Joint adaptive bias point adjustment and digital pre-distortion for power amplifier
One embodiment of the present invention relates to a method and apparatus are provided herein for reducing the power consumption of a transmission chain while maintaining an acceptable figure of merit (e.g., linearity). In one embodiment, an adaptive biasing element is configured to perform adaptive biasing to reduce current consumption of a transmission chain by adjusting the operating point of one or more transmission chain elements (e.g., power amplifier, mixer, etc.). However, since adaptive biasing may reduce the linearity of a transmitted signal, its use is limited by the degradation of figure of merit caused by the introduced non-linearities. Accordingly, a pre-distortion element may be configured to perform adaptive digital pre-distortion (DPD) on a transmission chain input signal to account for non-linearities generated through the adaptive biasing, therefore allowing the adaptive biasing to further reduce the current consumption while maintaining an acceptable figure of merit.
1. A transmitter circuit, comprising:
one or more transmission chain elements configured to receive an input signal and to generate an output signal;
a figure of merit measurement element configured to receive information about the output signal from a feedback loop, extending from the one or more transmission chain elements to the figure of merit measurement element, and to determine a measured figure of merit of the output signal;
an adaptive biasing element configured to adaptively bias the one or more transmission chain elements to iteratively reduce a current consumption of the one or more transmission chain elements until the measured figure of merit violates a predetermined quality standard; and
a pre-distortion element located upstream of the one or more transmission chain elements and configured to generate a distorted input signal to improve the measured figure of merit and thus account for non-linearities introduced into the output signal during the adaptive biasing, until the measured figure of merit no longer violates the predetermined quality standard.
2. The transmitter circuit of claim 1 , wherein the pre-distortion element is configured to generate the distorted version of the input signal when the measured figure of merit violates a first predetermined threshold value.
3. The transmitter circuit of claim 1 , wherein the adaptive biasing element and the pre-distortion element are configure to operate within a time slot.
4. The transmission chain element of claim 1 , wherein adaptively biasing the one or more transmission chain elements comprises dynamically adjusting a bias condition comprising one or more of: a bias voltage or a bias current of the one or more transmission chain elements.
5. A transmitter circuit, comprising:
one or more transmission chain elements configured to receive an input signal and to generate an output signal;
a figure of merit measurement element configured to receive information about the output signal from a feedback loop, extending from the one or more transmission chain elements to the figure of merit measurement element, and to determine a measured figure of merit of the output signal;
an adaptive biasing element configured to adaptively bias the one or more transmission chain elements to iteratively adjusting a current consumption of the one or more transmission chain elements; and
a pre-distortion element located upstream of the one or more transmission chain elements and configured to generate a distorted input signal to account for non-linearities introduced into the output signal during the adaptive biasing,
wherein the measured figure of merit is evaluated against a predetermined target range that defines a range of actual merit,
wherein if the measured figure of merit indicates that the actual merit is better than that defined by the predetermined target range, the adaptive biasing element is configured to reduce the current consumption and the actual merit in a stepwise manner,
wherein if the measured figure of merit indicates that the actual merit is within the predetermined target range, the non-linearities introduced by the adaptive biasing are evaluated and one or more pre-distortion coefficients used by the pre-distortion element to generate the distorted input signal are updated, and
wherein if the measured figure of merit indicates that the actual merit is worse than that defined by the predetermined target range, the adaptive biasing element is configured to increase the current consumption and the actual merit.
6. The transmitter of claim 5 , wherein the pre-distortion coefficients comprise amplitude distortion coefficients (AM/AM) coefficients.
7. The transmitter of claim 5 , wherein the pre-distortion coefficients comprise phase distortion coefficients (AM/PM) coefficients.
8. The transmitter circuit of claim 1 , further comprising one or more additional sensor coupled to the figure of merit measurement element, wherein the one or more additional sensors are configured to measure external variables used to assist determining the measured figure of merit.
9. The transmitter of claim 1 , wherein the adaptive biasing element is configured to initially operate to guarantee good linearity for an output power and wherein the pre-distortion element is configured to initially operate so as to not distort the output signal.
10. A method for reducing a current consumption of a transmission circuit, comprising:
adaptively biasing one or more transmission chain elements to reduce the current consumption of the one or more transmission chain elements, wherein adaptively biasing the one or more transmission chain elements produces non-linearities in an output signal;
evaluating the non-linearities based upon a feedback signal comprising information about the output signal; and
generating a distorted input signal, input to the one or more transmission chain elements, having distortions to account for non-linearities caused by adaptively biasing the one or more transmission chain elements,
wherein the measured figure of merit is evaluated against a predetermined target range that defines a range of actual merit,
wherein if the measured figure of merit indicates that the actual merit is better than that defined by the predetermined target range, the one or more transmission chain elements are adaptively biased to reduce the current consumption in a stepwise manner, thereby reducing the measured figure of merit,
wherein if the measured figure of merit indicates that the actual merit is within the predetermined target range, the non-linearities introduced by the adaptive biasing are evaluated and one or more pre-distortion coefficients used by to generate the distorted input signal are updated, and
wherein if the measured figure of merit indicates that the actual merit is worse than that defined by the predetermined target range, the one or more transmission chain elements are adaptively biased to increase the current consumption, thereby increasing the actual merit; and
wherein a value of the measured figure of merit is used to update the adaptive biasing of the one or more digital pre-distortion coefficients based upon one or more mathematical relationships, the mathematical relationships including parameters derived from one or more additional sensors configured to measure external variables including those used to assist determining the measured figure of merit.
11. The method of claim 10 , wherein evaluating the non-linearities produced by the adaptive biasing comprises generating a measured figure of merit by analyzing a crest factor of the feedback signal and comparing it to a crest factor of the input signal.
12. The method of claim 10 , wherein generating a distorted version of an input signal comprises updating one or more pre-distortion coefficients, which are applied to the input signal.
13. The method of claim 12 , wherein the pre-distortion coefficients comprise amplitude distortion coefficients (AM/AM) coefficients or phase distortion coefficients (AM/PM) coefficients.
14. The method of claim 12 , wherein an adaptive biasing working point is initially set high enough to guarantee good linearity for the output signal and wherein the one or more pre-distortion coefficients are initially set so as to not distort the input signal.
15. A method for reducing a current consumption of one or more transmission chain elements, comprising:
setting initial bias conditions of one or more transmission chain elements high enough to guarantee good linearity for an output signal and one or more initial pre-distortion coefficients so as to not distort an input signal,
determining a measured figure of merit of the output signal; and
alternatively or concurrently performing adaptive biasing and updating the pre-distortion coefficients in a stepwise iterative process based on the measured figure of merit,
wherein the measured figure of merit is evaluated against a predetermined target range that defines a range of actual merit,
wherein if the measured figure of merit indicates that the actual merit is better than that defined by the predetermined target range, adaptive biasing is performed to reduce the current consumption and the actual merit in a stepwise manner,
wherein if the measured figure of merit indicates that the actual merit is within the predetermined target range, non-linearities introduced by adjusting the bias conditions are evaluated and one or more pre-distortion coefficients are updated, and
wherein if the measured figure of merit indicates that the actual merit is worse than that defined by the predetermined target range, adaptive biasing is performed to increase the current consumption and actual merit.
16. The method of claim 15 , wherein adaptively biasing the one or more transmission chain elements comprises dynamically adjusting a bias condition comprising one or more of: a bias voltage or a bias current of the one or more transmission chain elements.
17. The method of claim 15 , wherein an adaptive biasing working point is initially set high enough to guarantee good linearity for the output signal and wherein the one or more pre-distortion coefficients are initially set so as to not distort the input signal.
18. The method of claim 15 , wherein the pre-distortion coefficients comprise amplitude distortion coefficients (AM/AM) coefficients or phase distortion coefficients (AM/PM) coefficients.