Amplifiers – With amplifier bypass means
Reexamination Certificate
1999-10-14
2001-05-15
Mottola, Steven J. (Department: 2817)
Amplifiers
With amplifier bypass means
C330S149000
Reexamination Certificate
active
06232837
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a feedforward linear amplifier for increasing linearity of a high power amplifier used in a radio communication system, and more particularly, to an optimal control method for an adaptive feedforward linear amplifier, whereby an adaptive controller can calculate an optimal control voltage by using an adaptive algorithm for the linear amplifier, providing for changes in environment.
2. Description of the Related Art
A feedforward linear amplifier includes two circuits and receives at least one carrier input signal at the predetermined range of frequency. The input signal is applied to the first circuit inclusive of a main power amplifier, in which case a distortion signal occurs. In the meantime, only the distortion signal component generated from the main power amplifier can be extracted by properly controlling variable attenuator and variable phase shifter in the first circuit. The distortion signal component thus extracted is transmitted to the second circuit. The second circuit amplifies the distortion signal component with an attenuation and phase shift such that the distortion signal component of the main power amplifier is removed from the final output terminal. In the present invention, emphasis is laid on the procedure of controlling the two variable attenuators and the variable phase shifter using the controller.
To read an output of the first circuit, the related art controller determines a desired frequency band, operates a voltage-controlled oscillator (VCO) at the frequency band and determines the position of a radio frequency (RF) switch. In order to minimize the signal component read out from the first circuit, a power detector detects the strength of the main signal component and after changing the phase shifter control voltage, the main signal strength is detected again. If the main signal strength is decreased, the phase shifter control voltage is changed in the opposite direction; and if the main signal strength is decreased, the phase shifter control voltage is changed in the same direction. Iterative procedures are performed N-M times for variations of the phase shifter and M times for the control of the variable attenuators. These procedures are iteratively performed for the phase shifter and the variable attenuator until the main signal strength is lower than a threshold. With the main signal strength lower than the predetermined level, then the second circuit is controlled. The procedures for the second circuit are analogous to those for the first feedback with an exception that the controller controls the distortion signal strength to be minimized.
There exist different methods to operate the controller appropriately, such as pilot signal method, vector modulator method, non-feedback loop method, loop method, trial-and-error method and a combination of them.
Among these methods, the trial-and-error method that is similar to the present invention requires more repetitions for calculating an optimal control voltage and the voltage value is controlled in the fixed step-size only. Therefore, different program steps are needed, resulting in retarded adaptation to changes in environment. It is further another disadvantage of the related art control method that the variation of the control voltage cannot be minimized sufficiently when the control voltage is close to the optimal value.
SUMMARY OF THE INVENTION
To solve the above problems with the related art, the present invention uses the existing LMS (Least Mean Square) method instead of the trial-and-error method, and a transversal filter structure as a fundamental structure for implementing the LMS method, thereby performing an adaptive algorithm continuously. The LMS method revised in the present invention is an algorithm that secures algorithm convergence.
It is, therefore, an object of the present invention to provide an optimal control method for a feedforward linear amplifier that enables an adaptive controller in the feedforward linear amplifier to rapidly calculate an optimal control voltage in an adaptive manner and stabilize the algorithm despite changes in environment.
To achieve the above object, there is provided 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 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.
REFERENCES:
patent: 4885551 (1989-12-01), Myer
patent: 5051704 (1991-09-01), Chapman et al.
patent: 5508657 (1996-04-01), Behan
patent: 5877653 (1999-03-01), Kim et al.
patent: 5952895 (1999-09-01), McCune et al.
patent: 5959500 (1999-09-01), Garrido
Eid E. Eid and Fadhel M. Ghannouchi, “Adaptive Nulling Loop Control for 1.7-GHzFeedforward Linearization Systems,” pp. 83-86.
James K. Cavers, “Adaptation Behavior of a Feedforward Amplifier Linearizer,” IEE Transactions on Vehicular Technology, vol. 44, No. 1, Feb. 1995.
Prof. S. Kumar, PhD and G. Wells, “Memory Controlled Feedforward Lineariser Suitable for MMIC Implementation,” IEE Proceedings-H, vol. 138, No. 1, Feb. 1991, pp. 9-12.
Chae Jong Suk
Choi Jae Ick
Kang Sang Gee
Yoo Ki Suk
Antonelli Terry Stout & Kraus LLP
Electronics and Telecommunications Research Institute
Mottola Steven J.
LandOfFree
Optimal control method for adaptive feedforward linear... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optimal control method for adaptive feedforward linear..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optimal control method for adaptive feedforward linear... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2551259