Oscillators can be built from many different types of resonators. Perhaps one of the most reliable for high-frequency applications is the yttrium-iron-garnet (YIG) sphere, the heart of YIG-tuned oscillators. At one time, such tunable sources were relatively large and heavy. But with new models such as the second-generation MLTO-Series of permanent-magnet YIG oscillators from Micro Lambda Wireless (www.microlambdawireless.com), these microwave oscillators take up no more space than a small coin on a printed-circuit board (PCB). Diminutive oscillators in the MLTO Series are supplied in tiny TO-8 housings and are available in selected tuning ranges from 3 to 13 GHz.

The MLTO-Series TO-8 permanent-magnet YIG oscillators can be constructed with pin or coaxial connectors (see figure). They are designed for operating voltages of +8 and -5 VDC and deliver consistent performance across operating (case) temperatures from 0 to +65°C. The oscillator series currently includes models MLTO-50365 for use from 3.0 to 6.5 GHz, MLTO-50409 for use from 4.0 to 9.0 GHz, and MLTO-50613 with a tuning range of 6.5 to 13.0 GHz. Each oscillator has a free-running frequency, such as 4.7 GHz in the MLTO-50365, which is varied as current is applied to the permanent-magnet resonant cavity with its YIG sphere.

Each of the models provides at least +10 dBm output power across its tuning range, with worst-case power variations contained within a 3-dB window. Frequency drift over temperature is a maximum of ±25 MHz in the two lower-frequency oscillators and only ±20 MHz in the MLTO-50613. This performance across temperature comes without need for an additional heater.

As an example of the large performance available from these small oscillators, model MLTO-50365 exhibits harmonics of -12 dBc or better and spurious levels of -70 dBc or better from 3.0 to 6.5 GHz. It has phase noise of -100 dBc/Hz or better offset 10 kHz from the carrier, improving to -128 dBc/Hz or better offset 100 kHz from the carrier, and typically -130 dBc/Hz offset 100 kHz from the carrier. It suffers typical pulling of frequency of a mere 2 MHz into a load with 12-dB return loss, and typical pushing with power supply of 2 MHz/V at +8 VDC.

As with the other oscillators in the series, the MLTO-50365 has a main tuning coil and a frequency-modulation (FM) coil for modulation and phase-locking purposes when used in a frequency synthesizer design. The main coil sensitivity is typically 9 MHz/mA while the FM coil sensitivity is 150 kHz/mA. The MLTO-50365 YIG oscillator draws a maximum of 60 mA from +8 VDC and 20 mA from -5 VDC.

Moving up in frequency, model MLTO-50409 tunes from 4.0 to 9.0 GHz, with harmonic and spurious levels that meet or exceed -12 and -70 dBc, respectively. The phase noise is -100 dBc/Hz or better offset 10 kHz from the carrier and -128 dBc/Hz or better offset 100 kHz from the carrier, with typical phase noise of -130 dBc/Hz offset 100 kHz from the carrier. Frequency pulling is typically 2 MHz into a 12-dB-return-loss load while frequency pushing is typically 2 MHz/V with supply variations centered at +8 VDC. The main tuning coil sensitivity is typically 15 MHz/mA while the FM tuning coil sensitivity is typically 150 kHz/mA. Model MLTO-50409 draws maximum power of 60 mA from a +8-VDC supply and 20 mA from a -5-VDC supply.

The highest-frequency model currently in the series, the MLTO-5613, operates from 6.5 to 13.0 GHz, with similar tuning characteristics as the other two units. It also exhibits harmonics of -12 dBc or better and spurious performance of -70 dBc or better. The phase noise is at least -98 dBc/Hz offset 10 kHz from the carrier and at least -123 dBc/Hz offset 100 kHz from the carrier, with typical phase noise of -125 dBc/Hz offset 100 kHz from the carrier. The MLTO-5613 operates on 60 mA at +8 VDC and 15 mA at -5 VDC.

This second generation of these tiny TO-8 YIG oscillators benefits from lessons learned in permanent-magnet construction and TO-8 packaging and enhanced performance from low-noise silicon-germanium (SiGe) transistors as the active devices. The TO-8 packages are only 0.5 in. tall with 0.675-in. diameter, facilitating attachment to tight spots on PCBs. Extended temperature models to +85°C are available for all models. P&A: 6 wks. ARO. Micro Lambda Wireless, Inc., 46515 Landing Pkwy., Fremont, CA 94538; (510) 770-9221, FAX: (510) 770-9213; www.microlambdawireless.com.