Investigation of Input Nonlinearity in Sequential Load Modulated Balanced Amplifiers

This paper investigates the impact of input nonlinearity in the sequential load modulated balanced amplifier (SLMBA) configuration. Theoretical analysis identifies that the utilization of Class-F-1 control amplifier (CA) can provide high and flat efficiency performance in low-power region and stable balanced amplifier (BA) load modulation in high-power region under second harmonic source (Z2S) variation. The immunity to input nonlinearity of Class-F-1 operation provides CA flexible Z2S design space in broadband SLMBA realization. Based on the load-pull experimental results, the optimum design space of ∠Γ2S over (-90°, 90°) is chosen as the safe design region for Class-B/J BA and Class-F-1 CA. Following the investigation results, an identical input matching network (IMN) with tuned Z2S terminations was designed for both CA and BA cells for an SLMBA operating from 1.8 to 2.6 GHz leveraging high efficiency back-off performance from a Class-F-1 CA. Measured results showed high drain efficiency (DE) of 53.2% to 64.7% at 8-dB back-off and 62.7% to 67.4% at peak power as well.