Dynamic RF amplifier bias control for digital wireless communications devices
First Claim
1. An apparatus for dynamically adjusting the bias of an amplifier, comprising:
- (a) an inverse Fourier transform processor receiving a plurality of inputs;
(b) a multiplexer, the input connected to the output of the inverse Fourier transform processor;
(c) a plurality of buffers connected to the output of the multiplexer;
(d) a demultiplexer receiving inputs from the plurality of output buffers, the output of the demultiplexer connected by a circuit to the input of the amplifier;
(e) a peak detector and hold circuit, the input of the circuit connected to the output of the inverse Fourier transform processor;
(f) a selection means, the selection means receiving an input from the peak detector and hold circuit, and responsive to the input selecting a bias point for the amplifier, the selection means output connected to a bias control circuit, the bias control circuit controlling the amplifier'"'"'s bias point.
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Accused Products
Abstract
An adaptive bias control scheme for an Orthogonal Frequency Division Multiplex (“OFDM”) transmitter. The transmitter chain is comprised of class A amplifiers. The amplifiers in the transmit chain are backed off from P1dB to ensure linear amplification of the signal. Amplifier back off is defined as (Amplifier P1dB) minus (Average Signal Power). Since the efficiency of the amplifier decreases in direct proportion, to the back off, it is desirable to minimize back off while maintaining linearity. The back off is dependent on the peak to average power ratio (“PAPR”) of the OFDM waveform. The PAPR is measured on a symbol by symbol basis and the amplifier P1dB is adjusted in proportion to the PAPR of the symbol, maintaining a P1dB sufficient to provide the required back off dictated by the maximum PAPR of the OFDM waveform, but can be lowered for symbols with PAPR below the maximum. The average operating point of the amplifiers is reduced by the adaptive bias control on a symbol-by-symbol basis.
87 Citations
21 Claims
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1. An apparatus for dynamically adjusting the bias of an amplifier, comprising:
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(a) an inverse Fourier transform processor receiving a plurality of inputs;
(b) a multiplexer, the input connected to the output of the inverse Fourier transform processor;
(c) a plurality of buffers connected to the output of the multiplexer;
(d) a demultiplexer receiving inputs from the plurality of output buffers, the output of the demultiplexer connected by a circuit to the input of the amplifier;
(e) a peak detector and hold circuit, the input of the circuit connected to the output of the inverse Fourier transform processor;
(f) a selection means, the selection means receiving an input from the peak detector and hold circuit, and responsive to the input selecting a bias point for the amplifier, the selection means output connected to a bias control circuit, the bias control circuit controlling the amplifier'"'"'s bias point. - View Dependent Claims (2, 3, 4, 5, 6)
(a) instructions for receiving an input;
(b) instructions for calculating an optimal bias point responsive to the instructions for receiving an input;
(c) instructions for outputting the bias point.
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7. A method for dynamically adjusting the bias of an amplifier, the steps comprising:
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dividing a long sequence of waveforms into a plurality of short waveform samples, wherein each of the plurality of short waveform samples having a maximum magnitude;
for each of the plurality of short waveform samples;
calculating a bias point for the amplifier based on the maximum magnitude setting the bias point of the amplifier; and
forwarding the short waveform sample to the amplifier after setting the bias point. - View Dependent Claims (8, 9, 10, 11)
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12. A computer readable medium of instructions, comprising:
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means for dividing a long sequence of waveforms into a plurality of short waveform samples, wherein each of the plurality of short waveform samples having a maximum magnitude;
means for calculating a bias point for the amplifier based on the maximum magnitude for each of the plurality of short waveform samples;
means for setting the bias point of the RF amplifier for each of the plurality of short waveform samples; and
means for forwarding the short waveform sample to the amplifier for each of the plurality of short waveform samples after the means for setting the bias point has set the bias point. - View Dependent Claims (13, 14, 15, 16)
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17. An apparatus for dynamically adjusting the bias of an amplifier, comprising:
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means for dividing a long sequence of waveforms into a plurality of short waveform samples, wherein each of the plurality of short waveform samples having a maximum magnitude;
means for calculating a bias point for the amplifier based on the maximum magnitude for each of the plurality of short waveform samples;
means for setting the bias point of the amplifier for each of the plurality of short waveform samples; and
means for forwarding the short waveform sample to the amplifier for each of the plurality of short waveform samples;
wherein the means for forwarding the short waveform sample waits until the means for setting the bias point has set the bias point. - View Dependent Claims (18, 19, 20, 21)
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Specification