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New VCO
The CRO2781A-LF in S-band operates at 2780 MHz with a tuning voltage range of 0.5 to 4.5 Vdc. It features a typical phase noise of -115 dBc/Hz @ 10 KHz offset and a typical tuning sensitivity of 9 MHz/V. Its industry standard MINI-16 package is just 0.5 x 0.5 x 0.22".

Wideband PA Module
A new wideband power amplifier module for use in microwave radio, VSAT, military & space, fiber optic and broadband test equipment applications from 100 MHz to 20 GHz has been introduced. The HMC-C057 is a GaAs pHEMT MMIC PA in a miniature hermetic module.

Coaxial to Waveguide Adapters
Coaxial to Waveguide Adapters are offered in a variety of configurations. Option A, broadband adapters, have excellent electrical specs that are maintained over the entire adapter bandwidth. Option B offers enhanced performance over a specific band of the unit’s bandwidth.


Digital Communication Analyzer
The latest addition to the PXIT product family, the PXIT 10G Digital Communication Analyzer (DCA) with Passive Optical Network (PON) filter rate options and smart post processing for the PXIT N2100B DCA, helps optical transceiver test vendors reduce their cost of test.

LED Drivers
This new family of LED driver ICs significantly reduces the number and size of external components required by drive circuits. Operating at switching frequencies up to 600 kHz, AP880X Series step-down, DC-DC converters require only four smaller and lower cost inductors and/or capacitors.

RF Interface DAS Panel
Created to control the output power from PAs, the 15C2NB is designed to combine and attenuate RF signals in steps of 1 dB up to 70 dB of maximum attenuation. With the operating frequency covering 800 MHz to 3 GHz, this design is ready for field deployment for GSM, PCS, WiMAX and LTE network architectures.

Phase-Locked Crystal Oscillator
The PLXO-50 Phase-Locked Crystal Oscillator is used as the frequency reference in a surveillance RADAR application. The PLXO, which operates at 50 MHz, maximizes system performance with its exceptional phase noise (<-150 dBc/Hz @ 10 KHz) and other features.

Directional Antenna
A wide angle 2.4 GHz antenna, model HG2405P-135, is designed for compact installations and is ideal for Wi-Fi, PCS, DCS, and custom applications. It gives the system designer wide angle coverage of an area without multiple antennas or larger footprint antennas.

Band Reject Filters - Tunable
Band stop and cavity filters that can be re-adjusted by the customer to new center frequencies are now available. These filters are tunable over a +/-7.5% center frequency range with minimal change in bandwidth. Operating temperature range is -55 to +85ºC.

Fast Rise/Fall Time Logic
Four new logic devices which are optimized for systems requiring fast rise/fall times, low jitter, and low DC power consumption have been released. They provide operating clock and data rates of 13 GHz/13 Gbps, and are ideal for deployment in ATE, broadband T&M equipment, frequency synthesis and radar signal processing systems.
 
Ultra Low Phase Noise VCO
Model CRO1220A-LF in L-band operates at 1220 MHz with a tuning voltage range of 0 to 5 Vdc. This VCO features a typical phase noise of -118 dBc/Hz @ 10 KHz offset and a typical tuning sensitivity of 2 MHz/V. It is well suited for satellite communication and microwave radio applications.


Design Verification Test Systems
The GS-9000 Assisted GPS (A-GPS) Design Verification Test systems were designed around the 8960 wireless communications test set’s new A-GPS assistance data messaging test capabilities. The capabilities support A-GPS validation, Total Isotropic Sensitivity testing and A-GPS pre-conformance testing for mobile devices.

 

 

August 2007

The Doherty Amplifier: New After 70 Years
By Freescale Semiconductor, RF Division

The Doherty amplifier architecture has in less than 5 years become the “amplifier of choice” for new wireless transmitters after essentially laying dormant since W.H. Doherty first described it in 1936. The Doherty’s obscurity is directly attributable to the predominant modulation schemes (AM and FM) employed in communication systems over the years, which do not possess high peak-to-average ratios (PARs). The resurgence of interest in the concept is based on its very high power-added efficiency when amplifying input signals with high PARs – precisely the type exhibited by WCDMA, CDMA2000, and systems employing Orthogonal Frequency Division Multiplexing (OFDM), such as WiMAX and the upcoming Long-Term Evolution (LTE) enhancement to the UMTS wireless standard.

In fact, when properly designed, a Doherty amplifier can produce increases in efficiency of 11% to 14% when compared to standard parallel Class AB amplifiers that have traditionally been employed in wireless base station transmitters. Since the transmitter accounts for a high percentage of overall system power consumption, the cost savings delivered by the Doherty amplifier’s efficiency can reduce base station annual electricity costs. Thus its appeal for wireless base station manufacturers and wireless service providers.

While the intrinsic high efficiency of the Doherty architecture makes it desirable for current and next-generation wireless systems, it presents unique challenges from a design perspective. The linearity and output power of the Doherty architecture are slightly less than exhibited by a dual Class AB amplifier, and it can produce higher distortion as well. Fortunately, the advancements in analog and digital predistortion and feed-forward linearization techniques can dramatically reduce the Doherty’s distortion. In addition, careful amplifier design can mitigate its inherently lower linearity. The remaining challenge is to create RF power transistors that can accommodate the requirements of the two types of amplifiers employed by the Doherty architecture and produce optimum RF output power over a wide array of signal conditions.

A Doherty overview
A “classic” Doherty amplifier (Figure 1) employs two amplifiers. The carrier amplifier is biased to operate in Class AB mode and the peaking amplifier is biased to operate in Class C mode. The input signal is split by a power divider equally to each amplifier with a 90-deg. difference in phase. After the signals are amplified, the signals are recombined with a power combiner. Both amplifiers operate when the input signal peaks, and are each presented with the load impedance that enables maximum power output. However, as the input signal decreases in power, the Class C peaking amplifier turns off and only the Class AB carrier operates. At these lower power levels, the Class AB carrier amplifier is presented with a modulated load impedance that enables higher efficiency and gain. The result is an extremely efficient solution for amplifying the complex modulation schemes employed in current and emerging wireless systems.

FREESCALE SEMICONDUCTOR
www.freescale.com
TXTLINX.COM105
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