Abstract:
A linearized channel amplifier comprising a linear channel amplifier circuit  20  and a nonlinear linearizer circuit located immediately before a high power amplifier. A common control circuit controls the linear channel amplifier circuit and the nonlinear linearizer circuit. The linearized channel amplifier functions as a driver amplifier and improves the linearity and efficiency performance of the high power amplifier across a desired frequency bandwidth. The linearized channel amplifier employs low cost temperature compensation circuits in an interface circuit and a temperature compensation network circuit, and uses a novel methodology to provide for command and control functions that includes a measurement, analytical calculation and setting process. An external personality plug may be to set the performance of the channel amplifier and linearizer.

Description:
BACKGROUND 
     The present invention relates generally to linearized channel amplifiers, and more particularly, to an improved low cost linearized channel amplifier designed for use with high power amplifiers. 
     Lockheed Martin Corporation has developed a linearized channel amplifier that is described in a paper entitled “Linearized Traveling Wave Tube Amplifiers for Space”, by Shabbir Moochalla, published in 1998 IEEE MTT-S International Microwave Symposium &amp; Exhibition. The Lockheed Martin linearized channel amplifier uses a passive FET technology developed by Lockheed Martin that is used to implement the linearizer circuit. 
     Nippon Electric Corporation has developed a linearized channel amplifier that is described in a document entitled “INTELSAT-VII Linearizer for Ku-Band TWTA”. The NEC linearized channel amplifier uses an FET amplifier as the nonlinear element for the linearizer. 
     Alcatel has developed a linearized channel amplifier that is described in a data sheet published by the company. The Alcatel linearized channel amplifier uses a MMIC amplifier as the nonlinear element for the linearizer. 
     Bosch Telecom, GmbH has developed a linearized channel amplifier that is described in a data sheet published by the company. The Bosch linearized channel amplifier uses a passive diode as the nonlinear element for the linearizer. 
     All of the four above-mentioned designs are different from the design approach used in the present invention. It would be desirable to have a low cost linearized channel amplifier designed for use with high power amplifiers that improves upon currently available approaches, such as those mentioned above. 
     SUMMARY OF THE INVENTION 
     The present invention provides for low cost linearized channel amplifier comprising a linear channel amplifier circuit and a nonlinear linearizer circuit located immediately before a high power amplifier. A common control circuit controls the linear channel amplifier and nonlinear linearizer circuits. The linearized channel amplifier functions as a driver amplifier and also improves the linearity and efficiency performance of the high power amplifier across a desired frequency bandwidth. 
     The linearized channel amplifier of the present invention may be used in any frequency band including L, C, X, Ku, K, Ka, Q, V, and W-Band, for example. The linearized channel amplifier may also be used with any high power amplifier including traveling wave tube amplifiers (TWTA) and solid state power amplifiers (SSPA). 
     The novelty of the present linearized channel amplifier is a result of a number of factors. The linearizer circuit is based on concepts developed by the assignee of the present invention disclosed in U.S. Pat. No. 5,789,978, entitled “Ku-Band Linearizer Bridge”. The linearized channel amplifier uses a simple low cost temperature compensation design approach. Also, the linearized channel amplifier uses a novel methodology to provide for all command and control functions that includes a measurement, analytical calculation and setting process. The conventional time-consuming tune and test process over temperature is thus eliminated. This translates to lower production costs. 
     The linearized channel amplifier may use an external personality plug to set the performance of the channel amplifier and linearizer. The use of the external personality plug makes the design extremely flexible for setting linearized channel amplifier performance to match to the high power amplifier performance. Alternatively, the functions of the external personality plug may be implemented in the control circuit. 
     Various advantages are provided by the linearized channel amplifier. A preferred embodiment of the linearized channel amplifier includes a channel amplifier and a linearizer integrated into one single package to save size, weight, interface complexity and cost. The interface of the linearized channel amplifier may transmit and receive either pulse commands or serial interface adapter (SIA) commands. 
     A reduced-to-practice embodiment of the channel amplifier provides both fixed gain operation (31 steps with 1 dB step) and ALC mode operation (31 steps with 0.5 dB step) over more than a 40 dB dynamic range. The channel amplifier has the ability to telemetry fixed gain/ALC mode (TTL) and output power (analog) status. The linearizer has independent controls of gain and phase over input power level and across wide bandwidth. The design of the linearizer is flexible to compensate power amplifiers (TWTA or SSPA) with any variation of gain and phase performance. 
     The linearizer has both active and bypass modes. A reduced-to-practice embodiment of the linearizer has a commandable output power range of 7.5 dB with 0.5 dB step size and an output level limiting capability. The linearizer has the ability to telemetry linearizer activelbypass mode (TTL) and output level (analog) status. The linearizer may be realized on a compact size, single alumina substrate using PIN and Schottky diodes or using MMIC chips to minimize production cost. Reduced-to-practice embodiments of both the channel amplifier and the linearizer may be temperature compensated to within less than +/−0.25 dB using a novel temperature compensation circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawing, wherein like reference numerals designate like structural element, and in which: 
     FIG. 1 is a block diagram that illustrates an exemplary linearized channel amplifier in accordance with the principles of the present invention; and 
     FIG. 2 is a block diagram that illustrates details of the control circuit and personality plug employed in the exemplary linearized channel amplifier FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawing figures, FIG. 1 shows a block diagram of an exemplary linearized channel amplifier  10  in accordance with the principles of the present invention. The linearized channel amplifier  10  is comprised of three major sections, including a channel amplifier  20  that feeds a linearizer  30 , and a shared control circuit  40  coupled to the channel amplifier  20  and linearizer  30 . The linearized channel amplifier  10  is located immediately before a high power amplifier (HPA). 
     The exemplary channel amplifier  20  comprises a first commandable gain block  21 , a bandpass filter  24 , a second commandable gain block  25  comprising a detector/coupler  26  that provides for commandable automatic gain level control (ALC) operation, and a detector/coupler  27  that provides for output level telemetry. The first commandable gain block  21  comprises a MMIC amplifier  22  and attenuator  23  that provide 30 dB range in 1 dB step size in a reduced to practice embodiment of the channel amplifier  20 . The attenuator  23  in the second commandable gain block  25  provides for a 15 dB power range in 0.5 dB step size in a reduced to practice embodiment of the channel amplifier  20 . 
     The command functions of channel amplifier  20  include fixed gain (FG) and automatic gain level control (ALC) mode selection, and commandable gain or power level. The telemetry capabilities of channel amplifier  20  include fixed gain or automatic gain level control mode and output power level status. A reduced to practice embodiment of the channel amplifier  20  provides up to 65 dB of gain, and may be operated in either fixed gain or automatic gain level control mode. The command functions are controlled by the control circuit  40  which are described in detail below. 
     The exemplary linearizer  30  comprises an integrated linearizer bridge  31  and a third commandable gain block  32  comprising a limiting amplifier  33  (an amplifier  22  and an attenuator  23 ) and the detector/coupler  27  that provides for output level telemetry. In a reduced to practice embodiment of the linearizer  30 , the third commandable gain block  32  provides for a 7.5 dB commandable output power range with 0.5 dB step size. The linearizer bridge  31  comprises a phase shifter  34 , a distortion generator  35 , a bridge circuit attenuator  36  and a delay line  37 . The linearizer bridge  31  is substantially similar to a linearizer bridge disclosed in U.S. Pat. No. 5,789,978 assigned to the assignee of the present invention. The contents of this patent are incorporated herein by reference in its entirety. The linearizer bridge  31  may be realized on a compact size, single alumina substrate using PIN and Schottky diodes or using MMIC chips to minimize production cost. 
     The linearizer  30  alters the output of the channel amplifier  20  by adding gain expansion and phase advance (or lag) as a function of power level to offset the gain compression and phase lag (or advance) of the high power amplifier up to and beyond saturation. The command functions of the linearizer  30  include active and bypass mode selection, commandable output power level and output power limiting capability. The command functions are controlled by the control circuit  40  and will be described in detail below. 
     The control circuit  40  comprises a number of analog and digital integrated circuits (shown in detail in FIG. 2) that provide regulated voltage supplies for circuits of the linearized channel amplifier  10 . The control circuit  40  also provides separate temperature compensated currents to control the attenuators  23  in the channel amplifier  20  and the output attenuator  23  of the linearizer  30 , as well as control currents for the phase shifter  34 , the distortion generator  35  and the bridge circuit attenuator  36 . 
     A reduced to practice embodiment of the control circuit  40  provides power and control paths that provide ±5 volt DC power and ground to the channel amplifier  20  and the linearizer  30 . A first channel amplifier control path  81  for the channel amplifier  20  provides 1 dB/step attenuation control and gain temperature compensation. A second channel amplifier control path  82  for the channel amplifier  20  provides 0.5 dB/step attenuation control and output level temperature compensation. 
     The control circuit  40  has control paths that provide for control over the linearizer  30 . A distortion control path  83  provides for distortion control of the linearizer  30 . A phase control path  84  provides for phase control of the linearizer  30 . An attenuation control path  85  provides for attenuation control of the linearizer  30 . A limiting control path  86  provides for limiting control of the linearizer  30 . An attenuation and temperature compensation control path  87  provides for 0.5 dB/step attenuation control and temperature compensation the linearizer  30 . 
     A number of sensor output signals are output by way of the control circuit  40 . An output signal from an ALC level detector (detector/coupler  26 ) is output by the control circuit  40  by way of path  91 . A signal from an output level detector (detector/coupler  27 ) in the channel amplifier  20  is output by the control circuit  40  by way of path  92 . A diode voltage signal from a temperature sensor in the third commandable gain block  32  is output by the control circuit  40  by way of a temperature sensor path  93 . A signal from an output level detector (detector/coupler  27 ) in the linearizer  30  is output by the control circuit  40  by way of path  94 . 
     FIG. 2 is a block diagram showing details of the control circuit  40  and personality plug  70  of the exemplary linearized channel amplifier  10  shown in FIG.  1 . The control circuit  40  comprises analog and digital integrated circuits that provide regulated voltage supplies for circuits of the linearized channel amplifier  10 . The control circuit  40  also provides separate temperature compensated currents to control the attenuators  23  in the channel amplifier  20  and the output attenuator  23  of the linearizer  30 , as well as control currents for the phase shifter  34 , the distortion generator  35  and the bridge circuit attenuator  36 . The personality plug  70  includes a temperature compensation network  72  and a telemetry level calibration circuit  74  as shown in FIG.  2 . 
     A gain control circuit  41  combines a temperature compensation signal output by the temperature compensation network  72  through path  81  and a gain command signal from either an ALC loop  44  or the 5 bit gain control D/A  47  as determined by the switches  48 . The 5 bit gain control D/A  47  receives commands from a command decoder  45 . The switches  48  receive commands from a FG/ALC command circuit  46 . The gain control circuit  41  outputs gain control signals that provide for fixed gain (FG) and ALC mode selection that are applied to the first commandable gain block  21 . 
     A power control circuit  41   a  combines a temperature compensation signal from temperature compensation network  72  received by way of the second channel amplifier control path  82  and a power command signal from the 5 bit gain control D/A  47  received by way of the switches  48 . The power control circuit  41   a  outputs power control signals that are applied to the second commandable gain block  25 . 
     A distortion control circuit  51  combines the temperature compensation signal from the temperature compensation network  72  received by way of the distortion control path  83  and a signal from a linearizer active/bypass command circuit  53  to produce a distortion control signal that is applied to the linearizer bridge  31 . A phase control circuit  43  receives the temperature compensation signal from the temperature compensation network  72  by way of the phase control path  84  and outputs a phase control signal that is applied to the linearizer bridge  31 . An attenuator control circuit  52  combines the temperature compensation signal from the temperature compensation network  72  received by way of the attenuation control path  85  and a signal from the linearizer active/bypass command circuit  53  and outputs an attenuation control signal that is applied to the linearizer bridge  31 . 
     A limiting control circuit  41   b  receives the temperature compensation signal from the temperature compensation network  72  by way of the limiting control path  86  and outputs a limiting control signal that is applied to the third commandable gain block  32 . A 4 bit gain control D/A  55  receives commands from a command decoder  54  and outputs a command signal. An output level control circuit  41   c  combines three signals, including the temperature compensation signal from the temperature compensation network  72  received by way of the attenuation and temperature compensation control path  87 , a linearizer active/bypsss command output by the linearizer active/bypsss command circuit  53  and the command signal output by the 4 bit gain control D/A  55 . The output level control circuit  41   c  outputs an output level control signal that is applied to the third commandable gain block  32 . 
     The voltage of the temperature sensor in the third commandable gain block  32  is input into the temperature compensation network  72  through the temperature sensor path  93 . This temperature sensor input is distributed inside the temperature compensation network  72  and controls temperature compensation signal requirements of paths  81 ,  82 ,  83 ,  84 ,  85 ,  86  and  87 . 
     The channel amplifier output telemetry circuit  49  receives a detector signal from the detector/coupler  27  in the second commandable gain block  25  and converts it to a proper output voltage using a telemetry level calibration circuit  74 . A linearizer output telemetry circuit  57  receives a detector signal from the detector/coupler  27  in the third commandable gain block  32  and converts it to a proper output voltage using the telemetry level calibration circuit  74 . 
     The control circuit  40  uses a novel analytical methodology to set proper controls for the linearized channel amplifier  10 . The use of the control circuit  40  eliminates a time consuming tune and test process of a predecessor linearized channel amplifier developed by the assignee of the present invention. The manner in which the controls for the linearized channel amplifier  10  are implemented is as follows. 
     The novel analytical methodology sets the proper controls for the linearized channel amplifier  10  is as follows. The setting methodology for the temperature compensation network  72  depends on the measured RF performance of linearized channel amplifier  10 . The measurement includes two settings and three measurements using either the signal generator  13  or the network analyzer  15  as shown in FIG.  1 . 
     The first measurement determines channel amplifier level settings over temperature using the signal generator  13  and detector voltages from the detector/couplers  26 ,  27  in the second commandable gain block  25  through paths  91  and  92 . This measurement determines the channel amplifier control voltage requirement over temperature through paths  81  and  82 . 
     The second measurement determines linearizer gain and phase settings over temperature using the network analyzer  15  and an input 20 dB attenuator  16 . This measurement determines the proper linearizer control voltage requirement over temperature through paths  83 ,  84  and  85 . 
     The third measurement determines the linearizer output level setting over temperature using the signal generator  13  and the power meter  14 . This measurement determines the proper linearizer control voltage requreiment over temperature through paths  86  and  87 . 
     Based on the measured requirement control voltages over temperature through paths  81 ,  82 ,  83 ,  84 ,  85 ,  86 ,  87  as described above and measured diode sensor voltage over temperature through path  93 , the resistor values in the temperature compensation network  72  may be calculated analytically. 
     Based on the measured detector voltages from the detector/coupler  27  in the second and third commendable gain blocks  25 ,  32  through paths  92  and  94 , the resistor values in the telemetry level calibration circuit  74  may be analytically calculated. The proper resistor values are selected in the temperature compensation network  72  and in the telemetry level calibration circuit  74  which are located inside the personality plug  70 . The linearized channel amplifier module (including circuits  10 ,  40  and  70 ) perform according the specifications over temperature when the personality plug  70  is connected through the control circuit  40  to command and control the linearized channel amplifier  10 . 
     The settings for components of the control circuit  40  (temperature compensation network  72  and telemetry level calibration circuit  74 ) may be accomplished using a personality circuit containing internal resistors disposed in the control circuit  40  or using the external configurable personality plug  70  containing the resistors in the temperature compensation network  72  and telemetry level calibration circuit  74 . 
     FIG. 2 illustrates circuit blocks of the configurable personality plug  70 . The configurable personality plug  70  comprises temperature compensation resistors contained in the temperature compensation network  72 . The configurable personality plug  70  also comprises resistors contained in the telemetry level calibration circuit  74 . 
     The linearized channel amplifier  10  may be used in any frequency band including L, C, X, Ku, K, Ka, Q, V, W, etc. bands. The linearized channel amplifier  10  may be used with any high power amplifier, including traveling wave tube amplifiers (TWTA) and solid state power amplifiers (SSPA). 
     Thus, an improved low cost linearized channel amplifier designed for use with high power amplifiers has been disclosed. It is to be understood that the described embodiment is merely illustrative of some of the many specific embodiments that represent applications of the principles of the present invention. Clearly, numerous and other arrangements can be readily devised by those skilled in the art without departing from the scope of the invention.