ADI's High Linearity RF Front-End Solutions for Base Stations and Satellite Communications

As terminal devices (such as mobile phones and PMPs) are becoming increasingly thinner and smaller, the prospect of single-chip RF (radio frequency) front-ends in the terminal application market is becoming more and more popular. However, unlike digital circuits, the high integration of single-chip RF is often at the expense of performance, which is why wireless terminal products can use single-chip RF front-ends, while applications such as mobile base stations, satellite communications, and point-to-point microwave radio equipment that have high performance requirements do not use single-chip RF front-ends.

“I could have integrated all the RF ICs on one chip like other suppliers do, but the performance would not be very good,” said Peter Real, vice president of RF and networking components at Analog Devices. “Our strategy is to maximize integration without sacrificing performance. That’s why ADI offers highly integrated single-chip transceiver solutions, high-performance RF functional blocks, and discrete RF ICs covering the entire RF signal chain.”

At present, ADI's RF IC products covering the entire RF signal chain include: direct digital frequency synthesizer (DDS), phase-locked loop synthesizer (PLL), TruPwr power detector and logarithmic amplifier, X-AMP variable gain amplifier (VGA), power amplifier (PA), low noise amplifier (LNA) and other RF amplifiers, mixers, and direct frequency conversion modulators and demodulators. Peter Real emphasized: "ADI is the only company that can provide products that cover the entire RF signal chain."

He said that ADI is the global market leader in PLL synthesizers and RF detectors. The industry's first and groundbreaking RF products we have developed include: Gilbert Cell mixers, TruPwr RMS power detectors, integrated PLL/VCOs, X-AMPs, and broadband mixers.

ADF4350 is the industry's first fully integrated frequency synthesizer launched by ADI. It has an on-chip VCO (voltage-controlled oscillator) and PLL (phase-locked loop) that can operate in an extremely wide continuous frequency range from 137.5MHz to 4.4GHz. The ADF4350 frequency synthesizer is the industry's broadband synthesizer with the lowest phase noise, supporting fractional-N and integer-N frequency divisions, and can be used with ADI's new dual-channel active and passive mixers to achieve high-linearity RF front-ends for mobile base stations, satellite communications, and point-to-point microwave radio equipment.

“The ADF4350 is the industry’s only integrated synthesizer that supports all 2G and 3G systems simultaneously and is the only part that offers fractional-N operation,” said Peter Real. “Its easy-to-use, flexible output stage drives both active and passive mixers (differential or single-ended) without the need for buffer amplifiers, which enables customers to save on cost, board area, and component count, allowing them to develop standard products for a wide range of applications.”

The ADF4350 integrated frequency synthesizer provides designers with a single-chip low phase noise solution, while other competing solutions require the use of up to 10 discrete VCO/PLLs. The VCO built into ADI's new ultra-wideband, fully integrated frequency synthesizer has a phase noise of –137 dBc/Hz at 2.1 GHz and 1 MHz offset, and a phase noise of -155 dBc/Hz at 137.5 MHz and 1 MHz offset, which is equivalent to an integrated root mean square (RMS) phase error of 0.36° at 2.1 GHz and 0.02° at 137.5 MHz. The ADF4350 provides two RF output ports, allowing users to digitally program the output power level.

Unlike competing products, the ADF4350 supports both integer-N and fractional-N operating modes, allowing users to determine the best spurious and phase noise performance through software control methods, thereby achieving optimal performance and accelerating time to market.

ADI has also introduced a series of highly integrated mixers that can be matched with ADF4350, such as the active ADL5802 and the passive ADL5356, ADL5358 and ADL5360, which are very suitable for combining to realize various communication applications, such as WCDMA, TD-SCDMA, MC-GSM, LTE and WiMAX. These two-channel diversity mixers expand ADI's main and diversity product series. When used with ADF4350, they can provide highly integrated two-chip diversity down-conversion solutions for mobile base stations, satellite communications, and point-to-point microwave radio equipment.

The ADL5802 broadband active device provides high linearity and appropriate gain in the industry's smallest package. The ADL5802 dual-channel active mixer has an IIP3 (third-order input intercept point) of 27dBm, a single-sideband noise figure of 11dB, a conversion power gain of 1.5 dB, and is packaged in a 4mm×4mm LFCSP. For high-linearity applications, the ADL5802 consumes less than 1W when powered by a 5V supply. The ADL5802 integrates a high-linearity double-balanced active mixer core and a local oscillator (LO) buffer amplifier to provide wide dynamic range frequency conversion from 10 MHz to 6 GHz. It also has a bias adjustment feature that can optimize input linearity, single-sideband noise figure, and DC current through a single control pin.

Peter Real emphasized: "The ADL5802 is both the industry's first dual-channel active mixer and the industry's largest bandwidth mixer. Its adjustable mixer bias circuit allows customers to achieve a balance between performance and power optimization, while its highly integrated design allows customers to save cost and space while improving performance."

There are only two differences between the ADL5801 and ADL5802: first, the ADL5801 is a single-channel high IP3 active mixer; second, the ADL5801 integrates a detector.

If customers want to choose passive mixers, they can choose the ADL5356, ADL5358 and ADL5360 dual-channel dedicated band passive mixers. These passive mixers integrate IF amplifiers and RF (radio frequency) baluns, with an IIP3 of 26 dBm, a single-sideband noise figure of less than 10 dB, and an industry-leading 10 dBm blocking noise figure (16.5dB). The passive mixers with built-in IF amplifiers can provide 8.5 dB to 9.5 dB of conversion power gain in a small 6 mm × 6 mm LFCSP package. The 5 V (nominal) ADL5356, ADL5358 and ADL5360 can also be powered by a 3.3 V supply for power-sensitive applications. They can provide higher gain than other active devices and similar passive devices.

In addition, the ADF4350 provides an ideal local oscillator source for ADI's ADL538X demodulators and ADL537x modulators. When these products are used in conjunction with ADI's AD837X wide dynamic range variable gain amplifier family and ADL552X low noise RF amplifiers, they provide an ideal RF receive signal path.

The ADF4350 is now in volume production and is available in a 5mm x 5mm, 32-lead LFCSP package at $7.86 for 5,000-unit quantities. The ADL5802, ADL5356, ADL5358 and ADL5360 are also in volume production. The ADL5802 is available in a 24-lead LFCSP package at $6.80 for 5,000-unit quantities. The ADL5356, ADL5358 and ADL5360 mixers are available in a 36-lead LFCSP package at $9.48 for 5,000-unit quantities.

Finally, two other broadband RF products worth mentioning are the ADL5902 TruPwr RMS detector and the ADL5604 1W broadband driver amplifier. The ADL5902 operates in a frequency range from 100MHz to 9GHz with a dynamic range of up to 60dB. It is the industry's highest frequency and most accurate RMS to DC detector with a rated operating temperature range of -40°C to +125°C. The ADL5604 is the industry's lowest power 1W RF driver with a quiescent current of only 325mA. It supports an operating frequency range from 400MHz to 2.7GHz and an ESD rated voltage of ±1kV. Made in a silicon germanium process, the chip uses a 4mm×4mm 16-lead LFCSP package and supports applications including cellular, ISM, wired, and instrumentation. ADI now offers samples of the ADL5902 and ADL5604