Freescale Designs LDMOS RF Power Transistors for Use with Doherty Amplifiers

June 7, 2007 // Published as a news service by IHS

The Doherty architecture presents design challenges due to conflicting requirements for both high efficiency and high linearity.

According to Freescale, the transistors were designed specifically to address these challenges and enable creation of base stations that consume less power than those using traditional transistor designs.

Two of the devices operate in the 865 MHz to 960 MHz band, two in the 1,930 to 1,990 band, and three in the 2,110 to 2,170 MHz band, covering popular cellular, personal communications services (PCS) and WCDMA frequencies.

The devices and their features include:

• The MRFE6S9205H/HS: 865 MHz to 960 MHz, 58 watt (W) average output power, 20.5 decibel (dB) gain, 34% efficiency, adjacent channel power ratio (ACPR) of -38 decibels relative to carrier (dBc) (5 MHz offset, 3.84 MHz channel).
• The MRFE6S9135H/HS: 865 MHz to 960 MHz, 39 W average output power, 20 dB gain, 34.5% efficiency, ACPR of -38 dBc (5 MHz offset, 3.84 MHz channel).
• The MRF6S19200H/HS: 1,930 MHz to 1,990 MHz, 58 W average output power, 17.2 dB gain, 29.5% efficiency, ACPR of -38 dBc (5 MHz offset, 3.84 MHz channel).
• The MRF6S19140HR3/HSR3: 1,930 MHz to 1,990 MHz, 29 W average output power, 16 dB gain, 27.5% efficiency, ACPR of -51 dBc (885 kHz offset, 30 kHz channel).
• The MRF7S21170HR3/HSR3: 2,110 MHz to 2,170 MHz, 50 W average output power, 16 dB gain, 31% efficiency, ACPR of -37 dBc (5 MHz offset, 3.84 MHz channel).
• The MRF6S21190HR6: 2,110 MHz to 2,170 MHz, 54 W average output power, 16.4 dB gain, 30% efficiency, ACPR of -38 dBc (5 MHz offset, 3.84 MHz channel).
• The MRF6S21140HR3/HSR3: 2,110 MHz to 2,170 MHz, 30 W average output power, 15.5 dB gain, 27.5% efficiency, ACPR of 41 dBc (5 MHz offset, 3.84 MHz channel).

Available on tape and reel, all of the devices operate from a +28 volt (V) supply and feature electrostatic discharge (ESD) protection. According to Freescale, they are designed to handle a 5:1 voltage standing wave ratio (VSWR) without damage and are housed in restriction of hazardous substances- (RoHS-) compliant, high-thermal-conductibility air-cavity ceramic packages.

"The Doherty amplifier's inherent high efficiency can help reduce a base station's annual power consumption when compared to other amplifier types, thus allowing Freescale to deliver to our service provider customers the least costly product to operate," said Gavin P. Woods, vice president and general manager of the Freescale RF Division.

Source: Freescale Semiconductor.