Electronic Design

SiGe:C Process Improves RF Device Performance

A recently perfected blend of silicon, germanium, and carbon (SiGe:C) is now available to make RF circuits even better. Motorola has announced its first standard product using this new semiconductor material. Complete with an integrated bypass switch, the MBC13720 low-noise amplifier (LNA) provides high gain and low noise for microwave signals.

Cell phones and other RF technologies are pushing silicon to its frequency limit. As feature sizes have steadily declined, bipolars and MOSFETs have extended their reach well into the gigahertz region. But the need for higher gains and lower noise with less current drain in the microwave region has forced most semiconductor vendors to re-examine their options in semiconductor materials and processes.

Gallium arsenide (GaAs) has been used for years to make high-gain, low-noise transistors for receiver front ends. SiGe has also demonstrated its effectiveness in the microwave region. Indium phosphide (InP) is beginning to show up in ultra-high-speed optical circuits for 40-GHz data rates. Motorola has added carbon to the mix, creating a SiGe:C process that further improves RF performance.

The company has successfully created a heterojunction bipolar transistor (HBT) with a transition frequency (fT) of 45 GHz and a maximum frequency (fMAX) of 90 GHz with this material. These bipolars are combined with standard CMOS to produce a new 0.35-┬Ám biCMOS process that's ideal for RF circuits.

This process was developed by Motorola's DigitalDNA Laboratory in cooperation with Germany's Innovations for High Performance Microelectronics, formerly known as the Institute for Semiconductor Physics. It addresses the needs of the wireless, broadband communications, networking, and multimedia markets.

The MBC13720 LNA operates over the 400- to 2400-MHz range, suiting 1900-MHz cell phones as well as applications in the 900- and 2400-MHz ISM bands. The overall gain varies with the operating frequency and mode, from 21 dB at 900 MHz down to 11.5 dB at 2400 MHz. The noise figure is a low 1.35 dB at 900 MHz and only 1.55 dB at 2400 MHz. The integrated bypass switch saves many external components and greatly reduces the insertion loss associated with a bypass switch from 4 to 5 dB to less than 3 dB. The MBC13720 has a two-bit input control, giving it four modes: standby, bypass, high IP3, and low IP3.

The LNA operates from a supply in the 2.5- to 3-V range. It's housed in a plastic 6-pin SOT-363 package. The MBC13720 will be available in production quantities in August. The price is expected to be $1.50 each in 10,000-unit quantities. For more information, contact Motorola at (800) 441-2447 or (480) 413-4991, or go to www.motorola.com/wireless-semi.

TAGS: Components
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