A 50 V LDMOS Power Transistor for High Impedance Mismatch Applications

Freescale Semiconductor has developed a RF LDMOS power transistor designed for operation from 1.8 to 600 MHz and optimized for use under the potentially-destructive impedance mismatch conditions encountered in applications such as CO₂ lasers, plasma generators and magnetic resonance imaging (MRI) scanners. The new MRFE6VP61K25H FET is the first 50 V LDMOS transistor to deliver its full-rated output power of 1250 W CW into a load after withstanding a Voltage Standing Wave Ratio (VSWR) of 65:1.

All solid-state RF power amplifiers operate most effectively when the greatest amount of power generated by their RF power transistors reaches the antenna. Under ideal conditions, this would result in a VSWR of 1:1, with all of the generated power reaching the load via the transmission line with none reflected back to the amplifier. VSWR levels in most applications rarely exceed 2.5:1 and most RF power transistors regardless of their technology can handle a VSWR of 5:1 to 10:1.

However, RF power amplifiers used to ignite CO₂ lasers and plasma generators, or to create an electromagnetic field in MRI systems, briefly encounter conditions in which nearly all of their generated power is reflected back to the amplifier. These extreme conditions present challenges for most RF power transistors.

The MRFE6VP61K25H LDMOS FET is designed primarily to serve these demanding applications and offers the ability to produce its full 1250 W of CW output power after withstanding a VSWR as high as 65:1 at all phase angles. It is the only 50 V LDMOS transistor commercially offered with this level of performance to date.

Freescale Semiconductor,
Austin, TX
(800) 521-6274,
www.freescale.com/rfpower
RS No. 303