Low phase noise oscillator frequency control apparatus and metho

Details Low phase noise oscillator frequency control apparatus and metho Low phase noise oscillator frequency control apparatus and metho

1993-10-14

1995-05-09

Coles, Sr., Edward

Pulse or digital communications

Synchronizers

Phase displacement, slip or jitter correction

331 18, H03L 700, H03D 324

Patent

active

054147417

ABSTRACT:
A low phase noise third order phase lock loop which can track and eliminate microphonic disturbances and phase hits. The PLL utilizes a third order loop filter which incorporates two integrators. These two integrators, when coupled with the integration which occurs at the voltage control input of the voltage controlled oscillator within the PLL yield an open loop transfer function with a --18 dB/octave rolloff over a band of frequencies which at least encompasses the spectral content of the microphonic or phase hit phase noise disturbance to be eliminated. The open loop gain of the phase lock loop must be set high enough such that the phase lock loop does not oscillate and such that the loop converges and locks. The integrators are implemented with operational amplifiers with RC feedback networks. The values of the components in the RC feedback networks set the frequencies of two zeroes in the transfer function. The frequencies of these zeroes are set by proper selection of the R and C values to cause a change in slope of the open loop gain frequency response curve at the frequency of the zeroes from the -18 dB/octave rollof to a -6 dB/octave rolloff at the frequency of the zeroes. This causes the phase angle of the open loop PLL transfer function to be more positive than -180 degrees at the frequency at which the open loop gain magnitude frequency response curve falls to unity gain thereby achieving conditional stability. The open loop gain of the PLL is set such that the -18 dB/octave rolloff of the frequency response does not result in a gain of unity until a frequency is reached which is above the highest expected frequency deviation of the carrier caused by microphonic disturbances or phase hits. In the preferred embodiment, the gain is set high enough that the -18 dB/octave rolloff of the open loop gain frequency response extends over at least two decades and extends up to 10 kHz which encompasses substantially all the spectral content of the microphonic disturbance caused by package resonance which sources the phase noise to be eliminated.

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