Designers of cellular phones can now get the output power and efficiency of gallium-arsenide RF power amplifiers without the need for a separate negative voltage supply - using two new chips introduced by Motorola. That's because the new Motorola RF power amplifiers have a negative voltage generator function integrated right on the chip.

Motorola engineers have designed the chips using an RF rectification method to generate the negative voltage, which eliminates spurious outputs often seen in designs that use a separate negative voltage supply - allowing the Motorola units to transmit "spur-free" signals. The units also include a Gate-Drain switching function which connects the negative voltage to the gate before the positive supply is connected to the drain - protecting the devices from any over current situation.

The two devices, types MRFIC0919 and MRFIC1819, are advanced three-stage gallium-arsenide (GaAs) Integrated Power Amplifiers (IPAs) that use these two key on-chip functions - the negative voltage generator and the Gate-Drain switching function - to lower system and manufacturing costs by simplifying the design process and reducing total parts count.

Because the new MRFIC0919 and MRFIC1819 are designed using a depletion mode MESFET process in GaAs, they exhibit the best tradeoff of gain, efficiency, cost and manufacturability available today. With the addition of the integrated negative voltage generator, these IPAs provide the best of both worlds, having high performance and efficiency with single supply operation. The on-chip negative voltage generator is implemented using RF rectification, preventing the generation of any spurious output signals.

The MRFIC0919 and MRFIC1819, operate at 900 MHz or 1.8 to 1.9 GHz respectively, and are ideal for use in GSM or PCS cellular phones. The MRFIC0919 3.6 V, 900 MHz IPA is capable of providing a peak output power of 3.0 W, and is designed to be used in 2.0 W GSM900 cellular phones. The MRFIC1819 1.8/1.9 GHz IPA is capable of providing a peak output power of 2.0 W, and is designed specifically for use in 1.0 W DCS1800 and PCS1900 cellular phones.

"The new MRFIC0919 and MRFIC1819 represent the second generation of GaAs integrated power amplifiers on our roadmap for 1998 and beyond," said Michael Civiello, Director of Marketing for Motorola's Wireless Subscriber RF/IF Division. "These products incorporate enhanced features and smaller surface mount packages which have not been available previously. We are also in the process of doubling our GaAs capacity - to give us strong leadership in manufacturing as well."

Both devices are packaged in a new high power, low profile surface mount package, a special 16-pin TSSOP with a backside metal contact. The package provides excellent thermal and electrical performance through this solderable metal contact. This large contact area is physically connected to ground of the MRFIC0919 and MRFIC1819, and is soldered to the pc board using the same standard reflow process used for other surface mount components, simplifying the system design and production processes. The high thermal conductivity of this special TSSOP-16EP package allows these devices to provide RF output power of at least 32 dBm, without consuming excessive board space. Click here for Motorola Wireless

Motorola certainly seems to have a handle on the problems of RF power amplifiers for consumer products, as it well should, and these parts overcome two major problems in one step. Providing the negative bias for the GaAs power amplifiers is another OEM design chore that has just "had to be done" to get through the process, but those designs nearly always caused spuriae; the RF rectification technique used here by Motorola fixes that completely. (And how does it all get started so that there is some RF to be rectified? Like a switching power supply it all turns on with noise?) The second problem has been to provide the care needed in getting bias before the drain supply (I nearly wrote plate!) is applied and that is taken care of here with the gate-drain switch.

Also, Motorola leave power in hand with these designs which should increase the life of the parts when used in their intended 2 W/1 W applications.

As noted the MRFIC0919 and MRFIC1819 are in Motorola's TSSOP-16EP with the metal, solderable contact on the backside and both are priced at $5.20 in 10,000 piece lots. The parts are sampling now.