Amplifiers – Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
2001-06-21
2003-10-14
Pascal, Robert (Department: 2817)
Amplifiers
Hum or noise or distortion bucking introduced into signal...
Reexamination Certificate
active
06633200
ABSTRACT:
BACKGROUND INFORMATION
The invention relates in general to the field of high power linear amplification and in particular to a technique of controlling the operation of a LINC style RF amplifier.
Many applications exist that require high power radio frequency (RF) amplifiers capable of linear operation while at the same time operate at high efficiency. Linear operation is desirable due to the presence of amplitude modulation on many types of input signals and regulatory requirements to minimize spurious or out of channel response. Efficiency is desirable due to the economics of minimizing thermal loading and operational costs. Normally, achieving the combination of linear operation and high efficiency has proven difficult.
An approach to implementing a high power amplifier that is both linear and efficient was first proposed by Chireix in 1935 as described in H. Chireix, “High Power Outphasing”, Proc. IRE, Vol. 23, No. 11, November 1935, pp 1370-1392. Chireix's concept was based on an outphasing approach in which the input signal is decomposed into a pair of constant amplitude signals, which are then amplified by a pair of efficient, possibly non-linear, RF amplifiers, and then linearly combined to form the high power output. Cox later revived this concept in the early 1970's and coined the term LINC (Linear Amplification Using Non-Linear Components) by which this amplifier design concept is popularly known today. See D. C. Cox, “Linear Amplification with Nonlinear Components”, IEEE Trans. Comm., December 1974, pp 1942-1945.
The LINC amplifier has a LINC modulator which decomposes an input signal into two or more constant-amplitude phase-modulated components. Each component is then amplified in a separate channel, by a phase-preserving high power amplifier (HPA, which may otherwise be nonlinear). A power combiner is also provided to combine the amplified components of the different channels, resulting in a linearly amplified version of the input signal. To improve overall linearity, the accuracy of the LINC modulator may be enhanced by implementing it using digital signal processing. See, e.g. S. A. Hetzel, A. Bateman, J. P. McGeehan, “LINC Transmitter”, pp 844-846, Electronic Letters, Vol. 27. No. 9, May 9, 1991; L. Sundstrom, “Effects of Reconstruction Filters and Sampling Rate For A Digital Signal Component Separator On LINC Transmitter Performance”, Electronic Letters, pp 1124-1125, Vol. 31, No. 14, Jul. 6, 1995; L. Sundstrom, “The Effect of Quantization In A Digital Signal Component Separator For LINC Transmitters”, IEEE Trans. Vehicular Technology, pp 346-352, Vol. 45, No. 2, May 2, 1996. Linearity is also improved by balancing the frequency response of the channels in which the components are amplified. This has been done using automatic digital equalization filters in one or more of the channels, which compensate the components for any expected imbalance between the channels that might cause distortion at the power combiner output. See e.g. WO 96/19063, “Method of Balancing the Channels of a LINC Amplifier”, Jun. 20, 1996; U.S. Pat. No. 5,886,673 “Amplification Using Amplitude Reconstruction of Amplitude and/or Angle Modulated Carrier”, Mar. 23, 1999; U.S. Pat. No. 5,990,738, “Compensation System and Methods for a Linear Power Amplifier”, Nov. 23, 1999; U.S. Pat. No. 6,215,354, “Closed Loop Calibration for an Amplitude Reconstruction Amplifier”. However, changing operating conditions internal to the amplifier can alter the overall gain of the conventional LINC amplifier. This means that the overall, or net, gain of the amplifier is varying during operation, which is an undesirable characteristic.
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H. Chireix, “High Power Outphasing Modulation”, Proceedings of the Institute of Radio Engineers, vol. 23, No. 11, pp. 1370-1392, Nov. 1935.
D. C. Cox, “Linear Amplification with Nonlinear Components”, IEEE Transactions on Communications, vol. COM-22, pp. 1942-1945, Dec. 1974.
Frederick H. Raab, “Efficiency of Outphasing RF Power-Amplifier Systems”, IEEE Transactions on Communications, vol. Com-33, No. 10, Oct. 84.
S. A. Hetzel, et al., “LINC Transmitter”, Electronic Letters, vol. 27, No. 10, May 1991.
L. Sundstrom, “Effects of reconstruction filters and sampling rate for a digital component separator on LINC transmitter performance”, Electronic Letters, vol. 31, No. 14, Jul. 1995.
Lars Sundstrom, “The Effect of Quantization in a Digital Signal Component Separator for LINC Transmitters”, IEEE Trans. on Vehicular Tech., vol. 45, No. 2, May 1996.
Bernoux, Jean-Paul et al., “Method of Balancing the Channels of a LINC Amplifier”, WO 96/19063, Jun. 1996.
Blakely , Sokoloff, Taylor & Zafman LLP
Celiant Corporation
Nguyen Khanh Van
LandOfFree
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