Raising The Performance Bar for Passive Mixers

Welcome to the RF/Microwave Tracker blog where latest developments in RF and Microwave systems related components and technologies will be presented. This premier blog focuses on an unprecedented highly integrated wideband tunable mixer that promises to handle multiband, multi-standard operation in wireless infrastructure and software-defined radio (SDR) applications.

This double balanced wideband passive mixer comes from Analog Devices, Inc. (www.analog.com). The maker claims it is the industry’s first to incorporate wideband LO amplifier, programmable RF balun and IF filter, and an IF amplifier on a single biCMOS chip. In fact, there are two mixers in this new wideband family. While the single channel is ADL5811, the dual-channel version is ADL5812. Both are implemented using 0.35 µm silicon germanium (SiGe) biCMOS process.

Designed to deliver unmatched linearity, low distortion and low noise combined with broadband frequency performance, the mixers offer a bridge between today’s leading edge active and passive mixers. Traditionallly, active mixers offer excellent frequency operation and moderate spurious-free dynamic range (SFDR), while passive mixers deliver greater SFDR performance but with much narrower operating bandwidth. The new ADI mixers eliminate the need for this trade off.

Few key specs for a single channel device include a 700-MHz to 2800-MHz frequency range, 24 dBm third order intercept point (IP3), an 11 dB single sideband (SSB) noise figure (NF) and 7 dB power conversion gain. These performance specifications are maintained across the full operating frequency range. Typical current consumption for the single channel version is 190 mA at 5 V operation.

Well, the high performance of ADI’s new passive mixers is the result of three technical advances. First, the most significant contribution comes from the limiting LO amplifier, which is capable of generating a high-voltage, fast-rise-time, square wave over a wide bandwidth with no DC current penalty compared to existing narrow band mixers. The second technique involves the integration of a tuned RF balun structure to ensure a well-balanced RF signal is applied to the mixer. In the past, narrowband mixers incorporated an RF balun consisting of a magnetic or transmission line transformer, which provided low loss but only moderate bandwidth. The third is a programmable low-pass filter that improves linearity by reducing early compression of the IF amplifier due to unwanted sidebands.

In short, for today’s RF/Microwave systems designers, key benefits offered by the new wideband passive tunable mixers include consistent performance across the frequency band, shorter design time, reduced number of components and bill of material (OM), and lower development cost.

Sampling now, ADI’s wideband passive mixers (ADL5811/12) are housed in LFCSP packages and are slated for production in the third quarter. Meanwhile, the new mixers are in the process of being fully characterized.

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One Response to Raising The Performance Bar for Passive Mixers

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