Calculation of feedforward amplifier transfer function considering loops imbalances

In this paper, a novel analytic method is proposed for calculating the transfer function of an RF feedforward linearizer circuitry considering imbalances in the two loops of the circuit. Using Taylor series with complex coefficients in RF amplifier modelling, both AM-AM and AM-PM distortions are considered. Finally, the function of output envelope versus input envelope is achieved. Simulations results represent that at best condition, the AM-AM and AM-PM characteristic are improved a little in spite of significant reduction of ACLR. Even, in some cases, the AM-AM characteristic of feedforward amplifier is worse than that of desired amplifier but ACLR becomes smaller. The loops imbalances affect the AM-AM characteristic strongly and their effects are calculated in our analysis. This paper demonstrates that AM-AM diagram is not an adequate characteristic to introduce ACLR improvement for feedforward amplifier.