You would think that attenuating a signal or providing a variable signal gain/attenuation path for RF would be the easiest design challenge there is. But the opposite is true, especially at very high radio frequencies. The most common solutions today involve either PIN diodes or MESFETs. And while they work okay, they have their limitations.

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For example, voltage variable attenuators (VVAs) using PIN diodes or MESFETs have nonlinear control slopes that complicate automatic gain control (AGC) and gain trim algorithms. Many of these designs require external control-slope linearization circuitry, which adds to the overall cost, complexity, and repeatability of the VVA design.

These attenuators also suffer from poor attenuation flatness over frequency as the VVA is cycled through its full adjustment range. Finally, the typical VVA “frequency tilt” may change as a function of the VVA’s attenuation settings and cannot be compensated by simple equalization schemes with fixed slopes. Degradations in system error-vector magnitude (EVM) and adjacent-channel leakage rejection (ACLR) then result as the VVA is cycled through its attenuation range.

The MAX19790 dual monolithic VVA from Maxim Integrated Products solves these problems. Designed as a general-purpose block for high-performance wireless infrastructure applications, it operates from 250 to 4000 MHz and delivers 44 dB of linearly controlled dynamic range with a significant S21 (S-parameter forward voltage gain) flatness over frequency and all attenuation settings. Its unique combination of superb flatness and linear attenuation control makes it an ideal VVA for broadband infrastructure applications like cellular basestations, microwave point-to-point systems, and satellite communications equipment.

The device comprises two state-of-the-art VVAs integrated into one monolithic IC. Designed using a proprietary, monolithic silicon-germanium (SiGe) biCMOS process, each attenuator incorporates a patented control circuit that provides 22 dB of attenuation range with a linear control slope of 10 dB/V. Both attenuators share a common analog control circuit, and they can be cascaded together to yield 44 dB of total dynamic range with a combined linear control slope of 20 dB/V. This wide-ranging linear control eliminates the need for complex linearization circuits and algorithms, reducing solution cost and complexity.

The attenuators used in the MAX19790 circumvent these degradations by offering excellent S21 flatness performance over wide frequency bands and attenuation ranges. When operating over any 125-MHz contiguous band between 950 and 2150 MHz (a common band for satellite communications applications), the MAX19790 delivers typical and maximum flatness levels of merely 0.13 dB and 0.89 dB peak-to-peak, respectively, through 30 dB to total attenuation. Its S21 response curves remain virtually flat through 30 dB of attenuation control range for a multitude of popular communications frequency bands, each spanning 125 MHz of contiguous frequency coverage.

The MAX19790 is available in a compact (6 by 6 mm), lead-free 36-pin thin quad flat no-lead (TQFN) package. Prices start at $5.24 for quantities of 1000 and greater.

Maxim Integrated Products