G = compressed power gain of the loop amplifier.

F = noise factor of the loop amplifier.

K = Boltzmann's constant.

T = temperature in kelvins.

P0 = carrier power level (in watts) at the output of the loop amplifier.

fm = carrier offset frequency in Hz.

Ql(= <t/\,r. < = loaded Q of the resonator in the feedback loop.

ctH and aE = flicker noise constants for the resonator and loop amplifier, respectively.

Fig 2A shows the noise spectrum that can be expected at this frequency range from a high-quality VCO. The performance of the oscillator, when part of the PLL, inside the PLL bandwidth, is determined by the noise contribution of the reference frequency, the phase detector, the dividers and other items in the loop. Outside the loop bandwidth, the phase noise is determined only by the quality of the oscillator, which explains the need to build a high-quality

1 Notes appear on page 11

Fig 2—A shows the measured phase noise of a "high end" ceramic-resonator-based VCO. B shows the predicted SSB phase noise of the multidiode oscillator operating from 75 to 105 MHz as shown above. Measurements and predictions agree within 1 dB. The flicker corner frequency can be observed. The good performance is due to the multiple parallel diodes and the limiting Schottky diode. This oscillator is used in the Rohde and Schwarz Model ESN test receiver.

C In dBc'Hz

Thu Fmb 03 16158102 1996

C In dBc'Hz

Thu Fmb 03 16158102 1996

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