Method of power amplifier predistortion adaptation using compression detection

A circuit for amplifying signals, comprising:

• a predistortion circuit distorting an input signal in dependence upon a predistortion correction value selected from a plurality of predistortion correction values stored in a look-up table (LUT), and adjusting the distorted signal in dependence upon a variation of circuit characteristics;
• a transceiver circuit coupled to received the output signal from the predistortion circuit and processing the received signal in dependence upon a certain transceiver transfer function;
• an amplification circuit coupled to receive the output signal from the transceiver circuit and amplifying the signal in dependence upon an amplification transfer function;
• a compression detector circuit coupled to the amplification circuit, detecting whether the amplification circuit is operating in a compression mode, and generating a compression indication signal, the compression detector circuit comprising:
• a first envelope detector circuit coupled to receive a first sampled signal from the input signal of the amplification circuit and generating a first envelope signal,
• a variable attenuator circuit coupled to receive a second sampled signal from the output signal of the amplification circuit and attenuating the received second sampled signal in dependence upon an attenuation factor,
• a second envelope detector circuit coupled to receive the attenuated signal and generating a second envelope signal,
• a difference amplifier circuit coupled to receive both the first envelope signal and the second envelope signal, and generating the compression indication signal in dependence upon the difference between the first envelope signal and the second envelope signal,
• a detection calibration circuit coupled to receive the compression indication signal, and controlling the variable attenuator circuit to adjust the attenuation factor in dependence upon the received compression indication signal, in order to maintain the attenuated signal to be equal to the first sampled signal when the amplification circuit is not operating in a compression mode;
• and
• a compare and adapt circuit coupled to receive the compression indication signal, controlling the predistortion circuit for controlling the adjustment of the distorted signal in dependence upon the received compression indication signal.

A circuit for amplifying signals, comprising:

• a predistortion circuit distorting an input signal in dependence upon a predistortion correction value selected from a plurality of predistortion correction values stored in a look-up table (LUT), and adjusting the distorted signal in dependence upon a variation of circuit characteristics, the predistortion circuit comprising:
• a Cartesian to polar conversion circuit coupled to receive the input signal and converting the received input signal into a sequence of amplitude samples,
• a predistortion look-up table storing amplitude sample values and corresponding predistortion correction values, coupled to sequentially receive the amplitude samples and outputting the corresponding sequence of predistortion correction values,
• a vector multiplier circuit coupled to sequentially receive the amplitude samples and the predistortion correction values and outputting a sequence of distorted amplitude samples,
• a multiplier circuit coupled to receive the sequence of distorted amplitude samples and a sequence of integrated error values from the compare and adapt circuit, multiplying the distorted amplitude samples with the corresponding integrated error values, and outputting a sequence of corrected amplitude samples, and
• a polar to Cartesian circuit coupled to convert the sequence of corrected amplitude samples;
• a transceiver circuit coupled to receive the output signal from the predistortion circuit and processing the received signal in dependence upon a certain transceiver transfer function;
• an amplification circuit coupled to receive the output signal from the transceiver circuit and amplifying the signal in dependence upon an amplification transfer function;
• a compression detector circuit coupled to the amplification circuit, detecting whether the amplification circuit is operating in a compression mode, and generating a compression indication signal;
• and
• a compare and adapt circuit coupled to receive the compression indication signal, controlling the predistortion circuit for controlling the adjustment of the distorted signal in dependence upon the received compression indication signal.

A method for amplifying signals, the method comprising the steps of:

• distorting, at a predistortion circuit, an input signal in dependence upon a predistortion correction value selected from a plurality of predistortion correction values stored in a look-up table (LUT), and adjusting the distorted signal in dependence upon a variation of circuit characteristics;
• processing, at a transceiver circuit, the output signal from the predistortion circuit in dependence upon a certain transceiver transfer function;
• amplifying, at an amplification circuit, the signal in dependence upon an amplification transfer function;
• detecting, at a compression detector circuit, whether the amplification circuit is operating in a compression mode based on a signal received from an input signal of the amplification circuit and the amplified signal output from the amplification circuit, and generating a compression indication signal;
• and
• controlling, at a compare and adapt circuit, the predistortion circuit for controlling the adjustment of the distorted signal in dependence upon the received compression indication signal.

A method for amplifying signals, the method comprising the steps of:

• distorting, at a predistortion circuit, an input signal in dependence upon a predistortion correction value selected from a plurality of predistortion correction values stored in a look-up table (LUT), and adjusting the distorted signal in dependence upon a variation of circuit characteristics;
• processing, at a transceiver circuit, the output signal from the predistortion circuit in dependence upon a certain transceiver transfer function;
• amplifying, at an amplification circuit, the signal in dependence upon an amplification transfer function;
• detecting, at a compression detector circuit, whether the amplification circuit is operating in a compression mode, and generating a compression indication signal, wherein detecting whether the amplification circuit is operating in a compression mode, and generating a compression indication signal comprises:
• generating a first envelope signal, at a first envelope detector circuit, based on a first sampled signal from the input signal of the amplification circuit,
• attenuating a second sampled signal, at a variable attenuator circuit, from the output signal of the amplification circuit,
• generating a second envelope signal, at a second envelope detector circuit, based on the attenuated signal,
• detecting, at a difference amplifier circuit, the difference between the first envelope signal and the second envelope signal, and generating the compression indication signal, and
• controlling, at a detection calibration circuit, the variable attenuator circuit in dependence upon the received compression indication signal to maintain the attenuated signal to be equal to the first sampled signal when the amplification circuit is not operating in a compression mode;
• and
• controlling, at a compare and adapt circuit, the predistortion circuit for controlling the adjustment of the distorted signal in dependence upon the received compression indication signal.

A circuit for amplifying signals, comprising:

• a predistortion circuit distorting an input signal in dependence upon a predistortion correction value selected from a plurality of predistortion correction values, and adjusting the distorted signal in dependence upon a variation of circuit characteristics;
• a transceiver circuit coupled to receive the output signal from the predistortion circuit and processing the received signal in dependence upon a certain transceiver transfer function;
• an amplification circuit coupled to receive the output signal from the transceiver circuit and amplifying the signal in dependence upon an amplification transfer function;
• a first envelope detector circuit coupled to receive a first sampled signal from the input signal of the amplification circuit and generating a first envelope signal;
• a variable attenuator circuit coupled to receive a second sampled signal from the output signal of the amplification circuit and attenuating the received second sampled signal in dependence upon an attenuation factor;
• a second envelope detector circuit coupled to receive the attenuated signal and generating a second envelope signal;
• a difference amplifier circuit coupled to receive both the first envelope signal and the second envelope signal and outputting a compression indication signal in dependence upon the difference of the first envelope signal and the second envelope signal;
• and
• a compare and adapt circuit coupled to receive the compression indication signal, controlling the predistortion circuit for controlling the adjustment of the distorted signal in dependence upon the received compression indication signal.

A method for amplifying signals, the method comprising the steps of:

• distorting, at a predistortion circuit, an input signal in dependence upon a predistortion correction value selected from a plurality of predistortion correction values, and adjusting the distorted signal in dependence upon a variation of circuit characteristics;
• processing, at a transceiver circuit, the output signal from the predistortion circuit in dependence upon a certain transceiver transfer function;
• amplifying, at an amplification circuit, the signal in dependence upon an amplification transfer function;
• generating a first envelope signal, at a first envelope detector circuit, based on a first sampled signal from the input signal of the amplification circuit;
• attenuating, at a variable attenuator circuit, a second sampled signal from the output signal of the amplification circuit in dependence upon an attenuation factor;
• generating a second envelope signal, at a second envelope detector circuit, based on the attenuated signal;
• detecting, at a difference amplifier circuit, the difference between the first envelope signal and the second envelope signal, and outputting a compression indication signal;
• and
• controlling, at a compare and adapt circuit, the predistortion circuit for controlling the adjustment of the distorted signal in dependence upon the received compression indication signal.