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Comb Generator
The CG1000 series comb generator provides a combline of CW outputs up to 26 GHz. Picket sizes of 500, 750 and 1000 MHz are available, A TCXO, PLO and integrated amplifier are all included in the compact design. Frequency range is 1 to 18 GHz.

QFN Packaged Up-Converter
A 37 to 40 GHz GaAs MMIC up-converter, model XU1019-QH, integrates an image reject balanced mixer, LO buffer amplifier, LO doubler and RF buffer amplifier within a fully molded 4 x 4mm QFN package. It delivers +20 dBm IIP3 and 7 dB conversion gain.

RF Transformers & Diplex Filters
A family of CATV RF transformers and RF diplex filters meets DOCSIS 3.0 design requirements for applications such as set-top boxes, cable modems, and gateways, supporting frequency bands 5 to 65/85 to 1002 MHz, 5 to 42/54 to 1002 MHz, and 5 to 85/108 to 1002 MHz.


SMA Transfer Switches
New micro miniature SMA transfer switches incorporate SMA connectors to allow high-density packaging and excellent electrical performance through 26.5 GHz. The switch is available in failsafe and latching configurations with a choice of three frequency ranges and three coil voltages.

Bluetooth Low Energy Test Solution
Designers and manufacturers of Bluetooth® products can now use a new Bluetooth low energy testing option to conduct radio layer testing that is in compliance with the newly adopted Bluetooth Core Specification 4.0. With the option, engineers can use the MT8852B to complete a test script covering Bluetooth Basic Rate, EDR, and low energy measurements in <15 seconds by pressing a single key, greatly simplifying production test programs.

LTCC Bandpass Filter
The BFCN-2435+ LTCC bandpass filter is constructed with 12 layers in order to achieve a miniature size and high repeatability of performance. Covering 2435 MHz +/-95 MHz, these units offer low insertion loss and good rejection. Frequency range is 2340 to 2530 MHz.

Coaxial to Waveguide Adapters
Now available are coaxial to waveguide adapters in a variety of configurations. Option A are broadband adapters with excellent electrical specs maintained over the entire bandwidth. Option B offers enhanced performance over a specific band of the adapters’ bandwidth.

RoHS Compliant VCO
Model ZRO2300A1LF in S-band operates at 2285 to 2315 MHz with a tuning voltage range of 0.5 to 4.5 Vdc. It is designed to deliver a typical output power of 3 dBm at 5 Vdc supply while drawing 18 mA (typ.) over the temperature range of -40 to +85ºC.

Scalable Microwave Switching Solutions
Two new RF/microwave switching solutions, the EX7105A and EX7204A, are part of the EX7000 series. These high-density instruments have an open-platform COTS core that can be easily configured for a variety of custom applications.

LTCC Bandpass Filter
The BFCN-7900+ LTCC bandpass filter is constructed with five layers in order to achieve a miniature size and high repeatability of performance. Wrap-around terminations minimize variations in performance due to parasitics. Frequency range is 7800 to 8100 MHz.
 
Transient Capture and Timestamp Module
The EX1200-7416 is a transient capture and timestamp module that further extends the capabilities of the popular EX1200 series of configurable LXI Class A instruments. With a rich feature set, it supports a broad range of applications that require level comparison, event detection, and time stamping.


SPDT T/R Switch
The HMC784MS8GE is a low loss, high linearity GaAs pHEMT 10W SPDT MMIC switch for use in transmit/receive applications which require very low distortion at high input power levels. It can control signals from DC to 4 GHz and is housed in a MSOP-8G leaded package.

 

 

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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