Performance analysis of analog-to-digital converters for wideband digitally modulated signals

In modern satellites systems, the uplink RF wideband signal after downconversion to IF is input to the analog-to-digital converter, the output of which is digitally processed for the purpose of channelization and switching of signals. In such systems, wherein the received wideband signal is comprised of many multiplexed signals, the spectral distribution of quantization noise is also of significant interest. Another very important consideration in the analog-to-digital converter (ADC) performance analysis is the signal clipping effect occurring whenever the instantaneous input signal amplitude exceeds the maximum linear range of the quantizer. Since clipping cannot be avoided in most practical situations, the signal power to the quantization plus clipping noise power ratio is of utmost interest. Such a ratio is studied in terms of the ADC load factor analysis. This paper presents simulation results on the performance of the quantizer in terms of the quantization noise spectral distribution and the load factor analysis when the input signal is comprised of a number of digitally modulated carriers. As simulation examples, 8-PSK and 16-QAM modulation schemes are considered with and without band limiting filtering. The results include both the ideal uniform and non-ideal quantizers.