The input signal (110) to a non-linear amplifier (112) is predistorted by injecting a correction signal at coupler (124). To generate the correction signal, a sample of the input signal is amplified using amplifier (130) which has substantially the same distortion generating characteristics as amplifier (112). The output of amplifier (130) is sampled, and the main tone energy is removed at (138), leaving the correction signal for injection to the main signal path. The main portion of the output of amplifier (130) is added coherently to the output of amplifier (112) to enhance efficiency. The correction signal can be manipulated to correct distortion in the output of combiner (152) due to the main portion of the output of amplifier (130).
The length of a transmission line delay circuit is halved by inserting a directional coupler in the signal path ahead of the transmission line and either open circuiting or short circuiting the other end of the transmission line. The signal traveling through the directional coupler and through the transmission line is reflected back at the end of the transmission line, and the reflected signal is carried to the coupled output of the directional coupler. Since the signal travels through the transmission line twice, the delay time is doubled. Therefore, for a given delay requirement, the length of transmission line required is only half of the length required for prior art transmission delay lines.
