Communication systems rely on stable oscillators to maintain phase-locked conditions and ensure transmitted data integrity. Many third- and later-generation systems incorporate multiple narrowband coupled-resonator oscillators (NCROs) to cover their required bandwidths. As an alternative, however, the new series of voltage-controlled oscillators (VCOs) from Synergy Microwave (Paterson, NJ)

can provide the equivalent bandwidth and tuning range of multiple NCROs, with the low phase noise and minimal system phase hits associated with narrowband CROs. The layout results in a dynamically tunable distributed coupled-resonator oscillator (DCRO) with high time-averaged loaded Q that is less prone to phase hits than conventional CROs. The new surface-mountable VCOs are currently available in bands from less than 1 GHz to 6 GHz, and can be designed for custom bands without the high non-recurring-engineering (NRE) costs associated with custom NCROs.

NCROs feature high quality factor (Q) and low phase noise. But they are limited in operating temperature range, tuning range, and susceptible to phase hits (which can be described as sudden, uncontrollable random changes in an oscillator's phase). Phase hits are often caused by microphonic vibrations that can trigger sudden shifts in an oscillator's phase and frequency. To overcome the limitations of NCRO sources, the new DCROs (Fig. 1) incorporate an innovative topology which is designed to minimize phase hits without sacrificing phase noise and wide tuning range. The novel topology acts as a Q-multiplier, based on cascaded regenerative noise filtering of the oscillator active-device emitter and feedback. The DCRO circuit topology and layout are selected to support uniform negative resistance over wide tuning ranges (Fig. 2).

A noise feedback circuit is included in the patent-pending topology to reduce thermal drift over a wide temperature range (the operating temperature range for the DCROs is −40 to +85°C). DCROs, which can generate frequencies to about 5 GHz, can also be made small compared to NCROs and surface-acoustic-wave (SAW) oscillators, especially for frequencies below 1 GHz.

New Technology
Model DCRO 245305 is an example of this new technology (Fig. 3). This model operates from 2450 to 3050 MHz with +5 dBm typical output power (see table). It tunes with nominal voltages from 0 to +25 VDC and has tuning sensitivity of 15 to 40 MHz/V. The phase noise is typically −107 dBc/Hz offset at 10 kHz from the carrier and −127 dBc/Hz offset 100 kHz from the carrier. Minimum harmonic suppression is −10 dBc while the bias requirements are nominally 30 mA at +8 VDC. Frequency pulling is 10 MHz maximum for a 1.75:1 VSWR while frequency pushing is 6 MHz/V maximum. This oscillator is supplied in a surface-mount package measuring just 0.5 × 0.5 in.

Additional standard models include: the DCRO 190240, which operates from 1950 to 2450 MHz; the DCRO 255315, which tunes from 2550 to 3150 MHz; the DCRO 287330, which tunes from 2875 to 3300 MHz; the DCRO 300345, which operates from 3000 to 3450; and the DCRO 315350, which tunes from 3150 to 3500 MHz. In addition, customer-specified frequencies are available from UHF through 5 GHz.

Dependable Performance
The DCRO oscillators suffer minimal phase hits over wide tuning ranges and with temperature extremes. As a result, they provide dependable performance in modern digitally modulated wireless communications systems, such as cellular networks, wireless local-area networks (WLANs), and terrestrial point-to-point and point-to-multipoint radio links. Their stable performance with tuning frequency and temperature also makes them series contenders for use with phase-locked-loop (PLL) synthesizer applications. The oscillators are supplied in REL-PRO surface-mount packages, lead free and small size measuring 0.5 × 0.5 × 0.22 in. Synergy Microwave Corp. 201 McLean Blvd., Paterson, NJ 07504; (973) 881-8800, FAX: (973) 881-8361, e-mail: sales@syner gymwave.com, Internet: www.synergymwave.com.