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Bandpass Filter
Part number 2926 is a bandpass filter with a minimum 3 dB bandwidth of 3 MHz and >60 dB at 50 and 70 MHz. Typical insertion loss is 5 dB. The filter is supplied in a surface mount package just 1.5 x 0.5 x 0.5" and can also be supplied connectorized.

Bandpass Filter for Iridium
Part number 6C9-1621.25-X10.5T11 is a bandpass filter for the Iridium band. It was designed with a narrow bandwidth and high rejection to isolate Iridium frequencies from outside interference. The unit may be outfitted with any RF connector the customer prefers.

Directional Coupler
The C10-0116 is a broadband (1 to 16 GHz) 10 dB directional coupler. This tri-plate stripline design exhibits excellent 1.17 VSWR, +/-0.5 dB typical coupling flatness, and 20 dB typical directivity.


SMT Comparators
A new family of 20 Gbps clocked comparators offers a unique combination of low propagation delay for low input overdrive while minimizing propagation dispersion and power dissipation. They are ideal for digital receivers, clock and data signal restoration, pulse spectro-scopy, and more.

Triplexer for Broadband
Model TR-A01 is a new triplexer that combines/separates DC to 2170 MHz, 2400 to 2500 MHz, and 5000 to 6000 MHz. It uses suspended substrate technology that provides the lowest insertion loss since the dielectric used is air. Insertion loss in the 5 to 6 GHz band is only 0.7 dB

RF Parametric Test Solution
The 7000 Series Vector Analyzer Generator (VAG) is a single, fully integrated RF parametric test system for RF test of wireless components and subsystems. It combines both vector signal generation and vector signal analysis in a single box, providing an integrated approach to measurements for complex wireless standards, including LTE.

New Chip Resistor
Featuring a working voltage rating of 3500 Vrms, the HVC3512 size chip is the latest addition to the HVC Series of chip resistors. The Series offers the highest working voltages per chip size in the resistor industry due to the fine-film patterning.

RoHS Compliant VCO
Model MW500-1838 ½" SMT VCO has a tuning range of 2570 to 2655 MHz from 1 to 5.5V tuning using a 5V supply. Output power is +2 dBm +/-1.5 dBm while using less than 30mA of current. This VCO meets all the requirements for RoHS compliancy.

Coaxial Terminations
A full line of RF coaxial terminations includes terminations with SMA, QMA, Mini-QMA, 2.92mm, TNC, N, HPQN, and 7/16 interfaces. Frequency ranges are offered from DC to 40 GHz with power up to 5W as standard products. Custom configurations available.

System Solution
A highly configurable system solution for testing receivers in radar systems can be used by manufacturers and operators in development, production and service to simulate phase-coherent multichannel signals. The radar test system generates simple modulated or unmodulated pulse sequences and can also be expanded to a maximum of 10 channels to create realistic scenarios.
 
Compact Network Analyzer
The E5061B is a versatile, compact network analyzer that analyzes a frequency range as low as 5 Hz up to the RF range of 3 GHz. This network analyzer’s broad range and versatility eliminates the need for additional low-frequency-dedicated instruments.


“Green Friendly” XO
Said to be the world’s first environmentally friendly ultralow power-driven crystal clock oscillator (XO), the NZ2520SF operates on as little as 0.8V, 50% lower than comparable XOs. When coupled with a 40% reduction in current draw, the unit delivers a 70% reduction in power consumption.

 

 

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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