A
feed forward power
amplifier is disclosed which utilizes three
signal cancellation loops. Loop 1 includes a main
amplifier and is used to derive a carrier cancelled sample of the main
amplifier output. Loop 2 includes an
error amplifier used to amplify the carrier cancelled
signal derived from Loop 1 operation in order to cancel
distortion products generated due to the nonlinear nature of the main amplifier. Loop 2 also utilizes a very
short Loop 2
delay line. A significant efficiency
gain is provided due to reduced output power losses associated with the Loop 2
delay line. Lower output losses also results in lower
distortion levels produced by the main amplifier. This, in turn, reduces the size and performance requirements placed on the
error amplifier. A smaller and more efficient
error amplifier is employed resulting in further amplifier
system efficiency improvement. A spurious
signal detector for out-of-band
distortion detection and an associated
microcontroller for Loop 1 and Loop 2 control are also provided. A third
signal cancellation loop is utilized to sample the amplifier output and reduce the carrier level of the signals sampled at the output of the amplifier before providing the sampled output to the spurious
signal detector. By significantly reducing the carrier
power level relative to distortion power levels a cost effective spurious
signal detector can be utilized. This also provides a faster conversion time in Loop 2 cancellation and enhanced cancellation of out-of-band distortion products due to a greater useful
dynamic range available for the DSP employed in the spurious
signal detector.