Direct RF sampling is a method which converts the passband signal to baseband or intermediate frequency band directly by sampling the signal at the RF band without using a mixer. The method is less complex than the conventional superheterodyne receiver which uses mixers to down-convert the signal before sampling. The method can sample the signals in several different bands with an ADC simultaneously and then select the desired signals in digital domain flexibly. From this fact, the direct sampling method is useful for the receivers of multitype and/or multiband signals such as global navigation satellite systems (GNSS) which have several modulation types at several signal bands. In designing the direct RF sampling receiver, the sampling frequency is the key factor. Theoretically, the minimum sampling frequency to recover the original signal depends on the signal bandwidth. In practical, however, some more conditions should be considered. In this paper, we design the direct RF sampling receiver for GNSS systems with additional considerations such as the number of desired signal bands, the relation between intermediate frequency and sampling frequency, the ratio of interpolation and decimation rate to achieve the sample frequency. With these conditions, we design the direct RF sampling receivers for single band and multiband signals.

Keywords: direct RF sampling receiver, GNSS signal