Modern radio astronomy with multiple antennas requires large amounts of computations in order to correlate the data from different telescopes and to reduce noise. The correlation of these data is currently done using programmable logic blocks, which are slow and power ineflcient. In this paper, an ASIC solution is presented to the problem, which gives large improvements to the previous solution in terms of speed and power consumption. The design is based on comprehensive studies of full-adders and flip-flops for maximum powereficiency. Also presented, is a complete testing methodology for the new digital correlator.