Abstract:
Reconfigurable distributed active transformers are provided. The exemplary embodiments provided allow changing of the effective number and configuration of the primary and secondary windings, where the distributed active transformer structures can be reconfigured dynamically to control the output power levels, allow operation at multiple frequency bands, maintain a high performance across multiple channels, and sustain desired characteristics across process, temperature and other environmental variations. Integration of the distributed active transformer power amplifiers and a low noise amplifier on a semiconductor substrate can also be provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 11/037,527 filed Jan. 18, 2005, now U.S. Pat. No. 7,119,619 which is a continuation of U.S. patent application Ser. No. 10/386,001 filed Mar. 11, 2003, now U.S. Pat. No. 6,856,199 which claims priority from U.S. Provisional Patent Application No. 60/363,424, filed Mar. 11, 2002, and is a continuation-in-part of U.S. patent application Ser. No. 09/974,578, filed Oct. 9, 2001, now U.S. Pat. No. 6,816,012 which claims priority to U.S. Provisional Patent Application No. 60/239,470 filed Oct. 10, 2000; U.S. Provisional Patent Application No. 60/239,474 filed Oct. 10, 2000; and U.S. Provisional Patent Application No. 60/288,601 filed May 4, 2001. 

   The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of ECS-0083220 awarded by NSF. 

   FIELD OF THE INVENTION 
   The present invention pertains to the field of distributed active transformers. More specifically, the invention relates to distributed active transformers that include features that provide additional control over operational parameters. 
   BACKGROUND OF THE INVENTION 
   A distributed active transformer includes a primary winding that uses active devices to control the current direction and magnitude on the winding. For example, U.S. patent application Ser. No. 09/974,578, filed Oct. 9, 2001, describes distributed active transformers that can comprise at least two push/pull amplifiers designed to amplify an RF input signal. The distributed active transformer can be operated where a first amplifier causes current to flow on the primary winding in a first direction, and where a second amplifier causes current to flow on the primary in a second direction. In this manner, an alternating current is induced on the secondary winding. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, a distributed active transformer is provided that overcomes known problems with existing transformers. 
   In particular, a distributed active transformer is provided that allows sections of the distributed active transformer to be independently controlled. 
   In accordance with an exemplary embodiment of the present invention, a distributed active transformer is provided. The distributed active transformer includes a primary winding having two or more sets of push/pull amplifiers, where each set of push/pull amplifiers is used to create an alternating current on a section of the primary winding. A secondary winding is disposed adjacent to the primary winding, such that the alternating current on the primary induces alternating current on the secondary. The primary winding and the secondary winding can be disposed on a semiconductor substrate. 
   The present invention provides many important technical advantages. One important technical advantage of the present invention is a distributed active transformer that allows sections of the distributed active transformer to be independently controlled, so as to adjust the operating parameters of the distributed active transformer. 
   Those skilled in the art will appreciate the advantages and superior features of the invention together with other important aspects thereof on reading the detailed description that follows in conjunction with the drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a diagram of a distributed active transformer in accordance with an exemplary embodiment of the present invention; 
       FIG. 2  is a diagram of a distributed active transformer with two primary windings in accordance with an exemplary embodiment of the present invention; 
       FIGS. 3 and 3A  are diagrams of a distributed active transformer with first and second primary windings and compensating capacitors in accordance with an exemplary embodiment of the present invention; 
       FIG. 4  is a diagram of a distributed active transformer with first and second primary windings and compensating capacitors in accordance with another exemplary embodiment of the present invention; 
       FIG. 5  is a diagram of a distributed active transformer with impedance transformation ratio correction and resonance frequency selection in accordance with an exemplary embodiment of the present invention; 
       FIG. 6  is a diagram of a distributed active transformer with switched-in capacitors that are in parallel with amplifiers in accordance with an exemplary embodiment of the present invention; 
       FIG. 7  is a diagram of a distributed active transformer with a low noise amplifier in accordance with an exemplary embodiment of the present invention; and 
       FIG. 8  is a diagram of a distributed active transformer with a low noise amplifier in accordance with another exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the description that follows like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale and certain features may be shown in somewhat generalized or schematic form in the interest of clarity and conciseness. 
     FIGS. 1 AND 1A  are diagrams of distributed active transformer  100  in accordance with an exemplary embodiment of the present invention. Distributed active transformer  100  allows the number of primary sections in the primary winding of a distributed active transformer to be reconfigured. 
   Distributed active transformer  100  includes primary winding sections  102 A,  102 B,  102 C, and  102 D, and secondary winding  104 . Each primary winding section has an associated push/pull amplifier pair that includes amplifiers  106 A and  108 A for primary winding section  102 A, amplifiers  106 B and  108 B for primary winding section  102 B, amplifiers  106 C and  108 C for primary winding section  102 C, and amplifiers  106 D and  108 D for primary winding section  102 D. The amplifiers can be implemented using bipolar junction transistors (BJTs), metal oxide semiconductor field-effect transistors (MOSFETs), hetero-junction bipolar transistors (HBTs), metal-semiconductor field effect transistors (MESFETs), lateral double-diffused metal oxide semiconductor transistors (LDMOSs), complementary MOS transistors (CMOS), or other suitable devices. Amplifier  106 A drives current to the positive terminal of primary winding section  102 A, whereas amplifier  108 A drives current from the negative terminal of primary winding section  102 A. The polarities of the amplifiers can be alternated to reverse the direction of current flow. A drain voltage V dd  (not explicitly shown) may alternatively be provided at a midway point, corner, or at other suitable locations on each primary winding section to provide the current source or other suitable configurations can be used to create time-varying current on the primary winding sections using the push/pull amplifier pairs. A similar configuration is used for primary winding sections  102 B,  102 C, and  102 D. 
   Each push/pull amplifier pair of each primary winding section can be controlled so that the current flowing on the primary winding section alternates in direction and magnitude in a manner that creates a magnetic field that induces an electromotive force (EMF) on secondary winding  104 . The EMF causes current to flow in secondary winding  104 , based on the impedance of that winding and any associated circuit. The current through the push/pull amplifier pairs can be controlled so as to adjust both the current and the voltage induced in this manner on secondary winding  104 . 
   Switches  110 A,  110 B,  110 C, and  110 D can be implemented as transistors, micro-electromechanical devices (MEMS), or other suitable devices, and are connected to a one amplifier out of each set of two adjacent push/pull amplifier pairs, such that the two adjacent push/pull amplifiers can be bypassed and a new push/pull amplifier pair can be created. As used herein, “connect” and its cognate terms such as “connects” or “connected” can refer to a connection through a conductor, a semiconducting material, or other suitable connections. In one exemplary embodiment, amplifiers  106 A and  108 B are connected to switch  110 A, such that the amplifiers can be bypassed by closing switch  110 A. In this embodiment, amplifiers  106 B and  108 A would then form the push/pull amplifier pair for primary winding sections  102 A and  102 B. Likewise, a similar configuration can be provided for switches  110 B,  110 C and  110 D. In this regard, it should be noted that the set of push/pull amplifiers that the switches are connected to is different from the set of push/pull amplifiers that service each primary winding section. Nevertheless, each switch can operate to bypass one amplifier from a first push/pull amplifier pair and a second amplifier from a second push/pull amplifier pair so as to result in the remaining amplifiers from those two push/pull amplifier pairs operating as a push/pull amplifier pair on a combined primary winding section. 
   For example, if switch  110 A is closed, the power level generated by distributed active transformer  100  is less than the power level that is generated for distributed active transformer  100  with all switches open. The current magnitude through secondary winding  104  will be determined by the sum of the electromotive forces induced on the secondary by each primary winding section, which equals the change in flux linkages over time (dΦ/dt) which is determined by the mutual inductance of the primary and the secondary and the change in the current of the secondary (M*dI/dt.) 
   When a push-pull configuration is used with no V dd  points, closing a single switch  110  results in an increased impedance for each remaining push/pull amplifier pair that drives current through the two connected primary winding sections. This configuration decreases the output power by increasing the impedance seen by the remaining amplifiers. Alternately, the winding sections can be capacitively coupled, such that the impedance seen by each amplifier remains the same, but where power is controlled by turning off or switching out amplifier sections. In either configuration, turning off amplifiers results in a decrease in output power and can be used to lower the overall power dissipation of the amplifier. 
   When a push-pull configuration is used that includes V dd  points, with a single switch  110  closed, one quarter of the primary winding section will not be carrying any current, as no current will flow between the V dd  points of the two connected primary winding sections. 
   In the described configurations, closing one switch can decrease the flux linkages between the primary and secondary windings, such that the open loop voltage on the secondary will be decreased to fraction of the maximum open loop voltage that could be realized with all switches  110 A through  110 D open. Likewise, with two and three switches  110  closed, the open loop voltage will drop more. Thus, distributed active transformer  100  can operate in four different modes of operation—a maximum power mode with all switches  110 A through  110 D open, a medium-high power mode, with any one of switches  110 A through  110 D closed, a medium-low power mode with any two of switches  110 A through  110 D closed, and a low power mode with any three of switches  110 A through  110 D closed. The power levels will be a function of whether the impedance seen by each amplifier is constant or varies as a function of the switches that are closed, as well as other factors. 
   In addition to providing different power modes of operation with switches  110 A through  110 D, the biasing current required for each of the bypassed amplifiers can also be decreased, such that the bias current requirements for distributed active transformer  100  can also be controlled. For example, with all switches  110 A through  110 D open, the bias current required for each of amplifiers  106 A and  108 A through  106 D and  108 D can be at a maximum. If switch  110 A is closed, then the bias current required for amplifiers  106 A and  108 B can decrease. In this manner, bias current requirements for distributed active transformer  100  can be controlled through the use of switches  110 A through  110 D, where suitable. Likewise, the bias current for a given power level can be optimized by determining the power level range for a given switch setting, and using the range that provides the lowest bias current for the expected range of operation. For example, if the expected power levels for the operating range of an application would fall within either the power level range for operation of distributed active transformer  100  with either two of switches  110  closed or three of switches  110  closed, then operation of distributed active transformer  100  with three of switches  110  closed would satisfy the power requirements for the operating range while minimizing the bias current required to support operation. 
     FIG. 1A  shows an exemplary configuration of switches  120 A and  120 B, which can be used to connect or disconnect amplifiers  108 A and  106 D, respectively, from distributed active transformer  100  while allowing  102 A and  102 D to be independently coupled or decoupled. The exemplary configuration of switches  120 A and  120 B can be implemented at each connection between each primary winding section, secondary winding sections (if such sections are used), or in other suitable locations. Switches  120 A and  120 B thus provide additional flexibility for the configuration of distributed active transformer  100 . 
   In operation, distributed active transformer  100  allows the power capability and biasing current requirements to be controlled through the operation of switches  110 A through  110 D. In this manner, additional control of the power output and power consumption of a distributed active transformer is provided. 
     FIG. 2  is a diagram of distributed active transformer  200  with two primary windings in accordance with an exemplary embodiment of the present invention. Additional primary and secondary windings can likewise be provided for additional power conversion control, either internal or external to the secondary winding. 
   Distributed active transformer  200  includes first primary winding sections  202 A,  202 B,  202 C, and  202 D, and second primary winding  212 . Secondary winding  204  is disposed between the first primary winding sections  202 A through  202 D and second primary winding  212 . For the first primary winding sections, push/pull amplifiers  206 A and  208 A are associated with primary winding section  202 A, push/pull amplifiers  206 B and  208 B are associated with primary winding section  202 B, push/pull amplifiers  206 C and  208 C are associated with primary winding section  202 C, and push/pull amplifiers  206 D and  208 D are associated with primary winding section  202 D. Likewise, push/pull amplifiers  210 A and  210 B are associated with second primary winding  212 , although a single driver amplifier can alternatively be used where suitable. The secondary winding has an output  214 . 
   Distributed active transformer  200  can operate with primary winding sections  102 A through  102 D active and second primary winding  212  inactive. In this mode, distributed active transformer  200  can provide higher power but with increased bias current requirements. Likewise, distributed active transformer  200  can operate with primary winding sections  102 A through  102 D inactive and with second primary winding  212  active. In this exemplary embodiment, the power delivered to output  214  can be lower than the power delivered to output  214  when first primary winding sections  202 A through  202 D are activated, but the bias current required can be lower than the bias required with primary winding sections  202 A through  202 D active. 
   In another exemplary embodiment, the spacing between second primary winding  212  and secondary winding  204  can be increased, so as to decrease the magnetic coupling between the primary and secondary windings. The power loss in second primary winding  212  when it is not being used can thus be decreased, as well as the voltage breakdown requirements of push/pull amplifiers  210 A and  210 B. Additional primary windings can likewise be provided, depending on the power levels required and the available space. 
   In operation, distributed active transformer  200  can be operated in a first mode for high power with high bias current requirements by activation of primary winding sections  202 A through  202 D, and in a second mode with lower power and bias current requirements by activation of second primary winding  212 . Use of a first primary winding and a second primary winding allows the power output and bias current requirements for a distributed active transformer to be adjusted as needed by switching between primaries. 
     FIGS. 3 AND 3A  are diagrams of distributed active transformer  300 A with first and second primary windings and compensating capacitors in accordance with an exemplary embodiment of the present invention. Distributed active transformer  300 A allows the power loss caused by circulating currents in an unused primary winding to be mitigated through the use of a switched series capacitance, as well as decreasing the breakdown voltage imposed on the associated primary winding amplifiers. 
   Distributed active transformer  300 A includes primary winding sections  302 A through  302 D with associated push/pull amplifier pairs  306 A and  308 A through  306 D and  308 D, respectively, and secondary winding  304  with output  312 . Likewise, second primary winding  310  includes push/pull amplifiers  314 A and  314 B, which can be connected using switch  316  through capacitor  318 . When capacitor  318  is connected in parallel with second primary winding  310  through switch  316 , an LC resonant circuit can be formed with secondary winding  304 . When second primary winding  310  is not in use, switch  316  can be opened to take second primary winding  310  out of resonance with secondary winding  304  and decrease losses due to circulating currents, as well as to decrease the peak voltage imposed on push/pull amplifiers  314 A and  314 B when they are inactive. In general, capacitors can be switched into and out of windings in other suitable configurations, to take the windings in and out of resonance with other windings. 
   As shown in  FIG. 3A , a suitable configuration of switches and capacitors can be used in lieu of a single switch  316  and capacitor  318 , where each switch-capacitor pair can be controlled separately, thus allowing the resonance frequency of the secondary loop to be adjusted. In one exemplary embodiment, this combination can be used to adjust the center frequency of a power amplifier so as to achieve a flat gain and efficiency response across multiple frequency bands or channels, to account for manufacturing process variations, to account for temperature variations, or for other suitable purposes. 
     FIG. 4  is a diagram of distributed active transformer  300 B with first and second primary windings and compensating capacitors in accordance with an exemplary embodiment of the present invention. Distributed active transformer  300 B allows the power loss caused by circulating currents in an unused primary winding to be mitigated through the use of switched capacitors, as well as decreasing the breakdown voltage imposed on the associated primary winding amplifiers. 
   Distributed active transformer  300 B includes primary winding sections  302 A through  302 D with associated push/pull amplifier pairs  306 A and  308 A through  306 D and  308 D, respectively, with secondary winding  304  and output  312 . Likewise, second primary winding  310  includes push/pull amplifiers  314 A and  314 B, which can be connected using switches  316  through capacitors  318 . When capacitors  318  are connected to second primary winding  310  through switches  316 , an LC resonant circuit is created with secondary winding  304 . When second primary winding  310  is not in use, switches  316  can be opened to take second primary winding  310  out of resonance with secondary winding  304  and decrease losses due to circulating currents, as well as to decrease the peak voltage imposed on push/pull amplifiers  314 A and  314 B when they are inactive. 
     FIG. 5  is a diagram of distributed active transformer  400  with impedance transformation ratio correction and resonance frequency selection in accordance with an exemplary embodiment of the present invention. Distributed active transformer  400  includes primary winding sections  402 A through  402 D with associated push/pull amplifiers  406 A and  408 A through  406 D and  408 D, respectively. Switches  418 A through  418 D are connected in series with capacitors  416 A through  416 D, respectively. Output  410  of secondary winding  404  includes switch  414  and capacitor  412  for impedance transformation ratio control. Alternatively, switch  414  and capacitor  412  can be omitted, such as where it is desirable only to allow the resonance frequency of distributed active transformer  400  to be controlled. Likewise, a suitable configuration of switches and capacitors can be used in lieu of a single switch  414  and capacitor  412 , where each switch-capacitor pair can be controlled separately, thus allowing the resonance frequency of the secondary loop to be adjusted. 
   In this exemplary embodiment, the power operation mode of distributed active transformer  400  can be controlled, such as by closing one or more of switches  418 A through  418 D, so as to insert capacitors  416 A through  416 D in series with primary winding sections  402 A through  402 D. In this manner, a series LC circuit is created to compensate for leakage inductance between the primary winding sections  402 A through  402 D and secondary winding  404 . Thus, by placing one or more of capacitors  416 A through  416 D in series with primary winding sections  402 A though  402 D, the maximum output power is decreased, but the bias current required to achieve a gain level is also decreased. Alternatively, if capacitor  412  is placed in parallel across the load by closing switch  414  to compensate for this leakage inductance, then the impedance transformation ratio is increased, which increases the maximum output power but which also increases the bias current requirements. 
   In addition, the resonant frequency of distributed active transformer  400  can be adjusted for a particular frequency of operation by switching in capacitors  416 A through  416 D. In this manner, the efficiency and power output by distributed active transformer  400  can be optimized for a desired frequency of operation by configuring it for resonance at that frequency. Thus, depending on the sizes of the capacitors, distributed active transformer  400  can be operated in a first mode either with or without switch  414  and capacitor  412  to change the impedance transformation ratio by compensating for winding leakage inductance, in a second mode without switch  414  and capacitor  412  to change the resonant frequency of distributed active transformer  400 , or in both modes simultaneously. Likewise, a suitable configuration of switches and capacitors can be used in lieu of switches  418  and capacitors  416 , where each switch-capacitor pair can be controlled separately, thus allowing the resonance frequency of the primary loop to be adjusted. 
     FIG. 6  is a diagram of distributed active transformer  500  with switched-in capacitors that are in parallel with amplifiers  506 A and  508 A through  506 D and  508 D, in accordance with an exemplary embodiment of the present invention. Distributed active transformer  500  includes primary windings sections  502 A through  502 D with associated push/pull amplifiers  506 A and  508 A through  506 D and  508 D, respectively. Switch pairs  518 A through  518 D are connected in series with capacitor pairs  516 A through  516 D, respectively. Output  510  of secondary winding  504  includes switch  514  and capacitor  512  for impedance transformation ratio control. Alternatively, switch  514  and capacitor  512  can be omitted, such as where it is desirable to allow the resonance frequency of distributed active transformer  500  to be controlled. 
   In this exemplary embodiment, the power operation mode of distributed active transformer  500  can be controlled, such as by closing one or more of switch pairs  518 A through  518 D, so as to insert capacitor pairs  516 A through  516 D in series with primary winding sections  502 A through  502 D. In this manner, a series LC circuit is provided to compensate for leakage inductance between the primary winding sections  502 A through  502 D and secondary winding  504 . Thus, by placing one or more of capacitor pairs  516 A through  516 D in series with primary winding sections  502 A though  502 D, the maximum output power is decreased, but the bias current required to achieve a gain level is also reduced. Alternatively, if capacitor  512  is placed in parallel across the load by closing switch  514  to compensate for this leakage inductance, then the impedance transformation ratio is increased, which increases the maximum output power but which also increases the bias current requirements. 
   In addition, the resonant frequency of distributed active transformer  500  can be adjusted for a particular frequency of operation by switching in capacitor pairs  516 A through  516 D. In this manner, the efficiency and power output of distributed active transformer  500  can be optimized for a desired frequency of operation by placing it in resonance for that frequency. Thus, depending on the sizes of the capacitors, distributed active transformer  500  can be operated in a first mode either with or without switch  514  and capacitor  512  to change the impedance transformation ratio by compensating for winding leakage inductance, in a second mode without switch  514  and capacitor  512  to change the resonant frequency of distributed active transformer  500 , or in both modes simultaneously. 
     FIG. 7  is a diagram of distributed active transformer  600  integrated with a low noise amplifier in accordance with an exemplary embodiment of the present invention. 
   In addition to the primary and secondary windings and associated push/pull amplifiers previously described, distributed active transformer  600  includes a low noise amplifier  614  and associated switch  612 . When switch  612  is closed, as shown, a transmitted signal can be provided by modulating the input through push/pull amplifiers  606 A and  608 A through  606 D and  608 D. When switch  612  is opened and push/pull amplifier pairs  606 A and  608 A through  606 D and  608 D are not operated, a received signal can be fed through an inductor coil formed by the secondary winding of distributed active transformer  600 , and low noise amplifier  614  can be used to process the signal. In this manner, integration of low noise amplifier  614  with switch  612  through a single-ended output of distributed active transformer  600  allows a receiver/transmitter architecture to be implemented. In one exemplary embodiment, distributed active transformer  600  can be used in place of a transmit switch in a transceiver, or for other suitable applications. 
     FIG. 8  is a diagram of distributed active transformer  700  with a low noise amplifier in accordance with another exemplary embodiment of the present invention. Although a low noise amplifier is shown, any suitable device can be used, including but not limited to a mixer, a transceiver, a filter, and a digital to analog converter. 
   In addition to the primary and secondary winding structures and associated push/pull amplifiers previously described, distributed active transformer  700  includes a split secondary winding  704  with switches  710 A and  710 B connected to low noise amplifier  712 . Distributed active transformer  700  can be operated in a first transmit mode with switches  710 A and  710 B closed, as shown, and in a second receive mode with switches  710 A and  710 B open. When switches  710 A and  710 B are open, low noise amplifier  712  can be used to amplify a signal received at input  714 . When switches  710 A and  710 B are closed, primary winding sections  702 A through  702 D of distributed active transformer  700  can be driven by push/pull amplifiers  706 A and  708 A through  706 D and  708 D, respectively, so that an input signal can be amplified and provided for transmission at input  714 . 
   Although exemplary embodiments of the system and method of the present invention has been described in detail herein, those skilled in the art will also recognize that various substitutions and modifications can be made to the systems and methods without departing from the scope and spirit of the appended claims.