| 摘要 |
A pulse voltage controlled oscillator running at four times the desired frequency f triggers a two stage shift register which has an inverted feedback loop. The outputs of both stages are similar square waves of frequency f, and they are set at a 90 DEG phase difference of each other. Since a square wave of frequency f possesses only harmonics of odd orders, a low pass filter which rejects 3f can admit a square wave frequency varying between f and 3f. A pair of identical filters coupled to the outputs of respective shift register stages provide output signals of corresponding frequency which are 90 DEG out of phase. For a frequency range extending between 3f and 9f, another pair of filters are required, etc. Additional shift registers may be added to the two stage shift register to provide output signals with a phase shift equal to the corresponding fraction of 360 DEG .
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