Solid state power amplifier with dynamically adjusted operating point

• US 5,119,042 A
• Filed: 08/30/1990
• Issued: 06/02/1992
• Est. Priority Date: 08/30/1990
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Davis, Joseph E., Berman, Arnold L., Crampton, David L.
• Primary Examiner(s): Mullins, James B.
• Application Number:
  US07/574,867
• Time in Patent Office: 642 Days
• Field of Search: 330/124 R, 330/133, 330/136, 330/144, 330/145, 330/279, 330/284, 330/285, 330/295, 343/701, 343/720, 343/DIG. 2, 455/116, 455/126, 455/127, 455/129
• US Class Current: 330/295
• CPC Class Codes: H03F 1/0216 Continuous control
• CPC Class Codes: H03F 1/3223 using feed-forward H03F1/3211 takes precedence
• CPC Class Codes: H03F 2203/7227 the gated amplifier being switched on or off by a switch in the supply circuit of the amplifier
• CPC Class Codes: H03F 2203/7236 the gated amplifier being switched on or off by putting into parallel or not, by choosing between amplifiers by (a ) switch(es)
• CPC Class Codes: H03F 3/602 Combinations of several amplifiers
• CPC Class Codes: H03G 3/004 Control by varying the supply voltage
• CPC Class Codes: H03G 3/3042 in modulators, frequency-changers, transmitters or power amplifiers transmission power control in bidirectional transmission systems H04W52/04

Abstract

RF power is sampled and measured at the input and output of a solid state power amplifier using directional couplers and matched square law detectors. Outputs from the detectors are applied to differential inputs of a DC operational amplifier. Outputs from the detectors are compared and filtered in the operational amplifier and the resulting difference signal is applied to a control input on a switching type power supply. The power supply converts a DC input voltage to the various positive and negative voltages required to operate the RF devices in the solid state power amplifier. When the control loop is closed, the supply voltage varies to maintain a constant operating point resulting in constant gain, efficiency, and linearity for the overall solid state power amplifier despite variations in signal levels and signal composition. In another embodiment, the solid state power amplifier has a series of single-ended low power amplifiers terminating in an output high power module. In the output module, one medium power device acts as a driver stage for four high power devices connected in parallel. The output stages are hybrid coupled, and isolators before and after these hybrid coupled output stages isolate the driver from the final amplifiers and protect the output devices from reflected signals. A dynamically controlled PIN diode variable attenuator at the amplifier input allows the operating point of the amplifier to be selected and adjusted while the closed loop function is in operation. A hybrid matrix power amplifier system is also disclosed.

Claims

1. A closed-loop power amplifier circuit having an RF input, RF output, and a controlled and constant compressed operating point, comprising:

an input sampling device electrically coupled to the RF input and adapted to electrically sample the power of an RF input signal applied to the RF input;

an input power detector connected to the input sampling device, for detecting and measuring the electrical power level of the RF input signal;

a solid state power amplifier connected to the input sampling device;

an output sampling device electrically coupled to an output of the solid state power amplifier and adapted to electrically sample an RF output signal produced from the RF output;

an output power detector connected to the output sampling device and matched in electrical characteristics to the input power detector;

a comparator/integrator means coupled to the input and output detectors for accepting outputs from both the input and output detectors and comparing them, for generating a difference signal as a measure of gain, and for filtering the difference signal;

a power supply coupled to the comparator/integrator means, which accepts the difference signal from the comparator/integrator means, and is adapted to supply varying bias voltages to the solid state power amplifier via electrical conductors, and feedback control voltages to the solid state power amplifier to dynamically maintain the compressed operating point of the closed-loop power amplifier circuit such that constant gain, linearity, and efficiency is maintained for a range of power variations of the RF input and output signals; and

,

wherein the solid state amplifier comprises;

an input amplifier stage adapted to receive the RF input signal from the input sampling device;

a PIN attenuator having one input connected to the input amplifier stage and having another input adapted to receive operating point settings;

a first isolator connected to an output of the PIN attenuator, in which reflected signals are dissipated in a resistive termination;

a pre-driver amplifier having an input connected to an output of the first isolator;

a driver amplifier having an input connected to an output of the pre-driver amplifier;

a second isolator connected to an output of the driver amplifier, in which reflected signals are dissipated in a resistive termination; and

a solid state hybrid power amplifier stage connected to the second isolator, comprised of multiple solid state power amplifiers, wherein the DC bias voltages of each solid state power amplifier is dynamically variable and controllable; and

wherein said closed-loop power amplifier circuit further comprises a third isolator connected to the output of the output sampling device, in which reflected signals are dissipated in a resistive termination.

2. The closed-loop power amplifier circuit of claim 1 wherein the power supply comprises:

a switching power supply coupled to the comparator/integrator means, which accepts the difference signal from the comparator/integrator means, wherein the switching power supply is adapted to supply varying bias voltages to each amplifier of the solid state hybrid power amplifier stage via electrical conductors, feed back control voltages, to dynamically change the applied voltages to the overall closed-loop hybrid power amplifier circuit, such that a constant operating point resulting in constant gain, linearity and efficiency is maintained for a range of input and output power variations.

3. A closed-loop hybrid power amplifier circuit having a RF input, RF output and an operating point, comprising:

an input sampling device electrically coupled to the RF input for electrically sampling the RF input signal power;

an input power detector connected to the input sampling device for detecting and measuring the electrical power intensity of the RF input signal;

an input amplifier stage for receiving the RF input from the input sampling device;

a PIN attenuator having one input connected to the input amplifier stage and having another input adapted to receive operating point settings;

a first isolator connected to the output of the PIN attenuator;

a pre-driver amplifier having an input connected to the output of the first isolator;

a driver amplifier having an input connected to an output of the pre-driver amplifier;

a second isolator connected to the output of the driver amplifier;

a solid state hybrid power amplifier stage connected to the second isolator, comprised of multiple solid state power amplifiers, wherein the DC bias voltages of each solid state power amplifier is dynamically variable and controllable;

an output sampling device electrically coupled to the output of the solid state power amplifier stage for electrically sampling the RF output signal;

an output power detector connected to the output sampling device and matched in electrical characteristics to the input power detector;

a third isolator connected to the output of the output sampling device;

comparator/integrator means coupled to the input and output detectors for accepting the outputs from the input and output detectors and comparing them, for generating a difference signal as a measure of the gain, and for filtering the difference signal; and

a switching power supply coupled to the comparator/integrator means, which accepts the difference signal from the comparator/integrator means, for supplying varying bias voltages to each amplifier of the solid state hybrid power amplifier stage via electrical conductors, feeding back control voltages, and for dynamically changing the applied voltages to the overall closed-loop hybrid power amplifier circuit, such that a constant operating point resulting in constant gain, linearity and efficiency is maintained for a range of input and output power variations.

4. A hybrid matrix power amplifier system for RF communication satellites comprising:

a beam forming network accepting a plurality of input electromagnetic wave beams and generating a plurality of corresponding RF output signals;

an input hybrid distribution matrix adapted to receive the RF output signals from the beam forming network;

a set of closed loop solid state amplifiers adapted to receive the RF output signals from the input hybrid distribution matrix, wherein the DC bias voltages of each solid state power amplifier within the set is under closed loop dynamic control, and wherein all of the solid state power amplifiers within the set are matched in gain and phase at the system operating point;

an output hybrid distribution matrix adapted to receive the RF output signals from the closed loop solid state power amplifiers, and adapted to refocus the RF signals to a corresponding output; and

an antenna feed distribution network connected to the output of the output hybrid distribution matrix, which provides a signal distribution function for transmitting antennas.