EP0598585A2
Expired / Lapsed
EP
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Automatic calibration of the quadrature balance within a cartesian amplifier
Assignee: Linear Modulation Technology Ltd
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Filing: 1993-11-15
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Granted: —
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Expires: 2013-11-15
Abstract
Abstract A Cartesian amplifier in which an input signal is pre-processed and split into two quadrature components. Both quadrature components are passed, in parallel, through an error amplifier (4), after which they are re-combined and up-converted to RF. The output of the amplifier is used to provide a feedback signal. This feedback is downconverted from RF to baseband and resolved into two quadrature components which are fed to the respective inputs of the error amplifier (4). Periodically the pre-processor (3) is switched into a calibration mode in which test signals are applied to the amplifier instead of the input signal. At these times the signal strength of the output of the power amplifier is measured and used to provide pre-distortion factors in the signal preprocessor (3) to improve amplifier linearity.
Inventors
- 👤 William James Whitmarsh
- 👤 Simon Maurice Whittle
- 👤 Ian Stuart Parry
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 07:07
CPC Classifications
H; H03; H03F; H03F1/00; H03F1/34; H03F1/345; H03C; H03C3/00; H03C3/38; H03C3/40; H03C3/406; H03D; H03D7/00; H03D7/16; H03D7/165; H03D7/166; H03D7/168; H03F1/32; H03F1/3241; H03F1/3247; H03F1/3282; H03F1/3288; H03F1/3294; H04; H04L; H04L27/00; H04L27/32; H04L27/34; H04L27/36; H04L27/362; H04L27/364; H04L27/366; H04L27/367; H04L27/368; H03F2200/00; H03F2200/102; H03F2200/438; H04L27/0014; H04L2027/0016; H04L2027/0018
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
227 words
A Cartesian amplifier system comprising: a) an input (2) for a signal to be amplified; b) a power amplifier (3, 4) for amplifying the input signal; c) a Cartesian loop feedback circuitry around the power amplifier having a pair of channels (4B, 4A) for processing "real" and "imaginary" quadrature signal components and being arranged to drive the power amplifier (3, 4) with a signal derived from the sum of real and imaginary signals from the respective outputs of forward paths of those channels (4B, 4A), characterised in that the Cartesian loop comprises, or is associated with, d) a signal pre-processor (3) for pre-distorting resolved real and/or imaginary components of the input signal in accordance with the value of at least one predistortion factor; in that the amplifier system is operative in a first, normal mode to amplify the input signal and a second, calibration mode to apply test signals to drive the Cartesian loop in place of the input signal; and in that e) the amplifier system comprises means (8, 20, 23,25) for measuring the response of the Cartesian loop to the test signals and for calculating and setting the value of the, or each, predistortion factor, the response of the Cartesian loop being measured by measuring the signal strength at the output of the power amplifier while the system is operated in the second, calibration mode.
Claim 2
Dependent Claim
81 words
A system according to claim 1, wherein the Cartesian loop includes an error amplifier (12A, 12B) for said pair of channels (4A, 4B) for amplifying the differences between i) the real components and imaginary components, respectively of the resolved input signal from the pre-processor (3) and ii) their respective feedback signals, and means (17) for obtaining real and imaginary components of the amplified signal for the respective feedback signals, to be applied to the inputs of the error amplifier (12A, 12B).
Claim 3
Dependent Claim
27 words
A system according to claim 2, wherein said means for obtaining components comprises resolving means (17) for resolving the summed output of the power amplifier (3, 4).
Claim 4
Dependent Claim
77 words
A system according to claim 3 wherein the power amplifier (3, 4) is an RF power amplifier, and the Cartesian loop further comprises a frequency up-converter (6) for converting the outputs of real and imaginary channels (4A, 4B) of the error amplifier (4) to RF to drive the power amplifier, and a frequency down-converter (10) for frequency downconverting the output of the power amplifier to baseband prior to said output being resolved by said resolving means (17).
Claim 5
Dependent Claim
29 words
A system according to claim 2, 3 or 4 wherein said differences amplified by said error amplifier (4) are between the components and said respective feedback signals at baseband.
Claim 6
Independent Claim
31 words
A system according to any one of claims 2 to 5, wherein the preprocessor (3) is operative to correct for imbalances in the real and imaginary channels of the feedback signals.
Claim 7
Independent Claim
41 words
A system according to any of claims 1 to 6 wherein the test signals include, or consist of, predetermined DC voltage levels applied in a number of combinations to the real and imaginary channels (4A, 4B) of the signal preprocessor (3).
Claim 8
Independent Claim
57 words
A system according to any one of the preceding claims wherein said at least one predistortion factor includes a factor which compensates or gain mismatch between the paths of said pair of channels (4A, 4B) and a factor which compensates for a relative phase shift which occurs between the two channels through the power amplifier (3, 4).
Claim 9
Independent Claim
21 words
A system according to any one of the preceding claims wherein said pre-processor (3) is implemented using a digital signal processor.
Claim 10
Independent Claim
23 words
A system according to any one of the preceding claims wherein said signal strength is measured at the output of the power amplifier.
Claim 11
Independent Claim
18 words
A system according to any one of the preceding claims wherein said calibration mode is set upon power-up.
Claim 12
Independent Claim
21 words
A system according to any one of the preceding claims wherein said signal strength is measured using a directional coupler (8).
Claim 13
Independent Claim
83 words
A system according to any one of the preceding claims, wherein five calibration signals are used, namely a) a predetermined signal level applied to at least one of the quadrature channels and used to determine the gain; b) respective predetermined signal levels applied to the quadrature channels and used to determine a factor representing the gain mismatch between the channels; c) respective predetermined signal levels applied to the quadrature channels and used to determine the phase mismatch from quadrature between the two channels.
Claim 14
Independent Claim
63 words
A system according to any one of claims 1 to 11, wherein three sets of calibration signals are used, namely a) first and second predetermined signal levels applied to respective ones of the quadrature channels; b) the first and second predetermined signal levels each applied to the other of the quadrature channels; c) a third predetermined signal level applied to both quadrature channels.
References Cited (Backward Citations)
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