Class-S power amplifier concept for mobile communications in rural areas with concurrent transmission at 450 MHz and 900 MHz

An 15th order bandpass delta-sigma modulator for class-S power amplifiers is presented. The modulator is based on a third order low pass prototype which is designed to meet the requirements for signal-to-noise ratio (SNR) of major mobile communication standards in a bandwidth of around 30 MHz. The transform z^-1 → z^-5 leads to a repetition of the low pass notch in the noise transfer function (NTF) at frequencies f = n/5f_s, n = 1, 2, 3, 4, 5, &. Apart from sinc filtering due to rectangular output pulses the NTF shape is equal in all frequency bands. The two lower frequency bands at f = 1/5f_s, 2/5 f_s are independent from each other and can be used for concurrent transmission in the 450 MHz and 900 MHz band. The paper investigates the modulator with respect to the signal to noise ratio, the stability and the coding efficiency versus input amplitudes of tones in both frequency bands.