Maxim Integrated Products introduces the MAX19790, a dual, monolithic voltage-variable attenuator (VVA) spanning the 250MHz to 4000MHz frequency band. Designed as a general-purpose block for high-performance wireless infrastructure applications, this VVA delivers 44dB of linearly controlled dynamic range with industry-leading S21 flatness over frequency and all attenuation settings.
Its combination of flatness and linear attenuation control makes the MAX19790 an VVA for broadband infrastructure applications like cellular base stations, microwave point-to-point systems, and SatCom equipment. The device is composed of two state-of-the-art VVAs integrated into one monolithic IC. Designed using a proprietary, monolithic SiGe BiCMOS process, each attenuator incorporates a control circuit that provides 22dB of attenuation range with a linear control slope of 10dB/V.
Both attenuators share a common analog control circuit, and they can be cascaded together to yield 44dB of total dynamic range with a combined linear control slope of 20dB/V. This wide-ranging linear control eliminates the need for complex linearization circuits and algorithms, thus reducing solution cost and complexity. Competing RF VVAs, such as PIN diode and MESFET-based attenuators, possess nonlinear control slopes that complicate automatic gain control (AGC) and gain trim algorithms.
Many of these alternative solutions require external control-slope linearization circuitry, which adds to the overall cost, complexity, and repeatability of the VVA design. These competing 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 attenuators used in the chip circumvent these degradations by offering excellent S21 flatness performance over wide frequency bands and attenuation ranges. When operating over any 125MHz contiguous band between 950MHz to 2150MHz (a common band for SatCom applications), the MAX19790 delivers typical and maximum flatness levels of merely 0.13dB and 0.89dB peak-to-peak, respectively, through 30dB to total attenuation. If even greater S21 flatness is desired, adding a simple equalizer can further improve the circuit's performance.
The MAX19790's S21 response curves remain virtually flat through 30dB of attenuation control range for a multitude of popular communications frequency bands (each spanning 125MHz of contiguous frequency coverage). The device is available in a 6mm x 6mm lead-free 36-pin TQFN package. Prices start at $5.24 (1000-up, FOB USA).
