Amplifiers – Modulator-demodulator-type amplifier
Patent
1994-11-22
1998-02-17
Grimm, Siegfried H.
Amplifiers
Modulator-demodulator-type amplifier
329325, 329346, 329360, 330103, 331 2, 331 23, 332127, 332162, H03C 106, H03D 324, H03F 132, H03L 707
Patent
active
057195277
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to method and circuits for processing components of an input signal to provide a highly efficient linear amplifier and/or modulator or a demodulator.
BACKGROUND OF THE INVENTION
A LINC amplifier has been proposed (see D. C. Cox, "Linear Amplification Using Non-Linear Components", IEEE Transactions on Communications, Vol. COM-22, 1974, pages 1942 to 1945) in which a modulating signal is split into two phase modulated components with constant envelopes which can be amplified separately using highly non-linear but power efficient amplifiers. Combining the two output signals yields the desired linearly amplified signal. With a LINC amplifier the potential for dc to RF conversion efficiency can approach 100%, assuming ideal matching amplifiers. However, in practical LINC amplifiers, the suppression of broadband phase modulation relies on a very tight tolerance on the gain and phase match between the two paths. A gain error of 0.01 dB and a phase error of 0.1.degree. give a component suppression of only 54 dB. Such a tolerance is impossible to achieve in a open loop system where much greater gain and phase variations can occur with changes in operating frequency, output power and temperature, and the ageing of components.
It is an object of this invention to provide a linear amplifier/modulator which does not suffer significantly from these problems.
From GB 2073516 an arrangement for amplifying a previously modulated carrier signal using two phase locked loops is already known and in which phase feedback and phase comparators are used. In one embodiment the feedback signals are taken from a point before the final summing circuit. In practice the summing circuit will be imperfect and any phase errors introduced by the summing circuit will degrade the performance of the system. The input signal is at or near the same frequency as the output signal and where the output is to be at radio frequencies (RF) implementation of the summing circuits 14 and 15 is, in practice, complicated. Such an arrangement could not receive a baseband signal and incorporate modulation of that signal within the phase locked loops.
In a second embodiment of GB 2073516, the feedback signal is taken from a point after the final summing circuit. However comparisons with the input signal are made in terms of the amplitude and phase and, when the input is at RF, such a system requires accurate RF envelope detection and subtraction and a wide dynamic range RF phase detector. Such devices are difficult to construct.
From U.S. Pat. No. 5,105,168 an arrangement for a vector locked loop for modulation of an input signal is already known. U.S. Pat. No. 5,105,168 incorporates a mixer in the feedback path so that comparisons may be made at or near the input signal frequency, which may be a baseband signal with an output signal at RF. However the realisation of envelope detectors for such an arrangement presents problems as they require subsequent filtering of the carrier components, which introduces an unacceptable amount of time delay. Additional significant time delays are introduced by the phase detector which is required to generate the difference component and the filter which is required to remove the sum component.
SUMMARY OF THE INVENTION
It is another object of the invention to provide an amplifier/modulator which may use the Cartesian components of an input signal. The advantage of the a Cartesian signal is that a representation of the signal can be produced with a low sampling rate, especially when derived by a digital signal processor (DSP).
It is a further object of the invention to provide an amplifier/modulator which incorporates modulation, amplification and summation within a feedback loop, so that there is compensation for any deficiencies in the system.
According to one aspect of the invention there is provided apparatus for processing components of an input signal to provide a processed output signal, comprising input signal, respective components of a processed output signal, or for use in gener
REFERENCES:
patent: 3748590 (1973-07-01), Gray
patent: 3953805 (1976-04-01), Couvillon
patent: 4420723 (1983-12-01), de Jager
patent: 5105168 (1992-04-01), DaSilva
Bateman Andrew
Chan Kam Yuen
British Technology Group Limited
Grimm Siegfried H.
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