Memory-based amplifier load adjust system

A power amplifier load adjust system for use in a radiotelephone, the radiotelephone operable over a predetermined band of frequencies, the power amplifier load adjust system comprising:

• a power amplifier having an input and an output;
• a variable impedance network coupled to the output of the power amplifier, the variable impedance network for presenting a plurality of impedances to the output of the power amplifier responsive to a load control signal;
• a control circuit for generating a transmit power command and a channel frequency command;
• a memory for storing a plurality of control values as a function of power amplifier output power and frequency of operation within the predetermined band of frequencies;
• a processing circuit coupled to the variable impedance network, the control circuit, and the memory, the processing circuit for retrieving the plurality of control values stored in the memory and using the plurality of control values to generate a digital load control signal in response to the transmit power command and in response to the channel frequency command;
• and
• a digital-to-analog converter (DAC) coupled to the processing circuit and the variable impedance network, the DAC for converting the digital load control signal to the load control signal.

A power amplifier load adjust system for use in a radiotelephone, the radiotelephone operable over a predetermined band of frequencies, the power amplifier load adjust system comprising:

• a power amplifier having an input and an output;
• a variable impedance network coupled to the output of the power amplifier, the variable impedance network for presenting a plurality of impedances to the output of the power amplifier responsive to a load control signal;
• a control circuit for generating a transmit power command and a channel frequency command;
• a memory for storing a plurality of control values as a function of power amplifier output power and frequency of operation within the predetermined band of frequencies;
• and
• a processing circuit coupled to the variable impedance network, the control circuit, and the memory, the processing circuit for retrieving the plurality of control values stored in the memory and using the plurality of control values to generate the load control signal in response to the transmit power command and in response to the channel frequency command,
• wherein a first set of the plurality of control values stored in the memory correspond to amplifier load impedances that cause the power amplifier to operate at substantially a first output power and produce an adjacent channel power substantially less than a predetermined adjacent channel power when the power amplifier operates over each of a plurality of frequencies within the predetermined band of frequencies.

A method of controlling a variable impedance network at an output of a power amplifier operable in a radiotelephone over a plurality of frequencies within a predetermined band of frequencies, the method comprising:

• receiving an indication of channel of operation and an indication of desired output power;
• retrieving control values from memory;
• producing a load control signal using the control values and in response to the indication of channel of operation and the indication of the desired output power;
• applying the load control signal to the variable impedance network;
• and
• setting an impedance the variable impedance network presents to the output of the power amplifier in response to the load control signal.

A method of controlling a variable impedance network at an output of a power amplifier operable in a radiotelephone, the method comprising:

• determining a plurality of control values that cause the variable impedance network to present impedances to the output of the power amplifier to cause the power amplifier to produce less than a predetermined amount of adjacent channel power when the power amplifier operates at each of a plurality of frequencies and at least one predetermined output power;
• storing the plurality of control values;
• generating a transmit power command;
• generating a channel frequency command;
• generating a load control signal using the plurality of control values and in response to the transmit power command and the channel frequency command;
• applying the load control signal to the variable impedance network;
• and
• presenting a load impedance to the output of the power amplifier responsive to the load control signal.