A feed-forward amplifier with an input arranged to receive wide-band signals and an output to supply a linearly amplified version of these has two parallel signal paths arranged between such input and output, one of the signal paths includes a cascade connection of a signal amplifier and a delay network and the second signal path includes an error amplifier, an error extraction circuit having a directional coupler in which an input side has a first pair of conjugate first and second ports and is connected partly to the input of the feed-forward amplifier and partly to an output of the signal amplifier and an output side has a second pair of conjugate third and fourth ports, the fourth port being connected to an input of the error amplifier, and an error injection circuit which has a first and a second input connected to an output of the delay network and to an output of the error amplifier, respectively and an output connected to the output of the feed-forward amplifier, the error extraction circuit having the third port of the directional coupler connected to an input of the signal amplifier and a summation circuit having a first and second input connected to the input of the feed-forward amplifier and to the output of the signal amplifier, respectively, and an output connected to the second port of the directional coupler.
There is disclosed, for use in a wireless network, a single-loop feedforward amplification system. The single loop comprises a main amplification branch and a feedforward branch in parallel to the main amplification branch. The main amplification branch contains a delay line that receives and delays the initial low-power input signal, and a power amplifier that amplifies the delayed input signal to produce an amplified output signal. The feedforward branch also receives the input signal and generates an distortion correction signal to compensate for the distortion produced at the output of the power amplifier due to its non-linearity. The distortion correction signal and the distorted amplified output signal are then combined to create a corrected amplified output signal without distortion.
Apparatus for interconnecting two or more high gain, low input impedance amplifier stages for high gain amplification. A first amplifier stage (12) provides a first amplified signal to a coupling circuit. The coupling circuit (26) divides the power of the first amplified signal between the input to a second amplifier stage (14) and a feed forward path (28). The output of the second amplifier stage is combined with the feed forward portion of the first amplified signal in a signal combiner (30). Embodiments (FIGS. 4, 5) employing more than two amplifier stages are described.
A push-pull microwave amplifier in which an input signal is split into two ransmission paths in a manner which simulates the behavior of a center-tapped transformer over a broad frequency range. The input signal is first divided into two identical paths and then passed down first and second transmission line segments in the two paths bi-directionally. One of the transmission line segments is terminated in an open circuit and the other in a short circuit so that the reflected signals have the opposite polarities. By making the transmission line segments of equal length, the opposite polarity signals emerge from the transmission line segments at the same time. The signals are then amplified and then passed again bi-directionally along third and fourth transmission line segments terminated in short and open circuits so as to re-convert the signals to the same polarity. The signals are then summed to produce the composite amplified output signal.
