LDMOS Transistor Provides High Efficiency in Doherty Config

I have more information on a breakthrough in high power UHF solid-state amplifier efficiency. Freescale announced last Friday that its MRFE6VP8600H LDMOS RF power transistor can use up to 15 percent less power than previous generations of LDMOS power transistors and can handle high peak to average power ratios present in OFDM. It is extremely rugged, capable of handing VSWR of greater than 5:1 at all phase angles.

The most interesting part of the announcement was this statement was that the new transistor could deliver 125 watts of linear power (more than 600 watts of peak envelope power) throughout the entire broadcast band. It noted that there was "exceptional efficiency," with "typically" 30 percent at 860 MHz, and as much as 45 percent "when employed in a Doherty configuration."

What's a Doherty configuration?

You may remember that Doherty "high-efficiency amplifier" technology was first used in AM transmitter, beginning in the 1930s. I did a little research and found this old technique is finding application in digital transmitter systems that require high peak-to-average ratios, and has been in use at microwave frequencies for several years. For details on one application of Doherty amplifier technology for digital systems see A High Efficiency Doherty Amplifier with Digital Predistortion for WiMAX from High Frequency Electronics.

This is probably the breakthrough that I was hearing about prior to IBC, although I have yet to see any reports from manufacturers describing a UHF transmitter using a Doherty amplifier that's capable of 45 percent efficiency.

Last week I reported on Thomson's new solid-state transmitter with improved efficiency. Rohde and Schwarz also introduced a new solid-state transmitter line that's more compact and offers higher efficiency. For details on that, see the TV Technology on-line article Rohde & Schwarz THU9 Claims Most Efficient Solid State Transmitter Title.

Doug Lung

Doug Lung is one of America's foremost authorities on broadcast RF technology. As vice president of Broadcast Technology for NBCUniversal Local, H. Douglas Lung leads NBC and Telemundo-owned stations’ RF and transmission affairs, including microwave, radars, satellite uplinks, and FCC technical filings. Beginning his career in 1976 at KSCI in Los Angeles, Lung has nearly 50 years of experience in broadcast television engineering. Beginning in 1985, he led the engineering department for what was to become the Telemundo network and station group, assisting in the design, construction and installation of the company’s broadcast and cable facilities. Other projects include work on the launch of Hawaii’s first UHF TV station, the rollout and testing of the ATSC mobile-handheld standard, and software development related to the incentive auction TV spectrum repack.
A longtime columnist for TV Technology, Doug is also a regular contributor to IEEE Broadcast Technology. He is the recipient of the 2023 NAB Television Engineering Award. He also received a Tech Leadership Award from TV Tech publisher Future plc in 2021 and is a member of the IEEE Broadcast Technology Society and the Society of Broadcast Engineers.