IF-THEN Adder Application in Online DALUT Implementation

Abstract

This paper presents the application of a proposed if-then rule based adder in implementing distributed arithmetic online lookup table (DALUT). The online DALUT development and implementation is a continuation of our previous work where we proposed this idea and use it in designing finite impulse (FIR) filter. In our LUT architecture we have been able to overcome the major disadvantage of the basic DA architecture reported as the exponential growth of the LUT size with the number of input variables. The if-then adder was proposed in another work where it shows an efficient performance when compared with the well known ripple carry adder (RCA) and the carry lookahead adder (CLA). The online DALUT with the if-then adder was applied in designing 70-tap finite impulse response pulse shaping filter and some other different order FIR filters. The design was coded with Verilog hardware description language (verilog HDL) and synthesized using the Xilinx technology after being simulated with ModelSim 7.5g. The synthesis report shows that the design preference when using the if-then adder more efficient than in the case of the RCA and CLA adder. The maximum frequency reached with the design using the if-then adder was 85.095MHz, whereas, when using CLA and RCA adders it 77.936MHz and 77.042MHz respectively. Finally the design has been successfully downloaded to Virtex-II FPGA fg456 and tested with the TLA5201 logic analyzer.