This paper studies the application of the Direct Sampling technique to GNSS receivers dedicated to Civil Aviation usage. After a description of the specific spectral environment to be withstood by such receivers, two previously proposed architectures are reviewed. In the first one the E5a/L5 band and the E1/L1 band are sampled by a unique ADC, providing full coherency between bands. In the second architecture each band is sampled separately. The minimum sampling frequencies are also recalled for each architecture. The quantization process is then analyzed and the required number of bits assessed in each case, taking into account the full range of the input signal, possibly tainted by strong interference. The high values found motivate the study of two low complexity non-linear functions dedicated to dynamic compression at the output of the ADCs, in order to decrease the computation workload of the following signal processing tasks. Finally the filters needed to separate the E5a/L5 and E1/L1 bands in the first coherent sampling architecture are specified and the induced computation workload is estimated.
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