Offset-frequency loop-back calibration
Embodiments of methods and means for calibrating a linearization characteristic within an RF transceiver system are provided. Such embodiments generally include extracting a portion of an output signal and frequency shifting or translating that signal by a predetermined value. The frequency shifted signal is then summed or otherwise introduced into a receiver signal pathway where it is analyzed by digital signal processing or other means to determine if linearization distortion is present. Linearization calibration of a power amplifier, a low-noise amplifier and/or other functionality within the system can then be performed in an automatic, reliable and ongoing manner.
1. A method, comprising:
providing a circuit configured to provide an output signal, wherein the output signal is provided by a power amplifier of a transmitter section of a discrete transmitter of the circuit;
frequency shifting a portion of the output signal to derive a shifted signal;
summing the shifted signal and an other signal to derive a loop-back signal, wherein the other signal is provided by a low-noise amplifier within a discrete receiver of the circuit;
determining a linearization characteristic of the circuit by way of the loop-back signal, wherein determining the linearization characteristic of the circuit comprises a digital signal processor analyzing the loop-back signal to detect phase, amplitude and frequency distortion within the output signal of the power amplifier, wherein determining further comprises deriving an Error Vector Magnitude (EVM) characteristic of the output signal; and
calibrating at least one operating characteristic of the circuit responsive to the determination.
2. The method of claim 1 , wherein the frequency shifting is performed by mixing the portion of the output signal with an offset frequency signal.
3. The method of claim 1 , wherein the calibrating comprises adjusting one or more operating coefficients within a lookup table.
4. The method of claim 1 , wherein the calibrating comprises adjusting at least one operating characteristic of the power amplifier or the low-noise amplifier of the circuit.
5. The method of claim 1 , further comprising attenuating the output signal by a predetermined value to derive the portion of the output signal.
6. The method of claim 1 , wherein the determining corresponds to a linearization characteristic of a predetermined portion of the circuit, the determining being performed so as to mitigate:
a linearization characteristic of another predetermined portion of the circuit; and
an unintentional coupling of the loop-back signal with any other signal.
7. An apparatus, comprising:
a circuit portion configured to provide an output signal;
a translator portion configured to frequency shift a portion of the output signal to derive a shifted signal;
a summation portion configured to sum the shifted signal and an other signal to derive a loop-back signal, wherein the other signal is provided by a low-noise amplifier within a discrete receiver of the apparatus; and
a signal processing portion configured to:
determine a linearization characteristic of the apparatus by way of the loop-back signal, wherein determining the linearization characteristic of the apparatus comprises a digital signal processor analyzing the loop-back signal to detect phase, amplitude and frequency distortion within the output signal of the power amplifier, wherein determining further comprises deriving an Error Vector Magnitude (EVM) characteristic of the output signal; and
calibrate at least one operating characteristic of the apparatus responsive to the determination.
8. The apparatus of claim 7 , wherein the translator portion comprises a mixer.
9. The apparatus of claim 7 , wherein the signal processing portion is further configured to perform the calibrating by adjusting one or more operating coefficients within a lookup table.
10. The apparatus of claim 7 , wherein the signal processing portion is further configured to perform the calibrating by adjusting at least one operating characteristic of the power amplifier.
11. The apparatus of claim 7 , further comprising a low-noise amplifier, wherein the signal processing portion is further configured to perform the calibrating by adjusting at least one operating characteristic of the low-noise amplifier.
12. The apparatus of claim 7 , further comprising an attenuator coupled to the circuit portion and configured to attenuate the output signal by a predetermined value so as to derive the portion of the output signal.
13. The apparatus of claim 7 , wherein the signal processing portion is further configured to determine a linearization characteristic of a predetermined portion of the apparatus, the signal processing portion also configured so as to mitigate:
a linearization characteristic of another predetermined portion of the apparatus; and
an unintentional coupling of the loop-back signal with any other signal.
14. A system, comprising:
a transceiver device comprising:
a processor configured to control one or more functions of the transceiver device;
a transmitter and a receiver respectively under the control of the processor; and
a loop-back calibrator in communication with the transmitter and the receiver, the loop-back calibrator configured to:
extract a portion of a signal present within the transmitter; frequency shift the extracted signal to derive a shifted signal; sum the shifted signal with an other signal present within the receiver so as to derive a loop-back signal, wherein the other signal is provided by a low-noise amplifier within the receiver; and
perform the determination of the linearization characteristic by way of analysis of the loop-back signal content
determine a linearization characteristic of the transceiver, wherein determining the linearization characteristic of the transceiver comprises a digital signal processor analyzing the loop-back signal to detect phase, amplitude and frequency distortion within the output signal of the power amplifier, wherein determining further comprises deriving an Error Vector Magnitude (EVM) characteristic of the output signal; and
adjust at least one operating characteristic of the transceiver device responsive to the determination;
wherein the loop-back calibrator is configured to mitigate unintentional signal coupling within the transceiver.
15. The system of claim 14 , wherein:
the transmitter comprises a power amplifier;
the receiver comprises a low-noise amplifier; and
the loop-back calibrator is further configured such that the determination corresponds to a linearization characteristic of one or more of the power amplifier, or the low-noise amplifier.