A comparison of D flip-flop and DDS quadrature LOs for a fast frequency-hopping synthesizer.

摘要

The objective of this thesis is to identify the advantages of using a quadrature local oscillator (LO) in a fast frequency-hopping synthesizer and to compare two quadrature oscillator designs.;A frequency synthesizer is a phase-locked loop (PLL) designed for high-speed data transmission. In designing frequency synthesizers, a significant tradeoff between output frequency step size and channel hopping time occurs. By traditional design methods, it is not possible to simultaneously obtain small step size and fast channel hopping capabilities. The insertion of a quadrature LO in a particular location of the synthesizer PLL eliminates the design tradeoff, but introduces an image signal in the PLL that must be attenuated for the loop to lock. A method of image cancellation using a quadrature LO and quadrature RF signals is presented.;Two complete quadrature LO designs are presented and compared. The delay (D) flip-flop quadrature LO consists of an input oscillator and two D flip-flops configured to produce quadrature outputs. The direct digital synthesizer (DDS) quadrature LO consists of a numerically-controlled oscillator (NCO) and dual digital-to-analog converters (DAC). The two designs differ in circuit size, cost, complexity, and performance. The theory of both quadrature LOs is discussed and the complete circuit designs are presented. The designs are fabricated and tested and an evaluation of the test results indicates which quadrature LO design is best for given frequency synthesizer specifications.