While choosing the best power-amplifier (PA) transistors for a cell-phone basestation is challenging, the drivers for PAs are just as tough to select. Most current designs use LDMOS PAs as well as drivers.
RF Micro Devices' latest line of gallium-arsenide heterojunction bipolar transistors (GaAs HBTs) gives designers another option. Created particularly for driver service, these devices let designers craft highly linear as well as efficient drivers at reduced cost. They're also a good fit as final amplifiers for lower-power applications like picocells.
The RF3800 line of GaAs HBT drivers covers all common RF bands from 450 MHz to 2.2 GHz. The power gain is in the 14- to 20-dB range with an output power of 36 dBm or more (approximately 4 to 7 W). In linear class AB service, efficiency runs about 35%. Third-order intercept is at 38 dBm. The devices operate from 8 V dc, with a typical quiescent current of about 500 mA.
Packaging consists of a low-cost but thermally efficient enhanced aluminum-nitride (AlN) LCC-8 housing. It can bring up to a 30% cost savings over ceramic metal flange LDMOS packages. Samples of the devices are available now, with full production coming next month. Pricing runs less than $10 in quantities of 5000 or more.