Current Issue
August 2008
• Electro-Mechanical Broadband RF Switch.
• Single-Stage Driver Amplifier
• Quad-Band EDGE Radio Solution
• Modeling 3G / WCDMA / HSDPA
• Composite Filters
• Integration of Waveguide
• Coaxial Components
• Antennas Needed
• And More...
 
Dow-Key Microwave
 
  Search by TXTLINX Number:
 
   

Broadband VCO
A new RoHS compliant UHF band (640 to 945 MHz) VCO, the V708ME02-LF, is ideal for broadband transmission applications. It provides an output power of 9.5+/-4.5 dBm at DC supply voltage of 9V drawing only 13mA (typ.) over -40 to +85ºC.

Broadband High Power Amplifier
Model AMF-6B-06001800-70-40P-PS is a self-cooled 3RU rack-mount high power amplifier covering 6 to 18 GHz and delivering approximately 10W of power. The SMA connectorized box is 3.47" high, 16.99" wide (excluding brackets), and 12.12” deep including fans.
 
High Power Directional Couplers
The C50-106-481/4N is capable of handling 500W input power over the frequency range of 500 to 1000 MHz with 0.2 dB insertion loss and 20 dB minimum directivity. Coupling is 50 +/-1 dB and VSWR is 1.15:1 maximum. Dimensions are 3.0 x 2.0 x 1.50".


Orthomode Transducer
A new Ka-band full band orthomode transducer, the QOT series operates in the full Ka-band waveguide band covering 26.5 to 40 GHz with less than 0.5 dB of insertion loss and greater than 32 dB of isolation. It is used mainly with antennas for EW systems.

Latched Comparators
A new family of 9.7 GHz latched comparators features low propagation delay, short minimum pulse width requirements and ultra low jitter performance, making them ideal for a wide range of applications including digital receivers, high speed instrumentation, and more.

Coaxial Circulators
RADC-225-400-S23-1WR is a coaxial circulator that covers the full band of 225 to 400 MHz. It has guaranteed specs of 1.0 dB insertion loss, 17 dB isolation, and 1.40:1 VSWR at room temperature and 1.5 dB insertion loss, 15 dB isolation and 1.50:1 VSWR over the full operating temperature range of -10 to +50ºC.

Two Way Power Divider
A new 12W power divider for antenna sharing, defense and test applications, Model 151-234-002 is a 12W average, 2 way power divider with SMA female connectors. This 50 ohm unit operates from 2400 to 2500 MHz with 25 dB typical isolation.

Jitter Attenuators
The VFJA910 and VFJA911 jitter attenuators are integrated clock/PLL timing solutions for 1GigE synchronous Ethernet applications. The VFJA910 provides two LVCMOS outputs and the VFJA911 has an LVPECL output, both with a frequency of 25 MHz.

New VCO
The CVCO55CW-1000-1500 VCO operates from 1000 to 1500 MHz with a control voltage range of 0.5~4.5V. This VCO features a typical phase noise of -95 dBc/Hz @ 10 KHz offset and has excellent linearity. It is presented in the 0.5 x 0.5” SMD package.

Integrated Microwave Assemblies
The company’s expertise in Integrated Microwave Assemblies is based on a knowledge of material science, strict process control and predictable manufacturing variations. Products are available from DC to 60 GHz, with multiple technologies in a single package, with higher reliability, and a high degree of functional integration.
 
UHF-Band VCO
Model V495ME01-LF is a UHF-band VCO for test and measurement applications. It offers an ultra low phase noise performance of -113 dBc/Hz @ 10 kHz offset (typ.). Average tuning sensitivity is 10 MHz/V and it covers the bandwidth between 0.4 to 4.5V.


MMIC Gain Blocks
Four new MMIC gain block amplifiers ideal for IF and RF applications from DC to 8 GHz have been introduced. They are a family of SiGe and GaAs HBT gain block SMT MMIC amplifiers that deliver up to 23 dB gain, +17 dBm output P1dB and +30 dBm output IP3, with noise figure as low as 2.5 dB.


 

 

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
Email this article to a friend!
 


Copyright © 2007 Octagon Communication Inc. DBA MPDigest / MPDigest.com, All Rights Reserved.