Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing heterocyclic carbon compound having only o – n – s,...
Patent
1995-07-19
1998-02-24
Eisenzopf, Reinhard J.
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing heterocyclic carbon compound having only o, n, s,...
455115, 455127, H01Q 1112, H04B 104
Patent
active
057220565
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a radio transmitter having a power amplifier and a linearizer arrangement for compensating for non-linearity in the power amplifier. An example of such an arrangement is Cartesian feedback with training.
BACKGROUND TO THE INVENTION
Linear transmitters use closed loop techniques to achieve high linearity. The Cartesian feedback loop is a closed loop that includes a nonlinear RF power amplifier (PA). The PA's linearity performance improves proportionally to the loop gain in which the PA is located.
Stability has to be ensured before closing the loop to avoid oscillators and splatter. One method that is used is applying a training signal to the open loop and using a unique method to adjust the loop's phase to be 180 degrees at the summing junction to ensure stability--(see WO-A-9208280).
A RF power amplifier tends to change its phase shift versus output power. Such a PA's AM to PM response reduces the effective phase margin of the loop. The phase adjust should be done at an input level which drives the PA to approximately average output power to maintain a correct phase. Incorrect phase adjust will reduce the effective phase margin and can cause oscillations to occur at peak output power where the PA adds its maximum phase shift.
Forward path gain variations (radio to radio variations, temperature variations and frequency variations) will result in different output powers for the same input level so the phase training will result in incorrect phase adjustment. Moreover, the gain variation that will increase the phase training output power will increase splatter.
In order to maintain the required linearity and good efficiency it is necessary to tune the drive level to be below clip. A method that is used is a training ramp at the baseband input that increases the input until clip is detected by comparing the loop error to a level that indicates clip. The ramp's input level is sampled at the time that clip is detected and the data input level is adjusted to be below clip.
The accuracy of the clip detection by this method and splatter caused while clip is detected depends on the error level before clip. This error level is proportional to loop gain so loop gain variations (typically 10-15 dB vs. temperature and frequency) will influence the detected clip point and splatter.
The problems with known techniques are: (1) additional splatter due to training; (2) over design safety margin:--phase margin and clip to peak power over head ratio.
GB-A-2265270 of Motorola Ltd, published on 22nd Sep. 1993, describes an arrangement which seeks to avoid amplifier training by providing a priori adjustment factors to adjust the loop as far as possible to match the operating conditions, using temperature and frequency look-up tables.
SUMMARY OF THE INVENTION
According to the a first aspect of the present invention, a radio transmitter is provided comprising: a power amplifier; linearizer means coupled to the amplifier for compensating for non-linearity in the power amplifier; feedback means for feeding a signal from an output of the power amplifier to the linearizing means, whereby said amplifier, feedback means and linearizer means form an amplifier loop having a varying loop gain, and training means for applying a training signal to the amplifier and adjusting the linearizer means during a training mode of operation. The arrangement is characterized by: a look-up table for storing predetermined operating condition adjustment parameters and control means having an operating condition input, said control means being coupled to the look-up table for selecting operating condition adjustment parameters according to the operating condition input during the training mode and adjusting the training signal to compensate for loop gain variations during the training mode.
In this manner, more accurate and consistent training can be achieved for varying operating conditions (e.g. temperature and frequency).
The training means preferably comprise switching means for opening and closin
REFERENCES:
patent: 5524285 (1996-06-01), Wray et al.
patent: 5584059 (1996-12-01), Turney et al.
Ayun Moshe Ben
Grabsky Nachman
Horowitz Ilan
Rozental Mark
Shamsian Roni
Banks-Harold Marsha D.
Doutre Barbara R.
Eisenzopf Reinhard J.
Motorola Inc.
LandOfFree
Radio transmitter with power amplifier linearizer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Radio transmitter with power amplifier linearizer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Radio transmitter with power amplifier linearizer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1883514