A Low-Cost Carry Look-Ahead Adder for Flying-Adder Frequency Synthesizer

This paper presents a compact and cost-effective carry look-ahead adder for fractional accumulator in flying-adder frequency synthesizer. The fractional accumulator design is critical in flying-adder frequency synthesizer. Conventional carry look-ahead adder is replaced with a two-bit carry look-ahead adder and another D flip-flop to serve as basic module to construct the adder. The power consumption is approximately 59% of conventional approach. The proposed method eliminates the large gate area in conventional method that can greatly reduce the hardware cost. Measurements show that the output frequency error is less than 3 ppm.