Detecting and maintaining linearity in a power amplifier system through comparing peak and RMS power levels
First Claim
1. A method of detecting linear operation in a power amplifier, the power amplifier being operative to amplify an input signal for transmission, the method comprising the steps of:
- detecting the output signal of the power amplifier;
converting the detected output signal into a digital signal;
examining the digital signal to determine the peak power represented by the digital signal;
examining the digital signal to determine the root-mean-square power of a portion of the digital signal;
decreasing the input power level of the input signal if the ratio of the peak power to the root-mean-square power below a first threshold level.
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Accused Products
Abstract
Small portable communication devices that support multiple modulation techniques cannot gain the benefits of using an isolator at the output of a power amplifier to provide stability in the load impedance. However, for communication devices that include amplitude modulation schemes, maintaining linear operation of the power amplifier is still required. In the presence of unstable load impedance, this can be a difficult task. As a solution, the linearity of the power amplifier is detected by determining the peak power of the output signal and the average or root-mean-square of a portion of the output signal, such as a mid-amble). The ratio of the peak power and the average power of the output signal are used to determine if the power amplifier is operating in the linear region. If the ratio is too high, then the power amplifier may be operating in the linear region. By adjusting the power level of the input signal to the power amplifier when the ratio increases, linearity of the power amplifier is maintained.
135 Citations
20 Claims
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1. A method of detecting linear operation in a power amplifier, the power amplifier being operative to amplify an input signal for transmission, the method comprising the steps of:
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detecting the output signal of the power amplifier;
converting the detected output signal into a digital signal;
examining the digital signal to determine the peak power represented by the digital signal;
examining the digital signal to determine the root-mean-square power of a portion of the digital signal;
decreasing the input power level of the input signal if the ratio of the peak power to the root-mean-square power below a first threshold level. - View Dependent Claims (2, 3, 4, 5)
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6. A circuit for maintaining linear operation of a power amplifier, the circuit comprising the components of:
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a power amplifier, a variable gain amplifier, a coupler, a voltage detector, and a processor, the power amplifier having a signal input and a signal output;
the variable gain amplifier having a signal input, a signal output, and a control input, the signal output of the variable gain amplifier being electrically coupled to the signal input of the power amplifier, the signal input of the variable gain amplifier receiving a modulated signal that has been modulated with a base band signal, the control input of the variable gain amplifier being connected to a first control output of the processor, the coupler being electrically coupled to the signal output of the power amplifier and operative, in cooperation with the voltage detector, to detect the envelope of an output signal at the signal output of the power amplifier and provide the detected envelope to a detected signal input of the processor;
the processor, being operative to;
receive the detected signal and determine the peak power of the detected signal and the root-mean-square power of at least a portion of the detected signal; and
adjust the first control output of the processor to limit the gain of the variable gain amplifier if the ratio of the peak power to the root-mean-square power is below a first threshold level. - View Dependent Claims (7, 8, 9, 10)
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11. A mobile station for use in a cellular system, the mobile station comprising:
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a power amplifier having a signal input received from a variable gain amplifier and a signal output for transmitting through an antenna;
a voltage detector coupled to the output of the power amplifier for detecting the output signal and obtaining a detected signal output;
an analog to digital converter electrically coupled to the output of the voltage detector for receiving the detected signal and for converting the detected signal from analog to a digital signal and providing the digital signal to a digital output;
a processor coupled to output of the analog to digital converter for receiving the digital signal, the processor being operative to;
determine the peak power of the digital signal;
determine the root-mean-square power of at least a portion of the digital signal;
determine the ratio of the peak power to the root-mean-square power; and
adjust the gain of the variable gain amplifier in accordance with the value of the ratio. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification