## Phase distortion – amplifiers

#### Just as high power sources such as amplifiers and lasers have non-linear amplitude response with input power, they also usually have a non-linear phase response with input power. The phase response with frequency, however, is in practice quite linear and does not pose a problem unless very wide modulation bandwidths are being employed. The effect of phase change with power level is to cause an amplitude-dependent phase distortion of the data signal, often termed AM-PM distortion, (Amplitude Modulation to Phase Modulation). This has a particularly detrimental effect on phase based modulation formats such as M-ary PSK or M-ary QAM which suffer unwanted rotation of the phase states of each symbol. |