Band-Limited Signal Sampling and Digital Coherent Processing
Nuaa Nanjing · Transaction of Nanjing University of Aeronautics and Astronautics · 1995
Studies a method of developing in-phase and quadrature samples of band-limited IF waveforms. The method employs only one analog to digital (A/D) convertor to sample and digitize the iF signal directly,eliminating the need for iF to be mixed to zero centre frequency in the form of two parallel baseband channels. An imaginary frequency rejecting filter and a secondary resampling circuit for frequency shifting are used to provide in-phase and quadrature components I and Q from the digital samples. Thus the problem of match.ing gain and phase response difference between the two components is avoided. The digital frequency shifting circuit is simplified by properly selecting the iF carrier and the sample interval. Experimental results show that the imaginary frequency level of less than-50'.dB is obtained by using an order filter. That is to say,the equivalent gain error is less than 0.05dB,or the equivalent phase error is less than 0.3 degree. The hardware implementation is relatively simple.