Efficiency enhancement of feedforward amplifiers by employing a negative group-delay circuit

We will demonstrate an alternative topology for the feedforward amplifier. This amplifier does not use a delay element, thus providing an efficiency enhancement and a size reduction by employing a distributed-element negative group-delay circuit. The insertion loss of the delay element in the conventional feedforward amplifier seriously degrades the efficiency. Usually, a high-power coaxial cable or a delay-line filter is utilized for a low loss, but the insertion loss, cost, and size of the delay element still act as a bottleneck. The proposed negative group-delay circuit removes the necessity of the delay element required for a broadband signal suppression loop. With the fabricated two-stage distributed-element negative group-delay circuit with 30 MHz of bandwidth and 9 ns of group delay for a wideband code-division multiple-access downlink band, the feedforward amplifier with the proposed topology experimentally achieved 19.4% power-added efficiency and 53.2-dBc adjacent channel leakage ratio with 44-dBm average output power.