Ultra Low Phase Noise 1 GHz OCXO

Abstract

Modern radar equipment, commercial and defense communication systems, point-to-point and point-to-multipoint microwave digital radios, microwave sources require excellent stability, extremely low phase noise frequency sources in UHF band. Existing HF OCXO at 100 MHz can achieve -90 dBc/Hz phase noise at 10 Hz offset from the carrier and -125 dBc/Hz at 100 Hz offset. The goal of this work was to create a 1 GHz OCXO with temperature stability performance of SC-cut (1E-8 or better), with the similar to 100 MHz phase noise close to the carrier, and noise floor reaching -150 dBc/Hz, while providing +7 dBm of output power. The goal was accomplished by integrating in a small SMD package (20 x 25 mm), or Europack (36 x 25 mm) high performance, low frequency, SC-cut reference OCXO, low noise off-the-shelf Phase Lock Loop (PLL) IC, and ultra low noise 1 GHz VCXO. Reference OCXO implemented in DIP 14 compatible format was described in previous papers. The key solutions for this development were optimization of the phase noise performance both close to the carrier frequency and on the noise floor, and design of a VCXO. The VCXO is based on a 3rd overtone 200 MHz AT-cut crystal resonator with relatively high Q, passive band-pass filter, tuned on the fifth harmonic of the 200 MHz VCXO, and a free-running L-C oscillator, which is injection locked to the above mentioned fifth harmonic of the VCXO. Dual stage multiplication of the lower frequency VCXO (100.00 MHz, and 111.111 MHz), and additional measures of phase noise reduction far away from the carrier were also investigated.