High precision, low phase noise synthesizer with vector modulator

摘要

An apparatus for generating a modulated signal which includes a modulator (4) operative for receiving a first signal (3) and input data signals (5), and modulating the first signal (3) in accordance with the input data signals (5) so as to produce a modulated reference signal; a first frequency divider (6) coupled to the modulator (4) output, operative to reduce the frequency of the modulated reference signal by a predetermined factor; a signal generator (10) operative to produce a second signal; a first mixer (8) having a first input coupled to an output of the first frequency divider (6) and a second input coupled to the output of the signal generator (10). The first mixer (8) operates to frequency translate the modulated reference signal by an amount equal to the frequency of the second signal. The signal generator (10) of the present invention contains a direct digital synthesizer (22) coupled to a second phase lock loop (26) which operates to up-convert the output signal of the direct digital synthesizer (22) to the microwave region. The feedback network of the second phase lock loop (26) utilizes frequency translation to down-convert the output signal in order to close the loop. <IMAGE>