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Device Advances Lead To Lower LNA Noise Levels

Next-generation communication receivers need to provide improved sensitivity and dynamic range over wide bandwidths. To accomplish this feat, the receivers are counting on low-noise amplifiers (LNAs) to deliver higher gain and linearity over broad frequency bands. These high-performance LNAs are exploiting recent advances in gallium-arsenide (GaAs) pseudomorphic high-electron-mobility transistors (PHEMTs) and silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). They also are exploring gallium-nitride (GaN) HEMTs for emerging applications. Both traditional and non-traditional amplifier suppliers are responding with a new round of LNAs to meet the ultra-low-noise requirements of applications like Global-Positioning-System (GPS) receivers, third-/fourth-generation (3G/4G) cellular base-station transceivers, wireless local-area networks (WLANs), satcom systems, and other microwave and millimeter-wave communications systems.

Utilizing its latest PHEMT7 technology, for example, analog and mixed-signal semiconductor supplier Skyworks Solutions, Inc. has developed both depletion- and enhancement-mode PHEMT (D-PHEMT and E-PHEMT) devices for a new line of ultra-low-noise amplifiers. Using an outside foundry, the manufacturer also has readied SiGe devices for applications that require very low current and integrated LNA solutions. The initial PHEMTs are depletion-mode transistors with enhancement-mode devices scheduled for release in late 2010.

In addition, Skyworks has designed discrete PHEMT devices and integrated multistage monolithic microwave integrated circuits (MMICs). The supplier's first part in this series is a discrete low-noise, n-channel D-PHEMT transistor that covers 850 MHz to 6 GHz. At 2.4 GHz, the SKY65050-372LF boasts +8 dBm output power at 1-dB compression, an output third-order intercept point of +20 dBm, and a noise figure of 0.4 dB. At 2 GHz, the device features gain of 16 dB with a noise figure of 0.4 dB. The transistor operates on 16 mA current. A higher-power version with a larger die size, dubbed the SKY65052-372LF, spans 450 MHz to 6 GHz. It can generate +19 dBm of output power at 1-dB compression. At 2.4 GHz, this version offers a noise figure of 0.85 dB and an output third-order intercept point of +34 dBm with 16 dB of gain. The device's operating current is 16 mA from a 3-V supply.

For those who require an integrated approach, Skyworks is offering two-stage LNAs with an integrated interstage matching network (Fig. 1). Both the SKY65037-360LF and SKY65040-360LF are fabricated using the firm's advanced PHEMT process. According to Alan Miller, the company's Product Marketing Manager, these devices boast noise figures of less than 1 dB while allowing designers to adjust current and gain without degrading the noise figure. For instance, the SKY65037-360LF offers a noise figure of 0.6 dB at 900 MHz. Its sibling, the SKY65040-360LF, provides a noise figure of 0.65 dB at 1.95 GHz.

While the SKY65037-360LF covers a frequency band of 0.7 to 1.2 GHz, the SKY65040-360LF operates from 1.5 to 2.4 GHz. For the SKY65037-360LF, gain can be varied over a range of 15 to 25 dB at 900 MHz by adjusting the supply current from 30 to 100 mA. Other salient features of the SKY65037-360LF include +18 dBm output power at 1-dB compression at 900 MHz and an output third-order intercept point of +32 dBm at 65 mA. For the SKY65040-360LF, gain can be adjusted from 15 to 25 dB at 1.95 GHz by adjusting current from 30 to 100 mA. The device provides an output third-order intercept point of +34.5 dBm at 65 mA with +16 dBm output power at 1-dB compression at 1.95 GHz.

Eying mobile-communications applications, Avago Technologies has readied an integrated GaAs broadband LNA MMIC to cover 1.5 to 8.0 GHz. Fabricated using 0.25-m, third-generation E-PHEMT technology, the MGA-21108 operates from a 1.4-to-3.3-V supply with nominal current of 18 mA. It flaunts a noise figure of just 1.5 to 2.8 dB with 18.7 to 10.7 dB gain.

For applications requiring less than 1 dB noise with higher gain and linearity, Avago has adopted a two-stage balanced configuration with active bias circuitry. Implemented using 0.25-m E-PHEMT technology, the MGA-13516 and MGA-14516 LNAs are designed for 400 MHz to 1.5 GHz and 1.4 to 2.7 GHz, respectively. The LNAs offer noise figures of 0.66 dB with 31.8 dB gain and an output third-order intercept point of +38 dBm. For both devices, the rated output power at 1-dB gain compression is +23.5 dBm.

If a noise figure of 0.5 dB or better is required, Avago has packed two balanced, low-noise E-PHEMT transistors in the same package. The matched-pair MGA-16516 is rated for a noise figure of 0.45 dB at 850 MHz with 17.5 dB of gain. While the MGA-16516 covers 700 MHz to 1.7 GHz, the MGA-17516 spans 1.7 to 2.7 GHz. The higher-frequency MGA-17516 flaunts a noise figure of 0.52 dB at 1.85 GHz with 17.2 dB of gain. It offers an input third-order intercept point of +13.7 dBm with +21.5 dBm output power at 1-dB compression. In contrast, the MGA-16516 provides an input third-order intercept point of +11.5 dBm and +18.0 dBm output power at 1-dB compression.

Integration also is the strategy adopted by Mimix Broadband for wireless-infrastructure applications. Using E-PHEMT process technology, the firm has created a MMIC LNA with an integrated active bias circuit on chip (Fig. 2). The XG1015-SE is the first member of this series, which is slated for release in the second half of the year, according to Product Manager Amer Droubi. Designed for operation from 100 to 3500 MHz, the XG1015 offers a noise figure of less than 1 dB and an output third-order intercept point above +34 dBm at 2 GHz. Although the device's noise figure is slightly higher compared to discrete devices, Droubi asserts that the XG1015-SE offers ease of use and a single supply voltage. The integrated active bias circuit allows direct connection to a 3-V supply. The LNA boasts 19 dB gain at 900 MHz and +18.5 dBm output power at 1-dB compression at +3 VDC.

In a similar move, Hittite Microwave has unveiled a wideband GaAs MMIC LNA that operates from 14 to 27 GHz. The HMC504LC4B features 19 dB of small signal gain. It boasts a noise figure of 2.2 dB with an output third-order intercept point of +26 dBm. The LNA requires just 90 mA from a 4-V supply. Developed to function as a local-oscillator (LO) driver for balanced in-phase/quadrature (I/Q) or image-reject mixers, the HMC504LC4B offers +17 dBm output power at 1-dB compression.

Another manufacturer delivering LNAs with high gain and linearity for wireless applications is RF Micro Devices. Using E-PEMT technology combined with integrated monolithic impedance matching, the firm already demonstrated a sub-1-dB noise figure with an output third-order intercept point above +40 dBm. Now, it is further improving its PHEMT technology to develop LNAs with a noise figure below 0.5 dB and high linearity for the same frequency range. By combining a shorter-gate-length E-PHEMT process with enhanced topology, the company has demonstrated a noise figure of 0.6 dB at 900 MHz, according to Engineering Director Terry Hon. Last year, RFMD released the SPF5122Z with a noise figure below 0.75 dB and output third-order intercept point of more than +40 dBm at 2 GHz. The SPF5122Z is designed to operate from 50 to 4000 MHz. It offers +23.4 dBm output power at 1-dB compression at 1900 MHz while providing 18.9 dB gain at 900 MHz. Internally matched to 50 Ω, the LNA operates from a single 3-to-5-V supply with 90 mA of current. A low-power version, which draws 46 mA at 5 V, also was launched. The SPF5043Z provides similar performance from 50 to 4000 MHz.

By leveraging the benefits of GaN HEMTs, RFMD also is striving to address the wideband, ultra-low-noise, and high-linearity requirements of next-generation multi-carrier base stations. At last year's Compound Semiconductor IC (CSIC) Symposium in Monterey, CA, the developer partnered with Northrop Grumman to demonstrate a sub-0.2-dB noise figure across 2 to 8 GHz while providing 2 W output power. To achieve these results for a GaN-HEMT-based, fully matched MMIC LNA, however, the amplifier had to be cooled to -30C.

Earlier this year, RFMD unveiled a GaAs-PHEMT-based GPS LNA with an integrated surface-acoustic-wave (SAW) filter and supporting components in a multichip module. According to the company, the RF2815 has been selected for a CDMA smartphone by a Taiwan-based manufacturer. Also offering ceramic filtered GPS LNAs with a low noise figure and high gain is Spectrum Microwave. Displaying more than 35 dB out-of-band rejection at 1575.42 MHz, these small surface-mountable LNAs permit designers to select gain stages of 26, 32, or 38 dB while maintaining a low noise figure of 1.8 dB. Crafted for applications where reliability is critical, the filtered LNA module operates from a 5-to-32-V supply while consuming just 77 mA.

Ultra-low noise also is the mantra at Mini-Circuits. Its latest debut, the TAMP-960LN+, boasts a noise figure of 0.55 dB with 18 dB gain and output power to 16.5 dBm. To target myriad cellular applications, the TAMP-960LN+ spans 824 to 960 MHz. Other developers pushing the microwave and millimeter-wave LNA performance envelope include B&Z Technologies, Endwave Corp., HXI Millimeter Wave, and M/A-COM Technologies. B&Z Technologies, for instance, has demonstrated low-loss waveguide input LNAs for satcom applications covering the S, C, X, Ku, and Ka bands. The output is coaxial and matched to 50 Ω. By cleverly incorporating a noise-matching circuit and impedance transformer in the waveguide itself, the firm's newest GaAs-HEMT-based waveguide input multi-stage LNAs connect directly to the antenna (Fig. 3). As a result, President and Founder Javed Siddiqui states that losses have been minimized between the antenna and the interface between the waveguide and the gain stage of the LNA.

The BZW-07250775-, a member of the firm's BZW112-1 series, flaunts a noise figure of 0.6 dB (or noise temperature of 40 K) from 7.25 to 7.75 GHz with typical gain of 34 dB. The LNA generally provides gain flatness of 0.5 dB while group delay is 10 ps. Typically, this LNA is rated for +10 dBm output power at 1-dB compression. It operates from a single +12-V supply while consuming 120 mA maximum. Siddiqui claims that the unit is unconditionally stable at all temperatures.

Utilizing GaAs MMICs, HXI Millimeter Wave Products, a subsidiary of Renaissance Electronics Corp., has readied an LNA that spans 50 to 65 GHz. The HLNAV-364 provides small-signal gain of at least 25 dB with gain flatness of 2 dB. It boasts a noise figure of 5 dB. Although input power is limited to 10 dBm, the device's output power is typically +13 dBm at 1-dB compression. Typical power requirements for this LNA are +6.5 VDC at 275 mA. The device is matched to the frequency range of the company's WR-15 waveguide-to-coaxial adapters, which allows it to be used for broadband test setups. A higher-gain version also is available.

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