIG.  4    is a schematic depicting an embodiment in which additional switches SW 5 , SW 6 , SW 7 , and SW 8  are coupled between the respective gates of the transistors Q 1 , Q 2 , Q 3 , and Q 4  and the bias circuitry  16 . The controller  18  is further configured to selectively couple the gates of the transistors Q 1 , Q 2 , Q 3 , and Q 4  to the bias circuitry  16  in the ON-mode and to selectively decouple the gates of the transistors Q 1 , Q 2 , Q 3 , and Q 4  from the bias circuitry  16  in the OFF-mode. At least one advantage of this exemplary embodiment is increased isolation of the amplifier system  10  from other portions of an FEM (not shown). The supply voltage VDD/VBAT is isolated from RF signals by way of an inductor L 1  coupled between the supply voltage VDD/VBAT and the RF output  12 . 
     As depicted in  FIG.  5    the cascode devices that are transistors Q 2 , Q 3 , and Q 4  need bypass capacitances when the power amplifier system  10  is operated in the ON-mode. Moreover, the transistors Q 2 , Q 3 , and Q 4  need to have large series resistors RG 1 , RG 2 , RG 3 , and RG 4  in the OFF-mode to ensure an even distribution of the large RF signal on the transistors Q 1 , Q 2 , Q 3 , and Q 4  that are stacked FETs in this and other embodiments. A first bypass capacitor C 1  is coupled between the fixed voltage node GND and the switch SW 6 . The controller  18  is configured to selectively couple the first bypass capacitor C 1  to the gate of the transistor Q 2  when the power amplifier system  10  is in the ON-mode amplifying signals that arrive at the RF input  14 . A second bypass capacitor C 2  is coupled between the fixed voltage node GND and the switch SW 7 . The controller  18  is also configured to selectively couple the second bypass capacitor C 2  to the gate of the transistor Q 3  when the power amplifier system  10  is in the ON-mode. A third bypass capacitor C 3  is coupled between the fixed voltage node GND and the switch SW 8 . The controller  18  is further configured to selectively couple the third bypass capacitor C 3  to the gate of the transistor Q 4  when the power amplifier system  10  is in the ON-mode. 
       FIG.  6    also depicts the gate resistors RG 1 , RG 2 , RG 3 , and RG 4  coupled in series to realize a series gate resistor bias network. In a single-ended power amplifier version of the power amplifier system  10 , it is advantageous to reconfigure the cascode devices that are the transistors Q 2 , Q 3 , and Q 4  to act as the series switch with the series gate resistor bias network. 
     In large signal RF circuits, it is dangerous to leave floating nodes, as they can pump to high signal levels through parasitic coupling. For this reason most FEMs use a series-parallel switch combination, operating in the opposite way and usually non-overlapping. When the series switch is ON, the parallel switch is OFF, and vice versa. 
     In this regard,  FIG.  6    shows an embodiment of the power amplifier system  10  that avoids floating nodes in the signal path when the power amplifier system  10  is not transmitting and is reconfigured as switch. In this embodiment, the transconductance device that is transistor Q 1  is selectably reconfigured as a parallel switch, while the cascode devices that are the transistors Q 2 , Q 3 , and Q 4  are reconfigured as series switches. The controller  18  generates appropriate on and off voltage levels at the ON/OFF voltage output terminal  22 , which is relabeled CTRL_SER to indicate that the control of the series switch made from the transistors Q 2 , Q 3 , and Q 4 . Moreover, in this embodiment a second ON/OFF voltage output terminal  26  is selectively coupled to the gate of the transconductance device that is transistor Q 1 . The controller  18  also generates appropriate on and off voltage levels at the second ON/OFF terminal  26 . The gate of transistor Q 1  is further selectively coupled to the fixed voltage node GND by a ninth switch SW 9  that is configured to be under the control of the controller  18 . During operation, the transistor Q 1  becomes a parallel switch when the ninth switch SW 9  is closed. 
     Dedicated amplifier-mode switches and switch-mode switches can be placed to route the desired signals to the gates of the stacked devices. The equivalent switch may use a parallel gate bias resistor network or a series gate bias resistor network. The switches need to be connected accordingly. The gate bias switching is a low-power network that does not need large area switches. It also does not contribute significantly to the power amplifier efficiency (losses) since the impedance level at the gates is much larger than the impedance in the drain output. The power amplifier system  10  is realizable with differential amplifier stages and other types of power amplifiers, for example, Doherty and quadrature amplifiers. 
     With reference to  FIG.  7   , the concepts described above may be implemented in various types of wireless communication devices or user elements  28 , such as mobile terminals, smart watches, tablets, computers, navigation devices, access points, and the like that support wireless communications, such as cellular, wireless local area network (WLAN), Bluetooth, and near-field communications. The user elements  28  will generally include a control system  30 , a baseband processor  32 , transmit circuitry  34 , receive circuitry  36 , antenna switching circuitry  38 , multiple antennas  40 , and user interface circuitry  42 . The receive circuitry  36  receives radio frequency signals via the antennas  40  and through the antenna switching circuitry  38  from one or more basestations. A low-noise amplifier and a filter 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. 
     The baseband processor  32  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  32  is generally implemented in one or more digital signal processors (DSPs) and application-specific integrated circuits (ASICs). 
     For transmission, the baseband processor  32  receives digitized data, which may represent voice, data, or control information, from the control system  30 , which it encodes for transmission. The encoded data is output to the transmit circuitry  34 , where it is used by a modulator to modulate 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  40  through the antenna switching circuitry  38  to the antennas  40 . The multiple antennas  40  and the replicated transmit and receive circuitries  34 ,  36  may provide spatial diversity. Modulation and processing details will be understood by those skilled in the art. 
     It is contemplated that any of the foregoing aspects, and/or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various embodiments as disclosed herein may be combined with one or more other disclosed embodiments unless indicated to the contrary herein. 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.