Impact of the amplifier-BandPass reconstruction filter interaction on the linearity of carrier amplitude-burst transmitters

Carrier amplitude-burst transmitters can ideally deliver 100% efficiency and perfect linearity. The amplitude to time conversion performed by a PWM or sigma-delta modulator allows the usage of switched mode power amplifiers, at the expense of introducing a large amount of out of band noise, which must be removed by a narrow bandwidth band-pass reconstruction filter. However, practical implementations suffer from several problems whose cause is the careless design of the amplifier-filter connection, which prevent the achievement of those ideal performance figures. This paper discusses how the linearity of these transmitters is affected by the interaction between the switched-mode amplifier and the band-pass reconstruction filter providing design rules for this amplifier-filter interconnection. The presented results are obtained by both simulations and practical measurements.