System and method for reducing output harmonics

A power amplifier system, comprising:

• an amplification stage having an input for receiving an input signal, and an output coupled to an integrated circuit terminal, said amplification stage comprises a plurality of amplifiers connected in series, each amplifier having an input, a control input for receiving a respective control signal, and an output;
• a low-pass filter having a first input coupled to outputs of each of said plurality of amplifiers, and an output;
• and
• a controller having a first input coupled to said output of said low-pass filter, and outputs coupled to respective control inputs of each of said plurality of amplifiers, wherein said controller varies said respective control signal of each of said plurality of amplifiers to reduce a difference between said output of said low-pass filter and respective target voltage levels when an input of said low-pass filter is coupled to a respective output of a corresponding amplifier.

A signal generation system, comprising:

• a first signal generation element having an input for receiving an input signal, a control input for receiving a coarse control signal, and an output;
• a second signal generation element having an input coupled to said output of said first signal generation element, a control input for receiving a fine control signal, and an output;
• a low-pass filter having a first input coupled to said output of said first signal generation element, a second input coupled to said output of said second signal generation element, and an output;
• and
• a controller having an input coupled to said output of said low-pass filter, a first output for providing said coarse control signal, and a second element for providing said fine control signal, wherein said controller varies said coarse control signal to reduce a difference between said output of said low-pass filter and a first target voltage level, and subsequently varies said fine control signal to reduce a difference between said output of said low-pass filter and a second target voltage level.

A method for calibrating an amplifier system having an amplification stage comprising a plurality of amplifiers connected in series including a first amplifier and a second amplifier having an input coupled to an output of the first amplifier, comprising:

• low-pass filtering an output of the first amplifier to provide a low-pass filtered signal;
• calibrating an even order harmonic of an output of the first amplifier, wherein said calibrating comprises changing pullup and pulldown strengths of the first amplifier until a difference between said low-pass filtered signal and a first target voltage level is less than a first threshold;
• low-pass filtering an output of the second amplifier to provide said low-pass filtered signal;
• calibrating an even order harmonic of the second amplifier, wherein said calibrating comprises changing pullup and pulldown strengths of the second amplifier to until a difference between said low-pass filtered signal and a second target
• voltage level is less than a second threshold;
• and
• amplifying an input signal using said first and second amplifiers to provide an output signal.