A low power correlator for CDMA wireless systems

The complex valued matched filter correlators consume maximum power in the DS/SS CDMA receivers. These correlators accumulate 1024 samples lying in the range -7 to +7. This accumulation needs 3 data bits, 1 sign bit and 10 extra bits for overflow. Hence, the correlator can be implemented as a cascade of 4-bit full adder and a 10-bit incrementer. As a ripple carry adder (RCA) consumes the least power among all the existing adder architectures, we have implemented the 4-bit adder as a RCA. Previous incrementers were implemented as ripple counters. In this paper we propose a novel incrementer which is faster than a ripple counter based incrementer. Hence, it can be operated at a reduced voltage resulting in considerable power reduction. The incrementer is implemented using multiplexers, AND gates and TSPC registers. The ripple-counter correlator and the proposed incrementer correlator were laid out in MAGIC using 0.5 μ CMOS technology followed by power estimation using HSPICE. It is shown that the proposed architecture requires 50% less power than a ripple counter based design.