Optimal control method for adaptive feedforward linear amplifier

• US 6,232,837 B1
• Filed: 10/14/1999
• Issued: 05/15/2001
• Est. Priority Date: 05/14/1999
• Status: Expired due to Term

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Chae, Jong Suk, Yoo, Ki Suk, Choi, Jae Ick, Kang, Sang Gee
• Primary Examiner(s): Mottola, Steven J.
• Application Number:
  US09/417,651
• Time in Patent Office: 579 Days
• Field of Search: 330/149, 330/151, 332/127, 332/128, 375/296, 375/297
• US Class Current: 330/151
• CPC Class Codes: H03F 1/3229 using a loop for error extraction and another loop for error subtraction

Abstract

Provided with an optimal control method for an adaptive feedforward linear amplifier that includes an adaptive controller connected to first and second PLLs (Phase Locked Loops) respectively determining frequency bands for a main signal component and a distortion signal component. The adaptive controller adaptively controls control voltages of a first variable phase shifter and a first variable attenuator constituting a main signal cancellation loop and control voltages of a second variable phase shifter and a second variable attenuator constituting an error signal cancellation loop. The optimal control method includes the steps of: (a) after initialization of necessary parameters, reading a strength of an input signal, determining the initial optimal control voltages of the first and second variable phase shifters and the first and second variable attenuators, outputting the corresponding control voltages, and setting the first PLL to read a main signal strength of the main signal cancellation loop; (b) controlling the optimal control voltages of the first variable phase shifter and the first variable attenuator until the main signal strength becomes lower than a first threshold, if the main signal strength exceeds the first threshold; (c) determining the main signal strength read out from the error signal cancellation loop, if the main signal strength is greater than the first threshold, repeat step (b), otherwise; and (d) controlling the optimal control voltages for the second variable phase shifter and the second variable attenuator until the difference between the main signal strength and the distortion signal strength becomes lower than a second threshold, if the difference is greater than the second threshold.

Claims

1. An optimal control method for an adaptive feedforward linear amplifier, which includes an adaptive controller connected to first and second PLLs (Phase Locked Loops) respectively determining frequency bands for a main signal component and a distortion signal component, wherein the adaptive controller adaptively controls control voltages of a first variable phase shifter and a first variable attenuator constituting a main signal cancellation loop and control voltages of a second variable phase shifter and a second variable attenuator constituting an error signal cancellation loop, the optimal control method comprising the steps of:

(a) after initialization of necessary parameters, reading a strength of an input signal, determining the initial optimal control voltages of the first and second variable phase shifters and the first and second variable attenuators, outputting the corresponding control voltages, and setting the first PLL to read a main signal strength of the main signal cancellation loop;

(b) controlling the optimal control voltages of the first variable phase shifter and the first variable attenuator until the main signal strength becomes lower than a first threshold, if the main signal strength exceeds the first threshold;

(c) determining a difference between the main signal strength and a distortion signal strength read out from the error signal cancellation loop, if the difference is greater than a second threshold; and

(d) controlling the optimal control voltages for the second variable phase shifter and the second variable attenuator until the difference between the main signal strength and the distortion signal strength becomes lower than the second threshold, if the difference is greater than the second threshold.

2. The optimal control method as claimed in claim 1, wherein the step (b) comprises the steps of:

checking upon whether the control of the first variable phase shifter is completed;

calculating the optimal control voltage of the first variable phase shifter until a predetermined loop count and outputting an estimated optimal control voltage for the first variable phase shifter, if the control of the first variable phase shifter is not completed; and

calculating the optimal control voltage of the first variable attenuator until the predetermined loop count and outputting an estimated optimal control voltage for the first attenuator, if the control of the first variable phase shifter is completed.

3. The optimal control method as claimed in claim 1, wherein in the step (c), the difference between the main signal strength and the distortion signal strength is obtained by setting the second phase locked loop to read out the main signal strength of the error signal cancellation loop, setting the second phase locked loop to read out the distortion signal strength, and subtracting the distortion signal strength from the main signal strength.

4. The optimal control method as claimed in claim 1, wherein the step (d) comprises the steps of:

setting a difference between the main signal strength and a distortion signal strength at the error signal err(n) when the difference is smaller than the second threshold;

checking upon whether the control of the second variable phase shifter is completed;

calculating the optimal control voltage of the second variable phase shifter until the predetermined loop count and outputting an estimated optimal control voltage for the second variable phase shifter, if the control of the second variable phase shifter is not completed; and

calculating the optimal control voltage of the second variable attenuator until the predetermined loop count and outputting an estimated optimal control voltage for the second attenuator, if the control of the second variable phase shifter is completed.

5. The optimal control method as claimed in claim 4, wherein the respective optimal control voltages of the first and second variable phase shifters and the first and second variable attenuators are obtained by means of a transversal filter structure, wherein the optimal control voltages are obtained by multiplying the estimated optimal control voltages according to the input signal strength of a certain device selected out of the first and second variable phase shifters and the first and second variable attenuators by the controller by M preceding transversal filter weights stored in a memory, wherein the optimal control voltage is given by:

6. The optimal control method as claimed in claim 5, wherein the transversal filter weight controlling step comprises the steps of:

after inputting the optimal control signal for the selected device to an LPA system, calculating a difference between the current signal strength and the previous signal strength, wherein the current signal strength is the main signal strength when the selected device is the first variable attenuator or the first variable phase shifter and the distortion signal strength when the selected device is the second variable attenuator or the second variable phase shifter, calculating a difference between the current control voltage and the previous control voltage, and determining the changing direction of the optimal control voltage by multiplying a sign of the difference between the current signal strength and the previous signal strength by a signal of the difference between the current control voltage and the previous control voltage;

multiplying the changing direction by an adaptive rate controlling parameter and the difference between the current signal strength and the previous signal strength, to determine an estimated error value given by;