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The following paper presents a novel 900MHz pulse-width-modulated current-mode class-S power amplifier. The conversion from an analog to a digital signal, which can be handled by the subsequent switch-mode-stage, is implemented using a fast pulse-width-modulator. The complete class-S amplifier is characterized using clipped WCDMA signals with 5MHz and 80MHz bandwidth, respectively. For the 5MHz signal, the measured spectrum at the amplifier's output shows good EVM of < 12% (approx. 1.5% degradation assumed for class-S PA) and also meets the 3GPP ACLR requirements within 9dB input power range. The capability to support large signal bandwidths is demonstrated, using an 80MHz WCDMA signal, thus meeting the expectations on class-S amplifier for the first time with respect to signal bandwidth.Index Terms -Class-S amplifier, switch-mode operation, linearity, large signal bandwidth, PWM.

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An open converged metro-access network approach allows for sharing optical layer resources like fibers and optical spectrum among different services and operators. We demonstrated experimentally the feasibility of such a concept by the simultaneous operation of multiple services showing different modulation formats and multiplexing techniques. Flexible access nodes are implemented including semiconductor optical amplifiers to create a transparent and reconfigurable optical ring network. The impact of cascaded optical amplifiers on the signal quality is studied along the ring. In addition, the influence of high power rival signals in the same waveband and in the same fiber is analyzed.