LDMOS Power Transistors Drive 200 W to 1300 MHz (.PDF Download)

Power transistors for RF/microwave applications exploit a range of different technologies, including substrate materials like the tried-and-true gallium arsenide (GaAs) to the somewhat more recent and intriguing gallium nitride (GaN). Still, silicon transistor substrates remain the longest-running foundations for high-power RF/microwave transistors in both commercial and military applications.

Among those silicon devices, lateral diffused metal-oxide-semiconductor (LDMOS) transistors have demonstrated good reliability with high performance levels. And when new silicon LDMOS power transistors arrive, they provide further options for RF/microwave power-amplifier designers faced with the challenges of trying to optimize performance parameters such as output power, gain, and efficiency over a given bandwidth.

A pair of recently released, +28-V dc silicon LDMOS power transistors from Polyfet RF Devices pack a great deal of punch for power amplifiers through about 1.3 GHz. Models LA2541 and LS2541 are impedance-unmatched silicon LDMOS transistors available in two slightly different push-pull packages. Each transistor is capable of as much as 200 W output power (at 1-dB compression), and versatile enough to drive continuous-wave (CW) or pulsed input waveforms with high efficiency and effective thermal management.

Depending on how they are source and load matched, the two packaged transistors (see figure) can be used in broadband or narrowband applications through 1300 MHz and deliver high output power with high gain and efficiency. Each device employs back-to-back gate diodes for enhanced electrostatic-discharge (ESD) protection. Their rugged metal-ceramic packages feature clearly marked and easily accessible gate, drain, and source connections to simplify installation into a circuit board for an amplifier designer.