The invention discloses a
digital down converter which comprises a
signal input end which is used for receiving input signals and a
signal output end which is used for outputting signals, wherein, N independent operation branches are arranged between the
signal input end and the signal output end; each operation
branch comprises an extractor the extraction factor of which is N, a multiphase
branch mixer which is constructed according to an N-phase digital mixer, and a multiphase
branch filter which is constructed according to an H(z) expression of an N-phase
digital filter which are connected with each other in order; input ends of extractors of various operation branches are coupled with the signal input end; outputs of branch filters of various operation branches are outputted to the signal output end through addition by an
adder; an i operation branch corresponding to the input signals comprises i-1
clock cycle time delays; N and i are all natural numbers, and i is more than or equal to 1 and less than or equal to N. Arithmetic speed of each operation branch is lowered to be 1 / N of the prior arithmetic speed, and modules for improving the arithmetic speed do not exist because each operation branch is completely independent, thereby
processing difficulty of a
system is reduced.