Broadband Amps Boost Linear Power To 26.5 GHz

March 17, 2005
These lines of efficient, high-power amplifiers cover frequency ranges as broad as 10 MHz to 26.5 GHz in support of emerging broadband-communications applications.

Microwave amplifiers were once designed in the bands favored by communications or military systems integrators, such as 2 to 4 GHz and 2 to 8 GHz. The influence of wireless applications changed those bands of interest to more narrowband coverage, such as the 800-to-900-MHz area of cellular systems, the 1800-to-2100-MHz range of Personal Communications Systems (PCS), and the 2.4- or 5-GHz bands of wireless local-area networks (WLANs).

However, an increasing number of military and commercial communications, as well as test and measurement applications, cover multiple octaves and require amplifiers with broadband, linear performance. To address this need, iTerra Communications (Palo Alto, CA) has introduced a family of die and packaged MMIC amplifiers as well as custom amplifier modules that deliver as much as 1 W CW output power over bandwidths as wide as 10 MHz to 26.5 GHz.

While typical wireless communications bands cover only a few hundred megahertz, other services either proposed or in development can benefit from devices that cover broad bandwidths. The advantage is derived from being able to use a single device rather than multiple devices to cover the entire operating bandwidth of a system that must accommodate multiple services. In addition, military systems, including communications, surveillance, electronic warfare, and electronic countermeasures commonly cover frequencies from HF through millimeter wavelengths. Microwave and optical test equipment has this requirement as well, since it is typically designed to make measurements contiguously from DC or near DC through millimeter wavelengths. The iTerra devices provide this capability in a single package with high output power and gain, and the modules build on this device technology to provide even higher RF power and gain.

The iTerra devices are GaAs pseudomorphic-high-electron-mobility-transistor (pHEMT) integrated circuits (ICs) formed with advanced molecular-beam-epitaxy (MBE) technology, Ti-Pt-Au gate metalization, and polyimide scratch protection. Full silicon-nitride passivation is provided over the active area and air bridges of the devices, which ensures high reliability and longevity. The latest MMIC pHEMT die include the iT2008 and iT2009 GaAs MMIC traveling-wave amplifiers. The iT2008 delivers as much as 1 W CW over a bandwidth extending as low as 10 MHz through 26.5 GHz. The RF output power ranges from +30 dBm (1 W) at 7 GHz, to more than +29 dBm at 15 GHz, and more than +25 dBm at 26.5 GHz.

The standard operating frequency range of the iT2008 GaAs MMIC amplifier is 2 to 26.5 GHz. However, the low end of its frequency range can be extended to 10 MHz with the use of external coupling capacitors. The amplifier typically operates with bias conditions of +9 VDC at 350 mA and has DC-coupled inputs and outputs. The gain is typically 10 dB with ± 1-dB gain flatness across the operating frequency range. Like the iT2008, the iT2009 provides saturated output of +30 dBm from 2 to 7 GHz, greater than +29 dBm at 15 GHz, and more than +25 dBm through 26 GHz (Fig. 1). However, it offers twice the gain (20 ± 1 dB). The device is biased to obtain high linearity, while drawing only 5.4 W from its +9-VDC supply. Like the iT2008, it incorporates on-chip input and output blocking capacitors.

Other MMIC amplifiers in the family include the iT2001P and iT2007 that have bandwidths as broad as 10 MHz to 22 GHz, power output to 1 W, and gain as high as 13 dB. The iT2007 has the broader bandwidth of the two devices. It achieves power-added efficiency of greater than 12 percent to 12 GHz and greater than 10 percent to 18 GHz. The iT2007 is typically biased at a saturated drain-source current (IDSS) of 40 percent for the best combination of power and linearity. Like the iT2008, the standard iT2007 covers 1 to 22 GHz. However, the input and output ports of the iT2007 are DC coupled, so designers can extend the low-end frequency coverage to 10 MHz using blocking capacitors (Fig. 2). The iT2007 provides saturated output power of +30 dBm to 6 GHz and greater than +28 dBm to 18 GHz. The small-signal gain is typically 7 dB with ±1-dB gain flatness to 22 GHz. In biased condition, the DC power consumption can be as low as 2.7 W; the nominal DC bias requirements are +9 VDC at 300 mA. In maximum output power condition, the power dissipation increases to about 3.8 W.

The iT2007 is typical of all iTerra MMICs in that its high efficiency makes it appealing when designing multidevice amplifiers with higher power outputs. Low current consumption allows more devices to be combined in parallel before the limits of a typical heat sink are reached. When operated under Class AB bias conditions, power dissipation is very low in the standby condition, which increases reliability and operating life because of lower channel temperatures. As a result, it is possible to build a power amplifier of modest dimensions (thanks to a relatively small heat sink) that delivers nearly 2 W CW output power from 2 GHz to 18 GHz using only four devices.

The iT2001P is a packaged amplifier that covers 1 GHz to 20 GHz and provides saturated output power of +30 dBm to 6 GHz and greater than +27 dBm to 18 GHz. Its gain is 13 dB, nearly double that of the iT2007. Its DC power consumption of 5.4 W is obtained under bias conditions optimized for best simultaneous output power and linearity. The base of the package is composed of copper to minimize thermal resistance while also ensuring compatibility between materials. The feedthroughs are realized on a ceramic frame, which maintains the device's broadband performance.

In addition to its standard product lines, the company also offers a variety of custom amplifier modules based on its experience in GaAs MMIC technology. These modules deliver higher power over broad bandwidths and are packaged in connectorized enclosures or in 16-mm metal-ceramic packages. The latest version is the iT2011 power amplifier module, housed in a compact enclosure measuring 2.54 × 2.2 × 2.1 in. enclosure (including heat sink), that delivers RF output power as high as +29 dBm from 10 MHz to 20 GHz (Fig. 3). The saturated power of the iT2011 is greater than +29 dBm at 2 GHz and greater than +28 dBm at 10 GHz. The gain is at least 23 dB through 20 GHz with excellent return loss. The iT2011 draws less than 1.25 A from a ±12-VDC source, for total power consumption of about 14 W. The amplifier module includes internal protection against polarity inversion, overload, and short-circuit conditions.

Biasing circuits are included in order to simplify switch-on operation and to provide protection for polarity inversion, overload/short circuit, and automatic sequencing biasing at switch-on. The iT2011 is mounted in a rugged housing that incorporates the DC power supply, and RF input and output connectors can be K or 3.5-mm types. The company can modify the standard configuration of the amplifier modules to accommodate application-specific mounting requirements. iTerra Communications, 2440-A Embarcadero Way, Palo Alto, CA 94303; (650) 424-1937, e-mail: [email protected], Internet:

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